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For the first time, hafnia (HfO2) nanoparticles have been produced by photochemical synthesis. The photochemical route has been proven to be scalable, affordable, and straightforward to create monoclinic HfO2 nanoparticles with a size of tens of nanometers. The exploitation of this route offers a chance to create large amounts of dense nanoparticles with reduced costs and time of production for future creation of large area composite scintillators for fast timing techniques. Specific annealing treatments from 450 °C to 1000 °C have been targeted to tune the structural and morphological properties and optimize the luminescence of the nanoparticles. Hafnia nanoparticles annealed at low temperature display an amorphous structure. After thermal treatment at 1000 °C, HfO2 nanoparticles crystallize into a monoclinic phase, as evidenced by thermal analyses and X-ray diffraction. Radioluminescence and photoluminescence of HfO2 have been investigated at room temperature and 77 K. The emission band of hafnia covers a range from 300 to 600 nm and it can be attributed to defects within the matrix. In particular, the highest radioluminescence intensity appears in the crystalline sample annealed at 1000 °C, thanks to the higher crystallinity degree and the reduction of non-radiative channels and quenching defects. Photoluminescence and scintillation decay have evidenced the presence of the fast decay in the nanosecond time range. Thus, due to their size, density, and spectroscopic and timing features, monoclinic hafnia nanoparticles obtained by photochemical synthesis are attractive for potential creation of large area scintillating composites. [ABSTRACT FROM AUTHOR]

Lutetium oxyorthosilicate Lu2SiO5 (LSO) and pyrosilicate Lu2Si2O7 (LPS) activated by Ce3+ or Pr3+ are known to be effective and fast scintillation materials for the detection of X-rays and γ-rays. Their performances can be further improved by co-doping with aliovalent ions. Herein, we investigate the Ce3+(Pr3+) → Ce4+(Pr4+) conversion and the formation of lattice defects stimulated by co-doping with Ca2+ and Al3+ in LSO and LPS powders prepared by the solid-state reaction process. The materials were studied by electron paramagnetic resonance (EPR), radioluminescence spectroscopy, and thermally stimulated luminescence (TSL), and scintillation decays were measured. EPR measurements of both LSO:Ce and LPS:Ce showed effective Ce3+ → Ce4+ conversions stimulated by Ca2+ co-doping, while the effect of Al3+ co-doping was less effective. In Pr-doped LSO and LPS, a similar Pr3+ → Pr4+ conversion was not detected by EPR, suggesting that the charge compensation of Al3+ and Ca2+ ions is realized via other impurities and/or lattice defects. X-ray irradiation of LPS creates hole centers attributed to a hole trapped in an oxygen ion in the neighborhood of Al3+ and Ca2+. These hole centers contribute to an intense TSL glow peak at 450–470 K. In contrast to LPS, only weak TSL peaks are detected in LSO and no hole centers are visible via EPR. The scintillation decay curves of both LSO and LPS show a bi-exponential decay with fast and slow component decay times of 10–13 ns and 30–36 ns, respectively. The decay time of the fast component shows a small (6–8%) decrease due to co-doping. [ABSTRACT FROM AUTHOR]

The glass‐ceramics (GC) of gadolinium aluminum gallium garnets with the expected composition of Gd3Al3Ga2O12:Ce and Gd3Al3Ga2O12:Ce,Be (GAGG:Ce and GAGG:Ce,Be, respectively) are fabricated by crystallization from the Gd2O3–Al2O3–Ga2O3–CeO2–SiO2–BeO (Gd:Ga:Al ratio is close to 3:2:3) glasses. The influence of Be2+ co‐doping (including doping level) on the luminescent properties of the GAGG is demonstrated. In particular, Be co‐doping results in the suppression of the Ce3+‐related radioluminescence (RL) and as a consequence, the light yield is lowered as well. The conclusion is made that Be2+ creates effective electron or hole trapping centers. [ABSTRACT FROM AUTHOR]

