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Effects of the tungsten (W) ions co-doping on the crystal growth, optical and scintillation properties for the Czochralski (Cz) grown Ce:Gd3Ga3Al2O12(GGAG) single crystals were investigated. The W 0%, 0.1%, 0.3%, 1%, and 5% co-doped Ce 1%:GGAG single crystals with a diameter of 1 in and length of 60–80 mm were grown by the Cz method. The effective segregation coefficient of the W ions was found as 0.002, 0.001, and 0.005 for W 0.1%, 0.3%, and 1%, Ce:GGAG, respectively. The segregation of W ions in GGAG host, light yield, and scintillation decay of the W co-doped Ce:GGAG were evaluated. The light yield decreased as the concentration of W co-dopant increased and toward the tail of the crystal. Furthermore, the defect role and related charge trapping in the W co-doped crystals were monitored by the thermo-stimulated luminescence.

The scintillation, optical, and photoluminescence properties of yttrium gadolinium aluminum perovskites activated by Ce3+ ions, (Y1− x Gd x )AlO3:Ce3+, were studied. A set of single-crystalline films with Gd content from $x = 0$ to 1 was grown by the liquid phase epitaxy. At higher Gd content, the bidirectional nonradiative energy transfer (ET) between Ce3+ and Gd3+ ions was observed, and an adequate model that took into consideration the energy migration over the Gd subsystem was suggested. The results decidedly showed that in samples with low Gd content, $x , the ET from Gd3+ to Ce3+ ions prevailed, which increased the light output. However, slow components appeared simultaneously in the scintillation decays. At high Gd concentrations, the nonradiative back ET from Ce3+ to Gd3+ predominated, which resulted in a considerable acceleration of scintillation decays from 28 ns in YAlO3:Ce to less than 2 ns in GdAlO3:Ce, but simultaneously the Ce3+ emission was significantly reduced.

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.

After the discovery of a cross-luminescence (CL) in BaF2 in 1982, a large number of CL scintillators were investigated. However, no CL scintillator superior to BaF2 has been discovered, and the research of CL scintillators has subsided. Recent technological development in medical imaging and high-energy physics created a new demand for ultra-fast scintillators further supported by the development of UV-sensitive semiconductor photodetectors. As a consequence, renewed interest in CL scintillators appeared. To satisfy the requirements of fast timing applications high photo-detection efficiency, e. i. a good spectral match between the scintillator and photodetector must be achieved. Cesium-based ternary chlorides could provide a red-shift (∼1.5 eV) of CL towards the sensitive region of the photodetector (PMT or SiPM) while keeping light output and timing characteristics comparable to BaF2.

CsPbBr3 nanocrystals have been identified as a highly promising material for various optoelectronic applications. However, they tend to coexist with Cs4PbBr6 phase when the reaction conditions are not controlled carefully. It is therefore imperative to understand how the presence of this phase affects the luminescence performance of CsPbBr3 nanocrystals. We synthesized a mixed CsPbBr3-Cs4PbBr6 sample, and compared its photo- and radioluminescence properties, including timing characteristics, to the performance of pure CsPbBr3 nanocrystals. The possibility of energy transfer between the two phases was also explored. We demonstrated that the presence of Cs4PbBr6 causes significant drop in radioluminescence intensity of CsPbBr3 nanocrystals, which can limit possible future applications of Cs4PbBr6-CsPbBr3 mixtures or composites as scintillation detectors.

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.

Charge trapping phenomena and recombination centers were studied in three Cs2HfCl6 single crystals of slightly different stoichiometry grown by the vertical Bridgeman method. Electron paramagnetic resonance (EPR) spectra measured both before and after X-ray irradiation show creation of two distinct Vk centers. One of them was Vk(a) already known from a recent work by “R. Král, V. Babin, E. Mihoková, M. Buryi, V. V. Laguta, K. Nitsch, and M. Nikl, Luminescence and Charge Trapping in Cs2HfCl6 Single Crystals: Optical and Magnetic Resonance Spectroscopy Study, J. Phys. Chem. C 121, 12375–12382 (2017)”. Its quantity was different in each of the samples studied; the smallest, however, was in the one with the best stoichiometry. The second Vk center presently observed has never been described before. Its existence at an almost undetectable level was observed only in two of the three crystals. Thermally stimulated luminescence (TSL) spectra measured in the three samples were evidently composed of at least 2–3 strongly overlapped components within the 10–500 K temperature range. This suggested the existence of several recombination centers activated by the depletion of specific charge carrier traps. The corresponding TSL glow curves composed of seven complex peaks demonstrated significant decrease of the peaks amplitude in the sample with the best stoichiometry. Along with decreased radioluminescence amplitude, the combined EPR and TSL study allowed us to assume the reduction of both the recombination and trap center concentration with the increased crystal quality

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.

