Article

Synthesis and luminescence properties of single‐component Ca5(PO4)3F:Dy3+, Eu3+ white‐emitting phosphors

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Abstract

A series of Ca5(PO4)3F:Dy³⁺, Eu³⁺ phosphors was synthesized by a solid‐state reaction method. The XRD results show that all as‐prepared Ca5(PO4)3F:Dy³⁺, Eu³⁺ samples match well with the standard Ca5(PO4)3F structure and the doped Dy³⁺ and Eu³⁺ ions have no effect on the crystal structure. Under near‐ultraviolet excitation, Dy³⁺ doped Ca5(PO4)3F phosphor shows blue (486 nm) and yellow (579 nm) emissions, which correspond to ⁴F9/2→⁶H15/2 and ⁴F9/2→⁶H13/2 transitions, respectively. Eu³⁺ co‐doped Ca5(PO4)3F:Dy³⁺ phosphor shows the additional red emission of Eu³⁺ at 631 nm, and an improved color rendering index. The chromaticity coordinates of Ca5(PO4)3F:Dy³⁺, Eu³⁺ phosphors also indicate the excellent warm white emission characteristics and low correlated color temperature. Overall, these results suggest that the Ca5(PO4)3F:Dy³⁺, Eu³⁺ phosphors have potential applications in warm white light‐emitting diodes as single‐component phosphor. This article is protected by copyright. All rights reserved.

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Chapter
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Eu³⁺/Dy³⁺-doped CaGdAlO4 phosphors were prepared by a typical sol-gel method. X-ray diffraction patterns indicate that all CaGd1-x-yAlO4:xEu³⁺, yDy³⁺ phosphors have the standard structure of CaGdAlO4. CaGd1-yAlO4:yDy³⁺ phosphors exhibit both blue and yellow emissions under the excitation of 274 nm, and CaGd1-xAlO4:xEu³⁺ phosphors show a strong red emission under the excitation of near-UV light, while only Eu³⁺ emission is appeared in the photoluminescence spectra of Eu³⁺, Dy³⁺-codoped CaGdAlO4 phosphors. But the red emission intensity of CaGd1-x-yAlO4:xDy³⁺, yEu³⁺ increases obviously with Dy³⁺ introduced, and the luminescence intensity of CaGd0.98AlO4:0.01Eu³⁺, 0.01Dy³⁺ is 3.0-fold higher than that of CaGd0.99AlO4:0.01Eu³⁺ phosphor. The chromaticity coordinates for CaGd0.99AlO4:0.01Dy³⁺, CaGd0.99AlO4:0.01Eu³⁺ and CaGd0.98AlO4:0.01Eu³⁺, 0.01Dy³⁺ are (0.311, 0.365), (0.645, 0.354) and (0.644, 0.356), respectively. The values of lifetime of CaGd0.99AlO4:0.01Eu³⁺, CaGd0.98AlO4:0.01Eu³⁺, 0.01Dy³⁺, CaGd0.97AlO4:0.01Eu³⁺, 0.02Dy³⁺ and CaGd0.96AlO4:0.01Eu³⁺, 0.03Dy³⁺ phosphors are 1.619, 1.456, 1.207 and 1.385 ms, respectively.
Article
Sr3(PO4)2:Re³⁺, Li⁺ (Re=Eu, Sm) red phosphors were prepared via a high temperature solid state reaction, and their structure and luminescence properties were investigated. X-ray diffraction patterns indicate that the phase of as-prepared samples is in good agreement with standard Sr3(PO4)2 structure. Under 395 nm excitation, the emission of Sr3(PO4)2:Eu³⁺ consists of a strong peak centered at 622 nm and two weak peaks centered at 598 nm and 660 nm, which correspond to ⁵D0→⁷F2, ⁵D0→⁷F1 and ⁵D0→⁷F3 transitions, respectively. Also, the emission spectrum of Sr3(PO4)2:Sm³⁺ shows three main peaks at 568 nm, 603 nm and 651 nm, which are attributed to ⁴G5/2→⁶HI/2 (I=5, 7, 9) transitions of Sm³⁺. Furthermore, luminescence properties of Sr3(PO4)2:Re³⁺, Li⁺ (Re=Eu, Sm) samples are enhanced significantly by Li⁺ ions doping as charge compensator. Results indicate that as-prepared Sr3(PO4)2:Re³⁺, Li⁺ (Re=Eu, Sm) could be the potential red phosphors used in white light-emitting diodes.
