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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.

Preparation and thermal properties of Er3+-doped lithium–yttrium meta-phosphate glasses with a nominal composition of Er:LiY(PO3)4 were studied as a new scintillating material for neutron detection. The glassy Er:LiY(PO3)4 ingots 10 × 10 × 25 mm3 in size were prepared by quenching of the molten mixture of the starting lithium carbonate, yttrium phosphate, and phosphorus oxide in stoichiometric relations. Crystallization kinetics was experimentally studied on powder samples with particle sizes ranging from 96 to 106 μm, 200 to 212 μm, and on bulk glassy samples using the non-isothermal differential scanning calorimetry. The evaluation of the measured data was performed using the Johnson–Mehl–Avrami, Matusita and Augis–Bennett models, and the y(α) and z(α) functions. In the case of the powder samples, the model analysis of the measured data showed that the crystallization mechanism was primarily performed through volume nucleation followed by 2D and 3D growth and in the bulk one by the surface and volume nucleation with 1D growth. Obtained kinetic parameters were used for reconstruction of the crystallization peaks using various models and compared with actual experimental data.

We report a breakthrough concept for a bulk single crystal as a heavy aluminum perovskite scintillator, where due to bandgap engineering by a balanced Gd admixture in a Lu cation sublattice, the scintillation performance dramatically increases. In an optimized composition of (Lu, Gd)AlO3:Ce (LuGdAP:Ce), the light yield approaches 21,000 phot/MeV, which is close to that of classical but much less dense YAP:Ce and 50% higher than the best LuYAP:Ce reported in the literature. Moreover, contrary to LuYAP:Ce, the LuGdAP host maintains a high effective atomic number close to that of LuAP:Ce (Zeff = 64.9), which is comparable to commercial LSO:Ce. An enormous decrease in afterglow on the millisecond time scale and acceleration in the rise time of the scintillation response further increase the application potential of the LuGdAP host. The related acceleration of the transfer stage in the scintillation mechanism due to diminishing electron trap depths is proven by thermally stimulated luminescence (TSL). Furthermore, we quantitatively characterize and model the energy transfer processes that are responsible for the change in the photoluminescence and scintillation decay kinetics of Ce3+ in the LuGdAP matrix. Such an innovative (Lu, Gd)AP:Ce scintillator will become competitive for use in applications that require heavy, fast, and high light yield bulk scintillators. The dependence of the afterglow in millisecond time scale and light yield (in the inset) on the Gd content in the GdxLu1-xAlO3 single crystal scintillator.

The paper addresses the development of composite scintillation materials providing simultaneous real-time monitoring of different types of ionizing radiation (α-, β-particles, γ-rays) in mixed fluxes of particles and quanta. The detectors are based on composite heavy oxide scintillators consisting of a thin single-crystalline film and a bulk single-crystal substrate. The film and substrate respond to certain types of ionizing particles, forming together an all-in-one composite scintillator capable of distinguishing the type of radiation through the different time characteristics of the scintillation response. Here, we report the structure, composition, and scintillation properties under different ionizing radiations of (Lu,Gd,Tb)3(Al,Ga)5O12:Ce films deposited using liquid phase epitaxy onto Gd3(Al1−xGax)5O12:Ce (GAGG:Ce) single-crystal substrates. The most promising compositions with the highest light yields and the largest differences in scintillation decay timing under irradiation with α-, β-particles, and γ-rays were selected. Such detectors are promising for environmental security purposes, medical tomography, and other radiation detection applications.

This paper reports on the preparation of undoped cesium hafnium chloride (Cs2HfCl6) and study of its thermal properties. The Cs2HfCl6 is considered, due to its excellent scintillation properties, as a promising candidate for cost-effective radiation detectors with potential to replace traditional halide scintillators, e.g., NaI:Tl and CsI:Tl. The Cs2HfCl6 material was successfully synthesized from a cesium chloride and a hafnium chloride mixed together in stoichiometric ratio. The presence of only one crystalline phase of the Cs2HfCl6 in the material was confirmed by the X-ray diffraction analysis. The simultaneous non-isothermal differential scanning calorimetry and thermogravimetry (DSC–TG) of the synthesized material under nitrogen atmosphere, vacuum, and in enclosed system was performed. The Cs2HfCl6 decomposition and melting of CsCl–Cs2HfCl6 mixture under nitrogen and vacuum were observed. On the contrary, the DSC measurement of the cesium hafnium chloride in enclosed system showed only one endothermic peak related to the congruent melting point. Furthermore, the repeated DSC–TG measurements to investigate the materials’ stability in enclosed system were carried out as well.

