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Dense ceramics of Ln:Lu2O3 (Ln = Pr, Eu, Tb, Dy) were obtained using spark plasma sintering (SPS) from co-precipitated nanocrystalline powders. X-ray diffraction, scanning and transmission electron microscopies were used for the characterization of Ln:Lu2O3 powders obtained by various annealing regimes. Transparency of the sintered ceramics was achieved when powders with highly developed crystallinity were used for sintering. Sintered ceramics exhibited luminescence with a characteristic emission based on the element doped into the Lu2O3 host. The light yield of the sintered ceramics improved when the sintered ceramics was further annealed. The annealing of the sintered ceramics also improved the transmittance in the visible region; however, the transparency was lost when the annealing temperature was too high. To our best knowledge, the SPS fabrication of dense ceramics of Pr3+, Tb3+ and Dy3+-doped Lu2O3 is reported here for the first time.

This work is devoted to the development of two novel types of advanced composite scintillators based on single crystalline films (SCFs) of Lu3Al5O12 garnet (LuAG), doped with Ce3+ and Pr3+ ions, and substrates from single crystals (SCs) of Sc3+ doped LuAG using the liquid phase epitaxy (LPE) method. We show the possibility for simultaneous registration of α-particles and γ-quanta using separation of the decay kinetics of the SCF and crystal parts of such composite scintillators. Namely, large differences in the respective scintillation decay kinetics and decay time values tα and tγ are observed for LuAG:Ce SCF/LuAG:Sc SC and LuAG:Pr SCF/LuAG:Sc SC composite scintillators under excitation by α-particles from an 241Am (5.5 MeV) source and γ-quanta from a 137Cs (662 keV) source. Thus, both developed types of composite scintillators can be applied for simultaneous registration of α-particles and γ-quanta in mixed radiation fluxes. The rate of discrimination of the scintillation signals, coming from the SCF and SC parts of the LuAG:Ce SCF/LuAG:Sc SC composite scintillator, expressed by the tγ/tα ratio, is equal to 1.34–1.96 in the 0–1100 ns time interval. For the LuAG:Pr SCF/LuAG:Sc SC composite scintillators, more significant differences in the scintillation decay kinetics are achieved. In this case, the tγ/tα ratio for these composite scintillators reaches the values 9.6–15.6 in the wide 0–2500 ns time interval. This is the best result among all the types of composite scintillators we developed based on epitaxial structures of garnet compounds.

Pr:Lu3Al5O12 transparent ceramics with different doping concentrations (0% − 1 at%) were fabricated using the solid-state reaction and vacuum sintering method. The influence of doping concentration on the luminescent properties was investigated in detail. The 5d-4f emission slightly redshifts with the increase of doping concentration under UV light and X-ray excitation. The slow emission below 290 nm related to antisite defects can be suppressed by the increase of doping concentration at room temperature. The suppression of exciton related emission around 250 nm at 77 K is remarkable. The 0.3 at% Pr doped ceramics show the highest light yield that is 6900 ph/MeV with 1 μs shaping time under the excitation of γ-rays (137Cs). There exists slow components of scintillation process in all the Pr-doped transparent ceramics. Higher doping concentration was found to be beneficial for the suppression of the slow components in the scintillation response and therefore acceleration of the scintillation decay and light yield increase up to certain level. These effects are mainly due to competition of Pr3+ ions with the antisite defects for charge carrier capture in the scintillation process which is also supported by the trends observed in the TSL measurements.

The single crystalline Lu3Al5O12: Ce3+0.6%,Ca2+0.6% garnet films co-doped with Si4+ ions were prepared by liquid phase epitaxy technique and their optical, luminescence, and scintillation properties were studied. The Ca co-doping into the Lu3Al5O12:Ce films resulted in a drastic acceleration of decay kinetics and decreased light yield due to the oxidization of Ce3+ into Ce4+ ions. The Si4+ co-doping regenerated the Ce3+ ions by virtue of charge compensation between Ca2+ and Si4+ ions. The Ce valence changes were evidenced from the optical, photoluminescence and scintillation studies. Significant differences between the photoluminescence and scintillation properties were observed in Si + Ca co-doped samples. The influence of Si co-doping and the effect of Ce3+-to-Ce4+ ratio on the scintillation properties of Lu3Al5O12:Ce epitaxial garnet films is discussed.

The cerium doped Gd2YGa3Al2O12 (Ce:GYGAG) scintillation ceramics were fabricated by the solid state reaction method. The microstructure, luminescence and scintillation properties have been studied. In photoluminescence decays, the decay times of Ce:GYGAG ceramic samples are close to monoexponential. Some slower component can be found, which can be related to the local inhomogeneities of ceramic sample and self-absorption of Ce3+. Meanwhile, the Ce:GYGAG ceramics perform excellent on scintillation efficiency which is evaluated by the XEL steady-state luminescence and its fast part characterized by light yield (LY). The LY value reaches ∼45000 ph/MeV with an energy resolution of 8.67% under the γ-ray excitation. The LY0.5μs/LY6μs value of Ce:GYGAG is calculated to be 87.5% which is much superior than 42.5% in compared Ce:LuAG ceramics. In the scintillation decays, a lower content of slow components are detected in Ce:GYGAG ceramic sample comparing to the Ce:LuAG ceramics.

For the first time, an effective photostimulated creation of defects is observed under selective irradiation of the undoped Gd3Ga3Al2O12 single crystal and the Ce - doped Gd3(Ga,Al)5O12 single crystal and epitaxial film in the Gd3+ - related 8S7/2 → 6IJ and 8S7/2 → 6PJ absorption bands. Defects creation processes are investigated by the thermally stimulated luminescence (TSL) method in the 4.2–500 K temperature range. The dependences of the TSL glow curve peak intensity on the irradiation photon energy, irradiation temperature, and irradiation duration are measured and analyzed. The activation energy of the TSL glow curve peaks creation is found to be about 0.02 eV. Possible mechanisms of defects creation under irradiation in the absorption bands of Gd3+ in Gd3Ga3Al2O12 and Gd3(Ga,Al)5O12:Ce are discussed.