Article
A series of novel green emission Whitlockite-type Ca8ZnLa(PO4)7:Eu2+ and color tunable Ca8ZnLa(PO4)7:Eu2+,Mn2+ phosphors were prepared by the solid-state reaction method in a reducing atmosphere. Its crystal structure and phase composition were identified by high-resolution transmission electron microscopy, selected area electronic diffraction, X-ray photoelectron spectroscopy, and X-ray powder diffraction Rietveld refinement, and it was found to be trigonal, belonging to R-3c(161) space group. The luminescence properties of Eu2+ singly doped and Eu2+/Mn2+ codoped Ca8ZnLa(PO4)7 phosphors were revealed in detail. Ca8ZnLa(PO4)7:Eu2+ is excitable over a broad range from 200 to 450 nm with a prominent green emitting. With varied Eu2+/Mn2+ ratios, fine-tune emission under 365 nm excitation can be achieved from green (0.221, 0.468) to magenta (0.391, 0.276), especially the warm white light (0.392, 0.352), and CCT 3500 K can be obtained by the process of energy transfer between Eu2+ and Mn2+. The ET mechanism in this system is managed via the dipole-dipole interaction with the maximum energy-transfer efficiency 82.8% based on the decay lifetime data. These results suggest that as-prepared phosphors can serve as promising candidates of UV-pumped w-LEDs.
Article
Herein, we report a series of phosphate phosphors Ca9Ce(PO4)7:xTb³⁺/yMn²⁺, exhibiting much efficient energy transfer, stable thermal stability and high quantum efficiency. First of all, Ca9Ce(PO4)7 host is full of sensitizers (Ce³⁺) and the maximum energy transfer efficiency from Ce³⁺ to Mn²⁺ and Tb³⁺ reaches 91% and 72%, respectively. In Ca9Ce(PO4)7:xTb³⁺/yMn²⁺ system, white light can be obtained by mixing the tricolor composition at a suitable ratio. Energy transfer from Ce³⁺ to Mn²⁺/Tb³⁺ is confirmed via an electronic dipole-dipole (d-d) interaction. We found that the Mn²⁺ emission intensity of Ca9Ce(PO4)7: Mn²⁺ keeps unchanged during the rising temperature and the Tb emission lines of Ca9Ce(PO4)7:0.15Tb³⁺ are not affected by the increasing temperature. Meanwhile, quantum efficiency (QE > 60%) of Ca9Ce(PO4)7:xTb³⁺/yMn²⁺ presents a stable output until the temperature rises to 150°C. We also report the luminescence quenching temperature (T > 300°C) and the activation energy for thermal quenching (ΔE > 0.2 eV). To prove the potential application, a proof-of-concept white LEDs is fabricated by combining the single-component phosphor Ca9Ce(PO4)7:Mn²⁺, Tb³⁺ with a UV LED chip, which has a CIE chromaticity coordinate (0.347, 0.344), color temperature (4770 K), color rendering index (Ra=80.4) and R9=92.3.
Article
The Mn4+ activated fluostannate Na2SnF6 red phosphor was synthesized from starting materials metallic tin shots, NaF, and K2MnF6 in HF solution at room temperature by a two-step method. The formation mechanism responsible for preparing Na2SnF6:Mn4+ (NSF:Mn) has been investigated. The influences of synthetic parameters: such as concentrations of HF and K2MnF6 in reaction system, reaction time, and temperature on crystallinity, microstructure, and luminescence intensity of NSF:Mn have been investigated based on detailed experimental results. The actual doping concentration of Mn4+ in the NSF:Mn host lattice is less than 0.12 mol%. The most of K2MnF6 is decomposed in HF solution especially in hydrothermal system at elevated temperatures. The color of the as-prepared NSF:Mn samples changes from orange to white when the temperature is higher than 120°C, which indicates the lower concentration of luminescence centers in the crystals. A series of “warm” white light-emitting diodes with color rendering index (CRI) higher than 88 and correlated color temperatures between 3146 and 5172 K were obtained by encapsulating the as-prepared red phosphors NSF:Mn with yellow one Y3Al5O12:Ce3+ (YAG:Ce) on 450 nm blue InGaN chips. The advantage of the synthetic strategy to obtain NSF:Mn can be extended to developing Mn4+-doped red phosphors from low-costing metals at room temperature for large-scale industrial applications.
Article
A very simple synthesis procedure based on precipitation reactions at moderate temperature (120 degrees C) from solutions containing calcium nitrate and sodium molybdate, using mixed solvents (polyols and water) has been developed, which produces uniform tetragonal CaMoO4 microarchitectures with different morphologies (peanuts, cocoons, spindles and spheres) composed of self-assembled entities. The morphology and crystal size of such assemblies could be tuned by a simple change of the nature of the components of the solvent mixture or their volumetric ratio in such a mixture. All particles presented similar excitation and emission spectra arising from a charge transfer process within the MoO4 2-groups. The emitted light presented a bluish-green color and its intensity was higher for the spindle-type particles. This synthesis procedure was also suitable for doping peanut-like CaMoO4 architectures with Eu3+ or Dy3+ cations up to a 1% molar ratio (Ln/Ln + Ca), without altering their morphology or crystalline structure. The so prepared phosphors emitted an intense red (Eu-doped) or greenish (Dy-doped) light when excited through the MoO42- group excitation band, indicating the presence of an energy transfer process from such groups to the Ln(3+) cations. Finally, a white light emitting phosphor with chromaticity coordinates x = 0.335 and y = 0.365 and a correlated color temperature of 5407 K was developed by codoping peanut-type CaMoO4 particles with suitable amounts of Dy3+ (0.35%) and Eu3+ (0.15%) cations, which could find applications in white light emitting diodes.
