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In this study, the structural, luminescence and photoconversion properties of novel composite color converters based on Tb1.5Gd1.5Al5O12:Ce (TGAG:Ce) single crystalline films, grown by the liquid phase epitaxy method onto Y3Al5O12:Ce (YAG:Ce) single crystal substrates, are investigated. The luminescence and chromaticity properties for the set of TGAG:Ce SCF/YAG:Ce composite color converters, including color coordinates, color rendering index (CRI), and luminous efficacy, were studied by varying the thickness of the TGAG:Ce film in the 12–48 μm range and the Ce3+ concentration in the 0.1–0.5% range in YAG:Ce substrates. Such combination of different YAG:Ce substrates with various TGAG:Ce films enables tuning the white light tones from cold white (correlated color temperature (CCT) > 6000 K) to neutral white (6000 K > CCT > 3300 K). The theoretical white light color coordinates on the chromaticity diagram were almost achieved for TGAG:Ce film/YAG:Ce (0.5 mm) crystal converters with a film thickness between 19 and 25 μm under 465 nm LED excitation, with the corresponding CRI values in the 79–74 range. The developed composite color converters allow the problem of a high color temperature and low color rendering index of conventional WLEDs based on conventional YAG:Ce phosphor converters to be solved. [ABSTRACT FROM AUTHOR]

The possibility of development of an efficient phosphor converters (PC) for white LED (WLED) based on single crystalline films (SCF) of Ce3+ doped Tb3Al5O12 garnet (TbAG:Ce), grown using liquid-phase epitaxy method onto Y3Al5O12 (YAG) substrates, is evidenced for the first time in this work. The detail investigation of the structural properties of the TbAG:Ce SCF/YAG epitaxial structures was performed. High-resolution scanning transmission electron microscopy and composition analysis revealed an interface with high structural quality including the formation of a transition layer with a 5–7 nm thickness between TAG:Ce SCF and YAG substrate. The transition layer consisted of solid solutions between Tb3Al5O12:Ce and Y3Al5O12 garnets gradually changing from undoped YAG in substrate towards TbAG:Ce in the film and allowed to reduce the mismatch-stress. The absorption, cathodoluminescence, photoluminescence properties of TbAG:Ce SCFs were investigated as well. Furthermore, the dependence of photoconversion properties on the film thicknesses was studied to construct the prototype of efficient warm white LEDs. The change in the crystal thickness enabled tuning of the white light tons from cold white/daylight to neutral white. These results can be useful for the development of a novel generation of phosphor converters for white LEDs. [ABSTRACT FROM AUTHOR]

This article is directed on the creation of composite scintillators which are based on the films and crystals of R2Si2O7:Ce (R = Lu, Gd, La) pyrosilicates using the liquid phase epitaxy (LPE) growth method for application in the radiation monitoring of different components of mixed ionization fluxes. Such types of composite scintillators are epitaxial structures containing film scintillators grown by the LPE method onto the substrates of crystal scintillators. In this article, the film and crystal parts of the composite scintillators were fabricated from effective scintillation materials on the base of Ce3+ doped Gd2-xLuxSi2O7 and Gd2-xLaxSi2O7, and x = 0 and 0.25 mixed pyrosilicates with various scintillation decay kinetics due to the different Lu/Gd/La cation content. We briefly report on the results of the LPE growth of the composite scintillators based on the Ce3+ doped (Lu,Gd)2Si2O7 films and (Gd,La)2Si2O7:Ce crystal substrates, as well as the results of investigation of their luminescent and scintillation properties. [ABSTRACT FROM AUTHOR]

This work reports the results of the optical and electron paramagnetic resonance (EPR) investigation of the Ce3+ incorporation in single crystalline film (SCF) scintillators of Ce-doped LuAlO3 perovskite, grown by the liquid phase epitaxy method onto YAlO3 substrates using a PbO–B2O3 flux. The absorption, luminescence and EPR spectra showed the presence of the main Ce3+ center type (CeLu) corresponding to the location of Ce3+ ions in the twelve-fold coordinated cuboctahedral positions of the LuAlO3 host. Also the dimer CeLu–CeLu centers were found in the EPR spectra of the LuAP:Ce SCFs. No EPR spectrum of the Ce3+ ions located in the octahedral positions of Al3+ cations has been detected indicating their negligibly small concentration (below 5 × 10−3 at%) in the SCFs. Pb3+ and Pt3+ impurity ions incorporated into the SCFs grown from the PbO–B2O3 flux and Pt crucible were also identified by resolving, in particular, the hyperfine structure from the 195Pt isotope in the EPR spectra. [ABSTRACT FROM AUTHOR]