LaAlO3 perovskite single crystals doped with Ce, Eu or Tb have been grown by micro-pulling-down method. X-ray diffraction analysis confirmed low-temperature rhombohedric phase. Energy-dispersive Laue mapping revealed sub-grains in the grown crystals. For the Ce-doped crystals, very low radioluminescence efficiency was found and the observed emission was ascribed to defects. Photoluminescence spectra were significantly different from the radioluminescence ones. They were significantly quenched at room temperature and the related luminescence showed also unusually high Stokes shift. High radioluminescence efficiency was found for the Tb-doped samples and especially for the Eu-doped ones, which would point to the fact that in LaAlO3 the scintillation process is more favorable for the luminescence ions which tend to capture an electron first.

Ce:(Gd,La)2Si2O7 (Ce:La-GPS) and Al co-doped Ce:(Gd,La)2Si2O7 (Al,Ce:La-GPS) single crystals were grown by the micro-pulling-down method to improve the mechanical, optical and scintillation properties. In a tensile test, the maximum strain and stress values in the stress-strain curve of the Al,Ce:La-GPS single crystal compared to the Ce:La-GPS single crystal and the result suggests that there is a possibility of the improvement on the mechanical property by Al co-doping. In addition, the light yield of the La-GPS single crystal under γ-ray irradiation was slightly increased and the decay time was accelerated by the Al co-doping.

In the doubly doped YAG:Ce,Er single crystal we show the effect of the nonradiative energy transfer from the donor (Ce3+) to the acceptor (Er3+) in terms of the Forster-Dexter model. Such an energy transfer process is enabled by the overlap of the donor and acceptor emission and absorption spectra, respectively, and makes the donor to de-excite faster. This phenomenon can be used to tailor the luminescence decay of a phosphor in order to increase the rate at which it converts incoming radiation, if the decrease of its quantum efficiency can be tolerated. Quantitative comparison of experimental data obtained at the sample set with large concentration interval of Er3+ acceptor (up to the concentration Y2.835Al5O12: Ce0.006Er0.159) with the mentioned theoretical model allows the determination of the microscopic parameters of the energy transfer process, such as the critical concentration of the Er3+ ions. The Er concentration higher than 1% has proven to shorten the 1/e decay time from 62 ns below 30 ns. The concentration dependence of the absorption lines of the Er3+ is also discussed.

We have grown Ce-doped (La,Y)$_2$Si$_2$O$_7$ single crystal by micro-pulling-down method and investigated its optical and scintillation properties. We have successfully prepared the single crystal with (Ce$_{0.015}$La$_{0.600}$Y$_{0.385}$)$_2$Si$_2$O$_7$ composition. The observed thermal quenching process could be characterized by the quenching temperature (T50%) of 526 K and its activation energy was determined to be 0.62 eV. Further considering the thermal quenching factors, it was found that the thermal quenching was caused by at least the thermal ionization and maybe also by classical thermal quenching. The light output and scintillation decay time were evaluated to be ~12,000 photons/MeV and ~42 ns, respectively. These results indicate that (Ce$_{0.015}$La$_{0.600}$Y$_{0.385}$)$_2$Si$_2$O$_7$ has a great potential for application in scintillation materials.

Electron and hole trapping is studied in the ${\mathrm{Ce}}^{3+}$- and ${\mathrm{Pr}}^{3+}$-doped ${\mathrm{Lu}}_{2}{\mathrm{Si}}_{2}{\mathrm{O}}_{7}$ scintillation single crystals (LPS:$\mathrm{Ce}$ and LPS:$\mathrm{Pr}$) by electron paramagnetic resonance (EPR). Detailed EPR measurements of the x-ray irradiated LPS crystals reveal that holes generated by irradiation are predominantly trapped at oxygen lattice ions creating ${\mathrm{O}}^{\ensuremath{-}}$ centers. The same x-ray irradiation creates also electron-type centers, which are attributed to ${\mathrm{Lu}}^{2+}$ ions, where the trapped electron at the Lu lattice ion is stabilized by a nearby defect, such as the oxygen vacancy and ${\mathrm{Ir}}^{3+}$ impurity ion. Both the hole and electron centers can be thus considered as a bound small polaron, which makes the charge trapping in a scintillation mechanism quite competitive. The hole ${\mathrm{O}}^{\ensuremath{-}}$ and electron ${\mathrm{Lu}}^{2+}$ centers show thermal stability well above room temperature. Thermal decays of their concentrations correlate well with the appearance of the thermally stimulated luminescence glow peaks at 470--550 K. The presence of the same intrinsic traps in the $\mathrm{Ce}\text{\ensuremath{-}}$ and $\mathrm{Pr}$-doped LPS crystals suggests that the difference in the light yield of these crystals is an intrinsic property of the ${\mathrm{Ce}}^{3+}$ and ${\mathrm{Pr}}^{3+}$ activator centers in the LPS lattice. An origin of charge traps in this pyrosilicate structure and their role in the scintillation mechanism is compared with the results previously described in the literature on orthosilicates.

