Article

Luminescent Properties of LuAG:Ce Phosphors With Different Ce Contents Prepared by a Sol-gel Combustion Method

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Abstract

Nanosized LuAG:Ce phosphors with different Ce concentrations were prepared by the sol–gel combustion method. Phase evolution, morphology and luminescent properties of the obtained materials were characterized by XRD, TEM, photoluminescent and radioluminescent spectra excited by blue light and X-ray, respectively. The purified crystalline phase of LuAG:Ce was obtained at 820 °C by directly crystallizing from amorphous materials. Both the photoluminescence and radioluminescence are the well-known Ce emissions located in the 470–600 nm consisting of two emission bands due to the transitions from the lowest 5d excited state (2D) to the 4f ground state of Ce3+, which matches well with the sensitivity curve of the Si-photodiode. The luminescent intensity of LuAG:Ce phosphors varies with the Ce contents and reaches the maximum at 0.5 at.% doped. There is a little red shift for the main emission component from blue light-excited emission spectra to X-ray-excited ones. The luminescent intensity of LuAG:Ce phosphors increases with increasing the calcining temperatures due to the improved crystallization.

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... Fig. 1a shows the XRD patterns (X-ray diffractometer with Cu Kα radiation, Bruker, D8 ADVANCE, US) of the CS and MW sintered Ce:-LuAG nano-ceramic powders prepared via the modified hydrothermal method. Trivalent Ce ions were incorporated into LuAG matrix, substituting Lu 3+ at the dodecahedral site of the garnet lattice (D 2 symmetry) [13]. The cubic phase was obtained at the sintering temperature of 1100°C without Lu 4 Al 12 O 9 /LuAlO 3 phases. ...
... Standard powder cell refinement software was used to determine the crystallographic parameters of the CS and MW sintered Ce:LuAG nano-ceramic powders. The experimental XRD peaks were in agreement with the standard JCPDS card No: 73-1368 [13]. The MW sintered sample showed higher crystallinity than CS sample due to the higher in situ temperature and reduced sintering time made possible due to MW heating. ...
... The unit cell lattice parameter values reported in Table 1 were greater than the theoretical value of the un-doped LuAG (a = 11.90 Å, JCPDS No: 73-1368) due to the ionic radii discrepancy between Lu 3+ (0.84 Å) and Ce 3+ (1.03 Å) at the dodecahedral site [13,14]. The lattice parameter of the MW sintered Ce:LuAG nano-ceramic powder was slightly lower compared to the conventionally sintered Ce:LuAG, as indicated by the higher angle peak shifting of the (420) diffraction plane (Fig. 1b). ...
Article
Herein, phase pure and highly crystalline Ce:LuAG nano-ceramics were fabricated using a novel, ultra-fast microwave sintering approach. The influence of microwave sintering on the microstructural, photoluminescence, and dielectric characteristics of Ce:LuAG nano-ceramic powders was examined. Microwave-assisted sintering of Ce:LuAG nano-ceramic powders yielded high crystallinity, low lattice strain, and reduced grain size. The process also improved the sintering kinetics and enhanced the surface diffusion between the grains, resulting in enhanced luminescence and dielectric properties. The Cole-Cole impedance plots showed single semicircular arcs, indicating non-Debye relaxation and a high dielectric constant in the microwave-sintered Ce:LuAG nano-ceramic and highlighting its potential for use in optoelectronics.
... This value is approximately 70 K lower than the quenching temperature previously measured for a sample of Ce:LuAG provided by a different manufacturer (Phosphor Technology Ltd.) [23]. Ce:LuAG 5d → 4f emission is broadband, centered between 500-550 nm [25], with a radiative lifetime of approximately 60 ns [23]. Its absorption spectrum has two bands, one centered around 450 nm and another at 349 nm [25,26], making 355 nm excitation possible. ...
... Ce:LuAG 5d → 4f emission is broadband, centered between 500-550 nm [25], with a radiative lifetime of approximately 60 ns [23]. Its absorption spectrum has two bands, one centered around 450 nm and another at 349 nm [25,26], making 355 nm excitation possible. ...
... This may be the result of pixel-to-pixel variations in seeding density for each image. Additionally, to evaluate the camera contrib ution in equation (25), the average value of S lum determined for each single-shot image was used, potentially leading to additional scatter from pixel-to-pixel variations in luminescence intensity, especially at low seeding concentrations. Finally, as previously mentioned, the effect of shot-to-shot laser fluence fluctuations needs to be experimentally isolated in the future, as neglecting this effect in equation (24) may also be responsible for a significant amount of the observed scatter. ...
Article
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This work presents a new thermographic phosphor particle-based gas thermometry technique that utilizes the ratio of temperature-dependent luminescence intensity and the temperature-insensitive elastic Mie scattering from phosphor particles seeded into the gas. This method has the potential for high temperature sensitivity. However, the large range of particle sizes typical of thermographic phosphors results in additional uncertainty in the measured ratio and temperature. The uncertainty in the intensity ratio is measured as a function of phosphor seeding density for the phosphor Ce:LuAG. The added uncertainty in the single-shot ratio measurements, assumed to be due to the non-uniform particle size distribution (PSD), was estimated to range from 20% for a seeding density of 40 mm ⁻³ to 10% at 210 mm ⁻³ . Measurements at heated jet exit temperatures of 750 K and 820 K revealed that, even with the added ratio uncertainty, single-shot temperature precisions better than 2% (<15 K) were achieved with seeding densities less than 150 mm ⁻³ . By combining ratio precision and temperature sensitivity measurements, it was estimated that the technique is capable of single-shot temperature precision better than 4% from 670 K to 1000 K, and better than 1.5% from 800 K to 900 K, for a seeding density of 300 mm ⁻³ . Measurements are limited to temperatures greater than approximately 600 K for Ce:LuAG due to low temperature sensitivity and a double-valued ratio below this temperature. These results demonstrate the potential of this new strategy to advance the state-of-the-art for APT measurements.
... 5 Therefore, YAG: Ce phosphor, especially nanoparticles are synthesized by glycothermal, sol-gel, carbonate precipitation, solvothermal reaction with sintering, vacuum sintering, and solid-state reaction methods. [6][7][8][9][10][11][12] The glycothermal method can produce well-dispersion of the YAG: Ce nanoparticles without their aggregation. 11,12 However, others are easily reaggregated by Van der Waals force, and Derjaguin, Landau, Vervey, and Overbeek (DLVO) theory. ...
... 11,12 However, others are easily reaggregated by Van der Waals force, and Derjaguin, Landau, Vervey, and Overbeek (DLVO) theory. [6][7][8][9][10] There are some reports preparation of nanoparticles by the laser ablation methods. [13][14][15] The laser ablation in liquid has several characteristics for synthesized nanoparticle, such as simple process, high efficiency, and use of highly dispersible pure colloidal solutions, as compared with the laser ablation method in gas phase. ...
... Subsequently, the recrystallized particles are reaggregated during the cooling process, resulting in the generation of nanoparticles with the oxidation by annealing around the laser irradiation area, as shown in Fig. 13c. 7,8,15,18,37 Moreover, it is observed that the peak intensities of Ba are decreased with increasing the laser energy density, as mentioned in the XRD and STEM-EDX analyses. This phenomenon suggests that the higher laser energy density is effective for promoting the generation of nanoparticles. ...
Article
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Y3Al5O12: Ce³⁺ (YAG: Ce) nanoparticles were generated by the laser ablation from the micron-size YAG: Ce particles suspended in deionized water as a target suspension. The mean diameter of nanoparticles observed by a scanning electron microscopy were about 15–300 nm, and the morphology showed a dependence on an average energy density of Nd: YAG laser. The photoluminescence spectra exhibited peaks at 510 and 560 nm which are attributed to the 5d→4f transition of the Ce³⁺ activator. The luminescence intensity for the nanoparticles generated by the suspension increased with increasing the average energy density of Nd: YAG laser, and the intensity of 510 nm peak also exhibited higher than that for the nanoparticles generated by the micron-size particles precipitated on a bottom of vial. It was found that the laser ablation in liquid using the suspension was effective to generate the YAG: Ce phosphor nanoparticles.
... On the other hand, wet chemical method is an effective way to resolve this problem due to the absence of sintering aids during ceramic sintering. In recent years, various wet chemical methods have been successfully developed to synthesize LuAG nano-sized powders such as co-precipitation method [8,12], sol-gel method [13,14] and solvothermal method [15,16]. These methods result in reactants mixing on a molecular level and reduction of the crystallization temperature of powders, which is usually 400-500°C lower than that using solid-state reaction method [7,8,[12][13][14]. ...
... In recent years, various wet chemical methods have been successfully developed to synthesize LuAG nano-sized powders such as co-precipitation method [8,12], sol-gel method [13,14] and solvothermal method [15,16]. These methods result in reactants mixing on a molecular level and reduction of the crystallization temperature of powders, which is usually 400-500°C lower than that using solid-state reaction method [7,8,[12][13][14]. Among these methods, co-precipitation method is a commonly used and promising technique since the particles can be prepared on a large scale in aqueous solution rather than in organic chemicals without using complicated apparatus. ...
