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Using content analysis and the Python programming environment, we have found a number of general relationships determining the thermal properties of fluoride and modified fluoride glasses. Their compositions have been classified according to their glass transition temperature (Tg) and the difference between their crystallization onset temperature (Tx) and glass transition temperature: Tx – Tg. The use of Kauzmann's rule for fluoride glasses, unmodified and modified with other halogens, has been shown to be more reliable if the Tg/Tm ratio is used, compared to the Tg/Tl ratio. We have qualitatively assessed how anion modification influences characteristic temperatures (glass transition temperature Tg, crystallization onset temperature Tx, crystallization peak temperature Tc, melting onset temperature Tm, and liquidus temperature Tl) and crystallization stability criteria (Hruby criterion K, Saad–Poulain criterion S, reduced thermal stability interval H, thermal stability interval Tx – Tg, and reduced glass transition temperatures Tg/Tm and Tg/Tl). [ABSTRACT FROM AUTHOR]

Ceramic samples of Y3MgGa3SiO12, Y3MgGa2AlSiO12, and Y3MgGaAl2SiO12 multicomponent garnets doped with 0.2 at % Cr3+ have been obtained by high-temperature solid-state synthesis. In the luminescence spectra of the synthesized garnet samples, overlapping broadband luminescence is observed in the far red spectral region caused by the 4T2 → 4A2 transition in Cr3+ ions, and a narrow band is observed in the range of 690–700 nm, corresponding to the zero-phonon line of the 2Е → 4A2 transition in Cr3+. The narrow-band and broad-band parts of the spectra are attributed to radiation from two different types of chromium centers, which are in octahedral coordination with different distortion degrees and strength of the crystal field. This results from the presence of two ions at the octahedral position of these garnets, which differ significantly in crystal chemical properties, namely, Mg2+ and Ga3+ (Al3+). The studied phosphors, which have broadband luminescence in the phytoactive far red region of the spectrum, have the potential for use in greenhouse LED lamps. [ABSTRACT FROM AUTHOR]

Ceramic LiAl5O8 lithium aluminate spinel materials doped with trivalent chromium ions have been prepared by high-temperature solid-state synthesis. The intensity, spectral shift, and width of two zero-phonon luminescence lines (R lines) due to transitions from the 2E excited state to the 4A2 ground state of Cr3+ ions have been measured as functions of temperature in the range 80–295 K. Analysis of luminescence and luminescence excitation spectra of the ceramics points to severe local lattice distortion around the Cr3+ ions, which shows up, in particular, as large inhomogeneous broadening of the zero-phonon Cr3+ luminescence lines. The temperature dependences of the relative intensity, spectral shift, and width of the two zero-phonon lines can be sufficiently well described in terms of existing models for optical centers in crystals. The feasibility of using these temperature dependences for noncontact luminescence thermometry is assessed. Analysis of the data obtained in this study provides no way to uniquely identify the observed zero-phonon lines as due to transitions from two sublevels of the 2E state of a single type of chromium center (that is, as R1 and R2 lines) or transitions of two inequivalent chromium centers coupled by nonresonant energy transfer. [ABSTRACT FROM AUTHOR]

To study chemical transport and refine synthetic routes, single crystals of vanadium and zirconium diselenides were grown by the chemical transport reaction method using I2 and Cl2 as transporting agents. The thermodynamic parameters of chemical transport have been evaluated, and the mass transfer direction in a growth ampoule has been determined. The phase composition of the samples has been examined by X‑ray powder diffraction. Analysis of X-ray powder diffraction patterns of samples from the low- and high-temperature zones of the growth ampoule has confirmed the predictions based on thermodynamic calculations. With both transporting agents, ZrSe2 transport occurs from the cold to the hot zone of the ampoule, while the direction of VSe2 transport depends on the nature of the transporting agent. With I2 as a transporting agent, transport occurs from the hot to the cold zone of the ampoule, while with Cl2, in the opposite mass transfer direction is observed. Microphotographs of the samples are consistent with thermodynamic and X‑ray diffraction data. The results can be used to optimize the technology of producing layered transition metal dichalcogenides. [ABSTRACT FROM AUTHOR]

A process has been proposed for ZrSe2 crystal growth with the use of ZrOCl2 as a transport agent source. The crystals thus grown have been characterized by X-ray diffraction. It has been shown that, unlike in the case of vanadium and molybdenum diselenides, the use of zirconium chloride causes no increase in crystal size. A mechanism of the chemical vapor transport process involved is proposed. [ABSTRACT FROM AUTHOR]