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Cubic and rhombohedral Ba 4 Lu 3 F 17 :Er 3+ in transparent glass ceramics: Crystallization and upconversion luminescence
Abstract
Novel Er³⁺ doped glass ceramics containing Ba4Lu3F17 nanocrystals were successfully prepared by heat treatment of melt-quenched glasses.
Highly efficient upconversion luminescence was detected under near-infrared excitation and it was at least two orders of magnitude higher than that in the precursor glass. The activator content in the crystalline phase was estimated using polycrystalline Ba4Lu3F17 with different Er³⁺ content as the reference and it was found to be higher than in similar glass ceramics.
The structure and thermal analysis of the glass ceramics revealed the formation of cubic and rhombohedrally distorted cubic modifications of Ba4Lu3F17. Phase transition between the two modifications was studied using site selective spectroscopy of Er³⁺ as a structural probe.
Unusually efficient incorporation of Er³⁺ ions in the Ba4Lu3F17 nanocrystals combined with the low phonon energy of the fluoride crystals make this material a desirable host for upconversion luminescence.
... Additionally, the energy level arrangement of Er 3+ is suitable for infrared radiation up-conversion into visible light, enabling erbiumdoped materials to be used as radiation visualization screens and temperature sensors [5][6][7][8]. Transparent glass ceramics containing fluoride nanocrystals have been studied as promising hosts for Er 3+ with up-conversion luminescence efficiency orders of magnitude higher in crystallized samples in comparison to precursor glasses [9][10][11][12][13]. Luminescence characteristics of a rare-earth ion are inextricably linked with its local environment, a complete analysis of which requires a combination of several complementary spectroscopic techniques. ...
... Er 3+ ground state can be split into either 5 Stark sublevels in cubic symmetry or 8 components in a lower symmetry field [18]. In luminescence spectroscopy, it appears as the fine structure of optical spectra and is a powerful tool for probing the structure of the host matrix [12][13][14]. The external magnetic field applied in conventional EPR experiments produces only a small perturbation of the lowest-lying Kramer's doublet of the 4 I 15/2 ground state in form of the Zeeman splitting. ...
Electron paramagnetic resonance (EPR) is a well-established spectroscopic technique for electronic structure characterization of rare-earth ion impurities in crystalline and amorphous hosts. EPR spectra of erbium-doped glass matrices and nanocomposites can provide information about local structure variations induced by changes in chemical composition or crystallization processes. Characterization possibilities of Er³⁺ ions in glasses and glass ceramics including direct EPR measurements, indirect investigations via secondary paramagnetic probes, and optically detected magnetic resonance techniques are considered in this article.
This review focuses on the upconversion luminescence properties of rare earth doped fluoride host in different crystal system such as cubic, hexagonal, monoclinic, rhombohedral, orthorhombic as well as in core shell structure. Also we reviewed the different methods of synthesis, for the preparation of lanthanide doped upconversion nanoparticles and their scope in different fields of technology. Further, it discussed interesting results obtained on photon assisted UC process in some fluoride crystal system. Also, it explore knowledge on spectroscopic transition and mechanism of energy transfer in selective pair of activator and sensitizer to achieve high UC efficiency under NIR laser excitation source. Some other important parameter such as PQEs and size dependent optical properties of the luminescent host material for UC processes which exhibit low phonon energy and high refractive index are taken into account. Hence, it provide a brief discussion on lanthanide doped upconverting fluoride materials those shows high photoluminescence quantum yields (PLQY) and their potential scope in bio imaging technology, photo therapy, solar cell , optical thermometry etc.
Significant developments have been made in the past few decades in lanthanide (Ln) ions doped fluorosilicate glass-ceramics (Flusi-GCs). As a novel generation of luminescence materials with a wide range of applications, Flusi-GCs as a single host combine the advantages of glass and ceramics/crystals as well as fluorides and silicates. In this review, the chemical design principles and experimental procedures of Flusi-GCs are summarized in detail. Flusi-GCs are categorized as those containing heavy metal fluoride PbxCd1–xF2, rare earth (RE) fluoride RF3 (R = Y, La, Gd), alkaline earth fluoride MF2 (M = Ca, Sr, Ba), fluoride xMF2–yRF3 (R = Y, La–Lu), mAF-nRF3 (A = Li, Na, K), KTF3 (T = Zn, Mn) and K2SiF6 nanocrystals (NCs). Theoretical breakthroughs mainly by molecular dynamic (MD) simulation have been recapitulated as efficient routes for composition-design, nano-crystallization-prediction, and performance-optimization of Flusi-GCs containing target fluoride NCs. Essential research progresses pertaining photonic applications have been made in random lasers, communication amplifiers, optical fibers, and spectral converters, white light-emitting-diodes (WLEDs), and thermal sensors. In the end, we propose three prospective future research directions for Flusi-GCs.