Single crystals of LiCaAlF6, undoped, Eu-doped and Na co-doped, were studied by electron paramagnetic resonance, radioluminescence and thermally stimulated luminescence techniques applied in a correlated manner. The undoped samples exposed to X-ray irradiation featured two hole-like charge trapping centers which were attributed to the perturbed F 2 − pseudomolecular ion and O− (as a result of the contact with air). Their trap depths (Et) and frequency factors (f0) were determined as follows: E t Perturbed F 2 − = 1.1 ± 0.1 eV , E t ( O − ) = 1.7 ± 0.1 eV , f 0 Perturbed F 2 − = f 0 O − ~ 10 13 s − 1 , respectively. Annealing in air caused the appearance of another defect, a new electron-like center as well. It was found that the europium dominating charge state is 2 + in the LiCaAlF6:Eu,Na samples, however, some amount of the Eu3+ is also present. Moreover, there were two Eu2+ centers: the dominating Eu 1 2 + = Eu Ca 2 + and the low-content Eu 2 2 + = Eu Li 2 + . The amount of the latter is easily governed by the sodium admixture while the former is insensitive to the Na co-doping. The Eu and Na co-doping affected the defects distribution and incorporation in the LiCaAlF6 host. Thermally stimulated luminescence yielded up to 8 peaks within the 100–600 K temperature range in glow curves of the undoped and doped crystals signalizing the presence of deep trapping states in the bandgaps. Along with the obvious degradation of the crystal surface in air by creation of new trapping centers this can contribute to the decreased light yield and downgrade of timing characteristics.

Photo- and thermally stimulated luminescence characteristics, as well as photostimulated defects creation processes are investigated in the 85–510 K temperature range for the Li+ co-doped single crystal of Gd3(Ga,Al)5O12:Ce (GAGG:Ce). The results for GAGG:Ce,Li are compared with the corresponding characteristics of the GAGG:Ce and GAGG:Ce, Mg single crystals of similar host composition. The influence of Li+ and Mg2+ ions on the Ce3+ - related emission band position, temperature dependence of the photoluminescence intensity, efficiency of the Gd3+ → Ce3+ energy transfer, intensity and decay kinetics of the afterglow, and thermally stimulated luminescence characteristics is revealed. The presence of the Ce3+ → Ce4+ conversion in GAGG:Ce,Li is confirmed. The conclusion is made that, unlike GAGG:Ce,Mg, the compensation of the Li+ excess negative charge in GAGG:Ce,Li occurs due to both the Ce3+ → Ce4+ conversion and the effective formation of intrinsic crystal lattice defects. The origin of these defects as well as the origin of the electron and hole trapping centers in the GAGG:Ce,Li crystal are discussed.

Cerium doped lutetium aluminum garnet single crystal has been drawing great research interest of scientists due to its superior performance in scintillation material for high energy particle detection. However, the problem about slow components in the scintillation response restricts the further improving. Here, we utilize the “band-gap engineering” strategy that the admixture of Ga3+ in Lu3Al5O12 can lower the conduction band edge and bury shallow traps, and get the Ce3+ doped Lu3Ga3Al2O12 scintillation ceramics sintered in the oxygen atmosphere and hot isostatic pressing post-treated. The luminescence and scintillation properties are investigated. A shortened dominant decay time and the presence of some second slower components in the photoluminescence decays prove that the admixture of Ga3+ in Lu3Al5O12 can lower the conduction band edge and consequently also the ionization barrier for Ce3+ emission from 5d1 level. Meanwhile, the Ce:Lu3Ga3Al2O12 ceramic sample shows good steady-state scintillation efficiency under the X-ray excitation. Furthermore, it performs excellent in terms of the fast-to-slow emission ratio in scintillation response with a LY0.5μs/LY6μs values ratio up to 92%.

This work is devoted to the development of new types of advanced composite scintillators based on the single crystalline films (SCFs) of Lu3Al5O12 (LuAG) garnet, doped with Pr3+ and Sc3+ ions, and substrate from single crystals (SCs) of Ce3+ doped LuAG using the technology of liquid phase epitaxy (LPE). We show the possibility of the simultaneous registration of α-particles and γ-quanta by means of separation of the decay kinetics of SCF and crystal parts of such composite scintillators. Namely, the significant differences in the pulse height spectra and the scintillation decay kinetics of LuAG:Pr SCF/LuAG:Ce SC and LuAG:Sc SCF/LuAG:Ce SC composite scintillators under excitation by α–particles of 241Am (5.5 MeV) source and γ-quanta of 137Cs (662 keV) source are observed. For these reasons, such types of composite scintillators can be applied for separation of the signals coming from their film and crystal parts at the registration of the mixed radiation fluxes of α-particles and γ-quanta.

LiAlO2 can be considered as a good candidate for neutron scintillator host matrix due to the high Li content and high energy deposit of reaction of 6Li isotope with neutron. Low density (2.75 g/cm3) is of advantage to achieve low sensitivity of background gamma radiation in mixed radiation fields. Ti-doped LiAlO2 shows relatively high neutron light yield comparable to that of the Li-glass standard neutron scintillator. At room temperature the Ti4+ charge transfer (CT) luminescence at 375 nm with the 2.5 µs decay time is the leading emission process. Besides the CT luminescence host emission at shorter wavelengths (350 nm), defect-related emission at 440 nm and impurity Fe3+ luminescence at 740 nm are observed. Their emission spectra, excitation spectra and decay kinetics including temperature dependences were studied. Luminescence mechanism in the material and interplay between the luminescence processes are discussed together with possible role of nonstoichiometry and Mg codoping.

Nondoped Cs2HfCl6 (CHC) and alkaline earth metal-doped CHC (AE:CHC) crystals were grown by the vertical Bridgman–Stockbarger method. The spectra of the AE:CHC under X-ray excitation were similar to those for the AE-free crystal; thus, AE doping did not change emission wavelength of CHC. We determined the light outputs and energy resolutions of nondoped CHC and AE:CHC by measuring pulse-height spectra under 662-keV gamma-ray excitation of a 137Cs source. Both light output and energy resolution were deteriorated with AE doping. For example, nondoped CHC had a light output of ~44 000 photons/MeV and energy resolution of ~5.2%; on the other hand, Sr 0.5 at.%-doped CHC had a light output of only ~28 000 photons/MeV and energy resolution of ~10%. Scintillation decay also did not change. The nonproportional response values of light output versus gamma-ray energy did not improve in AE:CHC either. Therefore, doped AEs can be responsible for creation of defect trap levels which would hamper the carrier transport in CHC structure.