The paper is dedicated to the development of scintillating screens for microimaging applications based on the single crystalline films (SCFs) of singly Tb3+ and doubly Tb3+–Ce3+ doped Gd1–xLuxAlO3 (x = 0–1) mixed perovskites grown onto YAlO3 (YAP) substrates using the liquid phase epitaxy (LPE) method. The cation engineering in Gd1–xLuxAlO3 (x = 0–1) solid solution enabled an improvement of the K-edge of X-ray absorption of SCF scintillators in the 50–63 keV energy range. The structural quality of the grown films was studied using X-ray diffraction and scanning electron microscopy. The optical properties of the Tb3+-doped and Tb3+–Ce3+-codoped Gd1–xLuxAlO3 (x = 0–1) SCFs were investigated by conventional spectroscopic methods, such as absorption, cathodoluminescence (CL), photoluminescence, the light yield of CL, and radioluminescence (RL) measurements under e-beam and α-particle excitation, respectively. Effective Gd3+→ Tb3+ and Gd3+→ Ce3+→ Tb3+ energy transfer processes were observed in Gd1–xLuxAlO3:Tb and Gd1–xLuxAlO3:Tb,Ce SCFs, respectively, explaining the increased efficiency of the Tb3+ luminescence in these perovskite hosts. We found that the highest efficiencies in terms of CL and RL were observed in the doubly Tb3+–Ce3+-doped Gd0.5Lu0.5AlO3 SCFs. [ABSTRACT FROM AUTHOR]

This work presents our latest achievements in the development of advanced composite scintillators for simultaneous registration of α-particles and γ-quanta in mixed ionizing fluxes based on single crystalline films (SCFs) of Tb3Al3O12 : Ce (TbAG : Ce) garnet and Gd3Al2.5Ga2.5O12 : Ce (GAGG : Ce) single crystal (SC) substrates using the liquid phase epitaxy (LPE) growth method from a melt-solution based on a PbO–B2O3 flux. The separation of the signals from the SCF and SC components of such composite scintillators can be realized by means of registration of the difference in the scintillation decay times of SCF and substrate scintillators and can be achieved at a large K = t(SCF)/t(SC) ratio, which is usually above 2. The TbAG : Ce SCFs exhibit relatively fast scintillation response under α-particle excitation with decay times of t1/e = 344–380 ns and t1/100 = 3130–3770 ns. Meanwhile, the scintillation response of TbAG : Ce SCFs under α-particle excitation is significantly slower in the 500–4000 ns range than that of the GAGG : Ce crystals with decay times of t1/e = 270–280 ns and t1/20 = 1280–1300 ns. We have found that for TbAG : Ce/GAGG : Ce composite scintillators, the optimal K ratio changes from 2.0 to 3.0 at the registration of scintillations with shaping times of 700–4000 ns. For this reason, TbAG : Ce/GAGG : Ce composite scintillators possess the best scintillation properties among all known LPE grown analogues for simultaneous registration of α-particles and γ-quanta in mixed fluxes. [ABSTRACT FROM AUTHOR]

The work is dedicated to comparative investigation of the luminescent properties of Y3Al5O12:Pr (YAG:Pr) single crystals and single crystalline films using excitation by synchrotron radiation with an energy of 3.7-25 eV in the exciton range of YAG host. We have found that the differences in the excitation spectra and luminescence decay kinetics of YAG:Pr crystals and films are caused by involving the YAl antisite defects and oxygen vacancies in the crystals and Pb2+ flux related dopants in the films in the excitation processes of the Pr3+ luminescence. Taking into account these differences, we have determined in more detail the energy structure of the Pr3+ ions in YAG host and estimated the differences in the energies of creation of the excitons bound with the isolated Pr3+ ions in YAG:Pr films and the dipole Pr-YAl antisite defect centers in the crystal counterpart. [ABSTRACT FROM AUTHOR]

The study is dedicated to the development of scintillating screens for microimaging applications based on the single crystalline films (SCFs) of Eu3+-doped (Y,Lu,Gd,Tb)AlO3-mixed perovskites grown onto YAlO3 substrates using the liquid phase epitaxy (LPE) method with the objective to optimize their X-ray stopping power and light yield. We confirm that the Eu3+-doped YAlO3 and TbAlO3 SCFs and full set of Lu1−xGdxAlO3 SCFs with x values in the x = 0–1.0 range can be crystallized on YAlO3 substrates using the LPE technique. The structural quality of films was studied using X-ray diffraction. The optical properties of Lu1−xGdxAlO3:Eu (x = 0–1) SCFs and TbAlO3:Eu mixed perovskites were also studied in this work in comparison with YAlO3:Eu SCF counterpart using the absorption, cathodoluminescence, photoluminescence (PL) emission and excitation spectra and PL decay kinetics as well as light yield measurements under e-beam and α-particles excitation. The Gd3+→ Eu3+ and Tb3+→ Eu3+ energy transfer processes are observed in Lu1−xGdxAlO3 and TbAlO3:Eu SCFs, respectively, increasing the efficiency of the Eu3+ luminescence in the perovskite hosts. Meanwhile, the highest light yield of the cathodoluminescence (CL) and radioluminescence (RL) under excitation by α-particles is found only in YAlO3:Eu, Lu0.5Gd0.5AlO3:Eu and GdAlO3:Eu SCFs. The light yield of CL and RL of these SCFs is notably higher than that in TbAlO3:Eu and LuAlO3:Eu SCFs and they even slightly (9–11%) overcome the light yield of the conventional Gd3Ga5O12:Eu SCF screens that are used in the microimaging detectors. [ABSTRACT FROM AUTHOR]

