Compositional Dependence of Fluorescence Spectra of Cr3+/Cr4+-Doped Calcium Alumino-Silicate Glasses for Broadband Telecommunication

The compositional dependence of the optical properties of Cr-doped glasses in a calcium alumino-silicate ternary system were investigated. By 792 nm excitation, two broad emission bands centered at 1000 and 1350 nm, which were attributed to Cr3+ and Cr4+ ions, respectively, were observed. The intensity ratio of these bands changed continuously as the host composition was varied; a positive correlation between the relative intensity of the Cr4+ band and the optical basicity Λ of the host glass was observed. In glasses with Λ=0.68–0.70, the two bands became comparable in their intensities and formed an extremely broad emission band with a bandwidth of more than 500 nm as their superposition.