Ce0.5%: Ce:Gd3Ga3Al2O12(GGAG) single crystals co-doped with 500at.ppm Li+, Na+ and K+ were grown by using the micro-pulling down method. The smooth Ce4+ charge transfer absorption below 350 nm and decay time acceleration were observed in Li co-doped sample. Na+ and K+ co-doping did not show a large effect on the acceleration of decay time compared with Li co-doping. Ce0.5%:GGAG single crystals co-doped with 500 at.ppm Li+ were also grown by the Czochralski method. Optical, scintillation properties and timing performance were evaluated to investigate the effect of univalent alkali metal ions co-doping on Ce:GGAG scintillators. The scintillation decay curves were accelerated by Li co-doping: the decay time was significantly accelerated to 54.8 ns (47%) for the faster component and 158 ns (53%) for the slower component. The light output was 94% of the non co-doped Ce:GGAG standard. The coincidence time resolution was improved to 258 ps by Li co-doping.

In order to obtain new scintillators with high light output and high effective atomic number (Zeff), we performed anion-substitution for Cs2HfCl6 (CHC) scintillator, and then, we succeeded in growing Cs2HfI6 (CHI) single crystalline scintillator. It had Zeff of 58, which is the same as that of CHC, and had high light output of ∼70,000 photons/MeV with 700 nm emission. However, its scintillation decay time of ∼2.5 µs was slow for practical use as gamma-ray monitor. In this study, we performed Ce3+/Eu2+ doping to Hf4+ site to improve decay time of CHI, introducing the fast 5d-4f luminescence. Ce:CHI and Eu:CHI single crystals were finally obtained by the vertical Bridgman-Stockbarger method. The luminescence spectra of the Ce:CHI and Eu:CHI were very similar to that of the non-doped CHI, which would mean that no 5d-4f luminescence of Ce3+/Eu2+ was observed. The measured light output and decay time of Ce:CHI were ∼48,000 photon/MeV and 2.3 ± 0.1 µs, respectively. As for Eu:CHI, light output and decay time were ∼69,000 photon/MeV and 2.8 ± 0.1 µs, respectively.

Eu-doped Li(Ca,Sr)AlF 6 [Eu:LiCSAF] single crystals with various Ca/Sr ratios were grown by the micro-pulling-down method, and their optical and scintillation properties were investigated to reveal the effects of Ca/Sr ratio on optical and scintillation properties of the Eu:LiCSAF single crystals. The Li(Ca 1− x − y Sr x Eu y )AlF 6 single crystals could be grown in 0 ≤ x ≤ 0.1, 0.5 ≤ x ≤ 1.0 and y = 0.02 while the Eu:LiCSAF crystals with x = 0.2, 0.25 and 0.4 included two colquiriite-type phases with different lattice parameters. The Li(Ca 1− x−y Sr x Eu y )AlF 6 single crystal with x = 0.25 and y = 0.02 showed the highest light yield under neutron irradiation.

Non-linear absorption spectroscopy in pump and probe configuration has been used to test the population of non-equilibrium carriers in Ce-doped Y$_{3}$Al$_{5}$O_${12}$ (YAG), Lu3Al5O12 (LuAG), and Gd3AlxGa(5-x)O12 (GAGG) crystals with and without codoping by Mg2+ ions. A faster rise time of the induced optical density has been observed in all crystals codoped with Mg with respect to that in Mg-free samples. A significant difference in the time evolution of the differential optical density in GAGG with respect to YAG and LuAG crystals has also been measured. In both GAGG:Ce and GAGG:Ce,Mg an absorption band with maximum in the blue-green range and a decay time of 1.4 ps is present. This band is due to the absorption by free electrons before they are trapped or re-captured by Ce3+ ions. A broad absorption band in the yellow-red region with very short rise time and a decay time longer than 150 ps has been observed in all the Ce-doped garnets under study and can be attributed to the absorption from the Ce3+ excited states.

The possibility of growth by the liquid phase epitaxy method of a new type of advanced composite scintillator based on Ce3+-doped single crystalline films (SCFs) of Lu1.5Gd1.5Al1.5Ga3.5O12 garnet and substrates from single crystals (SCs) of Gd3Al2.5Ga2.5O12:Ce garnet is evidenced for the first time in this work. We show the possibility of the simultaneous registration of α-particles and γ-quanta by way of separation of the scintillation pulse height spectra and decay kinetics of SCF and crystal parts of such a composite scintillator. Namely, the significant differences in the scintillation decay kinetics of Lu1.5Gd1.5Al1.5Ga3.5O12:Ce SCF/Gd3Al2.5Ga2.5O12:Ce SC composite scintillator under excitation by α-particles of a 241Am (5.5 MeV) source and γ-quanta of 137Cs (662 keV) source are observed. The respective tα/tγ decay times ratio in the 0–500 ns range reach up to 0.5 for this type of composite scintillator; e.g., the SCF scintillators is two times faster than the substrate scintillator. For this reason,...

Light yield (LY) and its ratio under excitation with α- and γ- rays (α/ γ ratio) were measured for Y 3 Al 5 O 12 :Pr (YAG:Pr) single crystals with Pr concentration of 0.16, 0.33 and 0.65 wt%. YAG:Pr (0.33 wt%) showed a highest LY value of 14,900 ph/MeV at 662 keV γ- rays, while a highest LY value of 3,700 ph/MeV at 5.499 MeV α- particles was measured for YAG:Pr (0.65 wt%) one, showing a highest α/ γ ratio of 0.26. A clear separation was observed for 5.155, 5.486 and 5.806 MeV α- particles from a mixed tri-nuclides alpha source. Light yield dependence on sample height was measured under excitation with α - rays and the light loss coefficient was estimated and compared to the value measured for the LuAG:Pr sample with comparable size and Pr concentration.