Article
A series of color tunable Dy³⁺/Eu³⁺ co-doped CsGd(MoO4)2(CGM) phosphors were prepared by the conventional solid state reaction. The crystal structure, morphology, vibrational modes, luminescence properties and energy transfer mechanism were investigated. Upon near ultraviolet (n-UV) excitation, Dy³⁺/Eu³⁺ co-doped phosphors exhibit the characteristics blue (⁴F9/2 → ⁶H15/2), yellow (⁴F9/2 → ⁶H13/2) and red (⁵D0→⁷F2) emission corresponding to transitions of Dy³⁺and Eu³⁺ions. By changing the doping concentration of Dy³⁺ and Eu³⁺, the emission hue could be controlled via the energy transfer mechanism. The energy transfer efficiency and critical distance of Dy³⁺ and Eu³⁺have been calculated. The calculated chromaticity coordinates and color correlated temperature of co-doped phosphors lieat the F4 warm white points of standard illuminants.
Article
M2Si5N8:Dy³⁺ (M=Ca, Sr, Ba) nitride phosphors with different Dy³⁺ ion concentrations were prepared via a novel sol-gel-nitridation method involving an annealing step at 1300 or 1400 °C. The X-ray diffraction patterns indicate that the structure of these phosphors is in good agreement with the standard M2Si5N8 crystal structure. The photoluminescence spectra recorded for the prepared phosphors exhibited an intense white emission consisting of a blue emission peak (485 nm) and a yellow emission peak (582 nm), which are attributed to the characteristic ⁴F9/2 → ⁶H15/2 and ⁴F9/2 → ⁶H13/2 transitions of the Dy³⁺ ions, respectively. When using a different alkaline earth metal, the structure of the resulting M2Si5N8 phosphors changed and the luminescence was also affected. The chromaticity coordinates of the prepared Sr2Si5N8:Dy³⁺, Ca2Si5N8:Dy³⁺, Ba2Si5N8:Dy³⁺ phosphors with blue and yellow emission peaks were (x = 0.391, y = 0.397), (x = 0.448, y = 0.433) and, (x = 0.42, y = 0.414), respectively, which are all close to the standard white light coordinates (0.33, 0.33). The lifetime values of the obtained Ca2Si5N8:Dy³⁺, Sr2Si5N8:Dy³⁺ and Ba2Si5N8:Dy³⁺ phosphors were determined to be 0.028, 0.0167 and 0.0113 ms, respectively.
Article
The alkaline-earth silicate Sr3MgSi2O8:Ce³⁺,Tb³⁺ phosphors have been synthesized via conventional high temperature solid-state method. The crystal structure, luminescence properties, morphology of phosphors are investigated systematically. The thermal quenching and concentration quenching mechanisms of phosphors are also discussed. The phosphors can be excited under near ultraviolet light ranging from 200 nm to 450 nm. The calcination temperature and calcination time are significant factors for luminescence property of phosphors. Increasing co-doping Tb³⁺ makes the emission intensity of Ce³⁺ decreases proportionally while the emission of Tb³⁺ increases. It indicates that it exists energy transfer between Ce³⁺ and Tb³⁺. The emission wavelength can be tuned from bluish violet region to blue region. The results imply Sr3MgSi2O8:Ce³⁺,Tb³⁺ phosphors can be a potential candidate for solid-state lighting.
Article
Selective laser lift-off (SLLO) is an innovative technology used to manufacture and repair micro-light-emitting diode (LED) displays. In SLLO, laser is irradiated to selectively separate micro-LED devices from a transparent sapphire substrate. The light source used is an ultraviolet (UV) laser with a wavelength of 266 nm, pulse duration of 20 ns, and repetition rate of 30 kHz. Controlled adhesion between a LED and the substrate is key for a SLLO process with high yield and reliability. This study examined the fundamental relationship between adhesion and laser irradiation. Two competing mechanisms affect adhesion at the irradiated interface between the GaN LED and sapphire substrate: Ga precipitation caused by the thermal decomposition of GaN and roughened interface caused by thermal damage on the sapphire. The competition between these two mechanisms leads to a non-trivial SLLO condition that needs optimization. This study helps understand the SLLO process, and accelerate the development of a process for manufacturing micro-LED displays via SLLO for future applications.