Cesium hafnium iodide (CHI) was reported as a novel red-emitting scintillator in our previous article, while optimization of the crystal quality and evaluation of the scintillation performance were insufficient. In this study, a large and transparent CHI single crystalline specimen was obtained using slow crystal growth speed. Coupled with a Si avalanche photo-diode, the full width at half maximum energy resolution was evaluated to be 4.2 ± 0.2% at 662 keV which was the best value among conventional red-emitting scintillators. The scintillation light output, non-proportional response of light output and scintillation decay were also evaluated with a photomultiplier tube.

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.

Luminescent properties of cerium-doped yttrium oxyorthosilicate (Y2SiO5; YSO) and lutetium oxyorthosilicate (Lu2SiO5; LSO) prepared by a room-temperature sol-gel route were studied and compared to those of YSO and LSO single crystals. Structural changes in the samples during calcination were also studied by X-ray diffraction and differential thermal analysis. Radioluminescence spectra of the samples show comparable emission intensity with the bulk materials. Photoluminescence decay measurements were used to investigate the decay characteristics of the prepared powders. Changes in luminescent properties after the reduction of particle size by grinding in a ball mill were also demonstrated on the YSO:Ce3+ sample. Acceleration of the faster component of the decay time from 7.1 ns to 6.2 ns was observed. Prepared YSO:Ce3+ and LSO:Ce3+ powders are suggested to be good candidates for fast imaging or other applications.

In this study, the Gd3+-substituted yttrium aluminum perovskite epitaxial films activated by Ce3+ ions, (YGd)AlO3:Ce3+ with Gd content 0–44%, were prepared by liquid phase epitaxy technique and their optical, luminescence, and scintillation properties were studied. The results showed that films with Gd content below 20% had greater photoluminescence and radioluminescence intensities. For higher Gd concentrations, the Ce3+ emission gradually decreased and the Ce3+ decays were accelerated. The model of bidirectional non-radiative energy transfer between Gd3+ and Ce3+ ions and energy migration over the Gd3+ sublattice is suggested and the processes responsible for the observed effects are discussed.

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.

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.

The use of radiosensitizers recently emerged as a promising approach to circumvent the depth penetration limitations of photodynamic therapy of cancer and to enhance radiotherapeutical effects. A widely explored current strategy is based on complex nanoarchitectures that facilitate the transfer of energy harvested from X-ray radiation by scintillating nanoparticles to the surrounding photosensitizer molecules to generate reactive oxygen species, mostly singlet oxygen O2(1Δg). We describe an alternative approach aiming at a considerable simplification of the architecture. The presented nanoparticles, made of the luminescent octahedral molybdenum cluster compound (n-Bu4N)2[Mo6I8(OCOCF3)6], efficiently absorb X-rays due to the high content of heavy elements, leading to the formation of the excited triplet states that interact with molecular oxygen to produce O2(1Δg). The activity of the nanoparticles on HeLa cells was first investigated under UVA/blue-light irradiation in order to prove the biological effects of photosensitized O2(1Δg); there is no dark toxicity at micromolar concentrations, but strong phototoxicity in the nanomolar range. The nanoparticles significantly enhance the antiproliferative effect of X-ray radiation in vitro at lower concentration than for previously reported O2(1Δg) radiosensitizing systems and this effect is more pronounced on cancer HeLa cells than non-cancer MRC cells. The results demonstrate that the cluster-based radiosensitizers of O2(1Δg) have strong potential with respect to the enhancement of the efficacy of radiotherapy with exciting opportunities for cancer treatment.

