Chemical Tuning, Pressure, and Temperature Behavior of Mn4+ Photoluminescence in Ga2O3-Al2O3 Alloys.

In this study, we carried out a detailed investigation of the photoluminescence of Mn4+ in Ga2O3-Al2O3 solid solutions as a function of the chemical composition, temperature, and hydrostatic pressure. For this purpose, a series of (Al1-xGax)2O3:Mn4+,Mg phosphors (x = 0, ..., 0.1.0) were synthesized and characterized for the first time. A detailed crystal structure analysis of the obtained materials was done by the powder X-ray diffraction technique. The results of the crystal structure and luminescence studies evidence the transformation of the ambient-pressure-synthesized material from the rhombohedral (α-type) to monoclinic (ß-type) phase as the Ga content exceeds 15%. Spectroscopic features of the Mn4+ deep-red emission, including the temperature-dependent emission efficiency and decay time, as well as the possibility of their tuning through chemical pressure in each of these two phases were examined. Additionally, it has been shown that the application of hydrostatic pressure of ≥19 GPa allows one to obtain a corundum-like α-Ga2O3:Mn4+ phase. The luminescence properties of this material were compared with ß-Ga2O3:Mn4+, which is normally synthesized at ambient pressure. Finally, we evaluated the possibility of application of the studied phosphor materials for low-temperature luminescence thermometry.

Sol-Gel-Prepared Nanoparticles of Mixed Praseodymium Cobaltites-Ferrites.

Two series of nanocrystalline powders of PrCo1 - x Fe x O3 (x = 0.1, 0.3, 0.5, 0.7 and 0.9) of high purity were obtained by sol-gel citrate method at 700 and 800 °C. The formation of continuous solid solution with an orthorhombic perovskite structure (sp. group Pbnm) was observed. A peculiarity of the PrCo1 - x Fe x O3 solid solution is the lattice parameter crossovers, which occurred at certain compositions and revealed in the pseudo-tetragonal or pseudo-cubic metric. An average crystallite size of the PrCo1 - x Fe x O3 samples estimated from the analysis of the angular dependence of the X-ray diffraction (XRD) line broadening varies between 30 and 155 nm, depending on the composition and synthesis temperature.