Article
The phosphors Sr3Y(PO4)3: Dy3+, Eu3+ have been synthesized by a high temperature solid-state reaction method in air atmosphere and their crystal structures, luminescence properties, lifetime, and energy transfer mechanism were investigated in detail. The co-doped Dy3+ and Eu3+ in Sr3Y(PO4)3 could enhance emission of Eu3+ ions and a series of characteristic emission of Dy3+ and Eu3+ were observed in the emission spectra at around 487 nm, 575 nm, and 615 nm excited at 350 nm. It indicated that the energy transfer occurs from Dy3+ to Eu3+ and the intensity ratio of multicolor emission could be tuned by adjusting their concentration ratio on the basis of efficient Dy3+ – Eu3+ energy transfer. The energy-transfer mechanism from Dy3+ to Eu3+ in Sr3Y(PO4)3 was determined to be a quadrupole-quadrupole interaction and the critical distance between Dy3+ and Eu3+ was 15.22 Å. The decay life time of the Dy3+ ions decreased with the increase of the Eu3+ dosage concentration.
Article
Two series of materials based on a strontium orthosilicate matrix doped with europium and different concentrations of aluminum ions were obtained using different solid state synthesis strategies. The phase composition of the samples was investigated using the X-ray diffraction (XRD) technique. The results of the optical characterization indicated that the incorporation of aluminum ions causes the stabilization of the Eu3+ ions under reductive atmosphere. The concentration ratio of europium ions incorporated into the matrix in both oxidation states ([Eu3+]/[Eu2+]) can be controlled by changing the Al3+ concentration. The observed effect is interesting from the point of view of the design of phosphors used to obtain white light emitting diodes (WLEDs). The influence of temperature on the relative intensity of Eu2+ and Eu3+ emission bands was studied to investigate the range of the impact of the created compensation defects. It is shown that the Eu3+ to Eu2+ reduction process in Sr2SiO4 takes place due to the migration of the strontium vacancies to the surface.
Article
Pure and samarium doped calcium oxide (CaO) is synthesized by solution combustion technique. The samples are annealed at 600 °C for two hours. X-ray diffraction (XRD) pattern of the annealed sample show cubic phase with space group Fm3m. The average crystallite size is found to be ∼54 nm. Fourier transform infra red (FTIR) spectrum exhibits bands at 424, 544 cm−1 (Ca–O bond), 875 cm−1 (C–O bond), 1460 cm−1 (C–O stretch) and 3640 cm−1 (O–H stretch). The samples are irradiated with gamma rays in a dose range 100–4000 Gy. Thermoluminescence (TL) glow curves are recorded at a linear heating rate (β) of 5 Ks−1. A prominent TL glow with a peak at 636 K is observed in undoped sample. A new TL glow with peak at ∼458 K is observed in addition to 636 K in samarium doped (1 mol%) CaO. TL glow peak intensity (Imax) at 636 K increases with γ – dose in the study range. TL emissions at 560, 600 and 640 nm are observed in doped samples corresponding to Sm3+ transitions along with pristine emissions. TL glow curves are deconvoluted to obtain kinetic parameters. The mean value of activation energy and the frequency factor of the prominent deconvoluted TL glow peak (626 K) are found to be 1.26 eV and 4.49 × 109 s−1 respectively.
Article
Bi doped Ca-5(PO4)(3)F phosphors were synthesized by the solid state reaction in air, and characterized by XRD and photoluminescence spectra. Including typical violet luminescence from Bi3+, broadband orange emission peaked at about 521 nm can be observed under UV light excitation. Emission data with the size available lattice sites suggest that there are two types of Bi, Bi3+ and Bi2+, in Ca-5(PO4)(3)F lattice, and each locates on one of the two available Ca2+ sites. Bi2+ occupying Ca2+(1) sites is considered to be reduced from Bi3+ to Bi2+ and presents efficient orange emission.
Article
A novel single-composition white-emitting phosphor Ca3(PO4)2:Dy3+ has been synthesized by a high-temperature solid-state reaction. The effect of charge compensators on luminescent properties of Ca3(PO4)2:Dy3+ is systematically investigated by the X-ray powder diffraction, UV-Vis diffuse reflectivity, photoluminescence (PL) properties and lifetime. It is observed that the PL intensity of Dy3+ under 350 nm excitation increases in the order of Ca2.95(PO4)2:0.05Dy3+, Ca2.90K0.05(PO4)2:0.05Dy3+, Ca2.90Na0.05(PO4)2:0.05Dy3+, Ca2.90Li0.05(PO4)2:0.05Dy3+, and Ca2.95(P0.95Si0.05O4)2:0.05Dy3+. The lifetimes of Dy3+ are 605.00, 604.67, 615.01, 645.64 and 621.26 μs, respectively. A charge compensation model is proposed to explain the changes in the emission intensity and lifetime of Dy3+ in Ca3(PO4)2 with different compensation methods. A white light-emitting diode (LED) was fabricated by using the white-emitting single-composition Ca2.95(P0.95Si0.05O4)2:0.05Dy3+ pumped by a 365 nm UV-chip. Our results indicated that the CIE chromaticity coordinates, color rendering index and correlated color temperature for white UV-LEDs were (0.302, 0.324), 83, and 6947 K, respectively. Therefore, our novel white Ca2.95(P0.95Si0.05O4)2:0.05Dy3+ can serve as a key material for phosphor-converted white-light UV-LEDs.