The spectroscopic and laser properties of Er:GGAG active medium, in temperature range from 80 K to 300 K, are presented in this work. The sample of Er:GGAG (20 at. % of Er3+) crystal had face-polished plan-parallel faces without anti-reflection coatings (thickness 3.6 mm). During all experiments the Er:GGAG was attached to temperature controlled copper holder and it was placed in a vacuum chamber. The transmission and emission spectra together with the fluorescence decay time were measured depending on temperature. The excitation of Er:GGAG was carried out by a fibre-coupled laser diode radiation (pulse duration 2 ms, repetition rate 25 Hz, wavelength 964 nm). Laser resonator was hemispherical, 100 mm in length with flat pumping mirror (HR @ 2.95 μm) and a spherical output coupler (r = 100 mm, R = 97.5 % @ 2.65 - 2.95 μm). The tunability of laser at 300 K was tested using MgF2 birefringent filter and several laser lines at several spectral bands 2800 – 2822 nm, 2829 – 2891 nm, and 2917 – 2942 nm were obtained. The fluorescence decay time of manifold 4I11/2 (upper laser level) is slightly increasing with rising temperature from 482 μs (80 K) to 466 μs (300 K) on the other hand the intensity of up-conversion radiation was increasing with decreasing temperature. In the pulsed laser regime, the highest slope efficiency with respect to absorbed energy 9 % and the maximum output energy 2.6 mJ were reached at 5 % duty cycle. The laser radiation generated by Er:GGAG laser (2.94 μm) is close to the absorption peak of water (3 μm) thus this wavelength can be used in medicine or spectroscopy.

The present work reports results of the electron paramagnetic resonance (EPR), optical absorption, radio- and photoluminescence (RL and PL) complex study of the Lu2Si2O7:Pr and Lu2Si2O7:Ce pyrosilicate crystals. In both crystals, the EPR spectra demonstrate the presence of characteristic signals originating from the Yb3+, Er3+, Nd3+, Dy3+, Gd3+ and V3+ ions existing in the material as uncontrolled impurities. The corresponding spectra (except for Gd3+) have been analysed in detail and g- and hyperfine tensors are determined for all these ions for the first time in the lutetium pyrosilicate lattice. Optical absorption, RL and PL measurements in the Lu2Si2O7:Pr crystal have shown only the characteristic Pr3+ transitions. In addition, the Pr3+- Pr3+ energy transfer was observed and confirmed experimentally.

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.

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%.

Europium-doped lutetium oxide (Eu:Lu2O3) nano-powders were synthesized by a co-precipitation method from europium and lutetium nitrates using ammonium hydrogen carbonate (AHC) as the precipitant. Fine and low-agglomerated powders with average particle size of 68 nm were obtained by calcining the precursor at 1100 °C for 4 h. Using this powder as starting material, Eu:Lu2O3 transparent ceramics with the average grain size of ∼46 μm were fabricated by vacuum sintering at 1650 °C for 30 h, whose in-line transmittance reaches 66.3% at 611 nm. The influences of air annealing on optical transmittance, decay time, spectroscopic properties, light output and thermally stimulated luminescence of Eu:Lu2O3 ceramics were investigated in detail. Based on radioluminescence spectra, the light output of the annealed Eu:Lu2O3 ceramics is 10 times higher than that of the commercially available BGO single crystal, and it indicates that transparent Eu:Lu2O3 scintillation ceramics is a promising candidate for X-ray radiation detectors.

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.

A highly prospective drug for the X-ray induced photodynamic therapy (PDTX), LuAG:Pr3+@SiO2-PpIX nanocomposite, was successfully prepared by a three step process: photo-induced precipitation of the Lu3Al5O12:Pr3+ (LuAG:Pr3+) core, sol–gel technique for amorphous silica coating, and a biofunctionalization by attaching the protoporphyrin IX (PpIX) molecules. The synthesis procedure provides three-layer nanocomposite with uniform shells covering an intensely luminescent core. Room temperature radioluminescence (RT RL) spectra as well as photoluminescence (RT PL) steady-state and time resolved spectra of the material confirm the non-radiative energy transfer from the core Pr3+ ions to the PpIX outer layer. First, excitation of Pr3+ ions results in the red luminescence of PpIX. Second, the decay measurements exhibit clear evidence of mentioned non-radiative energy transfer (ET). The singlet oxygen generation in the system was demonstrated by the 3′-(p-aminophenyl) fluorescein (APF) chemical probe sensitive to the singlet oxygen presence. The RT PL spectra of an X-ray irradiated material with the APF probe manifest the formation of singlet oxygen due to which enhanced luminescence around 530 nm is observed. Quenching studies, using NaN3 as an 1O2 inhibitor, also confirm the presence of 1O2 in the system and rule out the parasitic reaction with OH radicals. To summarize, presented features of LuAG:Pr3+@SiO2-PpIX nanocomposite indicate its considerable potential for PDTX application.

