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The CaWO4 crystal is a promising scintillation material for ionizing radiation detectors. Thermally stimulated luminescence, X-ray luminescence spectra, and decay time constants of the CaWO4 crystal were investigated to enhance our understanding of the factors governing the emission processes in this material and the potential utility of this crystal as a scintillators for cryogenic dark matter detection. X-ray luminescence spectra were recorded in the temperature range from 90 to 300 K. The maximum of the detected single band located around 2.80 eV (443 nm) is assigned to the emission inside of the anionic oxocomplexes (WO4)2-. The absence of a clearly defined green band, corresponding to the activator luminescence, indicates the high quality of the investigated CaWO4 crystal and absence of the impurities that would cause its appearance. The thermally stimulated luminescence (TSL) was measured after X- irradiation of a sample at 77 K and heating up to 310 K with a heating rate 0.1 K/s. The parameters of the TSL peaks observed in the calcium tungstate crystal were calculated. The conducted investigations provide evidence that the TSL band observed above 160 K results from the interaction between trapped electrons and self-localized holes (Vk centers). The peak at 220 K is attributed to a phototransfer process, whereby the trap responsible for the TSL peak at 308 K transfers its energy to shallower traps. The decay time values were determined for various luminescence components of CaWO4 arising due to irradiation with an 241 Am isotope. In particular, components with the short decay times (τ1= 3 ± 0.2 μs and τ2 = 10.25± 0.2 μs ) are considered primary and are attributed to the transitions within the tetrahedral complexes (WO4)2-distorted to C2v symmetry. [ABSTRACT FROM AUTHOR]

The CaWO4 crystal is a promising scintillation material for ionizing radiation detectors. Thermally stimulated luminescence, X-ray luminescence spectra, and decay time constants of the CaWO4 crystal were investigated to enhance our understanding of the factors governing the emission processes in this material and the potential utility of this crystal as a scintillators for cryogenic dark matter detection. X-ray luminescence spectra were recorded in the temperature range from 90 to 300 K. The maximum of the detected single band located around 2.80 eV (443 nm) is assigned to the emission inside of the anionic oxocomplexes (WO4)2-. The absence of a clearly defined green band, corresponding to the activator luminescence, indicates the high quality of the investigated CaWO4 crystal and absence of the impurities that would cause its appearance. The thermally stimulated luminescence (TSL) was measured after X- irradiation of a sample at 77 K and heating up to 310 K with a heating rate 0.1 K/s. The parameters of the TSL peaks observed in the calcium tungstate crystal were calculated. The conducted investigations provide evidence that the TSL band observed above 160 K results from the interaction between trapped electrons and self-localized holes (Vk centers). The peak at 220 K is attributed to a phototransfer process, whereby the trap responsible for the TSL peak at 308 K transfers its energy to shallower traps. The decay time values were determined for various luminescence components of CaWO4 arising due to irradiation with an 241 Am isotope. In particular, components with the short decay times (τ1= 3 ± 0.2 μs and τ2 = 10.25± 0.2 μs ) are considered primary and are attributed to the transitions within the tetrahedral complexes (WO4)2-distorted to C2v symmetry. [ABSTRACT FROM AUTHOR]

The paper reports the effect of low-temperature annealing (up to 150°C) and light irradiation from a quartz mercury lamp (up to 20 min) on the structural, optical, and electrical properties of Indium tin oxide (ITO) films. 0.8 μm thick ITO films were obtained by RF magnetron sputtering of a commercial target on the optically transparent glass substrates in an argon atmosphere without heating. Information about the morphology of the ITO films' surface was obtained and the surface parameters were calculated using the method of atomic force microscopy. It has been found that the low temperature annealing for one hour and short-term irradiation with a quartz mercury lamp lead to an increase in the average size of crystallites and root-mean-square (RMS) surface roughness, a decrease in the resistivity of ITO films as well as an increase in the optical transparency in the visible spectral range. After annealing the ITO film at 150°C, the average crystallite size and RMS roughness of the surface increased approximately three times, and after 20 min irradiation – approximately 1.6 times, respectively. The lowest optical transparency in the visible spectral range among the studied experimental samples was found to be for the non-annealed and non-irradiated ITO films, whereas the highest – for the samples annealed at the highest temperature (150°C) and irradiated for 5 min with the light from the DRT-125 lamp. On the basis of the analysis of optical absorption spectra of ITO films, we detected an increase in their optical band gap from 3.59 eV for the unannealed film up to 3.66 eV with an increase in the annealing temperature of the samples up to 150°C. The resistivity of ITO films decreases with an increase in the annealing temperature up to 150°C and with an increase in the irradiation time with a light of the quartz mercury lamp up to 20 minutes. These results may be useful in the engineering of electronic devices based on the materials of low thermal stability. [ABSTRACT FROM AUTHOR]