Article
Two series of phosphors, α-Sr2(1-x)Dy2xP2O7 and α-Sr2(1-2x)Dy2xLi2xP2O7, with different x values were synthesized successfully using a conventional solid-state method at high temperature for the first time, and their luminescence properties were investigated comparatively. The effect of Li(+) ions on the luminescence properties of Dy(3+) in α-Sr2P2O7 host, including luminescence intensity, optimal doping concentration, concentration quenching mechanism, and decay behavior, was discussed in detail by considering the defect generation in α-Sr2P2O7:Dy(3+), the charge compensation of Li(+) ions and the role of Li2CO3 as solid flux expected in phosphors. The obtained excitation and emission spectra indicate that these as-prepared phosphors can be excited by ultraviolet light and show white light emission due to the combination of the (4)F9/2→(6)H15/2 and (4)F9/2→(6)H13/2 transitions of Dy(3+) ions. The CIE chromaticity coordinates and color correlated temperature of Dy(3+) emission in the phosphor α-Sr2(1-2x)Dy2xLi2xP2O7 (x = 0.03) with optimal fluorescence intensity was also calculated. The present work could be helpful for understanding the effect of the charge compensator (e.g. Li(+) ion) on the luminescent properties of phosphors with non-equivalent ion-displacement and the design of novel phosphors by efficiently taking advantage of charge compensator (e.g. Li(+) ion).
Article
New non-rare-earth based oxide red phosphor discovery is of great interest in the field of energy-efficient LED lighting. In this work, a novel blue-light activated CaMg2Al16O27: Mn4+ (CMA: Mn4+) phosphor, showing strong red emission peaked at ~655 nm under 468 nm excitation, is prepared by a solid-state reaction route. The microstructure and luminescent performance of this red-emitting phosphor are investigated in detail with the aids of X-ray diffraction refinement, diffuse reflection spectra, steady-state photoluminescence spectra, and temperature-dependent PL/decay measurements. The crystal field strength (Dq) and the Racah parameters (B and C) are carefully calculated to evaluate the nephelauxetic effect of Mn4+ suffering from the CMA host. After incorporating CMA: Mn4+ and YAG: Ce3+ phosphor microcrystals into glass host via a "phosphor-in-glass (PiG)" approach, warm white-light is achieved in the assembled high-powered w-LED device, thanking to the improved correlated color temperature and color rendering index.
Article
Eu2+/Mn2+-co-doped white-emitting Ca5(PO4)3F phosphors have been synthesized by a combustion-assisted synthesis method. The PXRD patterns confirmed the single-phase fluorapatite crystal structure for all the samples independently of their substitution level. Their luminescence properties reveal that the developed phosphors can efficiently convert UV light in a broad range from 250 to 420 nm into tunable white emission. Based on the luminescence spectra and fluorescence decay curves, we can confirm that energy transfer from the Eu2+ to Mn2+ ions takes place in the Ca5(PO4)3F:Eu2+,Mn2+ phosphors, and that the energy-transfer efficiency increases with increasing Mn2+ content. The emission colors of the obtained phosphors can be tuned from blue to white and eventually to yellow by controlling the doping content of the Eu2+ and Mn2+ ions. These results suggest that these phosphors are potential single-component white-light phosphors for n-UV-pumped white LEDs.
Article
White light-emitting diodes (WLEDs) as new solid-state light sources have a greatly promising application in the field of lighting and display. So far much effort has been devoted to exploring novel luminescent materials for WLEDs. Currently the major challenges in WLEDs are to achieve high luminous efficacy, high chromatic stability, brilliant color-rending properties, and price competitiveness against fluorescent lamps, which rely critically on the phosphor properties. In recent years, numerous efforts have been made to develop single-phase white-light-emitting phosphors for near-ultraviolet or ultraviolet excitation to solve the above challenges with certain achievements. This review article highlights the current methods to realize the white light emission in a single-phase host, including: (1) doping a single rare earth ion (Eu(3+), Eu(2+) or Dy(3+)) into appropriate single-phase hosts; (2) co-doping various luminescent ions with different emissions into a single matrix simultaneously, such as Tm(3+)/Tb(3+)/Eu(3+), Tm(3+)/Dy(3+), Yb(3+)/Er(3+)/Tm(3+)etc.; (3) codoping different ions in one host to control emission color via energy transfer processes; and (4) controlling the concentration of the defect and reaction conditions of defect-related luminescent materials.