Yb³⁺/Er³⁺codoped La10W22O81 (LWO) nanophosphor rods have been successfully synthesized by a facile hydrothermal assisted solid state reaction method, and their upconversion photoluminescence properties were systematically studied. X-ray diffraction patterns revealed that the nanophosphors have an orthorhombic structure with space group Pbcn (60). A microflowers-like morphology with irregular hexagonal nanorods was observed using field emission scanning electron microscopy for the Yb³⁺(2 mol%)/Er³⁺(2 mol%):LWO nanophosphor. The shape and size of the nanophosphor and the elements along with their ionic states in the material were confirmed by TEM and XPS studies, respectively. A green upconversion emission was observed in the Er³⁺: LWO nanophosphors under 980 nm laser excitation. A significant improvement in upconversion emission has been observed in the Er³⁺: LWO nanophosphors by increasing the Er³⁺ ion concentration. A decrease in the upconversion emission occurred due to concentration quenching when the doping concentration of Er³⁺ ions was greater than 2 mol%. An optimized Er³⁺(2 mol%): LWO nanophosphor exhibited a strong near infrared emission at 1.53 μm by 980 nm excitation. The green upconversion emission of Er³⁺(2 mol%): LWO was remarkably enhanced by co-doping with Yb³⁺ ions under 980 nm excitation because of energy transfer from Yb³⁺ to Er³⁺. The naked eye observed this upconversion emission when co-doping with 2 mol% Yb³⁺. In order to obtain the high upconversion green emission, the optimized sensitizer concentration of Yb³⁺ ions was found to be 2 mol%. The upconversion emission trends were studied as a function of stimulating laser power for an optimized sample. Moreover, the NIR emission intensity has also been enhanced by co-doping with Yb³⁺ ions due to energy transfer from Yb³⁺ to Er³⁺. The energy transfer dynamics were systematically elucidated by energy level scheme. Colorimetric coordinates were determined for Er³⁺ and Yb³⁺/Er³⁺: LWO nanophosphors. The energy transfer mechanism was well explained and substantiated by several fluorescence dynamics of upconversion emission spectra and CIE coordinates. The results demonstrated that the co-doped Yb³⁺(2 mol%)/Er³⁺(2 mol%): LWO nanophosphor material is found to be a suitable candidate for the novel upconversion photonic devices.
Transparent glass ceramics incorporated with Ba4Y3F17: Yb3+, Er3+ nanoparticles were successfully elaborated through melt-quenching method. The crystal structure and morphology of Ba4Y3F17 nanocrystals was confirmed by X-ray diffraction, selected-area electron diffraction, and transmission electron microscopy. Compared to the glass counterpart, the pronounced enhancement of upconversion emission confirmed the incorporation of Yb3+ and Er3+ into precipitated Ba4Y3F17 nanocrystals. In addition, longer luminescence lifetimes as well as increased rise time in decay curve are also observed. Furthermore, the dependence of upconversion luminescence behaviors on temperature was systemically investigated through fluorescence intensity ratio technique under the excitation of 980 nm. FIR of the two thermally coupled energy levels of Er3+ ion was validated to be suitable used as temperature probes. The maximum thermal sensitivity was approximately 1.13% K-1 at 300K. Besides, the laser-induced thermal effect was demonstrated to be imperceptible in glass ceramic sample. The results imply that the Yb3+ and Er3+ codoped Ba4Y3F17 glass ceramics can be used as potential candidates for temperature sensing.
Assessment of activator distribution in lanthanide doped nanocomposites is an important and challenging task. Oxyfluoride glass ceramics have been chosen as a model system to characterize incorporation efficiency of Eu³⁺ ions in CaF2 nanocrystals using a combination of X-ray diffraction (XRD) and electron paramagnetic resonance (EPR) techniques. Lattice constant changes induced by size mismatch of Eu³⁺ and Ca²⁺ ions have been used to evaluate Eu³⁺ content in CaF2. The distortion of CaF2 lattice due to incorporation of europium ions can be detected from EPR investigations via Gd³⁺ paramagnetic probe spectra. It is shown that ratio of different symmetry CaF2:Gd³⁺ centres and linewidth of EPR transitions can be used to monitor europium content in the crystalline phase of glass ceramics.
Bright fluorescent rare-earth-ion-doped upconversion nanomaterials are attractive choices for photonic devices. A remarkable green upconversion emission has been obtained by the sensitizing effect of Yb3+ in a Yb3+/Er3+:NaLaMgWO6 (NLMWO) nanophosphor under near-infrared (NIR) excitation. A citrate sol-gel method was employed to synthesize the nanophosphor samples. The lack of a secondary phase in the X-ray diffraction pattern confirms that the Er3+ and Yb3+ ions are incorporated in the ordered double-perovskite structure. Surface analysis and particle evaluation are performed by field-emission scanning electron microscopy and transmission electron microscopy analysis. Upconversion and downconversion emission performances were systematically studied by varying the dopant concentrations. A strong upconversion green emission can be observed with the naked eye, and it resembles the upconversion spectra of Er3+-doped phosphors. Remarkably, because of an energy-transfer process, the green upconversion emission can be converted into a strong red emission by codoping with Yb3+ ions. We observed the color tuning effect from green to red, which can be controlled by varying the Yb3+ concentration in the codoped phosphors during NIR excitation. A systematic investigation of the upconversion mechanism from Yb3+ to Er3+ doubly doped NLMWO nanocrystals is demonstrated. The upconversion mechanism was evaluated only by varying the excitation power of the laser as well. A strong NIR emission at 1.57 μm corresponding to Er3+ can be significantly enhanced by increasing the codoping concentration of Yb3+ ions. The energy migration pathway is accurately presented. The Commission internationale de l'éclairage color coordinates were analyzed for singly and doubly doped nanophosphors. The cytotoxicity of the codoped nanophosphor system was evaluated using WI-38 cell lines. This optimized codoped nanophosphor material is noncytotoxic; thus, it can be useful for in vitro studies in biological studies. On the basis of the obtained results, the NLMWO:Yb3+/Er3+ nanophosphors can be a promising choice for novel upconversion photonic applications.