Homeland security is an emerging application field for inorganic scintillators. Detection and identification of radioactive materials in both individual and cargo transport requires scintillators with excellent energy resolution and high light output. On the other hand, the time characteristics of the scintillation are less crucial. Furthermore, price is a key parameter due to the large volume of the detectors. State-of-the-art halide scintillators e. g. SrI2:Eu or LaBr3:Ce can satisfy the requirements for light yield and energy resolution, but the production costs are very high due to complicated crystal growth and the high prices of rare earth metals. Cesium hafnium chloride (Cs2HfCl6) is a promising intrinsic scintillator with high light yield and excellent resolution. Moreover, its low hygroscopicity and cubic crystal structure could allow lower production costs compared to SrI2 or LaBr3. Intrinsic luminescence of Cs2HfCl6 is commonly attributed to self-trapped excitons. However, the luminescence of Cs2HfCl6 shows complex structure and temperature dependence. This might be explained by the presence of zirconium which is a common impurity in hafnium compounds. We present a study of the influence of zirconium doping on the scintillation properties of Cs2HfCl6. Single crystals of Cs2HfCl6 with zirconium doping from 0 to 1 mol% were grown by the vertical Bridgman method. Their phase purity, radioluminescence, scintillation decay, light yield, and afterglow were evaluated. Results show that zirconium doping can affect the scintillation properties of Cs2HfCl6 even at concentrations comparable to impurity levels of zirconium in hafnium compounds.

The luminescence and scintillation characteristics of Ce3+ - doped Gd3Sc2(Al3-xGax)O12 (x = 1, 2, 3) garnet crystals were investigated. The Ce3+ luminescence was blue-shifted with increasing Ga content due to the decrease of the crystal field strength. A decrease of Ce3+ luminescence intensity and luminescence decay time at high temperature was observed for all samples due to thermal ionization of the Ce3+ 5d1 excited levels. With increasing Ga content the decrease of thermal activation energies, determined from temperature dependence of decay times, was obtained. Both Gd3Sc2Al2GaO12:Ce and Gd3Sc2AlGa2O12:Ce samples exhibited a comparable light yield (LY) value of 24,000 photons/MeV while the latter sample showed faster scintillation decay time of 12 ns (11%) + 56 ns (89%) with respect to those of 55 ns (28%) + 105 ns (72%) for the former sample. An acceleration of scintillation decay time with an expense of LY value was also obtained for the Mg2+-codoped sample. At low temperature a decrease of scintillation yield was observed in correlation with the intense thermoluminescence peaks, attributing to the localization of electrons at intrinsic shallow traps.

Six Mg2+ co-doped Lu3Al5O12:Ce scintillating garnet films prepared by liquid phase epitaxy, with Mg concentration from 0 to 3000 ppm, were irradiated by X-rays and underwent a series of thermoluminescence measurements from 10 to 720 K. The thermoluminescence signal of epitaxial films originated purely from electron recombination at Ce ions. It was found that the area of all the peaks present in thermoluminescence glow curves decreased rapidly with the increase of Mg concentration; for 3000 ppm, the decrease was by 4–5 orders of magnitude. Moreover, the bright burn effect was significantly suppressed by Mg co-doping. Possible explanations, i.e., trap concentration reduction or increased competition in free electron capture between thermoluminescence traps and Ce4+ centers, were discussed.

Mixed LuxY1-xVO4 crystals, undoped and doped with Eu3+, were synthetized by the solid state reaction method. The crystal structure and phase composition were controlled by the X-ray diffraction (XRD), Raman analysis, and scanning electron microscope (SEM) measurements. The samples' crystallinity was improved by annealing. Nevertheless, the lattice distortion caused by the substitution of Y by Lu was detected. The lattice parameters derived from the XRD data are in good agreement with the calculated ones. It was found that the luminescence intensity increase in the annealed samples is related to the improvement of crystallinity of samples. According to the studies of X-ray excited luminescence at 300 K the relative luminescence intensity increases for the samples with intermediate values of x. For the LuxY1-xVO4:Eu3+ the highest luminescence intensity was detected for x=0.7 and ascribed to the effect of decrease of the mean distance between the thermalized electrons and holes. For the undoped crystals the luminescence is partially quenched at 300 K, however the sample with x=0.7 demonstrate highest intensity as well. The effect in the undoped samples is due to the increase of the temperature of luminescence quenching in samples with intermediate values of x.

In this work the structural and spectroscopic properties of several materials belonging to the K 3 Lu 1− x Y x (PO 4 ) 2 family and activated with 1% of Pr 3+ have been studied in detail. The structural characterization has been performed by X-ray diffraction. The crystal structure of the host has been determined by means of Rietveld refinement of the powder diffraction pattern, in the case of K 3 Y(PO 4 ) 2 doped with 1%of Pr 3+ .The optical emission upon UV direct excitation into the dopant ion is dominated by the Pr 3+ 4f 1 5d 1 →4f 2 interconfigurational transitions; the substitution of Lu by Y causes the blue shift of the 4f 1 5d 1 →4f 2 emission band. This is due to an important change of the Pr 3+ local environment. Upon X-ray excitation it has been found that the ratio between the 4f 1 5d 1 →4f 2 and 4f 2 →4f 2 emission intensities varies progressively when Y 3+ concentration is increased. This behavior is explained in terms of the favorable overlap between the defect-related luminescence of the host and the Pr 3+ 4f 2 →4f 2 intraconfigurational transitions. No thermal quenching of the Pr 3+ luminescence has been observed up to 500 K.

