Synthesis and kinetic study of fluorescent properties of solid solutions ($Y_{0,89-X}Yb_{0,1}Tm_{0,01}Ho_{X}$)$_3 Al_5O_{12}$

Background. At the present stage of development of science and technology there is an urgent need to find a material capable of efficient conversion of energy from near-infrared range to more than 2 microns. In the market of semiconductor devices today there are highly powerful light sources (incandescent lamps, light emitting diodes) capable of generating radiation in the range of 0.94-0.98 microns, however there are almost no phosphors and lasers comparable in effectiveness and accessibility, capable of being a source of radiation in the range greater than 2 microns. Existing luminescent and laser materials, capable of converting the energy in said band, are mainly made of glass, single crystals based on tellurides, sulfides that do not possess sufficient stability and chemical resistance, which severely limits their use in harsh environments such as high temperature, radiation exposure and high excitation densities. Polydisperse phosphors based on rare-earth aluminate garnet structure have long been known as a material having a large set of positive attributes, such as: high temperature, radiation and chemical resistance, and they positively manifest themselves at high densities or pumping excitement, possess excellent mechanical and optical properties. Materials and methods. In the course of the study the author synthesized polydispersed solid solutions by solid-phase synthesis at 1450 $^{\circ}$C for 24 hours. To obtain solid solutions, using the photodetector FPU-1 and MDR-204, the researcher detected Stokes IR-radiation in the area of 960-2200 nm with laser excitation wavelength of 940 nm. The phase composition of the synthesized samples was monitored by XRD (D-591 diffractometer, «Siemens» company, Cu K$\alpha$-radiation Ni filter). Kinetics IR-luminescence damping was studied using a photodetector FUP-2 and MDR-204. Results. The author synthesized the solid solutions of ($Y_{0,89-X}Yb_{0,1}Tm_{0,01}Ho_{X}$)$_3 Al_5O_{12}$, studied their luminescent and kinetic characteristics, determined the dependencies of the intensity of the Stokes IR-luminescence in the range of 0.96-1.1 microns and 1.62-2.04 microns, 2.04-2.15 microns, on the concentration of ions Ho${}$, when excited by laser light with a wavelength of 0.94 microns. The researcher analyzed the energy structures of ions of ytterbium, thulium, holmium. On the basis of this analysis the scientist suggested that the luminescence of 0.96-1.1 microns is caused by transitions between energy levels of the Stark components of $^2 F_{7/2} \to ^2 F_{5/2}$ ytterbium ion. The radiation of 1.8-2.05 microns is caused by radiative transitions between Stark components of the levels $^3 F_{4} \to ^3 H_{6}$ thulium ions, the emission of 2.05-2.15 microns is caused by radiative transitions between Stark components of the levels $^5 I_{7} \to ^5 I_{8}$ holmium ion. Conclusions. The author analyzed the luminescence spectra and kinetic characteristics, obtained the dependencies of the luminescence and the damping constant on the concentration of holmium ions. On the basis of the dependency graphs the researcher determined the optimal composition of phosphor to maximize the intensity of the luminescence in the area of 2000-2150 nm with laser excitation wavelength of 940 nm.