Abstract Charge trapping processes induced by the X-ray irradiation in the heavy Mo doped ZnO and MoO 3 micropowders synthesized by the hydrothermal growth method were investigated in detail. ...Electron paramagnetic resonance (EPR) and thermally stimulated luminescence (TSL) were applied in a correlated manner to discover the role of the Mo doping in the charge trapping processes in ZnO. Thermally unstable oxygen- and molybdenum-related charge trapping centers were studied. Molybdenum and oxygen created electron-hole trapping pairs in some cases were observed. Some part of the hole trapping centers seemed to be directly connected with the creation of Mo 5+ . The correlation between EPR and TSL data was found.
•Cs2HfCl6 single crystal preparation by miniaturized and standard Bridgman methods.•Cs2HfCl6 single-phase proved by XRD measurements.•Room temperature optical, luminescence, and scintillation ...properties of Cs2HfCl6.•Room temperature photoluminescence and scintillation decay kinetics of Cs2HfCl6.
Time and cost effective methods are highly desirable in research and development of new scintillators. Modern techniques like micro-pulling down (μ-PD) are suitable for material screening but are unfit for the growth of some crystals. These crystals must be grown by different methods that are usually very time demanding. Modification of halide μ-PD apparatus by custom made elements allowed us to grow cesium hafnium chloride (Cs2HfCl6) by vertical Bridgman method (VB) with significantly reduced growth time. Structural and optical properties of samples prepared from as-grown crystals were studied and compared to crystals grown by standard VB method. The X-ray diffraction confirmed the formation of cesium hafnium chloride single-phase and natural cleavage of the crystals along the (1 1 1) crystallographic plane. Photoluminescence emission, excitation, absorption, and radioluminescence spectroscopy revealed that the optical quality of the crystals grown by modified VB method was comparable to the quality of the crystals grown by standard VB method. Therefore we can use samples prepared by modified VB to estimate and optimize the performance of Cs2HfCl6 based crystals in scintillation detectors. This setup allows the time and cost-effective material screening and it is a powerful tool for the development of new halide based single crystal scintillators.
•ZnO:Er nano- and microrods were hydrogen or oxygen plasma treated.•Oxygen plasma treatment resulted in the crystalline Er2O3 phase and amorphous phase creation.•The removal of zinc from the ZnO ...surface is expected upon the plasma hydrogenation.•The participation of shallow donors and VZn in redistribution of charge have been proven.•Luminescence strongly depends on the type of plasma treatment and Er content.
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The effect of hydrogen and oxygen plasma treatment has been studied in erbium doped zinc oxide (ZnO:Er) nano- and microrods synthesized by the hydrothermal growth. It has been found that hydrogen plasma does not affect the phase purity of the samples whereas the oxygen plasma created the Er2O3 crystalline phase and led to partial powder amorphization only in the ZnO:Er(1%) sample. According to the X-ray photoelectron spectroscopy the modification/improvement of the ZnO surface structure can be expected after the oxygen plasma treatment. The exciton-related luminescence band was improved by the hydrogen plasma treatment whereas the VZn-related red luminescence band was moderated with the dependence on the Er content. The existence of energy transfer between the VZn and Zni was assumed. Correlated experiments of electron paramagnetic resonance and photoluminescence allowed to infer that hydrogen plasma also affects the Er3+ distribution and incorporation into ZnO rods. The red band appeared suppressed after oxygen plasma treatment while the exciton-related emission remained unchanged. The luminescence mechanism was proposed. Shallow donors also appeared affected by the plasma treatment in the low-level Er doped ZnO while the increased Er content seemed to protect them from the plasma influence. Moreover, plasma treatment resulted in the creation of new point defects.