... Emission spectrum excited by 355 nm shows a broad band emission peaked at 518 nm ranging from 460 to 630 nm due to the typical Ce 3+ : 5d 1 ? 4f transition [14]. ...
Article
Nanosized Ce3+ doped Lu3Al5O12 (Ce:LuAG) powder with narrow particle size distribution and high sinterability were successfully synthesized via a modified co-precipitation method using hydroxy propyl cellulose (HPC) as surfactant. It was suggested that a polymer layer was formed by HPC wrapping on the Ce:LuAG precursors instead of free water during precipitation and drying processes owing to its typical property of lower critical solution temperature (LCST), which could reduce the agglomeration among the particles. The green compact shaped by the powders exhibited a superior linear thermal shrinkage (19.7%) from room temperature to 1500 °C and could be subsequently densified into high optical quality Ce:LuAG transparent ceramics at 1750 °C for 10 h under vacuum sintering without any sintering aids. The in-line optical transmittance of the Ce:LuAG ceramic reached 73.48% at the wavelength of 550 nm without observable micro-pores and secondary phases at grain boundaries or within grains.
... 3+ phosphors synthesized at 1300-1600 • C under an excitation of 444 nm are represented in Fig. 7(a). All the phosphors exhibit a green-yellow emission through the transitions of Ce 3+ from the excited 2 D 3/2 state to the ground 4f 1 ( 2 F 5/2 and 2 F 7/2 ) state [38][39][40]. The emission spectra show a broad asymmetric band that covers from 460 to 700 nm, which can be represented by two Gaussian profiles. ...
... 3+ phosphors under an excitation of 444 nm. The spectra exhibit a strong green-yellow asymmetric emission, which is attributed to the transitions of Ce 3+ from the excited 2 D 3/2 state to the ground 4f 1 ( 2 F 5/2 and 2 F 7/2 ) state [38][39][40]. The LiF flux increases the emission intensity mainly due to the crystallinity improvement of the prepared phosphors, which can reduce the crystal defects on the surface of the phosphors and in the host lattice [27,53]. ...
Article
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Lu2.94Al5O12:0.06Ce³⁺ phosphors and LiF–, NaF–, and BaF2–added Lu2.94Al5O12:0.06Ce³⁺ phosphors were prepared by a sol−gel process. The effects of synthesizing temperature and fluoride fluxes such as LiF, NaF, and BaF2 on the photoluminescence properties of Lu2.94Al5O12:0.06Ce³⁺ phosphors are systematically investigated. The increase in synthesizing temperature and the addition of fluoride fluxes significantly enhance the PL properties due to the improvement in crystallinity. All the phosphors exhibit a green–yellow emission due to the ²D3/2 → ²F5/2, 7/2 transitions of Ce³⁺. Of the prepared phosphors, the 6 wt% BaF2–added Lu2.94Al5O12:0.06Ce³⁺ phosphor synthesized at 1400 °C shows the highest emission intensity, which is 173% stronger than that of the flux–free Lu2.94Al5O12:0.06Ce³⁺ phosphor.
... Wang Linxiang et al. [6] reported on luminescence properties of Ce:LuAG nano-sized powders obtained by combined co-precipitation and solvothermal methods. Li-Huli-Li et al. [18] prepared Ce:LuAG phosphors by nitrate-citrate sol-gel combustion process and studied its luminescence behavior. Praveena et al. [19] reported on temperature dependent photoluminescence behavior of Ce:LuAG nano-garnet prepared by Pichini's sol-gel method. ...
... The photoluminescence of Ce:LuAG nanophosphors prepared using a glass-beaker reactor at ambient temperature without refluxer route and calcined at 1300°C The high level of particulate agglomeration in the form of clusters increases the light scattering which in turn degrades the luminescence intensity. Jian Xu et al. [44] and Hui-Li-Li et al. [18] reported that the concentration quenching occurred in Ce 3+ doped LuAG nanopowder prepared by co-precipitation method. Whereas, in our modified synthesis approach by low-temperature refluxer method, luminescence quenching is not observed and found that the emission intensity of Ce:LuAG nanophosphors increases progressively with the increase in Ce 3+ doping concentrations (Fig. 8). ...
... as shown in figure 1 It can be observed that a platform of nearly 80% diffuse reflectance in the wavelength range of 530-750 nm, then it starts to decrease dramatically. The obvious absorption bands centered at 340 and 450 nm correspond to the allowed electric dipole transition of electrons from 2 F 5/2 and 2 F 7/2 ground state to the excited 2 D 5/2 , 2 D 3/2 levels of Ce 3+ ions, respectively [17,[23][24][25]. The origin of the band around 260 nm may be a transition to the third 5d level and the absorption of host lattice [6]. ...
... The effects of structure variations on the PL, PLE spectra and the luminescence efficiency can be observed obviously. From the PLE spectra (above), two high-efficiency broad bands are centered at 340 and 450 nm, which originate from 2 F 5/2 and 2 F 7/2 ground state to the excited 2 D 5/2 , 2 D 3/2 level of Ce 3+ ions [17,[23][24][25]. The intensity of excitation bands increases with varied Lu 3+ concentration. ...
Article
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A series of (Y,Lu)3Al5O12:Ce³⁺ (YLuAG:Ce) solid solutions were synthesized via the solid-state reaction route. The phosphors are all of the cubic garnet crystal structures confirmed by x-ray diffraction (XRD). The internal quantum efficiency and emission intensity of the phosphors can be enhanced by increasing the Lu³⁺ content in the host lattice, along with a blue shift of the emission peak. In addition, the blue shift of the emission peak correlates very well with the lattice contraction. Intense light-emitting diodes (LEDs) are successfully fabricated based on the YLuAG:Ce phosphors and 450 nm blue Ga(In)N chips. The luminous efficiency of YLuAG:Ce phosphors converted LEDs increases with elevating Lu³⁺ concentration. The results indicate that Ce³⁺ doped YLuAG solid solutions, especially LuAG:Ce phosphor is a promising green phosphor for solid-state lighting.
... 3+ phosphors, respectively, under an emission wavelength of 521 nm. The excitation spectra are characterized by the two strong peaks centered at ~345 nm ( 2 F 5/2 → 2 D 5/2 transition) and ~445 nm ( 2 F 5/2 → 2 D 3/2 transition) [19][20][21]. The energy states and transitions of the Ce 3+ ion are represented in Fig. 4(c). ...
... Due to atomic raw material mixing, more uniform ions doping and finer particle size are expected for the powders prepared by coprecipitation method compared with that prepared by traditional solid state reaction method [14]. It may bring about fewer structural and lattice defects [15] and thus better spectral and scintillation characteristics for Ce:LuAG ceramics prepared from the powder synthetized by the co-precipitation method [16][17][18][19][20]. Since 2005, Li et al. prepared Ce:LuAG powders by wet chemical method [21][22][23], and Cherepy et al. [16] prepared Ce:LuAG transparent ceramics by the citrate method and vacuum sintering. In 2011, Yanagida et al. [17] firstly reported 0.5 at.%Ce:LuAG transparent ceramics obtained from co-precipitated powders, which showed higher LY (14800 ph/MeV) than the Ce:LuAG single crystal grown by the Czochralski method [17]. ...
Article
In this work, Ce:LuAG and Ce,Ca:LuAG ceramic scintillators were vacuum sintered from the powders synthesized by the co-precipitation method. Composition and thermal behavior of the precursor, spectral and scintillation characteristics of the ceramics were investigated in detail. After calcination at 900 °C, amorphous precursor was completely transformed into LuAG and nano-powder with particle size of about 40 nm was formed finally. Light yield and relative intensity of the fast component of the Ce:LuAG ceramics are higher than those of Ce:LuAG ceramics prepared by the conventional solid-state reaction method. Furthermore, the scintillation decay of the Ce,Ca:LuAG ceramics is accelerated compared to the Ce:LuAG, with the LY(0.5 μs)/LY(3 μs) ratio of 93%.
... Ce 3+ activated Lu 3 Al 5 O 12 has numerous optical applications in the fields of green-orange phosphors for white LEDs [34,35], visible light amplifiers for dye-sensitized solar cells [36], fluorescence temperature sensors [37], and scintillating materials in nuclear dosimetry, computed tomography, and positron emission tomography [38,39]. Since the emission wavelength of the Ce 3+ activated Lu 3 Al 5 O 12 depends strongly on the Ga 3+ concentration, as discussed previously, the amount of Ga 3+ substituted for Al 3+ needs to be added appropriately into Lu 3 Al 5 O 12 considering its optical applications. ...
Article
Recent studies have revealed that the substitution of Ga³⁺ for Al³⁺ in garnet–type aluminate phosphors moves emission wavelength towards a short wavelength due to a decrease in crystal field strength. However, so far there has been no report on the empirical equations between emission wavelength (λ) and lattice distortion factor (d) in garnet–type aluminate phosphors. In this work, for the first time, to extract the correlation between λ and d in Lu2.94(Al1–xGax)5O12:0.06Ce³⁺ (0 ≤ x ≤ 0.5) phosphors, its emission wavelengths are measured using emission spectra, and its lattice distortion factors are calculated using crystallographic data. The empirical equation between λ and d is extracted as λ (nm) = 3365.42d – 3000.47. This empirical equation shows a good fit to the measured emission wavelengths. We believe that the empirical equation offers an effective and practical reference to design the chemical composition and to predict the emission wavelength in Lu3(Al1–xGax)5O12:Ce³⁺ phosphors.