The paper contains detailed crystal structure and photoluminescence studies of the Bi3+ and Bi3+-Eu3+ co-doped Gd3Ga5O12 (GGG) garnet. The studied materials have been synthesized in the form of microcrystalline powders by the common solid-state reaction method. Precise crystal structure parameters were derived from the X-ray powder diffraction data. Photoluminescence studies were done by the steady-state and time-resolved techniques in the 4.2–400 K temperature range. The studied materials show no UV luminescence caused by electronic transitions of a Bi3+ ion. The observed luminescence in visible is interpreted by excitons localized around Bi3+ ions. In particular, two emission bands located at 2.55 eV (486 nm) and 2.05 eV (605 nm) at 4.2 K were revealed. The main emission band at 2.55 eV is attributed to the triplet relaxed state of excitons localized around single (regular) Bi3+ ions, whereas the weaker band at 2.05 eV is related to some associates of a single Bi3+ ion with a crystal lattice defect. The performed studies for Bi3+-Eu3+ co-doped samples indicate that the energy transfer from Bi3+ to Eu3+ is radiative and is caused by reabsorption of the Bi-related exciton emission by Eu3+ ions. The studied materials were also characterized as a single-phase converting phosphor for near-UV excited white LEDs. The possibility of the emission color tuning from blue to orange-red at UV excitation by the way of changing of Bi3+ and Eu3+ concentrations was shown.

Ho3+ codoping of YAG:Ce induces an acceleration of Ce3+ decay. This is caused by a non-radiative energy transfer from Ce3+ to Ho3+ which is enabled by a multipolar interaction between the ions. The photoluminescence decay characteristics were examined in a wide range of Ho3+ concentrations and 1/e decay time of Ce3+ was accelerated more than six times. The decay curves were analyzed using the Forster-Dexter model. The critical concentration of Ho3+, useful for quantitative decay time tailoring, was calculated. These results of the decay evaluation of YAG:Ce codoped with Ho3+ were compared to those obtained from the recent study on YAG:Ce codoped with Er3+ [1].

UV irradiation of aqueous solutions containing various metal ions (Ag, Rh, Cu, Pb, Ba, …) and sensitizers was performed in order to synthesize a large variety of solid nano- or microcrystalline materials in the irradiated solutions and illustrate the chemical and photochemical reactions leading to their formation. Acetone was shown to be a very effective sensitizer and photoreducing agent when coupled with propan-2-ol, whereas formate HCOO– was introduced either mainly as a reducing agent in deaerated solution or as a source of nascent CO2 in the presence of air. It was shown that UV irradiation allows for the preparation of a wide variety of inorganic materials. Moreover, reactions mechanisms discussed may occur during Laser Ablation in Liquid processes.

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.

In this study, the distributions of aluminum and gallium atoms over the tetrahedral and octahedral sites in the garnet structure were investigated in mixed Lu3Al5-xGaxO12 crystals by using 27Al and 71Ga magic angle spinning nuclear magnetic resonance (NMR) and single crystal 71Ga NMR. The experimental study was supported by theoretical calculations based on density functional theory (DFT) in order to predict the trends in terms of the substitutions of Al by Ga in the mixed garnets. Both the experimental and theoretical results indicated the non-uniform distribution of Al and Ga over the tetrahedral and octahedral sites in the garnet structure, with a strong preference for Ga occupying the tetrahedral sites in the garnet structure at all Ga concentrations, despite Ga having a larger ionic radius than Al and tetrahedrons being smaller than octahedrons. The Ga occupation preference is primarily related to the involvement of Ga 3d10 electrons in interactions, and due to the different nature of the chemical bonds formed by Al and Ga when located in the tetrahedral and octahedral environments. The quadrupole coupling constants and chemical shift parameters for Al and Ga nuclei were determined for all of the compounds considered, and the electric field gradients at the Al and Ga nuclei were calculated in the DFT framework. Our results also showed that the structural relaxation after Al substitution with the larger Ga mainly occurs via deformation of the octahedrons, while leaving the tetrahedrons relatively undeformed.