The scintillation characteristics of Lu0.8Gd2.2 (Al5–xGax)O12:Ce,Mg (x = 2.6 and 3) single crystals grown by the micropulling down method are investigated. The light yield of 27600 photons/MeV obtained for Lu0.8Gd2.2Al2Ga3O12:Ce,Mg is higher than that of 25 400 photons/MeV obtained for Lu0.8Gd2.2Al2.4Ga2.6O12:Ce,Mg. The photoluminescence and scintillation decays measured at room temperature (RT) for Lu0.8Gd2.2Al2Ga3O12:Ce,Mg are faster than those for Lu0.8Gd2.2Al2.4Ga2.6O12:Ce,Mg. Temperature dependence of radioluminescence (RL) intensity indicates a lower quenching temperature for Lu0.8Gd2.2Al2Ga3O12:Ce,Mg. Coincidence time resolution of a Lu0.8Gd2.2Al2Ga3O12:Ce,Mg detector in coincidence experiment with a BaF2 detector was measured to be 410 ps. The afterglow and thermally stimulated luminescence (TSL) characteristics below RT are also measured. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electron and hole trapping centers were observed in the molybdenum doped zinc oxide rods. • Electron trapping centers were mostly molybdenum-based. • Holes were trapped at oxygen complexes. • Exciton- and defect-related emission bands appear suppressed after X-ray irradiation. • Zinc vacancies participated in the charge trapping processes. Peculiarities of the point defects creation under X-ray irradiation and the influence of Mo doping in ZnO powders of nano- and microrods fabricated by the hydrothermal growth method (as-grown and annealed in air) were studied in detail. Correlated experiments of X-ray diffraction, X-ray photoelectron spectroscopy, electron paramagnetic resonance, photo- and radioluminescence as well as thermally stimulated luminescence allowed us to trace the effect of the molybdenum inclusion on the phase purity of synthesized materials and the role of Mo in the creation of X-ray induced point defects. Oxygen-based hole trapping centers (most probably involving interstitial oxygen) as well as Mo5+-based electron trapping centers were observed and their thermal stabilities were studied. Some amount of the hole trapping centers seemed to be directly connected with the creation of Mo5+. Zinc vacancies and the Mo5+ centers up to some extent were assumed to act as recombination centers for the holes released from the hole trapping centers. The X-ray irradiation also affects the luminescence properties of the ZnO:Mo samples – the intensity of the luminescence bands in general becomes weaker. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Luminescence and scintillation properties of Lu 2 YAl 2.5 Ga 2.5 O 12 :Ce,Mg (0.02, 0.05 %) garnet crystals grown by the micro-pulling down method were investigated. The onset temperature for luminescence quenching at ∼365 K is determined from the temperature dependence of photoluminescence decay time. At room temperature, the Mg (0.05 %) sample exhibits high integral scintillation efficiency of ∼445 % of BGO crystal, light yield value of 23,500 photons/MeV, and fast scintillation decay times of 20 ns (15 %) + 54 ns (85 %). The higher radioluminescence intensity of the Mg (0.05 %) sample correlates with an appearance of its lower themally-stimulated luminescence intensity in 77–500 K range. • Luminescence and scintillation properties of Lu 2 YAl 2.5 Ga 2.5 O 12 :Ce,Mg (Mg = 0.02 %, 0.05 %) crystals are investigated. • Both crystals show onset of luminescence quenching at 365 K. • Lu 2 YAl 2.5 Ga 2.5 O 12 :Ce,0.05%Mg shows light yield of 23,500 photons/MeV. • Lu 2 YAl 2.5 Ga 2.5 O 12 :Ce,0.05%Mg shows scintillation decay time of 20 ns (14 %) + 54 ns (86 %). • Thermoluminescence characteristics are investigated. [ABSTRACT FROM AUTHOR]

The scintillation characteristics of Gd 3 Al 2 Ga 3 O 12 :Ce, Li (GAGG:Ce,Li) and Gd 3 Al 2 Ga 3 O 12 :Ce, Mg (GAGG:Ce,Mg) single crystals were compared. Radioluminescence spectra and photoluminescence decay curves were measured at various temperatures between 77 and 500 K to investigate the thermal luminescence quenching. At 662 keV γ rays, the LY value of 35,400 photons/MeV and energy resolution of 6.9% obtained for GAGG:Ce, Li are superior to those of 24,200 photons/MeV and 9.5% for GAGG:Ce,Mg. Scintillation decays are approximated by a double exponentials with a fast principal decay component of 47 ns (83%) for GAGG:Ce, Mg and 90 ns (86%) for GAGG:Ce,Li. Coincidence time resolution of 282 ps obtained for GAGG:Ce, Mg is better than that of 389 ps for GAGG:Ce,Li. GAGG:Ce, Mg shows a much lower afterglow and thermally stimulated luminescence intensity with respect to GAGG:Ce,Li. • Scintillation properties of Li+ and Mg2+ -codoped Gd 3 Al 2 Ga 3 O 12 :Ce are compared. • Gd 3 Al 2 Ga 3 O 12 :Ce, Mg exhibits better timing performance. • Gd 3 Al 2 Ga 3 O 12 :Ce, Mg shows lower afterglow and TSL intensity. • Gd 3 Al 2 Ga 3 O 12 :Ce, Li exhibits high light yield and good energy resolution. [ABSTRACT FROM AUTHOR]