Nonlinear optical (NLO) effects originating from materials doped with rare-earth ions possess colossal potential for application in all-optical switches. However, among previous studies, Er3+ ion-doped glass ceramics (GCs) with remarkable NLO features have been investigated with respect to optical modulation applications by tailoring their nonlinear transmittance upon excitation at various near-infrared (NIR) wavelengths, which might prove to be a simple way of achieving "on-off" optical modulation in future all-optical switches. Here, we present the first observation of tailorable nonlinear transmittance in germanate oxyfluoride GCs containing Er3+: LaF3 nanocrystals, manipulated by excitation at 808, 980, and 1550 nm, which is consistent with the results from theoretical calculations and simulations. Furthermore, we conduct experimental investigation and analysis related to energy level transitions and dynamical evolution, indicating that these intriguing NLO features can be attributed to the differentiation between excited state absorption accompanied by up-conversion luminescence and stimulated emission processes during excitation at discrepant NIR wavelengths. Importantly, bidirectional optical switching for the "on-off" toggle effect has been successfully demonstrated by selectively tailoring the nonlinear transmittance of the single Er3+-doped GCs. This tailorable NLO behavior of Er3+-doped GCs, which is dependent on excitation at different NIR wavelengths, might provide a versatile strategy for the development of next-generation bidirectional all-optical switches.
Oxyfluoride glasses doped with 2, 5, 8, 12, 16 and 20 mol% of ytterbium (Yb3+) ions have been prepared by the conventional melt-quenching technique. Their optical, thermal and thermo-mechanical properties were characterized. Luminescence intensity at 1020 nm under laser excitation at 920 nm decreases with increasing Yb3+ concentration, suggesting a decrease in the photoluminescence quantum yield (PLQY). The PLQY of the samples was measured with an integrating sphere using an absolute method. The highest PLQY was found to be 0.99(11) for the 2 mol% Yb3+: glass and decreases with increasing Yb3+ concentration. The mean fluorescence wavelength and background absorption of the samples were also evaluated. Upconversion luminescence under 975 nm laser excitation was observed and attributed to the presence of Tm3+ and Er3+ ions which exist as impurity traces with YbF3 starting powder. Decay curves for the Yb3+: 2F5/2 → 2F7/2 transition exhibit single exponential behavior for all the samples, although lifetime decrease was observed for the excited level of Yb3+ with increasing Yb3+ concentration. Also observed are an increase in the PLQY and a slight decrease in lifetime with increasing the pump power. Finally, the potential of these oxyfluoride glasses with high PLQY and low background absorption for laser cooling applications is discussed.
New Yb3+, Er3+ and Tm3+ doped fluoro-phosphate glasses belonging to the system NaPO3–YF3–BaF2–CaF2 and containing up to 10 wt% of rare-earth ion fluorides were prepared and characterized by differential scanning calorimetry, absorption spectroscopy and up-conversion emission spectroscopy under excitation with a 975 nm laser diode. Transparent and homogeneous glass-ceramics have been reproducibly obtained with a view to manage the red, green and blue emission bands and generate white light. X-ray diffraction as well as electron microscopy techniques have confirmed the formation of fluorite-type cubic nanocrystals at the beginning of the crystallization process while complex nanocrystalline phases are formed after a longer heat-treatment. The prepared glass-ceramics exhibit high optical transparency even after 170 h of thermal treatment. An improvement of up-conversion emission intensity – from 10 to 160 times larger – was measured in the glass-ceramics when compared to the parent glass, suggesting an important incorporation of the rare-earth ions into the crystalline phase(s). The involved mechanisms and lifetime were described in detail as a function of heat-treatment time. Finally, a large range of designable color rendering (from orange to turquoise through white) can be observed in these materials by controlling the laser excitation power and the crystallization rate.
Scherrer Equation, L=Kλ/β.cosθ, was developed in 1918, to calculate the nano crystallite size (L) by XRD radiation of wavelength λ (nm) from measuring full width at half maximum of peaks (β) in radian located at any 2θ in the pattern. Shape factor of K can be 0.62 - 2.08 and is usually taken as about 0.89. But, if all of the peaks of a pattern are going to give a similar value of L, then β.cosθ must be identical. This means that for a typical 5nm crystallite size and λ Cukα1 = 0.15405 nm the peak at 2θ = 170° must be more than ten times wide with respect to the peak at 2θ = 10°, which is never observed. The purpose of modified Scherrer equation given in this paper is to provide a new approach to the kind of using Scherrer equation, so that a least squares technique can be applied to minimize the sources of errors. Modified Scherrer equation plots lnβ against ln(1/cosθ) and obtains the intercept of a least squares line regression, ln=Kλ/L, from which a single value of L is obtained through all of the available peaks. This novel technique is used for a natural Hydroxyapatite (HA) of bovine bone fired at 600°C, 700°C, 900°C and 1100°C from which nano crystallite sizes of 22.8, 35.5, 37.3 and 38.1 nm were respectively obtained and 900°C was selected for biomaterials purposes. These results show that modified Scherrer equation method is promising in nano materials applications and can distinguish between 37.3 and 38.1 nm by using the data from all of the available peaks.
The up-conversion of Er3+/Yb3+ co-doped transparent glass-ceramics 50SiO2-10AlF3-5TiO2-30BaF2-4LaF3-0.5ErF3-0.5YbF3 containing Ba2LaF7 nanocrystals under the changing of heat treatment temperature and time were investigated. The Ba2LaF7 nanocrystals precipitated from the glass matrix was confirmed by X-ray diffraction (XRD). The structural investigation carried out by XRD and transmission electron microscopy (TEM) evidenced the formation of cubic Ba2LaF7 nanocrystals with crystal size of about 14 nm. Comparing with the samples before heat treatment, the high efficiency up-conversion emission of Er3+/Yb3+ co-doped samples was observed in the glass-ceramics under 980 nm laser diode excitation. The increase in red emission intensity bands was stronger than the green bands when the crystal size increased. The mechanism for the up-conversion process in the glass-ceramics and the reasons for the increase of Er3+/Yb3+ co-doped up-conversion intensity after heat treatment were discussed.
