Fabrication of the Сr4+:LiGaSiO4 nano-glass–ceramics

The α-LiGaSiO4:Cr4+ nano-glass–ceramic is a promising material for the application as an active laser medium. The challenges of development of the fabrication technique for this material are discussed. The main problems to be solved are as follows: reduction in the content of striae and bubbles in the vitreous precursors; diminishing the optical scattering losses of the glass–ceramic; enlargement of the fraction of the useful α-LiGaSiO4:Cr4+ crystalline polymorph in the samples; increase in the Cr4+ concentration in the crystallites.Crucial influence of the melt stirring, as well as of the initial charge composition onto the content of striae and of bubbles in the samples was observed. High evaporation losses of chromium and germanium from the melt were observed during the synthesis of the vitreous precursors. The influence of ceramming temperatures and of the precursors compositions onto the crystallization rates of the α-LiGaSiO4 and of the γ-LiGaSiO4 polymorphs has been evaluated. The refraction indices of the α-LiGaSiO4:Cr4+ crystallites, and of the initial glasses with different compositions were measured. The compositions of precursors, providing the least difference between the refraction indices of the glass and of the crystalline phases, were found. However, segregation of some components between the glasses and the crystallites during ceramming should also be taken into account when choosing the optimal charge composition for the synthesis of the transparent α-LiGaSiO4:Cr4+ nano-glass–ceramic.

► Factors studied promoting synthesis of the transparent Cr:LiGaSiO4 glass–ceramics.
► Stirring of the melt or some co-dopants help to avoid knags and bubbles formation.
► Excess of Li or Cr or increased temperature promotes formation of α-LiGaSiO4:Cr.
► At temperatures higher than 700 °C, γ→α-LiGaSiO4 transition becomes detectable.
► Glass composition ensuring the least Δn between crystallites and glass was found.