Luminescent nanoparticles are researched for their potential impact in medical science, but no materials approved for parenteral use have been available so far. To overcome this issue, we demonstrate that Eu3+-doped hafnium dioxide nanocrystals can be used as non-toxic, highly stable probes for cellular optical imaging and as radiosensitive materials for clinical treatment. Furthermore, viability and biocompatibility tests on artificially stressed cell cultures reveal their ability to buffer reactive oxygen species, proposing an anti-cytotoxic feature interesting for biomedical applications.

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.

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.

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 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.

The YAlO 3 :Ce scintillation crystal has excellent mechanical properties and is not affected if used in chemically aggressive environments. The detector with the diameter of Φ25.4 mm and thickness of 0.1 mm was coupled with the PMT, associated electronics and the MCA in order to study its alpha spectroscopy properties. The measured alpha spectra of the surface calibration sources of 241 Am and 230 Th were compared with results of a Monte Carlo simulation. The experiment and the simulation were carried out for three distances between the detector and the surface alpha source in order to assess the effect of the distance on the detected energy of alpha radiation. Finally, the detector was used for the monitoring of radon ( 222 Rn) decay products (radon daughters) in the air. It was concluded that the detector is suitable for the in-situ alpha spectroscopy monitoring under ambient atmospheric conditions. Nevertheless, in order to identify radionuclides and their activity from the measured alpha spectra a computer code would need to be developed.

Single crystals of the undoped Cs2HfCl6 were grown using the vertical Bridgman method. Photoluminescence spectra and decays were measured in the extended temperature range of 8–500 K and approximated by a phenomenological model. Self-trapped exciton and defect-related emissions were clearly distinguished with the onset of thermal quenching above the room temperature. Electron paramagnetic resonance experiment revealed the formation of two configurations of Vk center (Cl2– molecular ion) at low temperatures. One of the Vk centers is created by a hole self-trapping at two neighboring Cl ions. In the temperature range 70–80 K, this state is thermally disintegrated and reappears in another configuration formed most probably by an interstitial Cl ion (an analog of the H-type center in alkali halides).

We have studied the X-ray irradiated EuAl 3 (BO 3 ) 4 single crystals by means of luminescence and electron paramagnetic resonance (EPR) spectroscopy. It was found that the X-ray irradiation modifies the color of the EuAl 3 (BO 3 ) 4 crystal and leads to the formation of a stable Eu 2+ centers from the Eu 3+ centers located in a host matrix. Annealing of the crystal at 600 °C leads to the restoration of the original color and the disappearance of Eu 2+ centers. The EPR and luminescence spectra of the Eu 2+ ion were studied in a wide temperature range. The angular dependence of Eu 2+ EPR spectra is described by an axial spin Hamiltonian characterized by the spin of S = 7/2 with the following parameters: g z = g x = 1.991 (1); b 2 0 = −267,86 (16)*10 −4 cm −1 ; b 4 0 = −4,20 (8)* 10 −4 cm −1 ; b 6 0 = 0,37 (13)* 10 −4 cm −1 ; A (151) = 31,4 (3)* 10 −4 cm −1 ; A (153) = 13,9 (3)* 10 −4 cm −1 . Based on the comparison of spin Hamiltonian parameters of Eu 2+ and Gd 3+ ions, it was concluded that Eu 2+ ion located at the Eu 3+ site in the EuAl 3 (BO 3 ) 4 crystal lattice. Within the framework of the superposition model, the distortions introduced to the local environment by the Eu 2+ and Gd 3+ ions were analyzed. In the luminescence spectra, the bands associated with the Eu 2+ and Eu 3+ ions are detected. The photoluminescence decay kinetics of Eu 3+ -related emission (614 nm) has a single-exponential character, whereas the Eu 2+ -related band (323 nm) possess more complicated decay kinetics behavior that may point to the Eu 2+ excited state ionization and its delayed recombination.