This research deals with the luminescence and physical properties of Gd3(Ga,Al)5O12:Ce single crystal set and it is a complementary study to analogous (Y,Gd)3Al5O12:Ce and (Gd,Lu)3Al5O12:Ce single ...crystal sets. Those three groups of materials show similar luminescence and physical properties. In this research, the influence of substitution Ga for Al in Gd3(Ga,Al)5O12:Ce single crystals on the luminescence and scintillation characteristics as well as thermodynamical stability of the garnet phase is studied, and it is compared to (Y,Gd)3Al5O12:Ce and (Gd,Lu)3Al5O12:Ce single crystal sets. The unbalanced substitution Ga for Al makes garnet phase thermodynamically unstable and leads to the formation of the multiphase system with luminescence centers in UV and visible spectral ranges. The wavelength-dispersive X-ray spectroscopy, X-ray powder diffraction analysis, photoluminescence and decay kinetic measurements reviled all phase types within multiphase crystals. Temperature dependent measurements were applied to determine the quenching mechanism for Ce3+ luminescence. The timing characteristics are studied as the function of Ga content.
•Instability of the garnet phase and formation of the secondary phase inclusions discussed.•Temperature dependence of the decay time of Ce3+ emissions in garnet phase studied.•Energy transfer processes between secondary phase inclusion and target garnet phase discussed.
Multicomponent garnets (Y3−xGdxAl5−yGayO12) doped with Ce3+ ions are promising scintillators with a high density, fast response time and high light yield. To deepen the knowledge about the transfer ...stage of scintillation mechanism we discuss the energy migration and energy transfer processes in the set of undoped and Ce3+ activated multicomponent garnet single crystals. Temperature dependence of Gd3+ emission intensities as well as decay kinetics in Y3−xGdxAl5−yGayO12 (x,y=1,2,3) crystals point to the Gd3+→Gd3+ nonradiative energy migration, which is diffusion limited. Concentration quenching of Gd3+ emission occurs by energy migration to accidental impurities and/or structure defects. Temperature dependence of photoluminescence emission intensities and decay time measurements of Gd3+ as well as Ce3+ ions in Gd3Ga3Al2O12:Ce3+ single crystal reveal nonradiative energy transfer Gd3+→Ce3+ (including migration through Gd3+ sublattice) which is responsible for slow Ce3+ fluorescence decay component.
•Gd3+and Ce3+ luminescence features in Y3−xGdxAl5−yGayO12 measured.•Temperature dependence of emission spectra and decays studied.•Concentration dependence of Gd3+ emission and decay time features investigated.•Energy migration and transfer processes in Gd-sublattice discussed.
•Charge trapping processes were studied in LiCaAlF6:Eu,Na single crystals.•O- defect was detected in the undoped LiCaAlF6 single crystals aged in air.•Perturbed F2- hole trapping centers were ...detected in LiCaAlF6:Eu,Na single crystals.•Eu2+ ions predominately stay at Ca and only partly at Li sites.•Na co-doping results in decrease of the number of Eu2+ ions at Li site.
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 F2− pseudomolecular ion and O− (as a result of the contact with air). Their trap depths (Et) and frequency factors (f0) were determined as follows: EtPerturbedF2−=1.1±0.1eV, Et(O−)=1.7±0.1eV, f0PerturbedF2−=f0O−~1013s−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 Eu12+=EuCa2+ and the low-content Eu22+=EuLi2+. 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.
Abstract The paper discusses the process plan of the piston compressor package as well as the design of the gas separator. A technical proposal has been developed to improve the preliminary ...purification of the gas-liquid stream from hydrocarbon condensate, water and mechanical impurities. With the help of modern computer technologies, the design of the inlet device in the separator has been developed. The operation of the gas separator was simulated after the application developed by the devices. With the help of the program, the results of the study of the gas separator operation are presented.
•Cs2HfCl6 doped with Zr were prepared by vertical Bridgman method.•Room temperature scintillation properties of Cs2HfCl6:Zr were measured.•Zr doping induces red-shift in radioluminescence spectra.•Zr ...influences scintillation properties of Cs2HfCl6 at low concentrations.
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.
The InGaN multiple quantum wells (MQW) samples with the undoped and Si doped GaN barriers were grown by Metal Organic Vapour Phase Epitaxy (MOVPE). By comparing defects-related emission bands in the ...undoped GaN and InGaN layers, one may conclude that the band is complex in the InGaN layer, composed of at least two contributions peaking at 2.17 and 2.39 eV, respectively. In and Si affect the intensity of the defects-related band – the larger the In and/or Si concentration the stronger the band. The detailed investigation of the observed phenomena was conducted, and the observed peculiarities were explained.
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