The performance of cerium-doped Y3Al5O12 (Ce3+:YAG) often depends on cerium solubility achievable in a particular preparation technology. This solubility is kinetically affected by the synthesis process which allows for Ce3+ solubility to be generally much higher in a polycrystalline material than in single crystals. This work presents Y3−xCexAl5O12 polycrystalline thin films deposited by spin-coating where cerium is substituted on yttrium sites in an interval of 3.3–25 at%. Up to a concentration of 18 at%, the samples remain single-phase, which is the highest Ce3+ doping level in YAG published so far. Absorption, excitation and emission photoluminescence spectra are presented. The photoluminescence decays of the samples containing up to 6 at% cerium are comparable in radiative lifetime to those of Ce3+:YAG single crystals having the cerium concentration limit over one order smaller. The cathodoluminescence of the samples and soft X-ray nanosecond pulse-excited decays are examined. The scintillation decays appear much faster with a 1/e decay time well below 10 ns compared to that of a Ce3+:YAG single crystal which is 140 ns. After further optimization of the microstructure and the overall scintillation yield, sol–gel prepared Ce3+:YAG thin films are promising candidates for application in fast SEM scintillation detectors, currently intensively investigated in the scintillator technology field.

Charge trapping and energy transfer processes are investigated in PbMoO4 single crystals by electron paramagnetic resonance (EPR) and wavelength-resolved thermally stimulated luminescence (TSL) in a correlated manner. New signals produced by two differently perturbed Mo5+ centers (Mo2 and Mo3) were observed in EPR spectra measured in the crystals after 420 nm light irradiation. Two sets of spin-Hamiltonian parameters, g tensor and the 95,97Mo, 207Pb (super) hyperfine tensors, have been determined and analyzed in terms of crystal field and LCAO-MO theories. A significant overlap of the Mo 5d1 and 6s6p ligand Pb orbitals was deduced for the Mo3 whereas the Mo2 center seemed to be not or very slightly affected by the lead orbitals. The obtained TSL results allowed to suppose the existence of at least six glow peaks produced by the de-trapping of charge carrier traps either of intrinsic nature or somehow stabilized by nearby accidental impurities. The peaks having maxima at 51 K, 79 K, and 89 K, in particular, were attributed to the Mo2 and Mo3 centers thermal destruction due to the observed correspondence between the kinetic parameters (trap depths and frequency factors) determined separately for the glow peaks and the EPR intensity thermal decay curves of these centers. The Mo2 EPR decay curve is rather complex experiencing two-step trend probably due to trapped electron recombination with some holes released below 60 K. It was further confirmed by the TSL emission maximum relatively large red shift (~ 100 nm) compared to the much smaller offset measured in radioluminescence. This phenomenon, observed also in samples obtained from extra-pure starting materials, was explained by three-component origin of the spectra, each having its own thermal fading rate. One of them ceased to exist above 60 K. The discussion of the obtained results is provided in comparison with other representatives of the scheelite tungstate and molybdate-based single crystals.

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.