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.

Thulium doped solid state lasers are well-known sources of radiation tunable around 2 pm. Obtainable wavelengths cover important spectral regions such as absorption lines of water, characteristic spectra of some gases or the atmospheric transmission bands. Tunable Tm3+ lasing was accomplished using various matrices, such as YAG, YAP or YLF [1]. Recently an interest re-emerged in the mixed garnets as host materials. Their multi-site structure induces broadening of spectra of the active ions, improving overlap with pumping diode emission and extending emission spectra and tunability [2]. In this submission, Tm3+ doped mixed gadolinium-gallium-aluminium-garnet Gd 3 (Ga 5-x Al x )O 12 (GGAG) is investigated. Focus is given to the Tm3+ concentration dependence of lasing and tunability parameters as a follow-up work to the first Tm:GGAG lasing report with one Tm3+ concentration sample [3]. The Tm:GGAG crystal was grown using Czochralski method in a slightly oxidative atmosphere. Five plane-parallel face-polished Tm:GGAG samples with concentrations varying from 1.4 at.% to 8.4 at.% (Tm/Gd) and thicknesses ranging from 2.7 mm to 3.6 mm were cut from the crystal. The samples were longitudinally pumped by fiber coupled (core diam. 400 pm, NA = 0.22) laser diode at wavelength 785 nm in QCW regime (pulse length 5 ms, repetition rate 10 Hz). The 145 mm resonator consisted of a flat pumping mirror (HR @ 1.85–2.11 pm, HT @ 0.78 pm) and concave output coupler (r = 150 mm, R = 97.5 % @1.8–2.10 pm). For the wavelength tuning, 1.5 mm thick birefringent SiO 2 plate was inserted in the cavity at the Brewster's angle.

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.

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).

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.

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

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 Ce 3+ ions incorporation inside lutetium oxyorthosilicate (Lu 2 SiO 5 ) single crystals was studied by electron paramagnetic resonance. Already known Ce1 and Ce2 centers originating from the lattice peculiarity allowing two lutetium sites coordinated by different number of the oxygen ions were detected. Remarkably, for the Ce2 center, the determined g 2 tensor is asymmetric and could not be diagonalized as compared to the Ce1 center, for which the three principal values and corresponding axes orientation have been determined and reported previously. Besides, the much weaker resonance lines found in spectra close to those coming from the Ce1 and Ce2, and following them under crystal rotation with respect to the direction of an external magnetic field, have been revealed as well. They were classified as doublets produced by the exchange coupled Ce 3+ ions, creating the Ce1–Ce1, Ce2–Ce2 and Ce1–Ce2-like dimers. The corresponding spin–spin coupling constants were estimated. They are in the range 0.04–0.4 cm −1 . The Ce1, Ce2 and total dimer centers populations were calculated as 89%, 4.5% and 6.5%, comparing integral intensities of corresponding resonance lines.

Composite material consisting of highly luminescent Zn(Cd)O:Ga powder embedded in the silica matrix was prepared. It was found out that ZnO:Ga with less developed crystals (i.e. annealed at lower temperatures) is more prone to interact with the SiO 2 matrix and form zinc silicates, which in turn resulted in the decrease in the excitonic emission. Pre-annealing of the powders at temperatures above 600 °C prevented the interaction with the SiO 2 matrix. ZnO:Ga with well-developed crystals at such a high temperatures was not affected by the matrix and retained its properties, i.e. high radioluminescence intensity and ultrafast sub nanosecond photoluminescence decay. Introducing Cd into the ZnO lattice caused observable red shift in the excitonic luminescence, without negatively affecting the total intensity or the decay.

Luminescent properties and singlet oxygen production using CeF 3 :Tb 3+ -based nanoparticles modified with SiO 2 and protoporphyrin IX (PpIX) were studied. CeF 3 :Tb 3+ nanopowder was prepared via sol–gel route, with subsequent surface coating by SiO 2 layer and the conjugation with photosensitive PpIX molecules. Radioluminescence spectra suggest an energy transfer from Ce 3+ to Tb 3+ ions and from Tb 3+ to molecules of PpIX photosensitizer. The energy transfer was confirmed by photoluminescence decay curves. Singlet oxygen production was detected using a reaction of 1 O 2 with 3’-(p-aminophenyl) fluorescein (APF) chemical probe after X-Ray excitation. Qualitative changes in time resolved photoluminescence spectra in the region of 520 nm indicate 1 O 2 generation. Studied nanocomposites may be good candidates for the application in X-ray induced photodynamic therapy.