... Fig. 7(b) and (c) show the deconvoluted emission peaks of the y = 0.002 and 0.006 phosphors, respectively. The two emission peaks centered at 503 and 544 nm for the y = 0.006 phosphor lie in the 2 D 3/2 → 2 F 5/2 and 2 D 3/2 → 2 F 7/2 transitions of Ce 3+ [58,59]. The 4f 1 ground state of Ce 3+ forms two 2 F 5/2 and 2 F 7/2 states by spin− orbit coupling [60,61]. ...
... Fig. 7(b) and (c) show the deconvoluted emission peaks of the y = 0.002 and 0.006 phosphors, respectively. The two emission peaks centered at 503 and 544 nm for the y = 0.006 phosphor lie in the 2 D 3/2 → 2 F 5/2 and 2 D 3/2 → 2 F 7/2 transitions of Ce 3+ [58,59]. The 4f 1 ground state of Ce 3+ forms two 2 F 5/2 and 2 F 7/2 states by spin− orbit coupling [60,61]. ...
Article
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Ce³⁺ and Pr³⁺ co−doped Lu3Al5O12 phosphors were synthesized by the sol–gel process, and their crystal structure, photoluminescence (PL) properties, and energy transfer (ET) from the Ce³⁺ to Pr³⁺ were studied. The Lu2.94−yAl5O12:0.06Ce³⁺, yPr³⁺ phosphors (0.002 ≤ y ≤ 0.008) showed the green−yellow emission from the ²D3/2 → ²F5/2, 7/2 transition of Ce³⁺ and the red emission at 610 and 637 nm, which were caused by the ¹D2→³H4 and ³P0→³H5 transitions of Pr³⁺, respectively. The optimal concentration of Pr³⁺ for efficient ET was found to be x = 0.006. The electric quadrupole−quadrupole interaction was responsible for the concentration quenching in the Lu2.94−yAl5O12:0.06Ce³⁺, yPr³⁺ phosphors, based on Dexter's theory. The incorporation of Pr³⁺ for Lu³⁺ enhanced the red PL intensity in the Lu2.94Al5O12:0.06Ce³⁺ phosphor.
... Compared with YAG:Ce phosphor ceramic, LuAG:Ce transparent ceramic has higher reliability, lower thermal quenching, and relatively broad emission intensity and area [146,[254][255][256][257]. Ji 3 Al 5 O 12 ceramics with different Ce-doping concentrations by tape-casting method and direct-forming method in conjunction with vacuum sintering technology (as shown in Figure 5.29a) [263]. ...
Chapter
This chapter presents the introduction of light-emitting diodes (LEDs)-based solid-state lighting (SSL) as well as fundamental aspects of luminescence and characteristic parameters of LEDs, the state-of-the-art using transparent ceramics (TCs) and/or translucent optical ceramics as spectral converters for SSL, especially in high-power white LEDs (wLEDs) and laser-driven SSL. LED is a kind of solid-state device that is made of semiconductor materials and converts electricity into light through a p–n junction or a diode. In phosphor-converted-wLEDs (pc-wLEDs), luminescence properties of employed inorganic phosphors including excitation/emission wavelength, quantum conversion efficiency, and thermal quenching behavior, directly determine the final performance of LED devices. The thermal quenching property greatly determines the practical usage of phosphors and final performance of pc-wLEDs, which becomes even more critical in high-power LEDs or laser-driven lighting systems because of their much more severe heat generation upon high injection current.
... Therefore, it can be observed that 4f 8 -4f 7 ( 8 S 7/2 )5di turns into an isolated state. Ce 3+ is widely used as an activating ion in various fluorescent systems: Lu 3 Al 5 O 12 :Ce 3+ [17], LaSi 6 N 11 :Ce 3+ [18], Tb 3 Al 5 O 12 :Ce 3+ [19], In summary, so we prefer to use any one of Ce 3+ , Pr 3+ , Tb 3+ and Eu 2+ doping for the Sr 2 Si 5 N 8 matrix to explore the changes in molecular structure and properties. ...
Article
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We use density functional theory (DFT) to study the molecular structure and electronic band structure of Sr2Si5N8:Eu2+ doped with trivalent lanthanides (Ln3+ = Ce3+, Tb3+, Pr3+). Li+ was used as a charge compensator for the charge imbalance caused by the partial replacement of Sr2+ by Ln3+. The doping of Ln lanthanide atom causes the structure of Sr2Si5N8 lattice to shrink due to the smaller atomic radius of Ln3+ and Li+ compared to Sr2+. The doped structure’s formation energy indicates that the formation energy of Li+, which is used to compensate for the charge imbalance, is the lowest when the Sr2 site is doped. Thus, a suitable Li+ doping site for double-doped lanthanide ions can be provided. In Sr2Si5N8:Eu2+, the doped Ce3+ can occupy partly the site of Sr12+ ([SrN8]), while Eu2+ accounts for Sr12+ and Sr22+ ([SrN10]). When the Pr3+ ion is selected as the dopant in Sr2Si5N8:Eu2+, Pr3+ and Eu2+ would replace Sr22+ simultaneously. In this theoretical model, the replacement of Sr2+ by Tb3+ cannot exist reasonably. For the electronic structure, the energy level of Sr2Si5N8:Eu2+/Li+ doped with Ce3+ and Pr3+ appears at the bottom of the conduction band or in the forbidden band, which reduces the energy bandgap of Sr2Si5N8. We use DFT+U to adjust the lanthanide ion 4f energy level. The adjusted 4f-CBM of CeSr1LiSr1-Sr2Si5N8 is from 2.42 to 2.85 eV. The energy range of 4f-CBM in PrSr1LiSr1-Sr2Si5N8 is 2.75–2.99 eV and its peak is 2.90 eV; the addition of Ce3+ in EuSr1CeSr1LiSr1 made the 4f energy level of Eu2+ blue shift. The addition of Pr3+ in EuSr2PrSr2LiSr1 makes part of the Eu2+ 4f energy level blue shift. Eu2+ 4f energy level in EuSr2CeSr1LiSr1 is not in the forbidden band, so Eu2+ is not used as the emission center.
... The efforts on performance optimization were also carried out by powder engineering, Li et al. [7]. synthesized Ce:LuAG nano-powders by the co-precipitation method (average particle size is 50 nm), sol-gel combustion method (about 30 nm) [8] and urea homogeneous precipitation method (about 30 nm) [9] respectively to use them as raw materials for transparent ceramics sintering. The light yield of the Ce:LuAG ceramic prepared with powders of co-precipitation method is improved to 4818 ph/MeV, around the 60% value of BGO single crystal (8080 ph/MeV) [5] and the transmittance reached to 70% @ 1.5 mm at visible light range. ...
Article
Fabrication, microstructure and luminescence properties of Lu3A15O12 ceramic scintillators with different Ce³⁺ doping concentrations (0, 0.1, 0.3, 0.5 at. %) were investigated. Ceramics were vacuum sintered at 1550oC-1890 °C for 10h, respectively. Low amount of mono sintering aid (0.03 wt % MgO) was used. The optimum inline transmittance of the as sintered ceramics reaches to 80% in the visible light range (1 mm thickness). The photoluminescence shows characteristic Ce³⁺ emission peaking at around 530 nm 0.3 at.% Ce:LuAG ceramic has the most intense XEL intensity (peaking at around 519 nm). The light yield was optimized to 4.36 folds of BGO crystal. High radiation hardness of Ce:LuAG ceramics was proved under Proton-Irradiation (PI) with energy of 45 MeV. The results show Ce:LuAG ceramics have a potential application in calorimeters in the high energy physics and devices in the outer space environment.
... In order to enhance the performance of garnet ceramics, many efforts have been made so far, among which the synthese sis of highquality garnet powders were stressed [9]. In general, ultrafine garnet powders with good emission performance and uniform particle size are usually considered as the ideal candidate for ceramics preparation. ...
Article
The nano-sized neodymium doped aluminum lutetium garnet (LuAG:Nd) phosphors well crystallized with particle size of around 100–130 nm were successfully synthesized via microwave-induced solution combustion method. The optimal crystallization temperature of LuAG:Nd was determined at 900 °C based on controlled trials. XRD results showed an obvious distortion in lattice parameters of LuAG, which could be confirmed by the shift of diffraction peak towards lower degrees with Nd concentration increasing. Another evidence for successful doping of neodymium was the absorption line at around 808 nm in the absorption spectra, which could result from the Nd3+ 4I9/2-⁴F5/2 transition. Furthermore, the near-infrared spectra showed that the quenching concentration of Nd³⁺ in prepared LuAG:Nd polycrystalline samples with the highest intensity of 1064 nm was at 5 mol%.