Optical and scintillation characteristics of Mg2+-codoped Lu 2 Y(Al 5-x Ga x)O 12 :Ce (x = 2, 3) multicomponent garnet crystals grown by the micro-pulling down method were investigated. At RT, the shortening of scintillation decay time and a decrease of light yield (LY) value measured for a higher Ga containing samples can be explained by thermal ionization of the Ce3+ 5d 1 excited state. At 662 keV γ-rays, Lu 2 YAl 3 Ga 2 O 12 : Ce, 0.05%Mg exhibits high LY value of 29,000 ph/MeV along with scintillation decay times of 50 ns (86%) + 73 ns (14%). Co-doping with larger Mg2+ content leads to a decrease of LY value, scintillation decay time, and afterglow level. Radioluminescence quenching observed at low temperature region in correlation with large thermoluminescence peaks can be caused by trapping of electrons at intrinsic shallow traps. • Luminescence and scintillation properties of Lu 2 Y(Al 5-x Ga x)O 12 :Ce,Mg (x = 2, 3) crystals are investigated. • Temperature dependencies of photo-and radioluminescence are presented. • Lu 2 YAl 3 Ga 2 O 12 :Ce,0.05%Mg shows high light yield of 29,000 photons/MeV. • Lu 2 YAl 3 Ga 2 O 12 :Ce,0.05%Mg shows quenching temperature at 435 K due to thermal ionization. • Afterglow and thermoluminescence characteristics are investigated. [ABSTRACT FROM AUTHOR]

Mg2+-codoped Y 0.6 Gd 2.4 Al 2 Ga 3 O 12 :Ce (YGAGG:Ce,Mg) single crystal was grown by the Czochralski method and its luminescence and scintillation properties were investigated. Temperature dependence of radioluminescence (RL) yield and photoluminescence (PL) decay time was measured, and activation energy of thermal ionization process was determined from temperature-dependent PL decay time measurement. YGAGG:Ce,Mg exhibited high X-ray excited RL yield almost 5 times higher than BGO reference scintillator. Its light yield of 41,500 ph/MeV and scintillation decay times of 12 ns (2%) + 52 ns (65%) + 207 ns (33%) were measured under excitation with 662 keV γ rays from 137Cs source. Afterglow and thermally stimulated luminescence characteristics are also investigated. • Luminescence and scintillation properties of Y 0.6 Gd 2.4 Al 2 Ga 3 O 12 :Ce,Mg crystal are investigated. • Temperature dependence of photo-and radioluminescence are presented. • Y 0.6 Gd 2.4 Al 2 Ga 3 O 12 :Ce,Mg shows high light yield of 41,500 photons/MeV. • Luminescence quenching above RT can be caused by thermal ionization. • Afterglow and thermoluminescence characteristics are investigated. [ABSTRACT FROM AUTHOR]

Luminescence and scintillation characteristics of Mg2+-codoped (Lu x Gd 3-x)Al 2.4 Ga 2.6 O 12 :Ce (x = 0.2–0.8) garnet crystals grown by the micro-pulling down method are investigated. The Ce3+ 5d 1 → 4f luminescence is blue-shifted with increasing Lu content due to the decrease in crystal field splitting of the 5 d levels. With increasing Lu content, the shortening of scintillation decay time accompanied with a decrease of LY value as measured at room temperature can be explained by thermal ionization of the Ce3+ 5d 1 excited state. Co-doping with Mg2+ results in the shortening of scintillation decay time, the reduction of LY value and afterglow intensity. At low temperature the radioluminescence quenching is observed in correlation with large thermoluminescence peaks, which can be attributed to the localization of electrons at intrinsic shallow traps. • Luminescence and scintillation of (Lu,Gd) 3 Al 2.4 Ga 2.6 O 12 :Ce, Mg crystals are investigated. • Temperature dependence of photo-and radioluminescence are presented. • Luminescence quenching above RT can be caused by thermal ionization. • Afterglow and low-temperature TL characteristics are investigated. [ABSTRACT FROM AUTHOR]