Optimal conditions for synthesis of Cr4+ doped Li2CaGeO4 glass-ceramics for laser emission in the near IR region

The main goal of this research was to find a suitable starting glass composition and suitable conditions for it thermal treatment for preparing of Cr 4+ doped Li 2 CaGeO 4 glass-ceramics as an active medium for laser radiation in the range 1.1–1.6 nm. The crystallization of the glasses after thermal treatment from the four-component system Li2O-CaO-GeO2-B2O3 was studied, and the crystallization area of Li2CaGeO4 was determined for three sections of the system with content of B2O3 5.0, 7.5 and 10.0 mol%. The crystallization kinetic in the glass and the formation of different phases were experimentally investigated not only depending on the composition of the starting glass, but also on its thermal treatment regime. It is shown that the thermal treatment regime is decisive not only for the amount of a given crystallizing phase as well as the size and morphology of the nanoparticles , but also for the type, number and quantitative ratio of the crystallizing phases themselves. The obtained results are discussed in terms of the crystallization rules below the solidus line in multicomponent systems . As a result of the research, an optimal composition of the glass was found, allowing homogenization at 1150 °C for only 2 h, solidifying in an amorphous mass. An optimal heat treatment regime of the glass was chosen and as a result a Cr4+ glass-ceramic with very good properties was obtained. The obtained glass-ceramic contains up to 60 mass% Cr4+ doped Li2CaGeO4 nanophase with an average particle size of about 20 nm preserving transparency of about 70 % in relative to the no treated glass. X-ray powder diffraction, DSC , EPR , TEM and UV–VIS analysis were used for characterization of the glass-ceramics.