X-ray luminescence and scintillation characteristics of CsPbBr3 crystal from the perovskites family were investigated over the temperature range of 7-200 K. At low temperatures CsPbBr3 was found to be a very bright scintillator with the fast response demonstrating a very short decay time constant 1 ns at 7 K. The light output was measured to be 109 000 ±22 000 ph/MeV at excitation with α-particles of 241Am. The obtained results testify that CsPbBr3 is a very potent scintillation material, which would compete with the commercial analogues in the case of the cryogenic applications. Besides, the study has clarified the origin of the intense slow component observed below 70 K that would be considered an obvious disadvantage for the scintillator applications, since it causes an afterglow. It has been shown that the corresponding radiation is due to the impurities and capture centers. This implies possibility for elimination of the slow component by optimization of the material using an improved growth process. [ABSTRACT FROM AUTHOR]

microcomposite catalyst based on zinc oxide microstructures and silicon was synthesized for heterogeneous catalysis. ZnO microstructures with elements 6 μm in diameter, 15 μm long, were grown on conductive silicon (001) substrates by the vapor phase method. Methyl orange (C14H14N3NaO3S) was selected as an organic dye for testing the photocatalytic and photoelectrocatalytic properties of ZnO microstructures. The sample was placed in an aqueous solution of methyl orange in order to perform a photocatalytic decomposition of the dye. DRT-125 quartz lamp with a radiation power of no more than 26 W was used as the radiation source in the wavelength range from 315 to 400 nm. The sample with the aqueous solution of dye in a standard 3.5 ml quartz quvet was irradiated with the lamp at a distance of 10 cm from it. In order to perform the photoelectrocatalytic decomposition of the dye in the aqueous solution, an electric field of 1.5 V was applied between ZnO/Si and Al electrodes, that were simultaneously irradiated with UV for 5 cycles lasting 20 minutes (100 minutes). The degradation kinetics of the dye was determined by changing its concentration, on the basis of the optical density measurement at the absorption maximum of the dye (465 nm) using a Specord M 40 spectrometer. During the photocatalysis, the concentration of the dye decreased by 41 % in 100 min, and during the photoelectrocatalysis, by 59 % in 100 min. First-order kinetics was used for the kinetic analysis of the catalytic reactions. The reactions rate constants were found to be k = 5.1·10-3 min-1 in the case of the photocatalysis, and k = 8.8 ·10-3 min-1 in the case of the photoelectrocatalysis. The increase in the efficiency of the dye decomposition in the latter case was associated with a more efficient redistribution of charge when voltage (1.5 V) was applied and with a higher amount of hydroxyl radicals on the surface of the catalyst. [ABSTRACT FROM AUTHOR]

The influence of the Cu2+dopant on the temperature evolution of the optical absorption edge in the region of phase transitions of [(CH3 )2CHNH3 ]4 Cd3Cl10 (IPACC) ferroelastoelectric crystals was investigated. The relative amount of Cu2+ with respect to Cd2+ in the samples of [[CH3 ]2CHNH3 ]4Cd3Cl10:Cu (IPACCC) was examined using EDX analysis available in the scanning electron microscope and was found to be 0.6-0.1 %. The performed investigations ascertained a noticeable influence of the doping with Cu2+ ions on the electron- (exciton-) phonon interaction and respectively on the shape and temperature evolution of the optical absorption edge of IPACC crystals. It has been found that the characteristic parameters of the empiric Urbach's rule show anomalous behaviour at the phase transition point T2 = 293 K in IPACCC. It was shown that the low energy tail of the charge transfer band in this crystal is formed with the participation of internal vibrations of the metal-halogen complex. On the other hand, the low energy tail of the fundamental edge for both IPACC and IPACCC is formed with the participation of the internal vibrations of the metal-halogen complex or skeletal (or translational) vibration of IPA cation. [ABSTRACT FROM AUTHOR]