Bi-doped compounds recently became the subject of an extensive research due to their possible applications as scintillator and phosphor materials. The oxides co-doped with Bi3+ and trivalent rare-earth ions were proposed as prospective phosphors for white light-emitting diodes and quantum cutting down-converting materials applicable for enhancement of silicon solar cells. Luminescence characteristics of different Bi3+-doped materials were found to be strongly different and ascribed to electronic transitions from the excited levels of a Bi3+ ion to its ground state, charge-transfer transitions, Bi3+ dimers or clusters, radiative decay of Bi3+-related localized or trapped excitons, etc. In this review, we compare the characteristics of the Bi3+-related luminescence in various compounds; discuss the possible origin of the corresponding luminescence centers as well as the processes resulting in their luminescence; consider the phenomenological models proposed to describe the excited-state dynamics of the Bi3+-related centers and determine the structure and parameters of their relaxed excited states; address an influence of different interactions (e.g., spin-orbit, electron-phonon, hyperfine) as well as the Bi3+ ion charge and volume compensating defects on the luminescence characteristics. The Bi-related luminescence arising from lower charge states (namely, Bi2+, Bi+, Bi0) is also reviewed.

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.

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.

Photoluminescence, thermally stimulated luminescence (TSL) and EPR characteristics of the Ce3+-doped single crystals of multicomponent Y1Lu2GaxAl5-xO12 and Lu3GaxAl5-xO12 garnets with different Ga contents (x = 0, 1, 2, 3, 4, 5) excited in the Ce3+-related absorption bands are investigated in the 9–500 K temperature range. The distribution of Ga3+ and Al3+ ions in the crystal lattice is determined by the NMR method. The relative number of Ga3+ ions in the tetrahedral crystal lattice sites, the maxima positions of the TSL glow curve peaks and the corresponding trap depths are found to decrease linearly with the increasing Ga content. At the same time, the reduction of the activation energy Ea of the TSL glow curve peaks creation under irradiation in the 4f–5d1 absorption band of Ce3+ is strongly nonlinear. To explain this effect, the suggestion is made that Ea is the energy distance between the excited 5d1 level of Ce3+ and a defect level located between the 5d1 level and the bottom of the conduction band and arising from the Ga3+ ion perturbed by the nearest neighboring Ce3+ ion. The electrons thermally released from the excited Ce3+ ions are suggested to be trapped at the perturbed Ga3+ ions resulting in the appearance of electron Ga2+ centers. In spite of the fact that the paramagnetic Ga2+ ions were not detected by EPR, the process described above has been found for Fe3+ impurity ions, namely, the electron transfer from the 5d1 excited level of Ce3+ to Fe3+ is directly detected by EPR.

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,...

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.

Single crystals of PbMoO 4 were studied by means of light-induced electron paramagnetic resonance (EPR) and wavelength resolved thermally stimulated luminescence (TSL). The work is focused on the electron self-trapped at the (MoO 4 ) 2- complex. Detailed analysis of the EPR spectra of this complex allowed to determine a set of spin-Hamiltonian parameters including g factor and the 95,97 Mo, 207 Pb hyperfine tensors further used in calculations performed in terms of crystal field and LCAO-MO theories. They have shown a significant overlap of the Mo 5 d 1 and 6 s 6 p ligand lead orbitals. The contributions of oxygen and lead to the molecular orbitals with an electron trapped at the (MoO 4 ) 3- complex were about 14% and 38%, respectively. The decay of the molybdenum center EPR intensity with annealing temperature provided information about thermal stability of the center, which thermally destroys already at 40 K. Trap depth and frequency factor, E t = 0.05 eV, and f 0 = 10 4 s −1 , have been determined. The TSL glow curve displays two overlapping peaks in the 40–50 K temperature region, corresponding to the disappearance of the EPR signal from the (MoO 4 ) 3- center. By partial cleaning technique and initial rise method it is shown that the lower temperature peak is related to a trap with thermal parameters similar to those determined for the (MoO 4 ) 3- center. This allows to correlate it to the thermal destruction of the (MoO 4 ) 3- center. The obtained results are discussed in a broader frame of charge trapping mechanism in all the family of tungstate and molybdate-based single crystals.

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.

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.