UV emitting scintillating screens based on single crystalline films (SCFs) of Lu3Al5−xGaxO12:Pr garnet have been developed by the liquid phase epitaxy (LPE) growth method onto Y3Al5O12 (YAG) substrates using a lead-free BaO based flux. The absorbance, luminescence and scintillation properties of these SCFs have been investigated depending on the Ga content in the x = 0–1.9 range. We have found that the absorption and luminescence spectra of Pr3+ ions as well as the scintillation light yield (LY) and decay kinetics of Lu3Al5−xGaxO12 SCFs are non-linearly affected by the gallium concentration x in the mentioned solid solution due to preference for the distribution of Ga3+ and Al3+ ions between the tetrahedral and octahedral positions of the garnet host, respectively. The best scintillation properties of Lu3Al5−xGaxO12:Pr SCFs are achieved at the Ga content in the x = 1.0–1.2 range. The LY of the Lu3Ga1.2Al3.8O12:Pr SCF is comparable with the LY of the best reference LuAG:Pr single crystal counterpart and significantly (up to 3 times) overcomes the LY of LuAG:Pr and Lu3Al4–3.5Ga1.0–1.5O12 SCFs, grown onto the YAG substrates from the conventional PbO–B2O3 flux. [ABSTRACT FROM AUTHOR]

The results on crystallization and investigation of the luminescent properties of a new prospective ceramic phosphor based on the Ce3+ doped Ca2YMgScSi3O12 silicate garnet are presented for the first time in this work. The luminescent properties of Ca2YMgScSi3O12:Ce were compared with the properties of the reference Ca3Sc2Si3O12:Ce ceramic sample. Without any doubt, the results of this research can be suitable for the development of a new generation of white converters based on the Ca2+-Si4+ garnet compounds. [ABSTRACT FROM AUTHOR]

We report for the first time the optimized content and excellent scintillation properties of single crystalline film (SCF) scintillators of multicomponent Gd3- xLu x Al5- yGa y O12:Ce garnet compounds grown by liquid phase epitaxy (LPE) method. The Gd1.5Lu1.5Al2.75Ga2.25O12:Ce and Gd3Al2.75-2Ga2.25-3O12:Ce SCF show the light yield (LY) comparable with that of high-quality bulk crystal analogues of these garnets but faster scintillation decay and very low thermoluminescence in the above room temperature range. To our knowledge, these SCF possess the highest LY values ever obtained in LPE grown garnet SCF scintillators exceeding by at least 1.5-1.6 times the values previously reported for SCF scintillators. [ABSTRACT FROM AUTHOR]

Low temperature, infrared, and visible-ultraviolet absorption spectra of yttrium aluminum garnet (YAG) bulk crystals and epitaxial layers doped with Ce are presented. In the region of intra-configurational 4f-4f transitions, the spectra of the bulk YAG crystals exhibit existence of at least two different Ce3+ related centers, a major one associated with Ce in regular positions substituting yttrium and also additional center, due to so called antisite positions in the garnet host, i.e., ions in the Al positions. Crystal field analysis based on exchange charge model exhibit excellent agreement with the experimental data for major Ce3+ center. [ABSTRACT FROM AUTHOR]

The work is dedicated to the development of new types of UV--emitting scintillators based on single crystalline films (SCF) of aluminum perovskites and garnets grown by the liquid phase epitaxy method. The peculiarities of growth and properties of the following three types of UV SCF scintillators are considered in this work: i) Ce-doped SCF of Y-Lu-Al-perovskites with the Ce3+ emission in the 360-370 nm range of the decay time of 16-17 ns; ii) Pr-doped SCF of Y-Lu-Al garnets with the Pr3+ emission in the 300-400 nm range of the decay time of 13-17 ns; iii) La3+ or Sc3+ doped SCF of Y-Lu-Al-garnets, emitting in the 290-400 nm range due to formation of the LaY,Lu, ScY,Lu and ScA1 centers with decay time of the order of hundreds of nanoseconds. Preliminary test of these SCFs scintillators for visualization of X-ray images at European Synchrotrons Radiation Facility are presented as well. [ABSTRACT FROM AUTHOR]