Rare earth (RE) doped oxyfluoride glass ceramics possess interesting optical properties with applications in telecommunications and optoelectronics, such as solid state lasers, optical amplifiers, etc. These materials combine the transparency and mechanical and chemical resistance of aluminosilicate glasses with the low phonon energy and facile incorporation of RE ions in the fluoride crystals. The incorporation of RE ions in the crystalline phases enhances the laser emission intensity, a major property of these materials. Transparency is achieved when crystal size is in the nanometric scale, usually below 40 nm, which avoids light scattering. A strict control of the nucleation and crystal growth processes is therefore necessary which requires a deep knowledge of the crystallisation mechanisms. The great activity and publications in this field in the last decades merit a review providing a comparative study of the different nanoglass ceramic systems, their structural and optical characterisation and their main properties and applications. This is the objective of this review paper which includes 227 references. A general discussion on glass nucleation and crystallisation theories and more relevant crystallisation parameters and characterisation techniques are put forward in the first section of the review, focused on nanocrystallisation processes in oxyfluoride systems. In the second section, the principal RE doped glass ceramics are presented. After a general introduction about the luminescence processes, including up-and down-conversion, the behaviour of RE elements in glasses and crystals are discussed. Glass ceramic compositions have been divided as follows: glass ceramics with a glass composition following Wang and Ohwaki's oxyfluoride glass ceramic, and glass ceramics with different matrix compositions, arranged by crystalline phases. Relevant properties, mainly optical and laser, are described in each system along with the most relevant applications of these materials.
The crystal structures of two representatives of the family of ordered phases with the fluorite-based structure are determined from the X-ray diffraction data. The parameters obtained are a = b = 11.075(1) and c = 20.372(2) Å for the Ba4Y3F17 structure and a = b = 11.000(1) and c = 20.262(1) Å for the Ba4Yb3F17 structure, sp. gr. R3̄. The structures are refined in the anisotropic approximation of atomic thermal vibrations up to Rw = 0.0164 for Ba4Y3F17 and Rw = 0.0159 for Ba4Yb3F17. It is shown that Ba and R cations in these structures are ordered and arranged by the motif of the cubic close packing characteristic of the fluorite-type structures. The reconstruction of coordination polyhedra (cubes) of the fluorite-type structure into monocapped square RF9 antiprisms, ten-vertex BaF10, and eleven-vertex BaF11 polyhedra is considered as well as the relation between these polyhedra in the structures.
Single-phase samples of Ba4R3F17 · nH2O (R = La, Ce, Pr, Nd, Eu, Gd, Y, Er, or Yb; n = 2.5−3.2) were prepared by coprecipitation from nitrate solutions using hydrofluoric acid. The phases crystallize in a fluorite-type
face-centered cubic lattice. The dried precipitates are transparent. Scanning electron and atomic-force microscopy and X-ray
diffraction line broadening show a hierarchic structure in the samples: primary nanoparticles join into agglomerates with
characteristic sizes of about 150–200 nm, these agglomerates being self-packed into parallel layers with a thickness on the
order of 500 nm.
In this study, novel transparent Er³⁺ doped glass ceramics were prepared from melt-quenched oxyfluoride glasses with general composition of Na2O-NaF-BaF2-YbF3-Al2O3-SiO2. The crystallization of fluorite (BaF2, BaF2-YbF3, NaF-BaF2-YbF3 and Na0.5-xYb0.5+xF2+2x) and distorted fluorite (rhombohedral Ba4Yb3F17 and tetragonal NaF-BaF2-YbF3) phases was analysed in glass ceramics with different BaF2 and YbF3 ratio. The phase composition and microstructure were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Intense red upconversion luminescence (UCL) was detected under near-infrared excitation resulting from three photon upconversion followed by cross-relaxation between Er³⁺ and Yb³⁺ ions.The local environment of Er³⁺ ions in fluorite and distorted phases was analysed using site-selective spectroscopy. The Er³⁺ ions were found to act as nucleation centres in the glass ceramics containing BaF2. The phase transition from metastable fluorite to rhombohedrally and tetragonally distorted fluorite phases was detected using Er³⁺ ions as a probe.
Novel transparent Er³⁺ doped oxyfluoride glass-ceramics containing Ba4Gd3F17 nanocrystals were prepared by melt quenching followed by heat treatment of as-prepared glasses. The phase composition and microstructure were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Intense upconversion luminescence (UCL) was detected. Longer characteristic decay times and splitting of the luminescence bands compared to the precursor glass indicated the incorporation of erbium ions in the crystalline phase. The spectroscopic properties of glass ceramics were compared with single phase cubic and rhombohedral Ba4Gd3F17 ceramics. The unit cell parameters and atomic positions in the rhombohedral phase were calculated using Rietveld refinement. The local environment of Er³⁺ and the phonon energy of both polymorphs were analyzed using luminescence and Raman spectroscopy. In the glass ceramics, a phase transition from distorted metastable fluorite to ordered rhombohedral Ba4Gd3F17 was observed and resulted in the enhancement of the efficiency of UCL.
Novel Er³⁺ doped transparent glass ceramics containing hexagonal Na(Gd,Lu)F4 nanocrystals were prepared from oxyfluoride glasses. The distribution of rare earth ions in the crystalline and glassy phase has been analyzed by X-ray diffraction and erbium luminescence decay kinetics measurement. A strong deviation of rare earth ion content in fluoride nanocrystals in comparison to the base glass has been observed. Preferential incorporation of Gd³⁺ over Lu³⁺ ions in the fluoride lattice leads to the stabilization of hexagonal Na(Gd,Lu)F4 structure and prevents the formation of cubic fluorite type solid solutions. A considerable enhancement of upconversion luminescence correlates with the formation of hexagonal solid solutions and is attributed to an efficient energy transfer between Er³⁺ ions.