... Fig. 5a illustrates the emission spectra of the synthesized HAp:Ce 3þ phosphors with different doping concentration upon 313 nm excitation. Generally, emission lines attributed to allowed 5d-4f transition in Ce 3þdoped materials are quite broad [41,42]. Ce 3þ luminescence is ascribed to the electron transitions from the lowest crystal splitting component of 5d level to the ground state of Ce 3þ [43]. ...
Article
Ce³⁺-doped apatites have been synthesized by precipitation method in the range of the Ce/Ca atomic ratio in solutions from 0.05 to 5%. Obtained precipitates were studied with X-ray powder diffraction, infrared spectroscopy, scanning electron microscopy, EDX and luminescence spectroscopy. Cerium content in the synthesized apatites reaches 0.33 apfu (Ce/Ca = 3.9%). Relations between Ce content in the solution and precipitate have been established. It was revealed that during synthesis Ce-monazite starts to precipitate as a secondary phase at 1% Ce/Ca ratio in starting solution. Doping concentration effect on the luminescence intensity and lifetime of HAp:Ce³⁺ nanophosphors was studied in detail. Optimum doping concentration of Ce³⁺ ions in hydroxyapatite host was determined to be 0.3% of the Ce/Ca atomic ratio, which corresponds to 0.5% of the Ce/Ca ratio in the starting solution. The luminescence quenching occurs through energy transfer among the nearest neighbor Ce³⁺ ions.
... Recently, there are a lot of studies on this ideal green Lu 3 Al 5 O 12 :Ce 3+ phosphor powder which can be used in W-LEDs [11]. Many methods, such as molten salts method, spray pyrolysis [12], sol-gel method [13,14] and co-precipitation method [15,16] are extensively used to prepare the desired Lu 3 Al 5 O 12 :Ce 3+ phosphor powder. However, several disadvantages, such as low luminescence intensity and complicated synthesis process, limit its large-scale industrial production. ...
Article
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Lu3Al5O12:Ce3+ phosphor powder, which exhibits green emission band, was synthesized by the high-temperature solid-state reaction method with a flux BaF2. X-ray diffraction (XRD), photoluminescence (PL) spectra, and fluorescent lifetime spectra were used to characterize the structure and luminescent properties of the sample. The XRD patterns indicated that when prepared at 1550 °C for 3 h with 4 wt% flux, Lu3Al5O12:Ce3+ phosphors powder is the garnet cubic crystal system structure. Photoluminescence (PL) spectra showed that the Lu3Al5O12:Ce3+ phosphor powder can be effectively excited by near ultraviolet and blue light, emitting broad band peaking at 505 nm, which is attributed to 2F5/2 → 2D5/2 transition. The self-concentration quenching mechanism of Ce3+ is the dipole–dipole interaction. Small amount of Pr3+ increased red light emission at 610 nm. Photoluminescence (PL) spectra and fluorescent lifetime spectra indicated that there was an efficient energy transfer process between Ce3+ and Pr3+.
... The lutetium aluminum garnet doped with quadrivalent manganese, LuAG:Mn 4þ was synthesized by sol-gel method [21,22]. As reported in YAG, Mn 4þ ions can better enter the YAG crystal lattice when additional charge compensator is applied, e.g., Mg 2þ [23]. ...
Article
Optical thermometry based on luminescent materials has garnered much attention due to its many advantages. But higher sensitivity is still expected in physiological temperature range which is of special significance in medicine and biology. For this purpose, quadrivalent manganese doped lutetium aluminum garnet, Lu3Al5O12: Mn⁴⁺, or simply LuAG: Mn⁴⁺, has been successfully synthesized by sol-gel method and its temperature dependent luminescence has been investigated in the present work. Compared to the common red emission phosphors Y3Al5O12: Mn⁴⁺ (YAG:Mn⁴⁺) with same structure, LuAG:Mn⁴⁺ has a stronger crystal field strength and a higher thermal-quenching activation energy (ΔE) of 5732 cm⁻¹. Rapid thermal quenching of the Mn⁴⁺ luminescence occurred above room temperature around 90 °C for our LuAG:Mn⁴⁺ sample. Temperature dependent decay curves of Mn⁴⁺ emission from LuAG:Mn⁴⁺ revealed that an extraordinary high sensitivity can be achieved from luminescence lifetime measurements covering physiological temperature range with a sensitivity of 3.75% K⁻¹ at 38 °C.
... Ce 3+ -doped aluminum garnet (R 3 Al 5 O 12 ) systems are considered suitable phosphors for use in phosphor-conversion white light emitting diodes (pc-WLEDs) pumped by blue LED chips. Among these phosphors, Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce 3+ ) [1][2][3] and Lu 3 Al 5 O 12 :Ce 3+ (LuAG:Ce 3+ ) [4][5][6][7][8] are used predominantly as yellow-and green-emitting phosphors, respectively. In addition, aluminum garnets doped with Er 3+ and Yb 3+ have been investigated as upconversion (UC) phosphors, which convert near infrared (NIR, ~980 nm) to visible radiation through two-photon UC processes; these garnets include YAG:Er 3+ [9], YAG:Yb 3+ ,Er 3+ [10,11], and Yb 3 Al 5 O 12 :Er 3+ (YbAG:Er 3+ ) [12][13][14]. ...
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... Also, whereas a transition of 4f 7 → 4f 6 5d 1 in Ce 3+ occurs at 347 nm and 450 nm for the green phosphor Lu 3 Al 5 O 12 :Ce 3+, and green light is emitted in a wide range of 450~650 nm, a transition of 4f 7 → 4f 6 5d 1 in Eu 2+ occurs in the section of 300~550 nm for the red phosphor (Sr,Ca) AlSiN 3 :Eu 2+ to emit red light at 620~650 nm. [16][17] Eventually, two colors of light are overlapped at 450~550 nm, and the red phosphor is known to re-absorb light emitted by the green phosphor. Therefore, in the case of G7R3, the green light could be affirmed to have a remarkably low intensity despite of having a not so small amount of green phosphor. ...
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... It is consistent with the result of excitation spectra shown in Fig. 3. This phenomenon was also observed in SrZn 2 Si 2 O 7 :Eu 2+ powder [13], YAG: Ce 3+ powder [14] and LuAG: Ce 3+ powder [15], it ascribes improved crystallization of the powders. Both the XRD results in Fig. 1 and the TEM results in Fig. 2 support this interpretation. ...
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This chapter describes the applications of sol-gel methods to scintillation material development. Several approaches to the development of various kinds of scintillation materials are introduced, with main focus on rare-earth-doped silicate glasses and organic-inorganic hybrid materials. Three examples are introduced in detail, in which one is on Pr³⁺-doped silicate glasses and the other two are on the inorganic glass-polymer hybrids. From the viewpoint of practical applications, an enhancement in energy transfer efficiency from the host glass to the luminescence centers is necessary for silicate glasses. On the other hand, organic-inorganic hybrid materials are promising fast scintillation materials for high-energy photons and thermal neutrons. © Springer International Publishing AG, part of Springer Nature 2018.
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With the advanced formulation of new phosphors and latest progress in packaging design, technologies to obtain the higher color quality and healthier white LEDs are investigated. The luminescent properties were systematically characterized by the spectrum power distribution (SPD) and IES TM-30-15. By engineering the SPD of WLEDs, we developed light sources which present qualities closest to daylight with higher color rendering index (CRI), better spectral continuity and more nature color comparing to typical Ra 80 WLED on the market. Meanwhile, the white LEDs have been designed to assist human circadian rhythms. It offers benefits that are not available by normal LED light sources, including minimized the potential blue hazard, improved focus and increased productivity. The specific mechanism and relevant parameters of achieving high quality white LEDs will be investigated and analyzed in this paper.
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Thermographic phosphors continue to be investigated for gas thermometry in combustion applications due to their relative non-intrusiveness and ability to survive harsh environments. To further develop this technology, the mechanisms leading to their temperature-sensitive emission must be understood in greater detail. As a result, this work focuses on the quenching mechanisms of four different thermographic phosphors: Pr:YAG, Pr:LuAG, Ce:YAG, and Ce:LuAG. Spectrally- and temporally-resolved emission measurements were performed in a tube furnace, providing data on the emission properties of the phosphors at elevated temperatures. A quantum mechanical single configurational coordinate (QMSCC) model is used to understand the temperature sensitivity of the emission spectrum and of the nonradiative intersystem crossing. Energy diagrams for each phosphor are constructed to understand the likelihood of nonradiative ionization to the conduction band as a thermal-quenching mechanism. Configurational coordinate diagrams for each phosphor are constructed and used to interpret the mechanism responsible for thermal quenching. It is found that intersystem crossing is responsible for thermal quenching of Pr:YAG and Pr:LuAG, whereas ionization to the conduction band is the likely mechanism for Ce:YAG and Ce:LuAG. The ability to understand and model the mechanisms associated with the temperature-sensitive emission properties will be a valuable tool towards choosing appropriate thermographic phosphors for specific gas thermometry applications.