Article
In this paper, we report the obtention of red-emitting Ca-3(PO4)(2):Eu3+ phosphor by the solid-state reaction method. X-ray diffraction and photoluminescence (PL) measurements were used to investigate the crystal phases, luminescent properties, and optimal Eu3+ doping concentration. To further improve the PL intensity, Na+ acting as a charge compensator was incorporated into the phosphor. The effects of Na+ concentration on the PL properties were studied. It was found that the charge-compensation phosphor showed greatly enhanced red emission beyond the phosphor without charge compensation. Ca2.3Na0.4(PO4)(2):0.3Eu(3+) was determined to be the best composition. The charge-compensation mechanism was analyzed in light of the principles on defect formation and reaction, and the changes of the site centrosymmetry for the activator.
Article
In this article, the scheelite-structured phosphors of CaWO4 and Bi(3+) doped CaWO4 were successfully synthesized by the high temperature solid state reaction, and the photoluminescence (PL) properties and decay curves of the samples were investigated between 10 and 300 K. The results have shown clearly that the sample emission is tunable via tailoring the energy transfer between the Bi(3+) and WO4(2-) anion groups by the selection of either proper bismuth content or excitation scheme. Depending on the excitation scheme, energy transfer does happen from Bi(3+) to WO4(2-) or in the reverse, which, however, has never been noticed. Direct spectroscopic evidences as well as the mechanism have been presented for these processes in this work.
Article
Dy3+:Eu3+ doped calcium sulfate (CaSO4:Dy3+,Eu3+) phosphors co-doped with various K+ compensator concentrations were synthesized by recrystallization method. These orthorhombic phased phosphors showed intense multi-color near white light. The multi-color aspect ratios and the emission life times were strongly dependent on K+-concentration. These results suggest that the rare-earth (Re3+) ions are situated at the sites of Ca2+ and the site occupancy was being compensated by K+ ions. The near white light emission and large lifetimes suggest that present phosphor could be potentially applied as a blue excited white light-emitting phosphor for light emitting diodes.
Article
A series of Eu(2+) and Eu(2+)/Tb(3+) activated novel Ba3LaNa(PO4)3F phosphors have been synthesized by traditional solid state reaction. Rietveld structure refinement of the obtained phosphor indicates that the Ba3LaNa(PO4)3F host contains three kinds of Ba sites. The photoluminescence properties exhibit that the obtained phosphors can be efficiently excited in the range from 320 to 430 nm, which matches perfectly with the commercial n-UV LED chips. The critical distance of the Eu(2+) ions in Ba3LaNa(PO4)3F:Eu(2+) is calculated and the energy quenching mechanism is proven to be dipole-dipole interaction. Tunable blue-green emitting Ba3LaNa(PO4)3F:Eu(2+),Tb(3+) phosphor has been obtained by co-doping Eu(2+) and Tb(3+) ions into the host and varying their relative ratios. Compared with the Tb(3+) singly doped phosphor, the codoped phosphors have more intense absorption in the n-UV range and stronger emission of the Tb(3+) ions, which are attributed to the effective energy transfer from the Eu(2+) to Tb(3+) ions. The energy transfer from the Eu(2+) to Tb(3+) ions is demonstrated to be a dipole-quadrupole mechanism by the Inokuti-Hirayama (I-H) model. The Eu(2+) and Tb(3+) activated phosphor may be good candidates for blue-green components in n-UV white LEDs.
Article
A novel solvothermal route has been developed to synthesize mondispersed and different mophologies of Eu-doped CaTiO3 phosphors including magic-column spherical, magic-cube spherical and polyhedral shaped, using a mixture of ethylene glycol (EG) and ethylenediamine (EDA). By tuning the solvent ratio, the method exhibited excellent control over the morphology of CaTiO3:Eu3+, and magic-column spherical phosphors have higher luminous intensities than magic-cube spherical and polyhedral shaped phosphors. The synthesized phosphors had higher luminous intensity and better packing properties than those obtained by a solid-state method. The phosphors showed strong red emissions, corresponding to the 5D0 → 7F2 (617.6 nm) transition of Eu3+ under near-ultraviolet excitation (398.4 nm). X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescent (PL) analyses were used to characterize the structure, morphology and luminous performance of CaTiO3:Eu3+ phosphors.