In the present work, effect of glass composition as well as ceramization on visible and NIR luminescence properties along with their decay dynamics of Er3+ ions have been compared considering two different oxyfluoride glasses yielding BaF2 and BaGdF5 nanocrystals. Both the glass systems have exhibited an intense normal and up-conversion green emission under ultraviolet (378 nm) and NIR (978 nm) excitations, respectively. A remarkable enhancement of these emission intensities is observed for gadolinium (Gd)-containing glasses. Interestingly, NIR fluorescence intensity from Er3+ ions at 1540 nm has showed marginal decrease in gadolinium-containing glass which is attributed to occurrence of strong excited state absorption (ESA) due to higher fluorine content ensuing an augmentation of up-conversion green emission with a concomitant decrease in NIR emission. The quadratic dependence of up-conversion green emission intensity on its pump power for all the samples revealed biphotonic absorption process from ground state 4I15/2 to the excited state 4I11/2 followed by ESA of second photon to the 4F7/2 level. The intense green up-conversion emission as well as enhanced NIR fluorescence lifetimes indicate the suitability of these glass/glass ceramics for up-conversion lasers and amplification in the third telecom window.
Recent years have seen greater interest in developing new luminescent materials to replace scintillator panels currently used in medical X-ray imaging systems. The primary areas targeted for improvement are cost and image resolution. Cost reduction is somewhat straightforward in that less expensive raw materials and processing methods will yield a less expensive product. The path to improving image resolution is more complex because it depends on several properties of the scintillator material including density, transparency, and composition, among others. The present study focused on improving image resolution using composite materials, known as glass-ceramics that contain nanoscale scintillating crystallites formed within a transparent host glass matrix. The small size of the particles and in-situ precipitation from the host glass are key to maintaining transparency of the composite scintillator, which ensures that a majority of the light produced from absorbed X-rays can actually be used to create an image of the patient. Because light output is the dominating property that determines the image resolution achievable with a given scintillator, it was used as the primary metric to evaluate performance of the glass-ceramics relative to current scintillators. Several glass compositions were formulated and then heat treated in a step known as “ceramization” to grow the scintillating nanocrystals, whose light output was measured in response to a 65 kV X-ray source. Performance was found to depend heavily on the thermal history of the glass and glass-ceramic, and so additional studies are required to more precisely determine optimal process temperatures. Of the compositions investigated, an alumino-borosilicate host glass containing 56mol% scintillating rare-earth halides (BaF2, GdF3, GdBr3, TbF3) produced the highest recorded light output at nearly 80% of the value recorded using a commercially-available GOS:Tb panel as a reference.
A strategy to achieve high sensitivity of non-contact optical thermometer via the structure design of nano-glass-ceramic and the usage of Ln3+ (Ln=Eu, Tb, Dy) luminescence as reference signal and Cr3+ emission as temperature signal was provided. Specifically, the synthesized dual-phase glass ceramics were evidenced to enable spatially confined doping of Ln3+ in the hexagonal GdF3 nanocrystals and Cr3+ in the cubic Ga2O3 nanoparticles, being beneficial to suppressing detrimental energy transfer between Ln3+ and Cr3+ and thus significantly enhancing their luminescence. As a consequence, completely different temperature-sensitive luminescence of Ln3+4f→4f transition and Cr3+ 3d→3d transition in the present glass ceramic resulted in obvious variation of Cr3+/Ln3+ fluorescence intensity ratio with temperature and strikingly high detecting temperature sensitivity of 15~22 % per K. We believe that this preliminary study will provide an important advance in exploring other innovative optical thermometry.
In this study novel Er3+-doped transparent glass ceramics were prepared from melt-quenched glasses with general composition of Na2O-NaF-BaF2-YF3-Al2O3-SiO2. The phase composition of the annealed glass ceramics strongly depends on the BaF2 content in glass matrix. Crystallization of β-NaYF4, cubic fluorite type, tetragonal nanocrystals and rhombohedral Ba4Y3F17 was observed. An introduction of BaF2 in the glass matrix suppresses the crystallization of β-NaYF4, promotes the formation of Ba2+ containing fluoride phases and reduces the cross-relaxation between Er3+ ions in fluoride crystals. Small rate of the nonradiative processes and low local symmetry of rhombohedrally disordered Ba4Y3F17 enables an efficient upconversion luminescence surpassing that of the glass ceramics containing β-NaYF4 nanocrystals.
Upconversion of low-energy photons into high-energy photons increases the efficiency of photovoltaic devices by converting photons with energies below the absorption threshold of the solar cell into photons that can be utilized. In this review, an overview is provided of quantitative studies of the upconversion quantum yield of upconverter materials, and of the achieved efficiency enhancements in upconverting solar cell devices. Different materials and devices are compared based on well-defined figures-of-merit and the challenges to their accurate measurement are discussed. Internal upconversion quantum yields above 13% have been reported both for Er3+-based materials as well as for organic upconverters, using irradiance values below 0.4 W cm−2. On the upconverting solar cell device level, relative enhancements of the solar cells' short-circuit currents by up to 0.55% have been achieved. These values document progress by orders of magnitude achieved in the last years. However, they also show that the field of upconversion needs further development to become a relevant technology option in photovoltaics. Different options regarding how upconversion performance can be increased further in the future are outlined.
Luminescence-based techniques continue to attract considerable attention due not only to their current range of applications but also to their wide potential in the fields of optical devices and biomedicine. Applications in the bioimaging of living cells and small animals, biosensors, chemosensors, and other optical fields have undergone considerable development. Two-photon absorption-based luminescence and second harmonic generation are two kinds of anti-Stokes processes, which require coherent lasers as the excitation sources and which have been well-investigated. Energy-transfer upconversion is by far the most efficient upconversion process. Most lanthanide UCNPs achieve efficient upconversion emissions through an energy-transfer upconversion process.