Photoluminescence characteristics of Gd3Ga5O12:Bi single crystalline films with different Bi contents grown by the liquid phase epitaxy are studied by the steady-state and time-resolved luminescence spectroscopy methods in the 4.2–500 K temperature range under excitation within the 3.8–6.0 eV. No ultraviolet emission, which could be ascribed to the radiative decay of the triplet excited state of Bi3+, is observed. Only visible emission is shown to arise from the Bi3+–related luminescence centers. Both the intense 2.54 eV emission and the weaker 2.46 eV emission of Gd3Ga5O12:Bi are shown to be of exciton origin. We suggest that they are due to the radiative decay of an exciton localized around a single Bi3+ ion and a dimer {Bi3+–Bi3+} center, respectively. The characteristic parameters of the corresponding exciton states are determined. The photostimulated processes, resulting in the localized excitons formation under excitation in the Bi3+–related absorption bands, are discussed. Peculiarities of Gd3+–Bi3+ energy transfer processes in Gd3Ga5O12:Bi are investigated. The possibility of application of Bi3+–doped gadolinium gallium garnets in scintillation detectors and light emitting diodes is considered.

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.

Using single-crystal YAG:Ce plates with different dopant concentration under different sample temperatures (77-500(800)K), absorption, emission and luminescence decay characteristics were measured. Simulation is used to explain the luminescence decay time increase with growing temperature. For selected incident blue excitation band and given sample thickness the composed blue-yellow spectrum is calculated after passing through the sample. Temperature dependence of the color coordinates CIE-xy is calculated, arising mostly due to specific temperature dependence of the 4f-5d 1 absorption transition of Ce 3+ center in the garnet host.

The optical and scintillation characteristics of Gd 2 YAl 2 Ga 3 O 12 :Ce and Lu 2 YAl 2 Ga 3 O 12 :Ce single crystals are investigated. At 662 keV γ-rays, light yield (LY) of 37,900 ph/MeV and energy resolution of 7.0% obtained for Gd 2 YAl 2 Ga 3 O 12 :Ce are superior to those of 18,900 ph/MeV and 11.5% obtained for Lu 2 YAl 2 Ga 3 O 12 :Ce. Scintillation decays are measured using the time-correlated single photon counting technique. A fast component decay time of 45 ns with relative intensity of 88% obtained for Lu 2 YAl 2 Ga 3 O 12 :Ce is superior to that of 50 ns (65%) for Gd 2 YAl 2 Ga 3 O 12 :Ce. The linear attenuation coefficient at 662 keV γ-rays is also determined and discussed.

1 in. diameter Mg 0.05, 0.1, 0.2, 0.5 mol% and Zr 0.015% co-doped Ce1%:GGAG crystals were grown by Cz method. Relationship between Mg concentration and absorption, luminescence, light output, decay time, timing resolution was investigated. Mg 0.2 mol% co-doped sample showed the fastest timing resolution of 165 ps among the Mg-co-doped samples.

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.

Praseodymium-doped (Gd 2 Y)(Ga 3 Al 2 )O 12 (GYGAG: Pr) single crystals are grown by the micro-pulling down method with different Pr concentrations. The energy transfer process between Pr 3+ and Gd 3+ is investigated by photoluminescence excitation (PLE) and emission (PL) spectra measurements. Photoelectron yield measurements are carried out using photomultiplier. At 662 keV γ-rays, photoelectron yield of 2520 phe/MeV obtained for the GYGAG: Pr (0.01%) sample is larger than that of 1810 phe/MeV obtained for BGO crystal. Light yield degradation for the GYGAG: Pr scintillators is presumably due to the energy transfer from 5d state of Pr 3+ to 4f state of Gd 3+ together with the concentration quenching in the Gd 3+ -sublattice.

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.