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The substitutional solubility for the Ce³⁺ ions in Lu3Al5O12 was estimated using crystal structure refinement and measurement of the luminescence. The photoluminescence excitation spectra of Lu3Al5O12:Ce³⁺ powders were composed of two peaks at approximately 347 nm and 450 nm, respectively, owing to the ground-state doublet of the Ce³⁺ ions, while a single emission band was observed in the green region. The solubility limit for the Ce³⁺ ions was determined by measurement of the actual Ce³⁺ concentrations in the particles, the refined crystal parameters, the evolution of the photoluminescence spectra, and the critical distance for energy transfer between the Ce³⁺ ions; the limits were approximately 1.7 and 3 mol% for 1600 and 1700 °C, respectively.
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Mg4Nb2O9 single phase sample with corundum like hexagonal structure has been successfully synthesized by two stage processes. Thermal characterization of precursors has been studied by TG-DTA. The phase purity is identified by XRD and Raman spectroscopy. The structural analysis has been studied by FESEM, HRTEM including EDX for chemical identification. Optical behaviour is investigated by diffuse reflectance spectroscopy and dielectric property is accessed during investigation. The effect of annealing temperature, phase formation, chemical composition, morphology, band gap energy and dielectric behaviour of single phase Mg4Nb2O9 are examined. Average crystallite size of single phase Mg4Nb2O9 material is around 37.3 and 22 nm from XRD and HRTEM analysis, respectively for the 1000°C treated materials. The direct band gap energy is measured about 3.59 eV from diffuse reflectance spectra of the sample synthesized at 1000°C. Dielectric constant and loss tangent of Mg4Nb2O9 material is observed in the range of 40 Hz-110 MHz frequency.
Chapter
White Light-Emitting Diodes (WLEDs) is a promising conserve energy device for altering the traditional illuminating apparatus because of their high efficiency, high flexibility, long lifetime, low energy consumption, and friendly environment. Of course you can frequently find WLEDs in your daily life. Phosphor is an important component of WLEDs and has been investigated broadly. This chapter introduces readers who begin meeting these fields to understand phosphor including history, principle, application, and perspective. The first part is a fundamental definition to luminescent materials. The second part provides requirements, classifications, and applications of phosphors for phosphor-converted LEDs (pc-LEDs). Finally, we propose some prospects and challenges of optical materials in the future.
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A warm-white emitting persistent luminescence phosphor Lu3Al2Ga3O12:Pr³⁺ was synthesized by solid state method at 1600 °C in air. The refined crystal structure of Lu3Al2Ga3O12 host was solved by X-ray diffraction (XRD). The photoluminescence spectra, decay curve and thermoluminescence were investigated. It was revealed that the persistent luminescence originated from the f-f transitions of Pr³⁺ emitters at Lu³⁺ sites in LuO8 polyhedrons, and it showed white color due to the ³P0→³H4, ³P1→³H5, ³P0→³H5, ³P0→³H6, ³P0→³F2, ³P0→³F3 and ³P0→³F4 transitions of Pr³⁺ emitters in a wide range. The persistent luminescence of Pr³⁺ in this host could be promoted by f-d transition (278 nm) but f-f transitions, due to the different thermal activation energy. The persistent luminescence of the optimal sample could be actually recorded for 3 h by the definition of 0.32 mcd/m² and was visible for more than 7 h by dark-adapted vision in darkness. The initial depth of the dominant shallow traps was calculated to be about 0.56 eV, which is suitable for persistent luminescence. The different roles of the shallow and deep traps on the persistent decay process were investigated. Accordingly, the persistent luminescence processes and mechanism of the as-synthesized Lu3Al2Ga3O12:Pr³⁺ phosphors were proposed.
Chapter
Climate change affects people’s lives by altering temperature, water supply, and rainfall and by influencing the frequency of natural disasters. Researchers are actively looking for alternative energy sources that do not emit carbon dioxide. White light-emitting diodes (WLEDs) have been considered one of the most promising next-generation lighting technologies because they significantly reduce global power requirements and the use of fossil fuels. WLEDs have attracted considerable attention because of their significant luminous efficiency, low power consumption, reliability, and environmental friendliness. This chapter discusses the fundamental principles and optical properties of phosphors and quantum dots (QDs) for light-emitting diodes (LEDs). The discussions are mainly focused on the luminescent mechanisms, phosphor and QD components, and the corresponding effects on their optical properties and prospect. We also tackle a number of concepts involved in the nephelauxetic effect, crystal field splitting, energy transfer, thermal effect, and quantum confinement effect, which leads to luminescence. Illustrative examples from luminescent materials applied in lighting are used. Phosphors for ultraviolet (UV) LEDs and blue LEDs are treated separately because the processes leading to excitation, emission, color, bandwidth, and thermal stability are comparable with each other in fluorescent lamps. The production of semiconducting QDs will be discussed with the concept of “the separation of nucleation and growth.” The exploration of QD-emission colors emphasizes the core material and nanocrystal size for tuning from near-UV to near-infrared spectra.
Chapter
This chapter describes the applications of sol–gel methods to scintillation material development. Several approaches to the development of various kinds of scintillation materials are introduced, with main focus on rare-earth-doped silicate glasses and organic–inorganic hybrid materials. Three examples are introduced in detail, in which one is on Pr3+-doped silicate glasses and the other two are on the inorganic glass–polymer hybrids. From the viewpoint of practical applications, an enhancement in energy transfer efficiency from the host glass to the luminescence centers is necessary for silicate glasses. On the other hand, organic–inorganic hybrid materials are promising fast scintillation materials for high-energy photons and thermal neutrons.
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The spectra of pulsed cathodoluminescence (PCL) and optical transmission (OT) of crystals grown from Lu3.01−xYxAl4.99O12 melts doped with Cr³⁺, Ce³⁺, and Sc³⁺ ions before and after irradiation with gamma radiation of a ⁶⁰Co radioactive source are studied. The gamma radiation dose absorbed by samples was 45 Mrad. The maximum gamma-radiation-induced absorbance in the range of 525–700 nm was 0.48 cm⁻¹. Changes in the PCL and OT spectra of all samples after irradiation were detected. It was found that the relative intensity of Cr³⁺ bands increased after irradiation in relation to the Ce³⁺ band intensity by a factor of 1.6–8; the OT spectra of all samples after irradiation lost specific features and became identical. The results obtained are qualitatively explained. According to the explanation, the induced absorption is controlled first of all by optically active Frenkel defects formed after irradiation, which include an oxygen vacancy and an interstitial oxygen ion.
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Currently, phosphor-in-glass (PiG) approach draws great attention because of its excellent thermal resistance and facile process in WLED fabrication. However, the red light deficiency results in high correlated color temperature (CCT) and low color rendering index (CRI) in white light-emitting diode (WLED). Herein, a new LuAG:Ce3+ phosphor-in-glass (Lu-PiG) combining with the CaAlSiN3:Eu2+ red phosphor layer was synthesized by the low temperature co-sintering and screen-printing techniques, which was experimentally demonstrated to replace the conventional polymer-based phosphor converter and realized the chromaticity tuning for LuAG:Ce3+ phosphor with WLED. The Lu-PiG constructed WLED exhibited excellent thermal stability, but it still showed a typical cold white light resulting from the absence of red light component. Therefore, a stacking geometric configuration by screen-printing a red phosphor layer on the Lu-PiG substrate (R&Lu-PiG) was designed to solve red deficiency problem. The R&Lu-PiG color converter showed an excellent thermal stability with only 8.2 % emission loss compared to the Lu-PiG when elevating temperature from 303 K to 433 K. By adjusting the CaAlSiN3:Eu2+ phosphor content in the layer, we obtained a high-performance warm WLED with a luminous efficacy of 102.1 lm/W, a CCT of 3410 K and a CRI of 76.5 under 20 mA current driving. Thus, it is expected that this developed R&Lu-PiG color converters could have large potential applications in high-power warm WLED.
Chapter
White Light-Emitting Diodes (WLEDs) is a promising conserve energy device for altering the traditional illuminating apparatus because of their high efficiency, high flexibility, long lifetime, low energy consumption, and friendly environment. Of course you can frequently find WLEDs in your daily life. Phosphor is an important component of WLEDs and has been investigated broadly. This chapter introduces readers who begin meeting these fields to understand phosphor including history, principle, application, and perspective. The first part is a fundamental definition to luminescent materials. The second part provides requirements, classifications, and applications of phosphors for phosphor-converted LEDs (pc-LEDs). Finally, we propose some prospects and challenges of optical materials in the future.
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Aluminum Garnet (LuAG) precursors were co-precipitated by using ethanol–water as the precipitant solvent. The effect of different volume ratios of ethanol to water (R) on the preparation of pure-phase LuAG powders has been mainly studied. The evolution of phase, composition and micro-structure of the as-synthesized LuAG powders were characterized by TG/DTA, FTIR, XRD, BET, and SEM. The BET-equivalent diameter of LuAG nano particles increased with R. The ethanol–water solvent does not change the main composition of the LuAG precursors, but has great influence on the morphology of the final LuAG nano particles. Uniformly dispersed LuAG powders calcined at 1200 °C for 3 h with a particle size of approximately 120 nm were obtained by using ethanol–water solvent with proper R = 1. The mechanism of ethanol in the preparation process was discussed.