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.

This paper reports on the preparation and growth of Eu-doped strontium iodide ( ${\rm SrI}_{2}$ ) single crystals by modified micro-pulling-down method. Influence of the ${\rm Eu}^{2 + }$ and ${\rm Eu}^{3 + }$ (introduced in form of ${\rm EuI}_{2}$ and ${\rm EuCl}_{3}$ ) on the luminescence and scintillation properties is analyzed. Sufficient optical quality of prepared single crystals was obtained allowing further characterization of their absorption, radio- and photoluminescence spectra. Photoluminescence and scintillation decay time of grown ${\rm SrI}_{2}$ crystals irradiated under $\gamma $ -ray source were evaluated as well.

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.

Ce-doped lutetium aluminum garnet Lu3Al5O12 (LuAG) nanoceramics were fabricated at 1600 °C and 1700 °C by spark-plasma sintering (SPS) method from nano-powders prepared by radiation synthesis. Both undoped and Ce-doped LuAG ceramic samples were also prepared from the nano-powders at 1700 °C with significantly increased pre-heating rate. The backscattered electron images revealed large amount of pores in all the Ce-doped samples causing their significant opacity. On the other hand, very large grains and no pores were revealed in the undoped sample, which was the only transparent one. The radioluminescence measurements revealed superior overall scintillation efficiency of the samples sintered at the temperature 1700 °C, and their defect emission in the UV region was ascribed to oxygen-vacancy-related defects such as F+ centers. The photoluminescence decay of the defect emission was characterized by an extremely fast decay time of a few nanoseconds. Influence of sintering procedure and subsequent annealing on the luminescence and scintillation properties is discussed.

In the presented review paper, new potentially interesting material family, RE-doped ternary sulfides ALnS 2 (RE=Ce, Pr, Sm, Eu, Tb, Tm; A=Rb, K; Ln=La, Gd, Lu, Y) is discussed. Their synthesis is described and the structural and optical properties, characterized by methods of X-ray diffraction, time-resolved luminescence spectroscopy and electron paramagnetic resonance, are summarized and reviewed especially with respect to the influence of their composition. All samples discussed were synthesized in the form of transparent crystalline hexagonal platelets by chemical reaction under the flow of hydrogen sulfide. Their luminescence characteristics, including absorption, radioluminescence, photoluminescence excitation and emission spectra and decay kinetics, were measured and evaluated in a broad temperature (8–800 K) and concentration (0.002–20% of dopants) range. The application potential of mentioned compounds in the field of white LED solid state lightings or X-ray phosphors is thoroughly discussed.

For the first time, photoluminescence of PbWO4:Bi crystals with different bismuth contents is studied by the time-resolved spectroscopy methods at 4.2–300 K. Photo-thermally stimulated processes of electron and hole centers creation under selective UV irradiation of the crystal in the 3–5 eV energy range and the 4.2–200 K temperature range are clarified, and the optically created electron and hole centers are identified by the thermally stimulated luminescence and electron spin resonance methods. The 2.2 eV emission of PbWO4:Bi crystals, excited in the Bi3+-related absorption band overlapped with the exciton absorption band, is shown to be of an excitonic origin and is suggested to arise from the excitons of two types localized around two different Bi3+-related centers. No emission, arising from the electron transitions between the energy levels of Bi3+ ions, is observed. Photoexcitation of PbWO4:Bi crystals in the Bi3+-related absorption region results also in the creation of electron and hole centers. Three new paramagnetic centers are identified: (i) two holes trapped at two regular oxygen ions located close to a Bi3+ ion and a lead vacancy VPb (the {2O– − Bi3+ − VPb}-type hole centers); (ii) Bi4+ centers; and (iii) the O−-type hole centers. The concentration of single (non-compensated) oxygen and lead vacancies as traps for electrons and holes, respectively, is found to be small. The processes resulting in the appearance of the Bi3+-related localized exciton emission and in the creation of Bi-related electron and hole centers are discussed.