We have investigated Li 4 SiO 4 scintillation crystals for their possible application in neutron detection due to high Li content and low density of 2.35 g/cm 3 . The micro-pulling-down method employing the Ir crucible and afterheater was optimized for crystal growth of Li 4 SiO 4 taking into account the Li evaporation. To grow high-quality crack-free single crystals, the heating power was increased to establish milder temperature gradient, thicker meniscus, smaller crystal diameter and resulting smaller stress in the as-grown crystals. The undoped, Ti-, Cr-, and Al- doped crystals were prepared and studied. Radioluminescence measurements under X-ray excitation showed quite high overall scintillation efficiency of the Ti-doped sample reaching as high as 250% of that of Bi 4 Ge 3 O 12 reference scintillator. The emission spectrum was dominated by one broad band peaking at 350 nm related to Ti 4+ impurity. Reasonable light yield of 10000 photons/neutron was found. However, its long decay time of 54 μs might be a limitation especially for high counting rate applications. The overall scintillation efficiency of the Cr 3+ sample was much lower and the spectrum shows one broad peak at 463 nm which does not correspond to Cr 3+ luminescence. The radioluminescence spectrum of the Al-doped sample resembled to that of the Ti-doped one, just its magnitude is considerably lower, which was explained by Ti contamination. Peculiarities and optimization of crystal growth and a preliminary sketch of luminescence mechanisms and dopant incorporation are discussed.

KLuS2 single crystal samples undoped and doped with a low (5 %) or high (38 %) concentration of trivalent thulium or ytterbium ions were synthesized in the form of thin hexagonal plates. The low phonon energy ( ∼ 220 cm−1) was confirmed using Raman spectroscopy. Samples were studied also by using optical absorption and emission as well as electron paramagnetic resonance spectroscopy and the observed spectral features are discussed. In particular, the 5 % Yb doped samples demonstrate homogeneous dopant distribution inside the material over the lutetium sites. No other signals either from potassium site or the exchange coupled ions were detected. For infrared transitions the luminescence kinetic was determined. Significantly broad infrared emission bands (at 1.4, 1.8 and 2.3 μm for Tm3+, 1 μm for Yb3+) and long decay times (e.g. 0.4 ms from 3H4 to 19 ms from 3F4 levels of Tm3+, 1.4 ms from 2F5/2 level of Yb3+) make those materials perspective for future laser development.

This work presents the results of creation of novel composite scintillators based on the Gd3Al5-x GaxO12:Ce (x = 1.16–2.67) single crystalline films (SCF), grown by the LPE method onto Gd3Al2.5 Ga2.5O12:Ce single crystal (SC) substrates. The scintillation properties of film/crystal epitaxial structures were investigated under α–particle and γ–quantum excitations. Under α–particle excitation, the light yield of mentioned SCF scintillators is significantly less than that in their substrates due to the influence of Pb2+ flux contamination and formation of Pb2+-Ce4+ centers. Meanwhile, these SCF scintillators under α–excitation possess significantly faster decay kinetics than that of their substrates under γ–excitation. Therefore, the Gd3Al5-xGaxO12:Ce SCFs (x = 1.16–2.67) /Gd3Al2.5Ga2.5O12:Ce SC epitaxial structures can be used as composite scintillators for simultaneous registration of the components of mixed ionizing fluxes, specifically for detection of α–particles (SCF) and γ–quanta (substrate). The separation of the response from the SCF and substrate parts of composite scintillators under α–particle (241Am) and γ–quantum (137Cs) excitations occurs at large tγ/tα = 1.7–4.2 ratio.

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.

Photo- and X-ray-excited luminescence characteristics of Bi-doped LiLaP 4 O 12 phosphates with different bismuth contents (from 1 to 25 at% in the melt) are investigated in the 4.2–300 K temperature range and compared with the characteristics of the undoped LiLaP 4 O 12 phosphate. The broad 2.95 eV emission band of LiLaP 4 O 12 :Bi excited around 5.4 eV is found to arise from the bismuth dopant. Relatively large FWHM and Stokes shift of the emission band and especially the data on the low-temperature decay kinetics of the 2.95 eV emission and its temperature dependence, indicating a very small spin-orbit splitting energy of the corresponding excited state, allow the conclusion that this emission arises from the radiative decay of the triplet state of an exciton localized around a Bi 3+ ion. No spectral bands are observed, arising from the electron transitions between the energy levels of Bi 3+ ions. Phenomenological model is proposed for the description of the excited state dynamics of the Bi 3+ -related localized exciton in LiLaP 4 O 12 :Bi and the parameters of the triplet localized exciton state are determined. Keywords: Photoluminescence; Time-resolved spectroscopy; Excited states; Bi 3+ centers; LiLaP 4 O 12 :Bi powders