The luminescence properties of the Dy3+, Sm3+, Eu3+ and Tb3+ activated Gd3Ga3Al2O12 (GGAG) single crystals were investigated as a function of temperature. The photoluminescence excitation, emission and decay kinetic analysis revealed an efficient energy transfer from Gd3+ ions towards all the Dy3+, Sm3+, Eu3+ and Tb3+ activators. The intensity ratio between electric dipole and magnetic dipole emission transitions in activator׳s ions suggested a high homogeneity of the host lattice grown by Czochralski technique. Only the Gd3Ga3Al2O12 single crystal activated with Dy3+ ions exhibited a stable luminescence up to 800 K. The Sm3+, Eu3+ and Tb3+ doped Gd3Ga3Al2O12 single crystals showed the onset of the thermal quenching of luminescence at lower temperatures. We proposed three different models, very well-known from the literature, to explain the mechanisms responsible for thermal quenching of activator׳s luminescence in Gd3Ga3Al2O12 single crystal.

The luminescence and scintillation properties of gadolinium terbium aluminium garnet single crystalline films, Gd3−xTbxAl5O12, doped with Ce3+ are investigated as a function of the Gd/Tb ratio with the aim of an improved understanding of the energy transfer processes between Ce3+ and Tb3+ ions in the aluminium garnet hosts. Upon replacing the Gd3+ by Tb3+, the crystal field splitting for the 5d energy level of Ce3+ does not change significantly, due to comparable sizes of the Gd3+ and Tb3+ cations. Temperature dependence of the decay time of Tb3+ and Ce3+ luminescence confirms an efficient energy transfer from the Tb3+ to Ce3+ and provides a qualitative understanding of this process. Furthermore, bidirectional energy transfer processes between the Ce3+ and Tb3+ are revealed. Scintillation decays under α-particles excitation show the presence of the fast and slow sub-microsecond components.

Na co-doped Eu: LiCaAlF 6 (Eu, Na: LiCAF) single crystals were grown by the micro-pulling-down (μ-PD) method, and their optical and scintillation properties were examined to reveal the effects of the Na co-doping. The crystals were single-phase materials demonstrating structure isomorphic with that of undoped LiCAF. To perform the crystals characterization, the specimens with dimensions of several millimeters were cut from highly transparent and crack free fragments of the crystals and polished. It was observed that Na co-doping resulted modification of the transmittance and the excitation spectra, and increased the light yield detected under neutron irradiation.

The In-doped LiCaAlF6 [In:LiCAF] single crystals were grown by the micro-pulling-down (μ-PD) method, and the phases, chemical compositions, transmittance and radioluminescence spectra were investigated. All the grown crystals showed high transparency and single phase of LiCAF without visible cracks and inclusions except for the end part of In2%:LiCAF crystal which included the impurity phase. In the radioluminescence spectra of the In:LiCAF crystals under X-ray irradiation, the emission peak around 750 nm was revealed.

Monovalent Li+ codoped Lu3Al5O12:Ce (LuAG:Ce) optical ceramics were fabricated by solid state reaction method and further optimized by an air-annealing process. Optical absorption, radioluminescence spectra and scintillation properties such as light yield, scintillation decay times and afterglow were measured and compared with those of the Li+ free LuAG:Ce ceramic and the commercial LuAG:Ce single crystal samples. Positive effect of Li+ codopant consists mainly in the significant increase of scintillation light yield, acceleration of scintillation decay as well as the decrease of afterglow intensity. With 0.3% Li codoping, the obtained LuAG:Ce,Li ceramic displays a light yield of ∼29200 ph/MeV at 10 μs shaping time, higher than that of the LuAG:Ce single crystal and optical ceramic scintillators ever reported. The partial conversion of the stable Ce3+ to Ce4+ centers and the shallow and deep traps effect suppression by the Li+ codoping are discussed.

The influence of the Mg 2+ codoping and annealing in the air on the scintillation and luminescence characteristics of Pr-doped lutetium-aluminum garnet crystals (LuAG) was studied to find a possible positive effect of Pr 4+ . The overall scintillation efficiency under X-ray excitation of the annealed Pr- doped samples decreased with increasing Mg concentration. This was explained by increased overlap of the Pr 3+ 5d-4f emission with the charge-transfer (CT) absorption band of the Pr 4+ ion stabilized by Mg 2+ . This absorption caused even greater decrease of the light yield, as the light is collected from the whole sample volume in the pulse-height spectrum measurement. Electron centers based on oxygen vacancies (F + centers) which can have negative influence on scintillation mechanism were revealed by the electron paramagnetic resonance (EPR) experiments. The O - hole center was detected as well and the temperature dependences of the EPR spectra showed that its thermal stability was decreased by Mg codoping. Negligible changes in the decay time of Pr 3+ 5d-4f photoluminescence exclude the non-radiative energy transfer from relaxed 5d 1 excited state of Pr 3+ towards CT absorption transition of Pr 4+ and suggest that simple reabsorption of the emitted light takes place. Unlike for the Ce-doped analogs, promoting the Pr 3+ luminescence center to the tetravalent state by divalent ion co-doping and air annealing did not improve scintillation properties of Pr-doped LuAG.

For the first time, laser based on Yb,Ho:GGAG crystal emitting radiation at 2.09 µm and 2.94 µm is presented. The tunability of Yb,Ho:GGAG laser was obtained in spectral bands 2063 - 2113 nm and 2860 - 2944 nm.