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Cerium activated Lu3Al5O12 garnet, efficiently substituted by Y3+ doping, and has been developed for green-yellow emitting phosphors. The powder processing of [(Lu1−xYx)1−z Cez]3Al5O12 solid solution powder were achieved through synthesis via sol–gel method. The Y3+ cationic substitutions in the LuAG host matrix have been changed from 0.05 to 0.2 at%, and their effects on structural and luminescence properties were systematically investigated. The phase formation and characteristics of solid solution were studied by means of differential scanning calorimetry (DSC), X-ray diffraction technique (XRD), Fourier transforms infrared spectroscopy (FTIR) and photoluminescence spectroscopy (PL). The DSC result shows that the crystallization of the powder precursors started at 960 °C. X-ray diffraction analysis indicated that the single and pure cubic crystalline phase was formed and no secondary phases of the garnet structure are observed. The photoluminescence spectra of these solid solutions exhibit band edge emission at 500 nm in green-yellow region attributed to the interconfigurational 5d → 4f transitions of Ce3+ ions. Additionally, the evolution of crystallite size and photoluminescence spectra with the increasing of Y3+ content is studied and discussed.
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CaS: Ce, Sm films were fabricated by a sol-gel method, subsequently annealed at 500°C for 1 hr in N2 atmosphere. The optimum mole ratio of C2H4(OH)2 to Ca2+ is 2 : 1. The XRD results show that CaS: Ce, Sm is face-centered cubic structure and the lattice constant increases 0. 07 Å along all directions. Its diffraction peak has a certain broadening and moves to small angel, which is due to the surface effect of the nano particles. The AFM results show that the average grain size of CaS: Ce, Sm films is 30 nm and the grain size distribution is uniform. The strong emission peaking at 626 nm with 420 nm as excitation light corresponds to the 6H5/2→4M19/2(6P, 4P)5/2 transition.
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The isotypic nitridophosphates Ba3P5N10X (X = Cl, I) have been synthesized by high-temperature reaction under pressures between 1 and 5 GPa. The crystal structures of both compounds were solved and refined using single-crystal X-ray diffraction data. Accuracy of the structure determination as well as phase purity of the products were confirmed by Rietveld refinement and FTIR spectroscopy. The band gap values (4.0-4.3 eV) for the direct transitions were determined from UV-vis data using the Kubelka-Munk function and were confirmed by DFT calculations. Both compounds crystallize in the Ba3P5N10Br structure type (space group Pnma (No. 62), Z = 8; Ba3P5N10Cl, a = 12.5182(5) Å, b = 13.1798(5) Å, c = 13.7676(6) Å, R1 = 0.0214, wR2 = 0.0526; Ba3P5N10I, a = 12.6311(7) Å, b = 13.2565(8) Å, c = 13.8689(8) Å, R1 = 0.0257, wR2 = 0.0586) with a tetrahedra network being analogous to the topology of the JOZ zeolite structure type. The crystal structure is built up of all-side vertex-sharing PN4 tetrahedra leading to a zeolite-like framework with three-dimensional achter-ring channels containing alternately Ba and respective halide atoms. The condensed dreier-, vierer-, and sechser-rings form two different composite building units made up of 344286-cages. Upon being doped with Eu2+, the title compounds exhibit intriguing luminescence properties, which were compared with that of Ba3P5N10Br:Eu2+. Upon excitation by near-UV light, nonsaturated color luminescence from multiple emission centers was observed in the orange (X = Cl) and cyan to amber (X = I) spectral range of the visible spectrum.
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Three series of nanocrystalline powders of Lu2O3:Eu with Eu concentration varying from 0.05 to 13% were prepared. All specimens were obtained through combustion synthesis using urea or glycine as the fuel. The powders of the first series consisted of materials with crystallites about 13 nm in size and were prepared with urea. For the next series of powders, made with glycine, the crystallites were about 30 nm in size. The powders of the third series differed from those of the second one in that they were co-doped with 1% of Ca. For the series made with urea the quantum efficiency was highest for 3% of Eu and never exceeded about 30%. For glycine-prepared specimens the highest quantum efficiency was about 90%. Without the Ca co-doping such a value could be obtained for specimens doped with 5% of Eu, while in the series co-doped with Ca 85-90% quantum efficiency could be maintained for all concentrations in the range 3-10%. A significant number of OH groups were proved to be left in the final product obtained with urea. The low quantum efficiency of these powders is attributed to this effect. The results prove that properly prepared nanocrystalline phosphors can produce luminescence efficiently.
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A novel ceramic synthesis technique, combustion synthesis, was explored to produce red-emitting Cr3+-doped Y3A15O12 and Eu3+-doped Y2O3 phosphors with improved physical and luminescent properties. This technique involves the reaction of metal nitrates (oxidizers) and an organic fuel (urea, carbohydrazide, glycine) at 500°C. Resulting powders are well-crystallized, with a large surface area and small particle size. The spectral energy distribution was observed using photoluminescence measurements. The effects of processing parameters such as type of fuel, fuelto-oxidizer ratio, furnace temperature, and batch water content were studied. An increase in phosphor brightness with increasing reaction temperature was observed. Postreaction heat treatments (1000°, 1300°, and 1600°C) increased the luminous intensity of as-synthesized powders. Residual carbon content and chromium site symmetry were investigated as possible explanations for the increase in brightness with increasing heat treatment temperature. By tailoring the reaction chemistry, the optimal conditions for producing the most luminescent phosphors have been identified.
Article
Yb-doped Lu 3Al 5O 12 (Yb:LuAG) single crystals were grown by the micro-pulling-down (μ-PD) method. The crystals were seeded-grown in the <1 1 1> direction and dimensions up to 300 mm in length and 5 mm in diameter were achieved. Photoluminescence spectra and decay kinetics of Yb:LuAG were studied after annealing. Under 225 nm excitation the double-peak emission at 335 and 480 nm was observed. Photoluminescence decay time of 23.9 ns was evaluated at 340 nm and T=80 K. Similar emission properties as those reported earlier for Yb-doped YAG crystal were obtained.
Article
The photoluminescence of Ce3+, Tb3+ and Sm3+, and energy transfer from Ce3+ to Tb3+, Dy3+ and Sm3+ in Mg2Y8(SiO4)6O2 are reported and discussed. The Ce3+ ion shows blue luminescence under UV excitation, and occupies simultaneously the 4f site and 6h site in the host lattice. The optimum concentrations for the 5D3 and 5D4 emissions of Tb3+ and the 4G5/2 emission of Sm3+ are determined to be 0.04, 0.20 and 0.10 mol in every mol of Mg2Y8(SiO4)6O2, respectively. The critical distances responsible for the cross-relaxation between the 5D3–5D4 and 7F6–7F0 transitions of Tb3+ and between the 4G5/2–4F9/2 and 6H5/2–4F9/2 transitions of Sm3+ are estimated to be 1.43 and 1.06 nm, respectively. Both Tb3+ and Dy3+ can be sensitized by Ce3+, but Ce3+ and Sm3+ quench each other.
Article
The preparation of nanocrystalline YAG:Eu phosphor by nitrate-citrate sol-gel combustion process was described. The crystalline development of the product was identified by x-ray diffraction analysis (XRD). Luminescence spectra were measured at room temperature by a fluorescence spectrophotometer with a 75-W xenon lamp. It was found that the method yielded a homogeneous and stoichiometric product.
Article
Coprecipitation of yttrium and aluminium hydroxide for the preparation of pure yttrium aluminium garnet (YAG) powder with small grain size is the subject of this study. Starting materials are sulphates and chlorides of yttrium and aluminium. To obtain pure YAG (Y3Al5O12), the pH during flocculation of the precursor must be chosen carefully. The presence of water increases the degree of agglomeration. To minimize agglomeration, the influence of dispersion liquids has been studied, leading to optimized conditions for precipitation.ZusammenfassungDas Thema dieser Arbeit ist die Kopräzipitation von Yttrium und Aluminium zur Darstellung von reinem Yttrium-Aluminium-Granat-Pulver mit kleiner Korngröße. Ausgangsmaterialien sind die Sulfate und Chloride von Yttrium und Aluminium. Um reines YAG (Y3Al5O12) zu erhalten muss der pH-Wert während der Fällung des Zwischenproduktes sorgfaltig gewählt werden. Die Anwesenheit von Wasser hat einen nachteiligen Effekt auf den Grad der Agglomeration. Um diesen nachteiligen Effekt beseitigen zu können wird der Einfluß verschiedener Dispersionsflüssigkeite untersucht. Damit ist es möglich geworden die optimale Bedingungen für die Fällung festzustellen.RésuméOn décrit la coprécipitation d'yttrium et d'aluminium pour obtenir une poudre d'yttrium aluminate très fine et de haute pureté. Comme materiaux de départ sont employés des sulphates et des chlorures d'yttrium et d'aluminium. La préparation de YAG (Y3Al5O12) pur demande un choix précis du pH pendant la floculation de produit intermédiaire. En ce qui concerne l'hydrolyse, la quantité relative d'eau détermine le degré d'agglomérisation. L'influence des liquides de dispersion différentes est étudiée ce qui a conduit aux conditions optimalisées pour la floculation.