Article
Y2O3 ∶ Eu3+ phosphor particles were obtained by calcination of composite Y–Eu oxalate particles prepared in emulsion liquid membrane (ELM, water-in-oil-in-water (W/O/W) emulsion) systems. In the ELM systems, composite Y–Eu particles could be prepared by transporting either Y3+ and Eu3+ ions or oxalate ions from the external water phase into the internal water phase, employing proper ELM systems, where bis(1,1,3,3-tetramethylbutyl)phosphinic acid (DTMBPA) or 2-methyl-2-ethylheptanoic acid (VA-10) was used as an extractant (cation carrier), or tri-n-octylamine (TNOA) was used as an anion carrier. These ELM systems were effective for preparing size (submicrometer) and morphology (spherical) controlled composite Y–Eu oxalate particles in the internal water droplets. The Y2O3 ∶ Eu3+ particles obtained by calcination of the composite oxalate particles showed photoluminescence at 614 nm.
Article
Transparent Ce:YAG ceramic phosphors were synthesized from the oxide powder which was produced by co-preparation method of the hydroxides. The Ce:YAG ceramics had a broad emission band peaked at 530nm due to the 5d→4f transition of Ce3+. The transmittances of the samples obtained were 70–87% at 800nm. The absorption coefficient and emission intensity of Ce3+ were increased with increasing thickness. Under 465nm LED excitation, the color coordinates of the Ce:YAG ceramics shifted from the blue region to yellow region with increasing sample thickness, passing nearby the theoretical white point in the chromaticity diagram. The highest value of luminous efficacy of the ceramic white LED was 73.5lm/W.
Article
The X-ray powder diffraction, reflectance, photoluminescence, photoluminescence excitation and ESR spectra of Ca5(PO4)3F:Eu3+ phosphor have been studied. Three distinct variants of calcium substitutional Eu3+-sites have been observed in this host and the charge compensating species related to each of these sites has been identified. It is noted that the host related trace impurities those have prospects of acting as charge compensator, and the reaction environment that exists during the preparation of the material, greatly influence the preferential substitution of different Ca2+-sites by the Eu3+ ions. It is also noted that the charge compensating species in a suitable case, takes part in the photophysical process of luminescence of the Eu3+.
Article
The luminescence of Rb2ZnBr4-Eu2+ is reported and discussed. Efficient energy transfer occurs between inequivalent Eu2+ ions (Rc &bsime; 35 Å). This phenomenon is compared with similar situations in other host lattices.
Article
The Ce3+, Mn2+-codoped calcium fluorapatite [Ca5(PO4)3F, FAP] nanorods were prepared by a simple hydrothermal method. SEM and TEM images indicate that the FAP:Ce3+,Mn2+ sample consists of nanorods with lengths around 30–70 nm and diameters around 20 nm, respectively. The as-obtained FAPnanorods show an intense bright blue emission (centered at 432 nm, lifetime 7.5 ns) arising from CO2˙− radical impurities in the crystal lattice under UV light irradiation. In addition, codoped with Ce3+ and Mn2+, the as-synthesized FAP:Ce3+,Mn2+ sample shows the tunable luminescence from blue to white to yellow by the variation of excitation UV light. The emission spectra of the as-synthesized FAP:Ce3+,Mn2+ sample show three broad bands, which are associated with the CO2˙− radical impurities (blue emission), Ce3+ ions (ultraviolet emission), and Mn2+ ions (yellow emission), respectively. The coexistence of three broad emissions results in the bright white light directly under suitable excitation wavelength. The combination emissions of impurities and metal activator ions may provide a novel strategy to obtain white light and tunable luminescence.
Article
Photoluminescence investigation of Eu and Dy activated phosphate based phosphors prepared by combustion synthesis, characterized by XRD (X-ray diffraction) and photoluminescence techniques, has been reported. PL excitation spectrum of M5(PO4)3F:Dy phosphors shows the excitation peaks ranging from 300 to 400nm due to 4f→4f transitions of Dy3+ ions. PL emission spectrum of Dy3+ ion under 348nm excitation gives PL emission at 482nm (blue) due to 4F9/2→6H15/2 transitions, 574nm (yellow) emission due to 4F9/2→6H13/2 transitions and 670nm (red) due to 4F9/2→6H11/2 transitions, gives BYR (blue–yellow–red) emissions. The Eu2+ broad band PL emission spectrum was observed in M5(PO4)3F:Eu phosphor at 440nm in the blue region of the spectrum due to 5d→4f transition at 352nm excitation. The 300–400nm is Hg-free excitation (Hg excitation is 85% 254nm wavelength of light and 15% other wavelengths), which is characteristic of solid-state lighting phosphors. Hence PL emission in divalent europium and trivalent dysprosium may be efficient photoluminescent materials for solid-state lighting phosphors.
Article
In order to develop a suitable green phosphor for plasma display panels (PDPs), samples for , 0.35, 0.50, 0.65, 0.80, and 0.95 were prepared by a solid-state reaction technique at high temperature. The vacuum ultraviolet (VUV, wavelength and the energy )—vis spectroscopic properties and decay characteristic were investigated. Because the phosphor for shows broad and strong absorption in the vacuum ultraviolet (VUV) range, exhibits higher intensive emission under excitation, and has a shorter decay time in comparison with the commercial green PDP phosphor , it is considered to be a promising green phosphor in PDPs.