Glass ceramics NaYF 4 :Yb 3+ /Er 3+ Upconversion FIR technique Optical thermometry a b s t r a c t Yb 3+ /Er 3+ co-doped transparent oxyfluoride glass ceramics (GC) have been successfully fabricated and characterized for the purpose of optical thermometry by measuring the green upconverted fluorescence intensity ratio (FIR) between the two thermally coupled levels (2 H 11/2 and 4 S 3/2). The green upconverted emissions in the GC are enhanced by 15 times compared to that of the precursor glass. The dependence of the FIR on temperature ranging from 298 K to 693 K is well fitted with an exponential function by using an effective energy difference of 775 cm À1 . Owing to its low phonon energy and high thermal stability, an improved measurement accuracy and widened operating temperature range can be achieved with the GC sample, suggesting that transparent glass ceramics containing NaYF4:Yb 3+ /Er 3+ nanocrystals are promis-ing for application as optical-fiber temperature sensors. Ó 2014 Elsevier B.V. All rights reserved.
Novel Ho3+-doped transparent oxyfluoride SiO2-Al2O3-Na2CO3-CaO-BaF2-YbF3 glass ceramics (GC) containing BaYbF5 nanocrystals were fabricated via melt-quenching technique with subsequent heat treatment. The formation of crystalline fluoride phase was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Compared to precursor glasses, the greatly enhanced green emission (40-fold), new emission band at ultraviolet-blue region and stark splittings of emission in GC, indicate that Ho3+ enters into BaYbF5 nanocrystals with low phonon energy. Besides, the origin of the previously unconfirmed emission band at 440-460 nm is dearly identified by measuring spectra from thermally coupled luminescent levels at various temperatures. The outstanding upconversion properties of Ho3+ in GC may present potential application in all-solid-state upconversion lasers operating in the visible and ultraviolet range. (C) 2013 Elsevier B.V. All rights reserved.
Transparent glass-ceramic containing rare-earth doped halide nanocrystals exhibits enhanced luminescence performance. In this study, a glass-ceramic with Tb doped gadolinium fluoride nanocrystals embedded in an aluminosilicate glass matrix is investigated for X-ray imaging applications. The nanocrystalline glass-ceramic scintillator was prepared by a melt-quench method followed by an anneal. The GdF3:Tb nanocrystals precipitated within the oxide glass matrix during the processing and their luminescence and scintillation properties were investigated. In this nanocomposite scintillator system, the incorporation of high atomic number Gd compound into the glass matrix increases the X-ray stopping power of the glass scintillator, and effective energy transfer between Gd(3+) and Tb(3+) ions in the nanocrystals enhances the scintillation efficiency.
Unique Er3+ doped transparent BaLuF5 based glass–ceramics were triumphantly elaborated for the first time by melt-quenching technique and subsequent thermal treatment. The structural and luminescent properties were systemically investigated by XRD, TEM, absorption, excitation, down-shift and up-conversion spectra. All samples exhibit intense characteristic emissions of Er3+ (2H11/2, 4S3/2, 4F9/2→4I15/2) excited by 980 nm laser. The dramatically enhanced up-conversion (6500 times) and longer lifetime in glass–ceramics confirm that most Er3+ ions have preferentially entered into BaLuF5 nanocrystals with lower phonon energy after crystallization. Our results indicate BaLuF5 based transparent glass–ceramics may be excellent hosts for rare earth ions doping.
The manifestation of gross nonstoichiometry in MFm
-RFn
systems (m < n ≤ 4) has been studied. Fluorides of 34 elements, in the systems of which phases of practical interest are formed, are chosen. To search for new phases of complex composition, a program for studying the phase diagrams of the condensed state (∼200 systems) has been carried out at the Institute of Crystallography, Russian Academy of Sciences. The main products of high-temperature interactions of the fluorides of elements with different valences (m ≠ n) are grossly nonstoichiometric phases of two structural types: fluorite (CaF2) and tysonite (LaF3). Systems of fluorides of 27 elements (M
1+ = Na, K; M
2+ = Ca, Sr, Ba, Cd, Pb; R
3+ = Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; R
4+ = Zr, Hf, Th, U) are selected; nonstoichiometric M
1 − x
R
x
Fm(1 − x) + nx
phases, which are of greatest practical interest, are formed in these systems. The gross nonstoichiometry in inorganic fluorides is most pronounced in 80 MF2 − RF3 systems (M = Ca, Sr, Ba, Cd, Pb; R are rare earth elements). The problems related to the growth of single crystals of nonstoichiometric phases and basic fields of their application as new fluoride multicomponent materials, the properties of which are controlled by the defect structure, are considered.
The refractive indices n of Sr1 − x
R
x
F2 + x
crystals (R = Y, La-Lu; 0 ≤ x ≤ 0.5) have been measured at wavelengths of 0.436, 0.546, and 0.589 μm. It is established that n increases when there is an increase in the RF3 content x according to a weakly quadratic law for each R. For the isoconcentration series of Sr0.9R
0.1F2.1 crystals, the change in n in the series of rare earth elements has a pronounced nonlinear character, which reflects the nonmonotonous change in the properties of compounds in the R series. It is shown that the method of molecular refraction additivity can be used to calculate n for Sr1 − x
R
x
F2 + x
crystals. By varying the RF3 content in them, one can obtain optical media with a gradually varied refractive index n in the range 1.44–1.55, thus filling the gap in the n values between high ones for RF3 crystals and low ones for crystals of alkaline earth fluorides MF2.