This article studies the peculiarities of the ferroelastic domain structure in [NH2(CH3)2]Al0.8Cr0.2(SO4)2×6H2O solid solutions. The domain structure was investigated using optical, atomic force and scanning electron microscopy. It has been shown that the investigated crystals predominately grow in a polydomain ferroelastic state. According to the data of the energy-dispersive X-ray analysis, in the case of a polydomain as-grown crystal, the neighbouring domains are characterized by different contents of chromium - 17.6% and 20% respectively. This means that due to different signs of mechanical stress in the two groups of domains, they will be characterized by noticeably different levels of metal ion substitution. Therefore, it has been found that the thermodynamic conditions of growth are highly stress-dependent and allow a variation of the Cr distribution within the sample volume. The peculiarities of the formation of the specific nano- and microcrystalline structure on the single crystal surface were also investigated. It has been found that if the humidity of the atmospheric air is relatively high, the nanocrystals of a distorted hexagonal shape appear on the surface, growing to the sizes of a few tens micrometers during 72 hours.A model describing the nature and dynamics of this process is proposed. [ABSTRACT FROM AUTHOR]

Wastewater treatment to remove organic impurities remains the most important task of water resources recovery facilities. A promising method of purification of water from the organic dyes is photocatalysis with semiconductor materials. The most known and popular photoactive materials are based on TiO2, WO3, Zn2SnO4 and ZnO. The catalysts based on ZnO are low cost, stable, non-toxic and do not require reactivation. A composite photocatalyst formed by a layer of ZnO nuclei with n-type electric conductivity covered with ZnO nanoflowers with n-type electric conductivity and porous silicon with p-type electric conductivity has been obtained. The photodegradation of dye in the presence of the composite photocatalysts based on the thin films and nanoflowers was investigated. The photocatalytic properties of ZnO materials were tested using the photocatalytic degradation of an aqueous solution of methyl orange dye serving as a model water contaminant. It has been found that the usage of nanoflowers leads to an improvement in the photocatalytic properties of the composites. An increase of about 30% in the efficiency of dye photodegradation, when a composite photocatalyst based on ZnO nanoflowers and porous silicon was used instead of a composite photocatalyst based on ZnO film and porous silicon, was found to be due to a larger effective surface area of ZnO nanoflowers. The morphology of the samples was examined using a scanning electron microscope-analyzer. [ABSTRACT FROM AUTHOR]

The paper is devoted to the study of X-ray luminescence spectra, the scintillation light output and the decay time characterisation of undoped ZnTe at low temperatures down to 6 K. Also, the photoconductivity spectrum in a visible region has been investigated. Due to significant thermal quenching, the scintillations at α-particle excitation were detected in the sample only below T = 150 K. The emission of the crystal is attributed to the radioactive recombination of the holes trapped by Zn vacancies and electrons captured at the shallow levels of impurities or defects. The scintillation efficiency increased with further cooling. It has been found that at α-particle excitation undoped ZnTe exhibits a fairly competitive light output equal to 117 ± 20% of CaWO4 reference scintillator. This finding underpins potential applications of ZnTe as a scintillation detector in the cryogenic experiments, particularly for the cryogenic search for neutrinoless double beta decay of 130Te. It has been also found that ZnTe will be attractive as a conventional scintillation detector at the temperature of liquid nitrogen (T = 77 K). At this temperature, the scintillator exhibits a reasonably short decay time and a sufficient scintillation response to particle excitation. A practical implementation of this idea poses no real technical challenge since photomultipliers and Si-based photodetectors are proven to operate reliably and efficiently at this temperature. [ABSTRACT FROM AUTHOR]

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