The processes of excitation energy transfer in phosphors based on single-crystal Tb3Al5O12:Ce (TbAG:Ce) and Tb3Al5O12:Ce,Eu (TbAG:Ce,Eu) garnet films have been investigated. These films are considered to be promising materials for screens for X-ray images and luminescence converters of blue LED radiation. The conditions for excitation energy transfer from the matrix (Tb3+ cations) to Ce3+ and Eu3+ ions in TbAG:Ce and TbAG:Ce,Eu phosphors have been analyzed in detail. It is established that a cascade process of excitation energy transfer from Tb3+ ions to Ce3+ and Eu3+ ions and from Ce3+ ions to Eu3+ ions is implemented in TbAG:Ce,Eu via dipole-dipole interaction and through the Tb3+ cation sublattice. [ABSTRACT FROM AUTHOR]

Intrinsic and Ce-related luminescence of LuAP:Ce single crystalline films (SCF) in comparison with their bulk single crystal (SC) analogs were analyzed for the first time using the time-resolved luminescence spectroscopy under synchrotron radiation excitation. Difference in luminescent properties of SCF and SC are due to the absence of the Lu-at-Al-site antisite defects (AD) and extremely low concentration of vacancy-type defects (VD) in SCF. SCF contamination by Pb ions from flux is noted, which gives rise to an additional emission band in UV range. In SCF, the absence of emission and trapping centers formed by the mentioned AD and VD can explain their favorable timing characteristics with respect to SC. The role of Pb2+ trace impurities in LuAP-based SCF scintillators is considered as well. [ABSTRACT FROM AUTHOR]

The nature of the intrinsic luminescence of the lutetium aluminum garnet Lu3Al5O12 (LuAG) has been analyzed on the basis of time-resolved spectral kinetic investigations upon excitation of two model objects, LuAG single crystals and single-crystal films, by pulsed X-ray and synchrotron radiations. Due to the differences in the mechanisms and methods of crystallization, these objects are characterized by significantly different concentrations of LuAl antisite defects. The energy structure of luminescence centers in LuAG single crystals (self-trapped excitons (STEs), excitons localized near antisite defects, and LuAl antisite defects) has been established. For single-crystal LuAG films, grown by liquid-phase epitaxy from a Pb-containing flux, the energy parameters of the following luminescence centers have been determined: STEs in regular (unperturbed by the presence of antisite defects) sites of the garnet lattice and excitons localized near Pb2+ ions. The structure of the luminescence centers, related to the background emission of impurity Pb2+ ions, has also been established in the UV and visible ranges. It is suggested that, in contrast to the two-halide hole self-trapping, a self-trapped state similar to STEs in simple oxides (Al2O3, Y2O3) is formed in LuAG; this state is formed by self-trapped holes in the form of singly charged O− ions and electrons localized at excited levels of Lu3+ cations. [ABSTRACT FROM AUTHOR]

We have investigated the photoluminescence (PL) and photostimulated luminescence (PSL) spectra at 300 K to study the effect of isoelectronic impurities K+ and I− on the formation and energy structure of Eu2+-VCs isolated dipole centers and aggregate centers in the form of single crystals of CsEuBr3 in CsBr:Eu2+ single crystals. We have shown that K+ and I− impurities in a concentration of 5 mol% do not have a substantial effect on the energy spectrum of isolated dipole centers in CsBr:Eu2+ single crystals and the processes for the formation of such centers during growth of CsBr:Eu single crystals from the melt by the Bridgman method. We have established that in Cs0.95K0.05Br:Eu2+, more favorable conditions are realized for the formation of aggregate centers than in CsBr:Eu2+ and CsBr0.95K0.05Br:Eu2+ single crystals. So in order to improve the storage properties of phosphors based on CsBr:Eu2+, in particular for increasing the efficiency of PSL excitation, it is expedient to dope them with K+ impurity in a concentration up to 5 mol%. [ABSTRACT FROM AUTHOR]

We have used the Bridgman method to grow CsBr:Eu2+ single crystals, adding an activator to the mix in the form of Eu2O3 in amounts of 0.0125, 0.0250, and 0.0500 mole %. At T = 300 K, we studied the absorption spectra, the photoluminescence (PL) spectra, and the photostimulated luminescence (PSL) spectra of the grown crystals. We have established that the structure of the photoluminescence and photostimulated luminescence centers in crystals grown from the CsBr:Eu2O3 mix includes isolated dipole centers Eu2+-VCs, emitting in bands with maxima at 432 nm and 455 nm respectively, and in crystals grown at activator concentrations of 0.025 and 0.050 mole % they also include aggregate centers (AC) based on CsEuBr3 nanocrystals with emission bands at 515 m and 523 nm. We have shown that the maximum concentration of aggregate centers of the CsEuBr3 nanocrystal type in CsBr:Eu2+ crystals is achieved for an activator content in the mix within the range 0.01–0.05 mole %. [ABSTRACT FROM AUTHOR]