EPR spectroscopy in X- and Q-bands was employed to trace charge carrier trapping upon exposure to X-rays of LuPO4:Eu, LuPO4:Eu,Hf and YPO4:Eu,Hf flux-grown single crystals, as well as LuPO4:Eu sintered ceramics. These data were complemented with thermoluminescence (TL) studies on the same compositions. EPR spectra proved that all the single crystals contained Pb impurity incorporated from the flux. Upon exposure to X-rays the concentration of Pb3+ changed proving that Pb participated in carrier trapping. The ionizing radiation caused also partial conversion of Eu3+ into Eu2+ and in the (Eu,Hf) doubly doped crystals also Hf4+ was transformed into Hf3+ upon exposure to X-rays. In the LuPO4:Eu sintered ceramics X-rays transformed Eu3+ into Eu2+ and the strong EPR signal of a hole trapped at O2− in the vicinity of a defect (presumably Lu3+-vacancy) was recorded. Some contribution from the PO42− molecular ion could also be observed. However, in crystals the EPR signal from the latter was much more intense compared to the former. In ceramics, the trapped hole was found to hop between the O2− ions and only below ∼70 K it localized at just one of them. Complementary measurements of TL of the samples showed meaningful differences between the glow curves of the crystals and of the ceramics. The TL glow curve of the latter contained only one band peaking around 120 °C which is related to destruction of the trapped hole being mainly the O− center. All single crystals showed multi-peak TL glow curves covering the range of 30–500 °C. They were found to result mainly from a hole released from the PO42− molecular complex and to some extent also from the O− center. The results relative to EPR and TL spectroscopy proved that in orthophosphates Eu3+ is an effective electron trapping center while holes may be trapped at impurity ions, like Pb2+, or localized at oxygen ions possibly stabilized by nearby defects, e.g. Lu-vacancies.

The work was supported by the ERDF funding in Estonia granted to the Center of Excellence TK141 “Advanced materials and high-technology devices for sustainable energetics, sensorics and nanoelec-tronics“ (project No. 2014-2020.4.01.15-0011). Partial support of the projects from the Ministry of Education, Youth and Sports of the Czech Republic no. LO1409, LM2015088 and CZ.02.1.01/0.0/0.0/16 013/ 0001406 is also gratefully acknowledged., Temperature dependences of the photoluminescence and X-ray excited luminescence intensity and thermally stimulated luminescence glow curves are measured in the 4.2–300 K temperature range for the undoped and Ce3+ - doped Gd3(Ga,Al)5O12 crystals. The conclusion is made that no low-temperature quenching of the Ce3+ - related photoluminescence takes place. In both the undoped and the Ce3+ - doped crystals, temperature dependences of the X-ray excited recombination luminescence intensity correlate with the position and shape of thermally stimulated luminescence glow curve peaks of the hole origin. Low-temperature quenching of the X-ray excited luminescence in these crystals is explained by the fact that at low temperatures, free holes are trapped at oxygen ions while electrons are trapped at various intrinsic defects. In Ce3+ - doped Gd3(Ga,Al)5O12 crystals, thermally stimulated release of the trapped holes and electrons and their subsequent recombination at Ce3+ ions result in the enhancement of the Ce3+ - related electron recombination luminescence with the increasing temperature in the 10–180 K range., ERDF TK141 No. 2014-2020.4.01.15-0011; Ministry of Education, Youth and Sports of the Czech Republic no. LO1409, LM2015088 and CZ.02.1.01/0.0/0.0/16 013/ 0001406; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

The paper is dedicated to the investigation of the luminescence of Sc 3+ and La 3+ isoelectronic impurities in Y 2 SiO 5 (YSO) single crystalline films (SCF), grown by the liquid phase epitaxy (LPE) method, and in the powder analogs of these compounds prepared using the ceramic technology. The Sc 3+ and La 3+ dopants replacing the Y 3+ cations in Y1and Y2 positions of YSO host introduce the strong complex emission bands in the UV range peaked at 330 and 345 nm, respectively. The Sc 3+ and La 3+ dopant in YSO matrix yields also the strong TSL peaks at 400 and 405 K related to the ScY and ScLa centers formation, respectively. The luminescence and scintillation properties of YSO SCFs doped with Sc 3+ and La 3+ ions and co-doped with Ce 3+ ions on the trace impurity level have been also studied in our work. We have found that the light yield (LY) of these YSO:Sc and YSO:La SCFs can reach 50–65% of LY in reference YSO:Ce SCF due to strong quenching influence of Pb 2+ ions. Finally, the potential of Sc 3+ and La 3+ doped SCF of orthosilicates for creation of heavy scintillation screens, emitting in the UV range, is discussed.

Luminescence characteristics of epitaxial films of Ce 3+ -doped multicomponent garnets of the type of Lu 3− x Gd x Ga y Al 5− y O 12 , where x varies from 0.14 to 3 and y varies from 0 to 3.54, are investigated in the 4.2–400 K temperature range by the steady-state and time-resolved spectroscopy methods. Their dependence on the film composition is clarified. The presence in the same film of different Ce 3+ -related luminescence centers is revealed, and a possible structure of these centers is discussed. The processes of the electron and hole centers creation under irradiation of the films in the Ce 3+ -related absorption bands are studied by thermally stimulated luminescence method. The location of the excited 5d 1 level of Ce 3+ with respect to the bottom of the conduction band and the origin and thermal stability parameters of electron traps in the epitaxial films and in the single crystals of the same composition are found to be different.

Lutetium aluminum garnet nanopowders doped with Pr in concentration range 0.1–10 at% prepared via photo-induced synthesis were studied in this work. The preparation and luminescence properties of these high-density materials are reported, featuring fast response and high scintillation efficiency. Prepared samples were characterized using several analytical methods to determine the structure of the prepared materials and their luminescent properties, which are discussed and compared with analogous bulk material (single crystal).

The 3 in. size Ce1%:Gd 3 Al 2 Ga 3 O 12 single crystals were prepared by the Czochralski (Cz) method. Optical constants were measured. Chemical composition analysis and uniformity of scintillation decay and light yield along growth direction were evaluated. The timing resolution measurement for a pair of 3 mm×3 mm×3 mm size Ce:GAGG scintillator crystals was performed using Si-PMs.