Several glasses were synthesized to explore cation ordering at fluorine sites in silicate and aluminosilicate glasses. Utilizing 19F NMR, we found a significant (at least ∼30% of the total intensity) amount of the fluorine signal to be due to F–Mg(n) (fluorine with an unknown number of exclusively Mg2+ nearest neighbors) bonding in the Mg-aluminosilicates. By combining this with previous data on Ca- and Ba-aluminosilicate glasses, we demonstrated a clear trend of an increasing amount of F–M(n) type bonding with increasing field strength of the network modifying cation. This indicates that the higher field strength cations can more effectively compete with Al3+ for fluorine bonds. The mixed-modifier (Na,La)-silicate glasses have primarily F–M(n) type bonding, with a pronounced preference for bonding to the higher field strength La3+ over Na+. In addition, Si–F bonding was found in the (Na,La)-silicate glasses at a level (∼2% of the total intensity) comparable to that found in other silicate glasses, suggesting that Si–F bonding is consistently present in silicate glasses. The (Na,La)-silicate glasses also had unusually short spin–spin relaxation times, suggesting short (similar to crystalline fluorides) fluorine–fluorine distances in environments associated with La3+.
Transparent oxyfluoride glass–ceramics containing BaYF5 nanocrystals were successfully synthesized by appropriate heat-treatment on the SiO2–Al2O3–Na2O–BaF2–Y2O3–Pr6O11 precursor glass. The structure and luminescence properties of the precursor glass and glass–ceramics were investigated by DSC, XRD, TEM, optical transmission, photoluminescence, decay time and radioluminescence spectra. The XRD results indicate that the BaYF5 nanocrystals can percitated in the precursor glass and the sharper emission peaks of Pr3+ in glass ceramic suggests that Pr3+ ions are incorporated into the BaYF5 nanocrystals. The higher the heat-treatment temperature is, the more the Pr3+ ions are centered into BaYF5 nanocrystals, which results in the optimal concentration of Pr3+ in glass ceramic changes on heat-treatment temperature. It is notable that the emission intensity of both photoluminescence and radioluminescence for 0.1 mol% Pr3+ in the glass ceramic (GC665) are stronger than those in the precursor glass. The mechanism of enhanced luminescence is also discussed.
Thermal analyses on samples of the composition (Ba,RE)F2,33 revealed seven new compounds Ba2REF7 (RE Dy-Lu, Y). They are stable only above about 940 °C but can be quenched after annealing for several days at 950–1000 °C. These phases which are metastable at room temperature were characterized by X-ray powder diffraction. A tetragonal distortion of the fluorite parent structure was detected, analogous to that in the Ln3F7, Ca2REF7 and Sr2REF7 phases. In contrast, however, the superstructure is not fully pronounced and only tripling along the c axis is observed. This indicates that only the cation order and not the reorganization of the highly mobile anion sublattice is fully developed in these layer structures. This behavior is not unexpected for fluorite-related high temperature phases which belong to the class of fast anionic conductors.
Previous experimental results, using techniques associated with transmission electron microscopy (TEM), suggested that rare-earth dopants prefer the precipitated fluoride nanocrystals to the glass matrix. By contrast, this work shows that contradicting results can be obtained under different experimental conditions. In the silicate glass containing LaF3 nanocrystals, the Eu dopants distribute indistinguishably in the precipitated LaF3 and the silicate glass matrix. However, electron beam exposure during the measurement can relocate Eu, leading to the false conclusion that apparently Eu prefers the precipitated LaF3 nanoparticles to the glass matrix. Fortunately, the artefact can be avoided by shortening the exposure time. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Data are presented on phase equilibria at 877 +/- 10°C in the systems BaF2-(Y,Ln)F3, where Ln = Sm-Lu. All the systems show cubic solid solutions based on BaF2 and variable composition phases of structure derived from the CaF2 type (rhombohedral distortion). Syngony and unit cell dimensions have been determined on monocrystals; crystallographic parameters of ten trigonal phases have been adduced. The existence of solid solutions of BaF2 in high-temperature alpha-LnF3(LaF3 type) at the given isothermal section indicates stabilization of the LaF3 structure type by heterovalent isomorphous replacement. In the systems BaF2-(Y,Ln)F3 with Ln = Dy-Yb, monoclinic compounds BaR2F8 are formed. X-ray parameters, derived from single crystal and polycrystalline specimens, of six monoclinic BaR2F8 compounds are presented. In the BaF2-LuF3 system we have isolated and studied for the first time a compound of the approximate composition BaLu2F8 which crystallizes in rhombic syngony and has a marked range of homogeneity.
In this paper we investigate the holographic recording properties of the fluorescent photosensitive glass-ceramics The materials described here stable up to 400 C represent a substantial advancement in the development of long lifetime media for holographic data storage A detailed physical-chemical characterization of the proposed material is presented It is shown that volume holograms were obtained after the recording process using a continuum high power laser in an off-axis setup (C) 2010 Elsevier BV All rights reserved
The individual charge compensated sites of Er3+ have been identified in BaF2 crystals containing 0.01–1.0 mole % Er3+ using a narrow bandwidth tunable dye laser and it was found that the sites are not adequately described by the model of single Er3+–F−I pairs. The sites have been classified as single Er3+–F−I pair sites or cluster sites on the basis of the concentration dependence, the number of transitions exhibited, and the existence of efficient nonresonant energy transfer between ions within a site. The energy transfer rates have been found for the cluster sites for two different transfer processes and are compared with previous results reported for similar processes in CaF2:Er3+. The appearance of cluster sites at concentrations as low as 0.01 mole %Er3+ is in agreement with previous work in CaF2 and SrF2 and exemplifies the need for consideration of clustering to describe the defect site equilibria in crystals of this type.
