Gulnara Beketova

A purification and growth process for alkali halide crystals (AHCs) is demonstrated using KCl: Li as a model system and employing an experimental crystal growth setup manufactured by Across International, USA. The process involves the following sequential stages: (i) deposition of a thin pyrolytic carbon coating (pyrolysis) onto the inner surface of a quartz ampoule in order to suppress the adhesion of molten alkali halide compounds (AHCs) to the ampoule walls; (ii) generation of a high vacuum (10 ^–6 Тоrr) inside the quartz reactor to purify the alkali halide raw materials from oxygen-containing impurities; (iii) establishment of an argon atmosphere (1.1–1.3 bar) and the quartz ampoule shielding as a technological approach for suppressing the evaporation of aggressive halogen vapors. Flame photometry, absorption spectroscopy, and luminescence spectroscopy analyses demonstrate that the KCl crystal matrix was purified from oxygen-containing impurities (OH) down to 0.2 ppm, divalent impurities (Me ²⁺ ) down to 0.1 − 0.3 ppm, and alkali-metal homolog cations (Li ⁺ , Na ⁺ ) down to 1–3 ppm. Unique capabilities of the facility were further realized in the growth of KCl single crystals doped with hygroscopic lithium ions. Enhanced scintillation and dosimetric properties of KCl: Li crystals were demonstrated.

The article presents the synthesis and characterization of double halide perovskites (DHPs) with the nominal composition Cs₂Ag_0.2Na_0.4In_0.6M_0.4Cl₆ (M = Si, Ti, Zr), including photoluminescence (PL), photoluminescence excitation (PLE) spectra measured over a range of temperatures and kinetics of luminescence. The materials were synthesized via a hydrothermal method. The phase purity and elemental composition of the synthesized perovskites were confirmed by X-ray diffraction (XRD), Rietveld refinement, scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS) and elemental analysis, which demonstrated that the samples showed a close match to the target stoichiometry. The PL spectra exhibit a systematic shift toward the lower-energy region with substitution from Si to Zr, correlating with the progressive increase in the ionic radii of the substituting cations. All samples display broad, asymmetric emission bands, characteristic of self-trapped excitonic (STE) states. Temperature-dependent PL measurements reveal a gradual decrease in emission intensity with increasing temperature for all samples. The maximum emission intensity is observed in the range of ~160–200 K, corresponding to optimal conditions for radiative recombination, whereas the lowest intensity is recorded at ~80–100 K, where thermal activation of radiative centers is minimal. An increase in temperature is accompanied by a red shift in the PL bands across all compositions. In the Ti-doped DHP, a pronounced blue shift at low temperatures is observed, which can be attributed to the involvement of Ti³⁺-related electronic states. An analysis of the activation energy of thermal luminescence quenching and the results of time-resolved spectroscopy revealed the activation of thermal processes in the titanium-containing sample and their rapid decay, whereas replacing titanium with silicon leads to more stable luminescence in the crystal under study. Thus, the enhanced luminescence characteristics of double halide perovskites doped with Ti, Si, and Zr highlight their potential for advanced photonic and optoelectronic applications.

The article presents the results of measuring the luminescence spectra, luminescence excitation spectra and luminescence spectra under high pressures for LaAlO₃:Pr with concentration of 1%. The materials were synthesized by solid phase synthesis. Diffraction pattern is fully relates to LaAlO₃ phase. The photoluminescence spectra show the main energy transitions. The change in the position of the main bands under the hydrostatic pressure of 23, 55, 160 and 191 kBar was demonstrated. The main band at 491 nm is slightly red-shifted, while the line at 605 nm is shifted to the high-energy part of the spectrum. The intensity of all bands increases with increasing hydrostatic pressure. The dynamics of changes in the intensities of maxima and emissions from different transitions are analyzed. Studies of luminescence under high hydrostatic compression are important in observing changes in the internal structure and electronic states of materials under the influence of high pressure, studying internal processes such as recombination of electrons and holes, transitions between energy levels and the release of photons. Understanding the changes that occur under compression can help researchers develop new materials with unique properties.