The time-resolved luminescence and luminescence excitation spectra, and luminescence decay kinetics at 8 and 300 K of Lu3A15O12 (LuAG) single-crystal films doped with Sc3+ and La3+ isoelectronic impurities and excited by synchrotron radiation are investigated. It is established that the La3+ isoelectronic impurity in the ⨑ub; c⫂ub; positions of the garnet lattice forms La luminescence centers emitting in the band with λmax = 280 nm and the decay time of the main component τ = 300 ns at 300 K. The Sc3+ isoelectronic impurity located in the ⨑ub; c⫂ub; and ( a) positions of the LuAG lattice forms two luminescence centers, Sc and Sc, emitting in the bands with λmax = 290 nm and τ = 240 ns and λmax = 335 nm and τ = 375 ns, respectively, at 300 K. It is shown that the luminescence excitation of the La3+ and Sc3+ isoelectronic impurities in LuAG single-crystal films occurs through radiative decay of excitons localized near La, Sc, and Sc centers. The energies of formation of these excitons are determined to be 6.8, 6.88, and 7.3 eV, respectively. It was found that the excited state of the excitons genetically related to the La, Sc, and Sc enters has two radiative levels with different transition probabilities. This configuration leads to the presence of fast (2.3–8.4 ns) and slow (150–375 ns) main components in the luminescence of the centers formed by isoelectronic impurities in garnets. [ABSTRACT FROM AUTHOR]

Special features of the incorporation of a copper impurity into CsBr crystals are studied for different types of impurities (metallic copper, CuO, and CuBr2) and crystal-growth techniques (the Bridgman method or the method of isothermal evaporation from solution). The optical characteristics of these crystals (absorption, photoluminescence, and photostimulated-luminescence spectra) are investigated. The copper impurity is shown to enter CsBr:Cumet crystals in the monovalent state Cu+ and CsBr:CuO and CsBr:CuBr2 crystals in the divalent state Cu2+. It is found that the CsBr crystals doped with Cu+ and Cu2+ ions exhibit intense photostimulated luminescence and can be used as storage phosphors for visualization of X-ray images. [ABSTRACT FROM AUTHOR]

By liquid-phase epitaxy from an aqueous alcoholic solution, we have obtained films of the well-known storage phospor CsBr:Eu, and we have studied their cathodoluminescence and photoluminescence (PL) spectra compared with the undoped CsBr films. We have established that the structure of the photoluminescence centers of the CsBr:Eu films when excited by laser radiation in the absorption band of the Eu2+ ions (λ = 337 nm) includes Eu2+-VCs isolated dipole centers and CsEuBr3 aggregate centers, and also luminescence centers based on inclusions of hydroxyl group OH− with the corresponding emission bands in the 440 nm, 520 nm, and 600 nm regions. We have studied the dependence of the spectra and the intensity of the photoluminescence for CsBr:Eu films on annealing temperature in air at 423–483 K, compared with analogous dependences for CsBr:Eu single crystals obtained from the melt. We have shown that annealing the films at T = 423–463 K leads to rapid formation of CsEuBr3 aggregate luminescence centers, while for T > 473 K thermal degradation of these centers occurs. We conclude that the observed differences between the photoluminescence spectra of CsBr:Eu films and CsBr:Eu single crystals may be due to additional doping of the films with OH− ions. [ABSTRACT FROM AUTHOR]

The luminescence of excitons and antisite defects (ADs) was investigated, as well as the specific features of the excitation energy transfer from excitons and ADs to the activator (Ce3+ ion) in phosphors based on Lu3Al5O12:Ce (LuAG:Ce) single crystals and single-crystalline films, which are characterized by significantly different concentrations of ADs of the Lu3+Al type and vacancy-type defects. The luminescence band with λmax = 249 nm in LuAG:Ce single-crystal films is due to the luminescence of self-trapped excitons (STEs) at regular sites of the garnet lattice. The excited state of STEs is characterized by the presence of two radiative levels with significantly different transition probabilities, which is responsible for the presence of two excitation bands with λmax = 160 and 167 nm and two components (fast and slow) in the decay kinetics of the STE luminescence. In LuAG:Ce single crystals, in contrast to single-crystal films, the radiative relaxation of STEs in the band with λmax = 253.5 nm occurs predominantly near Lu3+Al ADs. The intrinsic luminescence of LuAG:Ce single crystals at 300 K in the band with λmax = 325 nm (τ = 540 ns), which is excited in the band with λmax = 175 nm, is due to the radiative recombination of electrons with holes localized near Lu3+Al ADs. In LuAG:Ce single crystals, the excitation of the luminescence of Ce3+ ions occurs to a large extent with the participation of ADs. As a result, slow components are present in the luminescence decay of Ce3+ ions in LuAG:Ce single crystals due to both the reabsorption of the UV AD luminescence in the 4f–5d absorption band of Ce3+ ions with λmax = 340 nm and the intermediate localization of charge carriers at ADs and vacancy-type defects. In contrast to single crystals, in phosphors based on LuAG:Ce single-crystal films, the contribution of slow components to the luminescence of Ce3+ ions is significantly smaller due to a low concentration of these types of defects. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

