Spectroscopic study of chromium-doped transparent calcium germanate glass-ceramics

The optical properties of transparent chromium-doped glass-ceramics with the chemical composition similar to that of cunyite (Cr4+:Ca2GeO4) laser crystal were investigated. Room and low temperature absorption, excitation, fluorescence and Raman spectroscopy, as well as lifetime measurements were used to develop a model for the optical centers in the glass and nanocrystals. Parent (as quenched) glass does not exhibit any fluorescence; after the heat treatment Cr4+ fluorescence band appears at ∼1280 nm. Optical properties of nanocrystals formed in the glass-ceramics differ from those in the bulk single crystal Ca2GeO4. By comparison of Ca2GeO4 – like glass-ceramics with the Ca2GeO4 bulk single crystals and Mg2SiO4 – glass-ceramics we concluded that the nanocrystal phase is a modified Ca2GeO4 structure. Broadband fluorescence and a high quantum efficiency of new glass-ceramics make the new Cr-doped glass-ceramics promising medium for fiber lasers and amplifiers.