Article
By using metal nitrates and oxides as the starting materials, Y3Al5O12 (YAG) and YAG:Re3+ (Re=Ce, Sm, Tb) powder phosphors were prepared by solid-state (SS), coprecipitation (CP) and citrate gel (CG) methods. The resulting YAG and YAG-based phosphors were characterized by XRD, FT-IR, SEM and photoluminescent excitation and emission spectra. The purified crystalline phases of YAG were obtained at 800 °C (CG) and 900 °C (CP, SS). At an identical annealing temperature and doping concentration, the doped rare-earth ions showed the stronger emission intensity in the CP- and SS-derived phosphors than the CG-derived YAG phosphors. The poor emission intensity for the CG-derived phosphors is mainly caused by the contamination of carbon impurities from citric acid in the starting materials.
Article
Yttrium aluminium garnet (YAG), represented by the chemical formula Y3Al5O12, was synthesised from the stoichiometric mixture of the metal nitrate solution by boiling with glycerol. For a fixed batch size, the glycerol amount was systematically varied to study its effect on the specific surface area and phase purity of the YAG powder. The quantity of glycerol was optimised to get the desired powder characteristics. Using this technique, single phase YAG powder of high specific surface area was obtained at 1000 °C. Characterisation was done by thermogravimetry (TG), differential thermal analysis (DTA), X-ray diffraction (XRD), particle size analysis and by measuring the specific surface area, as well as the carbon content, at various stages, to ascertain the quality of the product.
Article
Europium-doped cubic Gd2O3:Eu3+ nanoparticles containing various activator content in the range of 5–15wt% were synthesized by a liquid-phase reaction method to investigate the influence of Eu3+ loading on the optical properties of phosphors by using XRD, TEM, BET, spectrometer and fluorometer. The size of Gd2O3:Eu3+ powders was in the range 21–41nm. The phosphors showed an initial increase in luminescence and then a subsequent decrease with further doping (above 10wt%). The decay time was reduced with increasing Eu loading; however, it decreased significantly above the 10% Eu doping. From spectroscopic studies, the Eu3+ doping ion distribution was uniform and homogeneous up to the 10wt% loading because no concentration quenching effect was observed. However, further Eu3+ doping above 10wt% reduced the luminescence due to the concentration quenching effect, as deduced from the shortening of the decay time.
Article
The reaction of a stoichiometric mixture of aluminium isopropoxide and yttrium acetate in 1,4-butanediol at 300 °C yielded crystalline yttrium aluminium garnet having an approximate particle size of 30 nm. No other phases were detected. Similarly, all the lanthanide elements from Nd to Lu gave essentially single-phase aluminium garnets. Samarium and europium aluminium garnets were also formed by this method, but the products contained corresponding lanthanide acetate oxide. The use of ethylene glycol instead of 1,4-butanediol afforded amorphous products.
Article
The possibility of obtaining scintillators for X-ray detectors by liquid-phase epitaxy of Lu3Al5O12:Ce single-crystalline films (SCF) on Y3Al5O12 substrates is studied. Optical, luminescent and scintillation characteristics of Lu3Al5O12:Ce SCF doped by isoelectronic La, Y, Sc impurities are analyzed. The possibility of crystallization of Lu3Al5O12:Ce SCF on Y3Al5O12 substrates by means of matching of lattice parameters of these garnets due to the occupation of Al3+ octa-sites by Lu3+ ions is proved. Lu3Al5O12:Ce-based SCF containing Gd3+, Tb3+, and Eu3+ dopants were investigated with the aim of matching the emission spectra with the spectral sensitivity of radiation detectors like CCD cameras. The maximum light yield, exceeding that of analogs based on Y3Al5O12:Ce SCF by a factor of 1.1–1.5, is found in Lu3Al5O12:Ce3+-, Lu3Al5O12:Ce,Y,La- and Lu3Al5O12:Ce,Tb-SCF. An increase of the effective atomic number Zeff and density ρ up to the values of 60.6 and 7.35g/cm3, respectively, allows to raise the efficiency of X-ray absorption in comparison with Y3Al5O12:Ce3+-SCF by a factor of 2.5–8 and to reach a spatial resolution not
Article
Long emission wavelength scintillators are strongly required from the viewpoint of the practical use of silicon photo-diode, which has higher resolution with lower cost compared with photo-multipllier. Among the various scintillator emission centers, we regard emission from Yb3+ charge-transitions state (CTS) as a candidate. In order to investigate proper hosts for Yb3+ CTS, the yttrium gallium garnet host and lutetium aluminum garnet host were studied. Transparent and crack-free heavily Yb-doped YGG, i.e. {Y1−xYbx}3[Ga]2(Ga)3O12 (Yb: YGG, x=0.15, 0.5, 1.0) and heavily Yb-doped LuAG, i.e. {Lu1−xYbx}3[Al]2(Al)3O12 (Yb: LuAG, x=0.15, 0.5, 1.0) single crystals could be grown by the Modified Pulling Down method with 〈111〉 orientation. Emission, excitation spectra and decay kinetics were measured for these crystals. The CT transition of Yb3+ in the yttrium gallium garnet host was discussed compared with the Yb3+ one in the lutetium aluminum garnet host.
Article
Thermal decomposition of the amorphous coprecipitate of yttrium and aluminium hydroxides forming yttrium aluminium garnet has been investigated employing thermal analyses, X-ray diffraction and IR spectroscopy. On heating, the coprecipitate progressively loses water forming a stable but highly disordered hydroxy garnet which crystallizes at ∼1180 K and decomposes to YAG at ∼1290 K. Nucleation of the crystalline phase appears to begin at ∼800 K.
Article
Yttrium aluminum garnet (Y3Al5O12, YAG) powders were synthesized by a sol–gel combustion process from a mixed solution containing aluminum and yttrium nitrates. The thermal behavior of the precursor was determined by DSC–TG–MS techniques. FTIR and XRD techniques were used to characterize the processed precursor. It was found that excess citric acid and carboxylate mixture decomposed at about 400 °C to form carbonates. The YAG phase was supposed to nucleate directly from the amorphous precursor at about 800 °C. Mono-phase YAG crystallites could be formed without the formation of any intermediate phase at 900 °C.
Article
We studied the dependency of the photoluminescence (PL) intensity of Y2O3:Eu (15 wt%≤Eu≤25 wt%) nanocrystals from the viewpoint of surface area and amount of Eu concentration. Nanoscale Y2O3:Eu was synthesized by a liquid-phase reaction method The surface area and PL intensity of the sintered nanocrystals at 500 °C in air are dependent on the amount of Eu. The PL intensity increased with increasing surface area and decreasing Eu concentration in the Y2O3:Eu nanocrystals. These results indicate that the influence on PL in Y2O3:Eu nanocrystals above Eu=15 wt% was not caused alone by the concentration quenching effect due to an excess of Eu concentration or the surface area effect, caused by surface luminescence, but rather by their combined effects.
Article
The phase development and luminescence of chromium-doped yttrium aluminum garnet (Y3Al5O12:Cr or YAG:Cr) phosphors, prepared by both a chemical precipitation technique and a solid-state reaction, were studied. The YAG structure formed at a much lower temperature and by a different phase development sequence when the chemical method was employed. The light output of the chemically synthesized powders, measured by laser excitation, was discovered to increase with increasing heat treatment temperature and was found to be brightest when the YAG:Cr phosphor had excess aluminum.
Article
Drug-eluting stents (DES) have been shown to reduce the need for repeat revascularization compared with bare metal stents (BMS). However, there is little information regarding the safety and long-term efficacy of DES in patients with acute myocardial infarction (AMI). The aim of this study was to evaluate the safety and efficacy of DES in patients with AMI. Data from 211 consecutive patients with AMI treated with DES were compared with those from 228 consecutive patients with AMI treated with BMS. All patients were treated within 7 days of symptom onset. The incidence of major adverse cardiovascular events ([MACE]: death, reinfarction, and target vessel revascularization) was evaluated at 30 days and 1 year. Baseline clinical and angiographic characteristics were similar for both stent groups. However, patients who received DES had longer lesion lengths (23.0 +/- 12.7 vs. 18.8 +/- 10.6 mm, respectively; p < 0.001) and smaller reference diameters (2.97 +/- 0.52 vs. 3.19 +/- 0.63 mm, respectively, p < 0.001). At 30 days, the incidence rates of MACE (DES vs. BMS: 2.2 vs. 1.9%, p = 1.000) and stent thrombosis (BMS vs. DES: 0.9 vs. 1.7%; p = 0.434) did not differ significantly between the groups. At 1 year, patients with DES had a lower rate of MACE (BMS vs. DES: 14.0 vs. 6.6%; p = 0.011) primarily due to a lower target vessel revascularization rate (BMS vs. DES: 9.6 vs. 4.8%; p = 0.028). The DES appear to be superior to the BMS in reducing the risk of MACE in patients with AMI.
Article
Polycrystalline, transparent LuAG:Ce ceramics were fabricated by a solid-state reaction method using high-purity Lu2O3, Al2O3 and CeO2 powders. The mixed powder compacts were sintered at 1770°C for 10 h under vacuum and annealed at 1450°C for 20 h in air. The transmittance in the visible light region reaches 70%. The emission spectra at 470–650 nm wavelengths are consistent with that of LuAG:Ce single crystals, and satisfy the property requirements of a scintillator.