The paper reports on a study of exciton luminescence in single crystals (SCs) and single-crystal films (SCFs) of YAlO3, which have substantially different concentrations of vacancy-type and substitutional defects, under excitation by synchrotron radiation near the fundamental absorption edge. The radiative annihilation of excitons in SCFs was shown to occur primarily at regular perovskite lattice sites and to be accompanied by luminescence in a band peaking at λmax = 295 nm with τ = 5.2 ns. In contrast to SCFs, the radiative exciton decay in YAlO3 SCs takes place predominantly near vacancy-type defects (F+ and F centers) and is accompanied by luminescence in the bands at λmax = 350 nm (τ = 2.5 ns) and 440 nm (τ1 = 1.9 ns, τ2 = 30 ms). Photoexcitation in the 175-nm band of YAlO3 SCs revealed photoconversion of the centers F→F+. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

Scintillation detectors in the form of luminescent films on a bulk substrate have been developed and explored. Thin doped garnet films on the basis of Lu3A15 012 were grown on an undoped Y3Al5 O12 nonluminescent substrate for the application as X-ray imaging screens in microtomography. The introduction of Lu provided a strong absorption for X-rays and a possibility to reduce the film thickness down to 1 - 2 μm and to achieve a spatial resolution of 0.8 to 1.2 pm. Doped luminescent films of various materials with the thickness adapted to the path length of short-range particles, were grown or deposited on a doped luminescent substrate intended for detecting long-range particles. Such phoswich-detectors are used for radiation monitoring of low-activity nuclides. Ways to improve the operation characteristics of such detection systems are proposed. [ABSTRACT FROM AUTHOR]

In YAlO3 crystals grown in vacuum or reduced by annealing at low oxygen pressure, the luminescence of F centers in the band at 420 nm, with τ = 30 ms at 9 K, excited in the bands at 212 and 242 nm, as well as the luminescence of F+ centers in the band at 355 nm, with τ = 2.7 ns, excited in the main band at 220 nm and weaker bands at 190 and 288 nm, was detected. On the basis of the results obtained and data in the literature, the behavior of the emission of F+ and F centers in oxides of the Al2O3–Y2O3 system is analyzed on the example of the compounds α-Al2O3,YAlO3, and Y3Al5O12. The role of antisite defects in the stabilization of F-like luminescence and absorption centers in multisublattice oxides is discussed. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Comparative studies of the luminescence of Y[sub 3]Al[sub 5]O[sub 12]:Ce and Lu[sub 3]Al[sub 5]O[sub 12]:Ce single-crystal films and their volume analogues—Y[sub 3]Al[sub 5]O[sub 12] and Y[sub 3]Al[sub 5]O[sub 12]:Ce single crystals, excited by synchrotron radiation with energy E = 120–150 eV, have been performed. The films were grown from melt–solution by liquid-phase epitaxy and the crystals were grown from melt. The single-crystal films and single crystals studied are characterized by different degrees of structural order, in particular, different concentrations of substitutional defects of the Y[sup 3+][sub Al] and Lu[sup 3+][sub Al] types. It was ascertained that the bands at 260 and 250 nm in the intrinsic luminescence spectra of Y[sub 3]Al[sub 5]O[sub 12]:Ce and Lu[sub 3]Al[sub 5]O[sub 12]:Ce single-crystal films and single crystals are due to the emission of self-trapped excitons. The luminescence band with λ[sub max] = 300 nm and τ = 0.36μs, which is present in the luminescence spectrum of single crystals and absent in the spectra of single-crystal films, is due to the recombination of electrons with holes localized at Y[sup 3+][sub Al] centers. It is shown that an efficient energy transfer by excitons to activator ions occurs in Y[sub 3]Al[sub 5]O[sub 12] and Lu[sub 3]Al[sub 5]O[sub 2] single-crystal films doped with Ce[sup 3+] ions. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The nature of intrinsic emission bands of yttrium orthoaluminate in the UV spectral region at λ[sub max] = 220 nm (5.63 eV) and 330 nm (4.13 eV) is studied on the basis of the luminescence of single crystals and single-crystal films of YAlO[sub 3] and Ce: YAlO[sub 3] excited by synchrotron radiation sources with an energy of 3–25 eV at 9 and 300 K. The single crystals and single-crystal films were obtained, respectively, from solution and solution–melt by liquid-phase epitaxy and are characterized by considerably different concentrations of substitutional and vacancy defects. It is found that only the luminescence band at 300 nm, which has the decay time τ = 4.1 ns and is excited in a band shifted from the range of interband transitions by 0.25 eV, has exciton-like character. The luminescence band at 220 nm with τ = 0.1μs at 9K, which is observed only for YAlO[sub 3] single crystals and is absent in the luminescence of single-crystal films, is associated with antisite defects of the Y[sub Al][sup 3+] type, which are a specific type of cationic isoelectronic impurities. It is shown that the phosphors based on single-crystal films of YAlO[sub 3] have a simpler scintillation decay kinetics than their bulk analogues due to the absence of channels of excitation energy dissipation associated with the antisite defects of Y[sub Al][sup 3+] type and vacancy defects. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The possibility of obtaining scintillators with a high effective atomic number of the element Zef based on Lu3Al5O12:Ce3+ single crystal films (SCF) on doping with La3+ and Sc3+ ions on Y3Al5O12 substrates has been investigated. It is established that the SCF of (LuLaY)3Al5O12:Ce3+ ( Zef = 58.9 and ρ = 6.67 g/cm2) does not rank below those of Y3Al5O12:Ce3+ ( Zef = 29 and ρ = 4.52 g/cm2) in the conversion efficiency of radiation at the band with λmax = 515 nm. This allows their use as screens of x ray images with a space resolution of 0.75–1.00 μm. It is suggested that in the SCF of Lu3Al5O12 the isoelectronic impurities of lanthanum and scandium form radiative recombination centers of the type LaLu, ScLu, and ScAl as well as the centers Lu as a consequence of the effect of replacement of some Lu3+ ions by the La3+ ions to octanodes of the garnet lattice. The low efficiency of Ce3+ radiation in the SCF of (LuSc)3(AlSc)5O12:Ce is explained by substantial losses due to excitation of the recombination luminescence in the UV region of the centers formed by the isoelectronic impurities of scandium and to the possible existence of the channel of energy excitation dissipation related to the transitions between extrema of the allowed energy bands and activator levels. [ABSTRACT FROM AUTHOR]