Intense red ( Er <sup>3+</sup>:<sup>4</sup>F<sub>9/2</sub>→<sup>4</sup>I<sub>15/2</sub> , Tm <sup>3+</sup>:<sup>1</sup>G<sub>4</sub>→<sup>3</sup>F<sub>4</sub> ), green ( Er <sup>3+</sup>:<sup>2</sup>H<sub>11/2</sub> , <sup>4</sup>S<sub>3/2</sub>→<sup>4</sup>I<sub>15/2</sub> ), and blue ( Tm <sup>3+</sup>:<sup>1</sup>D<sub>2</sub>→<sup>3</sup>F<sub>4</sub> , <sup>1</sup>G<sub>4</sub>→<sup>3</sup>H<sub>6</sub> ) upconversion emissions were simultaneously generated in the transparent glass ceramics containing Tm <sup>3+</sup>/ Er <sup>3+</sup>/ Yb <sup>3+</sup>:β- Y F <sub>3</sub> nanocrystals under single 976 nm laser excitation. It was demonstrated that Tm <sup>3+</sup> behaves as the sensitizer for red luminescence of Er <sup>3+</sup> and Er <sup>3+</sup> as the quenching center for blue, red, and near-infrared upconversion emissions of Tm <sup>3+</sup> . Various colors of the luminescence, including perfect and bright white light with CIE -X=0.310 and CIE -Y=0.358 , can be easily tuned by adjusting the concentrations of the rare earth ions in the material.
Some F-rich granitic rocks show anomalous, nonchondritic ratios of Y/Ho, extreme negative Eu anomalies, and unusual, discontinuous, segmented chondrite-normalised plots of rare earth elements (REE). The effects of F-rich fluids have been proposed as one of the explanations for the geochemical anomalies in the evolved granitic systems, as the stability of nonsilicate complexes of individual rare earths may affect the fluid-melt element partitioning. The lanthanide tetrad effect, related to different configurations of 4f-electron subshells of the lanthanide elements, is one of the factors affecting such complexing behaviour. We present the first experimental demonstration of the decoupling of Y and Ho, and the tetrad effect in the partitioning of rare earths between immiscible silicate and fluoride melts. Two types of experiments were performed: dry runs at atmospheric pressure in a high-temperature centrifuge at 1100 to 1200°C, and experiments with the addition of H2O at 700 to 800°C and 100 MPa in rapid-quench cold-seal pressure vessels. Run products were analysed by electron microprobe (major components), solution-based inductively coupled plasma mass spectrometry (ICP-MS) (REE in the centrifuged runs), and laser ablation ICP-MS (REE and Li in the products of rapid-quench runs). All the dry centrifuge runs were performed at super-liquidus, two-phase conditions. In the experiments with water-bearing mixtures, minor amounts of aqueous vapour were present in addition to the melts. We found that lanthanides and Y concentrated strongly in the fluoride liquids, with two-melt partition coefficients reaching values as high as 100–220 in water-bearing compositions. In all the experimental samples, two-melt partition coefficients of lanthanides show subtle periodicity consistent with the tetrad effect, and the partition coefficient of Y is greater than that of Ho. One of the mixtures also produced abundant fluorite (CaF2) and cryolite (Na3AlF6) crystals, which enabled us to study fluorite-melt and cryolite-melt REE partitioning. REE concentrations in fluorite are high and comparable to those in the fluoride melt. However, fluorite-melt partition coefficients appear to depend mostly on ionic radii and show neither significant tetrad anomalies, nor differences in Y and Ho partitioning. In contrast, REE concentrations in cryolite are low (∼5–10 times lower than in the silicate melt), and cryolite-melt REE partitioning shows very strong tetrad and Y-Ho anomalies. Our results imply that Y-Ho and lanthanide tetrad anomalies are likely to be caused mainly by aluminofluoride complexes, and the tetrad REE patterns in natural igneous rocks can result from fractionation of F-rich magmatic fluids.
We show theoretically with the simplest possible model that the intensity of an upconversion luminescence that is excited by the sequential absorption of n photons has a dependence on absorbed pump power P, which may range from the limit of Pn down to the limit of P1 for the upper state and less than P1 for the intermediate states. The two limits are identified as the cases of infinitely small and infinitely large upconversion rates, respectively. In the latter case, the dependence of luminescence intensities from intermediate excited states on pump power changes with the underlying upconversion and decay mechanisms. In certain situations, energy transfer upconversion and excited-state absorption can be distinguished by the measured slopes. The competition between linear decay and upconversion in the individual excitation steps of sequential upconversion can be analyzed. The influence of nonuniform distributions of absorbed pump power or of a subset of ions participating in energy-transfer upconversion is investigated. These results are of importance for the interpretation of excitation mechanisms of luminescent and laser materials. We verify our theoretical results by experimental examples of multiphoton-excited luminescence in Cs3Lu2Cl9:Er3+, Ba2YCl7:Er3+, LiYF4:Nd3+, and Cs2ZrCl6:Re4+.
The anti-Stokes emissions or upconversion processes, for which emissions was found to exceed excitation energies by 10-100 kT, were presented. The dissolution of nanoparticles (6-8 nm) of Yb-Er- and Yb-Tm doped LuPO 4 as colloids in chloroform solutions was demonstrated. The Nd 3+-Yb3+ codoped YA nanocrystalline cemramics were also studied. It was observed that in thermoluminescence, where traps were emptied by excitation energies of the order of kT, constituted a field of anti-Stokes emission of its own.
We report an efficient glass-ceramic fiber laser and show that its slope efficiency (~30%) is not compromised by the presence of Nd-doped fluoride crystals embedded within the core of the single-mode optical fiber. In contrast, the spectroscopy (fluorescence and gain spectrum) of the Nd(3+) ions is dramatically changed by the ceramming process, an indication of strong partitioning of the rare-earth ions into the CdF(2):PbF(2):YF(3) crystal environment. The enormous potential for a new range of optical devices based on transparent glass-ceramic materials is highlighted.