Article
Single crystal of heavily Yb3+-doped Lu3Al5O12 (Yb:LuAG) were grown by the micro-pulling-down method. Radio- and photoluminescence spectra of the Yb:LuAG were studied. Two bands peaking round 340–350 and 480–500 nm could be ascribed to charge transfer (CT) luminescence of Yb3+, as their position nearly coincide with the Yb3+-related CT emission in YAG matrix. The highest emission intensity was observed for Yb concentration of 5% with respect to the Lu site. Temperature dependence of photoluminescence spectra of the Yb: LuAG (5%) was measured and points to remarkable thermal quenching above liquid nitrogen temperature.
Article
Lutetium aluminum garnet (LuAG) precursor was co-precipitated from a mixed solution of aluminum and lutetium nitrates using ammonia water as precipitant. Phase evolution and thermal decomposition of the precursor during calcination was studied by TG-DSC and XRD. The particle size and morphology of the synthesized powders were determined by TEM. It was found that the precursor was amorphous and transformed to pure LuAG at about 900 °C. The crystallization stage was characterized by an exothermic peak of DSC curve at 1032 °C. The resultant LuAG powders were loosely agglomerated with an average particle size 50 nm. The addition of small amount of ammonia sulfate to mixed solution reduces the agglomeration and produces more uniform spherical particle.
Article
A YAlO3 (hexagonal) solid solution with and crystallizes at 880–935°C from an amorphous material prepared in the mole ratio Y3+/Al3+=3:5 by a sol–gel technique using hydrazine. The hexagonal YAlO3 phase transforms to Y3Al5O12 (YAG) at 1005–1075°C. The YAG powder calcined at 1200°C can be densified to transparency under vacuum for 2 h at 1600°C without additives.
Article
Scintillation response [Nphels(E) and LY(E) yields and energy resolutions] of well-defined and efficient Ce3+-doped aluminium perovskite (YAP) and garnets (YAG and LuAG) was investigated using the experimental set-up with HPMT multiplier. Possibilities of increasing scintillation response with growth of mixed (Y,Lu) crystals or with suitable co-doping are presented and also the influence of re-absorption of Ce3+ emission.
Article
Yttrium aluminum garnet (YAG) precursors for transparent ceramics were synthesized by the urea method under various [urea]/[metal ions] ([U]/[M]) conditions. Monophase YAG was obtained from solutions with a high [U]/[M] ratio after calcination at a temperature of 1200°C. The condition of the precipitates seemed to indicate that the yttrium compounds had precipitated onto the aluminum compounds. The surface morphology and size of the particles were controlled by the [U]/[M] ratio. The different reaction sequences of YAG crystallization for low- and high-ratio samples were dependent on morphology, size, and the quantity of chemical species that was precipitated as carbonate and/or sulfate compounds.
Article
Gels of yttrium aluminum garnet (YAG) with the stoichiometric composition 3Y2O35AI2O3, were prepared by a sol-gel technique and dried by supercritical extraction with CO2. Powders were produced by lightly grinding the dried gels. Crystallization of the powder occurred at 900C and within the limits of detection, the X-ray diffraction pattern of the crystallized material was identical to that of the stoichiometric composition. Powder compacts with a green density of 0.50 of the theoretical were sintered to nearly full density in O2 during constant heating rate sintering at 5 C min–1 to 1600 C. This is better than the density obtained with powders from a similar gel dried conventionally (by evaporation of the liquid) and considerably better than that obtained with powders prepared by solid state reaction. The room temperature flexural strength and fracture toughness of the material fabricated from the supercritically dried gels were 190 MPa and 2.2 MPa.m1/2, respectively. These strength and fracture toughness values are higher than those reported in other studies for YAG produced by the sintering route.
Article
Amorphous oxide combustion products with compositions corresponding to Y4Al2O9, YAlO3, and Y3Al5O12 were synthesized by the glycine-nitrate process and heat-treated to induce crystallization. The crystalline structure of the resulting powders was determined by powder X-ray diffraction techniques. The phase stabilities of the crystalline phases were investigated as functions of the glycine-to-nitrate ratio, the yttrium-to-aluminium ratio, and the heat-treatment conditions. Heat treatment for short durations resulted in incompletely crystalline powders that consisted of a mixture of Y4Al2O9, YAlO3, and Y3Al5O12 phases, regardless of the chemical composition of the amorphous combustion product. However, heat treatment for longer durations or higher temperature generated both pure-phase, monoclinic Y4Al2O9 and Y3Al5O12 with the garnet structure. Prolonged heat treatment at high temperature failed to generate pure-phase orthorhombic YAlO3. Subsequent analysis revealed a sluggish, complex crystallization process involving the formation and decomposition of several phases.
Article
Ultrafine luminescent yttrium aluminum garnet (YAG):Tb powders doped with different Tb concentration are prepared by a nitrate–citrate sol–gel combustion process. Single-phase cubic YAG:Tb crystalline is obtained at 800 °C by directly crystallizing from amorphous materials as determined by X-ray diffraction (XRD) techniques. The resultant YAG:Tb powders heat-treated at 1000 °C are uniform and in good dispersity with particle size of about 100 nm. The photoluminescence (PL) spectrum of Tb3+ substituted for Y3+ in YAG with different contents has been measured on samples calcined at 1000 °C.
Article
YAG precursors were co-precipitated from a mixed solution of aluminum and yttrium nitrates using ammonia water and ammonium hydrogen carbonate as precipitants, respectively. Phase evolution of the precursors during calcination and sinterability of the resultant YAG powders were compared between the two methods. The use of ammonia water produced a hydroxide precursor with an approximate composition of Al(OH)3·0.3[Y2(OH)5(NO3)·3H2O] which transformed to pure YAG at about 1000°C via YAlO3 phase. Severe agglomeration caused poor sinterability of the resultant YAG powders. The use of ammonium hydrogen carbonate produced a carbonate precursor with an approximate composition of NH4AlY0.6(CO3)1.9(OH)2·0.8H2O. The precursor directly converted to pure YAG at about 900°C. The precursor was loosely agglomerated and the resultant YAG powders showed good dispersity and excellent sinterability. For the same calcination temperature of 1100°C, YAG powders from the hydroxide precursor and the carbonate precursor densified to ∼81.2 and ∼99.8% of the theoretical, respectively, by vacuum sintering at 1500°C for 2 h.
Article
Ultrafine terbium-doped yttrium aluminum garnet (YAG:Tb) phosphor powders are prepared by a nitrate–citrate sol–gel combustion process using 1:1 ratio of citrate/nitrate. Phase evolution of the synthesized powder is determined by X-ray diffraction (XRD) techniques. Single-phase cubic YAG:Tb crystalline powder is obtained by calcinating the amorphous materials at 900 °C and no intermediate phase is observed. Transmission electronic microscope (TEM) morphology shows that the resultant YAG:Tb powders have uniform size and good homogeneity. The particle size of the product is investigated as a function of the calcination temperature. The photoluminescence (PL) spectrum of Tb3+ substituted for Y3+ in YAG with 5.0% content has been measured on samples calcined at different temperatures.
Article
A study was performed to characterize the homogeneous precipitation of yttrium aluminum garnet (YAG) precursor particles by the thermal decomposition of urea in aqueous solutions. Cation concentrations were varied from 0·005 m to 0·30 m. Observation of powder morphology together with chemical analysis suggests a sequential precipitation process with aluminum ions forming a solid phase first. Fine-grained, reactive powders were obtained that crystallized to single-phase YAG upon heating to 850°C. The precipitate was a hydrated basic carbonate.ZusammenfassungDie homogene Ausscheidung von Yttrium-Aluminium-Granat (YAG) Vorläuferteilchen, deren Herstellung durch thermische Zersetzung von Urea in wässriger Lösung erfolgte, wurde untersucht. Die Kationenkonzentration wurde zwischen 0·005 m und 0·3 m variiert. Aus der Pulvermorphologie in Kombination mit der chemischen Analyse läßt sich schließen, daß ein sequenzieller Ausscheidungs-prozeß stattfindet, beginnend mit den Aluminiumionen, die eine feste Phase bilden. Es konnten feinkörnige, reaktive Pulver hergestellt werden, die bei einer Erwärmung bis zu 850°C zu einem einphasigen YAG kristallisierten. Bei der Ausscheidung handelte es sich um ein hydratisertes, einfaches Karbonat.RésuméL'objet de cette étude est de caractériser la précipitation homogène de particules de précurseur pour le grenat d'yttrium et d'aluminium (YAG) par décomposition thermique d'urée en solution aqueuse. La concentration en cations est comprise entre 0·005 m et 0·30 m. L'observation de la morphologie des poudres associée à l'analyse chimique suggère un mécanisme de précipitation par étape, les ions aluminium formant d'abord une phase solide. On a obtenu des poudres fines et réactives qui cristallisent en un composé monophase de YAG par chauffage à 850°C. Le précipité est un carbonate hydrate basique.
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