We analyze the optical characteristics of crystals within the framework of a model representation that presupposes the entry of the background impurity of iron ions in two valence states, Fe3+ and Fe2+, into regular lattice nodes. The spectral manifestation of intrinsic defects of vacancy-type structure depending on the conditions of crystal growth and heat treatment is comprehensively investigated. With allowance for the specific features of the technology applied, we have tested the technique suggested in scientific periodicals for bleaching ZnWO4 and CdWO4 crystals by doping with nonisovalent ions, in particular, with Sb and Ag impurities. [ABSTRACT FROM AUTHOR]

We consider the factors determining the energy yield of crystallophosphors based on single-crystal films of oxides of the system Al2−Y2O3−R2O3 (R is the rare-earth ions) that are used as different types of luminescent converters. Special features of producing the films by the method of liquid-phase epitaxy from Pb−B2O3 and Bi2O3-based fluxes are analyzed, and the advantages of this method for production of efficient luminophors, which are based on high-melting oxides doped with mercury-like impurities, are shown. It is established that the main factor that bounds the crystallophosphor luminous yield is the presence of donor-acceptor complexes of the Pb2+−Pb4+ and Fe3+−Fe2+-type that form different channels of dissipation of excitation energy. The means of minimizing the contribution of these ions to the processes of excitation-energy relaxation are discussed. [ABSTRACT FROM AUTHOR]

YAG:Ce crystals have been grown by a new gas-phase horizontal directional crystallization (HDC) technique in a protective atmosphere and their cathodoluminescence (CL) spectra and scintillation characteristics have been studied. Using this HDC technology, it is possible to obtain large (110 × 150 × 35 mm) crystals with a high specific light yield (15 000–18 000 Ph/MeV) and good amplitude resolution (8–10%) for the excitation with 5.15-MeV α particles from a 239Pu source. In addition to an intense band at 550 nm due to Ce3+ ions, the CL spectra of crystals display an intrinsic emission band of YAG in the UV spectral range, which is due to the presence of YAl antisite defects. [ABSTRACT FROM AUTHOR]

Liquid phase epitaxy grown Lu3Al5O12:Ce (LuAG:Ce) 20 μm thick films and plate cut from the bulk Czochralski-grown LuAG:Ce crystal were prepared for comparison of photoelectron yield (PhY) and PhY dependence on shaping time (0.5–10 μs). 241Am (α particles) was used for excitation. At the 0.5 μs shaping time, the best film shows comparable PhY with the bulk sample. PhY of bulk material increases noticeably more with shaping time than that of the films. Energy resolution of films is better. Influence of Pb2+ contamination in the films (from the flux) and antisite LuAl defect in bulk material is discussed. [ABSTRACT FROM AUTHOR]