Article
Rare-earth-doped polycrystalline Ca3(PO4)2:Eu, Ca3(PO4)2:Dy and Ca3(PO4)2:Eu,Dy phosphors prepared by a modified solid-state synthesis has been studied for its X-ray diffraction, thermoluminescence (TL) and photoluminescence (PL) characteristics. The PL emission spectra of the phosphor suggest the presence of Eu3+ ion in Ca3(PO4)2:Eu and Dy3+ ion in Ca3(PO4)2:Dy lattice sites. The TL glow curve of the Ca3(PO4)2:Eu compounds has a simple structure with a prominent peak at 228 °C, while Ca3(PO4)2:Dy peaking at 146 and 230 °C. TL sensitivity of phosphors are compared with CaSO4: Dy and found 1.52 and 1.20 times less in Ca3(PO4)2:Eu and Ca3(PO4)2:Dy phosphors, respectively. The Ca3(PO4)2:Eu,Dy phosphors shows switching behavior under two different excitation wavelengths and enhancement in PL intensity of Dy3+ ions were reported. The paper discusses the photoluminescence and thermoluminescence behavior of Eu3+ and Dy3+ ion in Ca3(PO4)2 hosts, it may be applicable to solid-state lighting as well as thermoluminescence dosimetry applications.
Article
A novel white-light-emitting phosphor Ca(9)Lu(PO(4))(7):Eu(2+),Mn(2+) has been prepared by solid-state reaction. The photoluminescence properties indicate that there is an efficient energy transfer from the Eu(2+) to Mn(2+) ions via a dipole-quadrupole reaction. The obtained phosphor exhibits a strong excitation band between 250 and 430 nm, matching well with the dominant emission band of a UV light-emitting-diode (LED) chip. Upon excitation of UV light, white light is realized by combining a broad blue-green emission band at 480 nm and a red emission band at 645 nm attributed to the Eu(2+) and Mn(2+) ions. The energy-transfer efficiency and critical distance were also calculated. Furthermore, the phosphors can generate lights from blue-green through white and eventually to red by properly tuning the relative ratio of the Eu(2+) to Mn(2+) ions through the principle of energy transfer. Preliminary studies showed that the phosphor might be promising as a single-phased white-light-emitting phosphor for a UV white-light LED.
Article
Yttrium aluminum garnet (YAG) doped with Ce3+ is the phosphor of choice for the conversion of blue to yellow light in the rapidly expanding market of white light LEDs, but it is generally thought to suffer from a low luminescence quenching temperature. The luminescence quenching temperature is an important parameter, especially in high-power LEDs, but surprisingly no systematic research has been done to measure and understand the temperature quenching of the yellow Ce luminescence in YAG:Ce. Here we report on the luminescence temperature quenching in YAG:Ce. For a wide range of Ce concentrations (between 0.033% and 3.3%) the temperature dependence of the emission intensity and the luminescence lifetimes are reported. The intrinsic quenching temperature of the Ce luminescence is shown to be very high (>700 K). The lower quenching temperatures reported in the literature are explained by thermally activated concentration quenching (for highly doped systems) and the temperature dependence of the oscillator strength (for low doping concentrations). In addition, high-resolution spectra are reported, which provide insight into the position of the zero-phonon transition (20450 cm-1), the Stokes shift (2400 cm-1), the energy of the dominant phonon mode (200 cm-1), and the Huang-Rhys parameter (S ) 6). These parameters are compared with ab initio calculations on the position of and relaxation in the excited 5d state of Ce3+ in YAG, which can aid in providing a better theoretical understanding of the temperature quenching.
Article
Energy efficiency is in! New inorganic luminescent materials can help to increase energy efficiency when used in plasma display panels and white-light-emitting diodes (see color diagram; mixing the three emissions A–C produces any given point within the triangle). In mercury-free fluorescent lamps these phosphors might contribute to environmental protection, and they provide better scintillation materials for medical diagnostics. Because fossil fuels are becoming scarce and because of the expected climate change, our standard of living can only be maintained by a significant increase in energy efficiency. Large amounts of energy are consumed for lighting and during operation of displays. Thus, the targets are the development of economical light sources like white-light-emitting diodes and display panels with enhanced efficiency. Solar energy is converted into electricity by solar cells, and their efficiency must be improved considerably. A possible contribution might be delivered by phosphors which allow the conversion of thermal radiation into electrical energy. Although the target of energy efficiency is very important, we must not overlook that medical imaging diagnostic methods require efficient and sensitive detectors. For the solution of these central questions, inorganic solid-state materials doped with rare-earth ions are very promising and are therefore in the focus of current research activities.