A set of Eu-doped Y3Al5O12 (YAG) phosphors in the powder form was successfully synthesized by multiple-step solid-state reaction under the reducing Ar:5%H2 atmosphere. Their physical properties were investigated by means of X-ray diffraction, time-resolved luminescence spectroscopy, and electron paramagnetic resonance (EPR). Special attention was given to well-grounded confirmation of Eu2+ occurrence in the YAG structure. X-ray diffraction confirmed the presence of a major YAG phase in all samples. The influence of Eu concentration, form of doping (EuS, EuF2, or Eu2O3) and number/form of annealing steps was studied. Corresponding characteristics were measured and evaluated in a broad temperature range (8–800 K). The correlated measurements showed that the single Eu2+ ions stabilized in YAG in the yttrium position are responsible for the 440 nm emission. The corresponding lowest energy excitation band is situated at 300 nm, and the radiative lifetime of Eu2+ emission is about 500 ns. A phenomenological model of excited state dynamics was used to explain the experimentally observed features. Possible practical exploitation of the Eu2+ center in the YAG host is discussed.

We grew Na and K co-doped Eu:SrI 2 [Na,Eu:SrI 2 and K,Eu:SrI 2 ] crystals by a modified micro-pulling-down method to reveal the co-doping effects on the crystal growth and scintillation properties. The non-codoped, Na0.5%, Na1.0%, K0.5% and K1.0%,Eu:SrI 2 crystals indicated high transparency while the milky parts were generated in the Na5.0% and K5.0%,Eu:SrI 2 crystals. The light yields of Na,Eu:SrI 2 and K,Eu:SrI 2 crystals under γ-ray irradiation were decreased by the Na and K co-doping. On the other hand, there was a small change within 940–1020 ns in the decay times by the Na and K co-doping. In the light yield proportionality under γ-ray irradiation, the non-proportionality in the low energy region was improved by Na and K co-doping.

The ns2-type metal elements (Pb and Sn) doped LiCaAlF6 single crystals were grown by a micro-pulling-down (μ-PD) method. Pb doped LiCaAlF6 [Pb:LiCAF] crystals showed high transparency and single phase of the LiCAF structure. However, we could not obtain Sn:LiCAF crystals due to the evaporation of SnF2 during the crystal growth. There was an absorption peak around 193 nm in the transmittance spectrum of Pb:LiCAF crystal. In the radioluminescence spectrum of the Pb:LiCAF crystal under X-ray irradiation, two emission peaks around 200 and 830 nm were observed.

The luminescence properties of terbium lutetium aluminium garnet single crystalline films, Lu 3− x Tb x Al 5 O 12 , doped with Ce 3+ are investigated as a function of the Tb/Lu ratio with aim of an improved understanding of the energy transfer processes between Ce 3+ and Tb 3+ ions in the aluminium garnet hosts. Due to replacing the smaller Lu 3+ ion with the larger Tb 3+ ion, the crystal field splitting for the 5d energy levels of Ce 3+ ions increases, causing the shift of the lowest 5d state of Ce 3+ below the 5 D 4 energy level of Tb 3+ . This allows for the efficient energy transfer from Tb 3+ to Ce 3+ even at the low temperatures. The measurements of temperature dependence of the decay time of Tb 3+ and Ce 3+ luminescence confirm an efficient energy transfer from Tb 3+ to Ce 3+ and provide a qualitative understanding of this process. Furthermore, bi-directional energy transfer processes between Ce 3+ and Tb 3+ are revealed. Scintillation decays under α-particles excitation show presence of the fast and slow sub-microsecond components.

Inorganic scintillators with high density and high light yield are of major interest for applications in medical imaging and high energy physics detectors. In this work, the optical and scintillation properties of Mg co-doped Ce:Gd 3 Al 2 Ga 3 O 12 crystals, grown using Czochralski technique, have been investigated and compared with Ce:Gd 3 Al 2 Ga 3 O 12 ones prepared with identical technology. Improvements in the timing performance of the Mg co-doped samples with respect to Ce:Gd 3 Al 2 Ga 3 O 12 ones have been measured, namely a substantial shortening of the rise time and scintillation decay components and lower afterglow were achieved. In particular, a significantly better coincidence time resolution of 233 ps FWHM, being a fundamental parameter for TOF-PET devices, has been observed in Mg co-doped crystals. The samples have also shown a good radiation tolerance under high doses of γ-rays, making them suitable candidates for applications in harsh radiation environments, such as detectors at future collider experiments.

Scintillation properties of multicomponent (GdLuY) 3 (GaAl) 5 O 12 :Ce 3+ epitaxial garnet films were studied under electron beam excitation. The role of the shallow traps was investigated using the scintillation decay kinetics and cathodoluminescence spectroscopy. Tunneling-driven recombination, which provides a physical ground for the slow scintillation decay component in LuAG:Ce single crystals, is discussed in detail.

The photopeak and escape peak processes were studied in heavy Ce3+-doped LuAG and GGAG, Pr3+-doped LuAG and undoped BGO scintillating crystals. Energy resolution measurements were performed with 511 keV photons of 22Na radioisotope. In the pulse-height spectra the escape peaks were resolved clearly on thin samples (up to 3 mm). If sample thickness increases the escape peak cannot be resolved anymore (for thicknesses approx. above 5 mm, especially). Consequently, energy resolution increases by about 40% compared with that measured at 1 mm thick samples.

Pr doped (Lu,Gd) 3 (Ga,Al) 5 O 12 single crystals were grown by the micro-pulling down (μ-PD) method. The crystals were greenish and transparent with 3.0 mm in diameter, 10–30 mm in length. Neither visible inclusions nor cracks were observed. Luminescence and scintillation properties were measured. The substitution at the Al 3+ sites by Ga 3+ in garnet structure has been studied. The Pr 3+ 5d–4f emission is observed within 300–380 nm wavelength superposed with 312 nm emission line of Gd 3+ . Pr0.2%:Lu 2.5 Gd 1 Ga 3 Al 2 O 12 shows highest emission intensity. The light yield of Pr0.2%:Lu 2.5 Gd 0.5 Ga 2 Al 3 O 12 sample with diameter 3 mm×1 mm size was around 8000 ph/MeV. Two-exponential approximations of scintillation decay showed 39.6 ns (30.6%) and 151 ns (69.4%) decay times.