The luminescence spectra of single-crystal films and bulk crystals of yttrium-aluminum garnet Y3Al5O12 and Ce3+-activated Y3Al5O12 were investigated. It was shown that the room-temperature luminescence intensity of the Ce3+-free single-crystal Y3Al5O12 film was considerably lower than that of the bulk crystals, while the luminescence intensity of the Ce3+ ions in the Y3Al5O12:Ce films was considerably higher than that one for the corresponding bulk crystal. [ABSTRACT FROM AUTHOR]

Mechanisms of dissipation of the excitation energy in garnet crystal phosphors Y[sub 3]Al[sub 5]O[sub 12] and Y[sub 3]Ga[sub 5]O[sub 12] doped with rare-earth ions with interconfiguration transitions are studied depending on the Ga concentration. [ABSTRACT FROM AUTHOR]

This work is dedicated to the preparation and characterization of the radio-, thermo-, and photoluminescent properties of Lu2O3:Eu and Lu2O3:Tb nanopowder (NPs) scintillators, prepared by means of hydrothermal processing, and their film analogues made of these NPs by the spin coating method. The luminescent properties of NPs and films were characterized by cathodoluminescence (CL), photoluminescence (PL), X-ray excited radioluminescence (RL), and thermoluminescence (TL) at low and high temperatures. In Lu2O3:Eu NPs and films, mostly the luminescence of Eu3+ ions occupying the C2 site of the host, with the most intensive peaks at 611.6 nm and a decay time of 1.5 ms, was observed. On the contrary, two types of Tb3+ centers in the C2 and C3i sites with the main emission lines at 542.4 and 544.0 nm and the corresponding 4f→5d excitation bands at 270 and 305 nm and decay times of t1/e = 2.17 and 3.96 ms were observed in the case of Lu2O3:Tb NPs and films. Indications were noted that Tb3+ in the C3i symmetry position was most active in the CL spectra of Lu2O3:Tb NPs and a respective film. Thermoluminescent peaks at 110 °C and 170 °C for Lu2O3:Eu NPs and at 75 °C and 120 °C in Lu2O3:Tb NPs were observed corresponding to the hole and electron traps, respectively. Significantly different onsets of temperature quenching of Eu3+ and Tb3+ luminescence in Lu2O3:Eu and Lu2O3:Tb NPs were found at ~90 °C and ~320 °C, respectively. [ABSTRACT FROM AUTHOR]

In our article, we had mentioned a wrong affiliation for the third author O. Sidletskiy. The correct affiliation is now given. [ABSTRACT FROM AUTHOR]

The steady-state and time-resolved emission and excitation spectra and luminescence decay kinetics of nominally undoped Lu2SiO5 single crystalline films (SCFs) grown by the liquid phase epitaxy method from the PbO-based flux are studied in the range 4.2–300 K. Due to the preparation method, the films contain lead ions. Luminescence characteristics of Pb-related centres of different types are identified. A weak 3.65 eV emission is ascribed to the radiative decay of the triplet relaxed excited state (RES) of Pb2+ ions substituting for Lu3+ ions in the Lu1 lattice sites of the X2 structure. Possible origins of the intense complex lead-related ≈2.8 eV emission are discussed. We propose phenomenological models describing the excited-state dynamics of the studied luminescence centres. We also determine the characteristic parameters of the corresponding RESs, in particular, the energy separations between the excited states and the rates of the radiative and non-radiative transitions from these states. [ABSTRACT FROM AUTHOR]

Luminescence characteristics of single crystals (SC) and single crystalline films (SCF) of YAlO3 and YAlO3 : Ce are studied at 4.2-300 K under photoexcitation in the 4-20 eV energy range. The origin and structure of the intrinsic and impurity defects responsible for various exciton-related emission and excitation bands are identified. The [?]5.6 eV emission of YAlO3 SCF is ascribed to the self-trapped excitons. In YAlO3 SC, the dominating 5.63 eV and 4.12 eV emissions are ascribed to the excitons localized at the isolated antisite defect {\rm Y}_{{\rm Al}}^{3+} and at the {\rm Y}_{{\rm Al}}^{3+} defect associated with the nearest-neighbouring oxygen vacancy, respectively. The thermally stimulated release of the electrons, trapped at these defects, takes place around 200 K and 280 K, respectively. The presence of {\rm Y}_{{\rm Al}}^{3+} -related defects and isolated oxygen vacancies (AlO5 units) in YAlO3 SC is confirmed by NMR measurements. The formation energies of various {\rm Y}_{{\rm Al}}^{3+} -related defects are calculated within the density functional theory. The influence of various intrinsic and impurity defects on the luminescence characteristics of Ce3+ centres is clarified. [ABSTRACT FROM AUTHOR]