The properties of electrically conductive CsPbBr3 single crystals obtained from the melt have been studied. According to the results of Raman spectra, the covalent bonds in the octahedra [PbBr6](4-) have different strengths in different directions. This bond anisotropy promotes the formation of bromine vacancies located along selected crystallographic directions, which become sites of crystal degradation and the formation of Cs4PbBr6 microformations. A potential barrier at the boundary between the Cs4PbBr6 single crystal and the Cs4PbBr6 microformations was found.

Luminescence probes that facilitate multimodal non-contact measurements of temperature are of particular interest due to the possibility of cross-referencing results across different readout techniques. This intrinsic referencing is an essential addition that enhances accuracy and reliability of the technique. A further enhancement of sensor performance can be achieved by using two luminescent ions acting as independent emitters, thereby adding in-built redundancy to non-contact temperature sensing, using a single readout technique. In this study we combine both approaches by engineering a material with two luminescent ions that can be independently probed through different readout modes of non-contact temperature sensing. The approach was tested using Al2O3 co-doped with Cr3+ and Mn4+, exhibiting sharp emission lines due to 2E → 4A2 transitions. The temperature sensing performance was examined by measuring three characteristics: temperature-induced changes of the intensity ratio of the emission lines, their spectral position, and the luminescence decay time constant. The processes responsible for the changes with temperature of the measured luminescence characteristics are discussed in terms of relevant models. By comparing temperature resolutions achievable by different modes of temperature sensing it is established that in Al2O3-Cr,Mn spectroscopic methods provide the best measurement accuracy over a broad temperature range. A temperature resolution better than ±2.8 K can be achieved by monitoring the luminescence intensity ratio (40-145 K) and the spectral shift of the R-line of Mn4+ (145-300 K range).

The degradation processes under the influences of atmosphere moisture, current passage, and ultraviolet radiation were studied in CsPbBr3 single crystals grown by the vertical Bridgman-Stockbarger method. According to the results of luminescent and photoelectric measurements the formation of CsPb2Br5 and Cs4PbBr6 phases in the result of CsPbBr3 crystal degradation was observed. Based on the spectral measurements of the photodiffusion current, the position of the energy levels of the intrinsic structural defects V-Br and (V-Br + e) in the forbidden bandgap of the CsPbBr3 crystal and the change of the defects concentration was determined. It is assumed that the darkening of the crystals in the degradation process during the passage of current is due to the formation of metallic phases of lead. (C) 2021 Published by Elsevier B.V.

In order to identify the mechanisms of the scintillation process under the size confinement, the study of luminescence parameters under the optical and X-ray excitation of SrF2:Ce nanoparticles obtained by the chemical precipitation method has been performed. The main features of the X-ray-excited and photoluminescence spectra of SrF2-Ce nanoparticles of 82 nm and 65 nm sizes well match with the luminescence parameters of bulk materials and reveal the characteristic doublet emission band of Ce3+ ions with maximums at 310 and 329 nm, which correspond to the electronic transitions from 5d-levels to the 4f ground state of cerium ion (F-2(5/2) and F-2(7/2)) split by spin-orbital interaction. In the luminescence excitation spectra in the matrix transparency range between 3.9 and 7.1 eV, the excitation bands corresponding to intracenter 4f-5d-absorption transitions of cerium ions are observed. The observed drop at 10.7 eV in the range of exciton reflection maximum is associated with the near-surface radiation-free loss of excitation energy. The structure of luminescence excitation spectra in the band-to-band region (12-20 eV) corresponds to the combined density of states of valence band and conduction band. The excitation threshold at 21.9 eV is related to the multiplication of electronic excitations in particular with the creation of secondary electrons. The intensity and time parameters of the luminescence, the features of the luminescence excitation spectra essentially depend on the nanoparticle sizes. The decrease of the luminescence intensity of cerium ions in the case of intracenter excitation is due to the resonant transfer of excitation energy to surface defects. The decrease of the luminescence decay time constant becomes significant for nanoparticles of sizes smaller than 20 nm, which indicates the dominant role of surface defects in this process. In the case of recombination luminescence (h(v) > E-g), an additional quenching channel appears caused by the escape of electrons from the nanoparticle volume when the thermalization length exceeds the nanoparticle size.

8nm and 16 nm YVO4:Eu nanoparticles have been synthesized by the low temperature chemical method and annealed at T - 800 degrees C. The nanocomposite films based on scintillation polystyrene loaded with YVO4:Eu (40 wt%) nanoparticles have been obtained. The luminescence- kinetic characteristics of YVO4:Eu nanoparticles and nanocomposites have been investigated. The luminescence of the polystyrene nanocomposite loaded with YVO4:Eu (40 wt%) nanoparticles reveals the bands characteristic of the luminescent impurities of p- Terpinil (370 nm), POPOP (420 nm) and of YVO4:Eu nanoparticles (D-5(0) -> F-7(1) band) at 590 nm, the band D-5(0) -> F-7(2) at 617 nm, and the weaker D-5(0) -> F-7(3) (590 nm) and D-5(0) -> F-7(4) (700 nm) bands. The intensity of X-ray excited luminescence of the polystyrene composites loaded with YVO4:Eu nanoparticles (40 wt%) increases 3 times. The luminescence decay kinetic of the polystyrene composite in the case of X-ray excitation reproduces the decay kinetic curve of pure polystyrene scintillator with the time constant of similar to 2.7 ns. The contribution of Eu3+ luminescence to the scintillation pulse is insignificant due to the significant decrease of the luminescence intensity of Eu3+ centers with decreasing nanoparticle sizes, and the decay time constant of Eu3+ luminescence (tau = 0.8 ms) is significantly greater than the duration of the main scintillation pulse. The increase in the detection efficiency of the ionizing radiation by the nanocomposite is caused by the increase in the absorption capacity. The increase in absorption is caused by the presence of heavy inorganic YVO4:Eu nanoparticles compared to the polystyrene matrix without any nanoparticles and by the transfer of excitation energy from embedded nanoparticles to the polystyrene matrix due to the electron escape from YVO4:Eu nanoparticles into the host matrix. The discrepancy between the calculated and observed efficiency detection for the nanocomposite is due to the aggregation of nanoparticles, which prevents the escape of electrons from nanoparticles into the polystyrene matrix.