Characteristics of a Cr$^{4+}$-doped glass-ceramic; a new material for photonic devices

The compound 1.0(Cr-doped Ca$_{2}$GeO$_{4})$-1.0(Li$_{2}$O)-0.2(A$l_{2}$O$_{3})$-0.5(B$_{2}$O$_{3})$, on quenching from the melt and subsequent heat treatment, yields a transparent glass-ceramic. The nanocrystallites formed by the ceramming procedure are distributed homogeneously in the bulk. Differential scanning calorimetry was used to determine the glass to crystal transformation temperature, T$_{g}$, and its dependence on heating rate. The activation energy for the glass to crystallite nucleation is 62kJ/mol. The calculated Avrami exponent is 1, in agreement with scanning electron microscopy observations. X-ray diffraction data indicates that the structure of the nanocrystallites is that of distorted Cunyite (Ca$_{2}$GeO$_{4})$. Electron microscopy indicates that the crystallite sizes are less than 1$\mu $m. The growth mode of the crystallites is ``needle'' like. The material exhibits broadband emission between 1050 to 1600 nm, with a maximum at $\sim$1260 nm. The spectroscopic and optical properties indicate, that this material is a promising candidate for use in microelectronics, micro lasers and as fiber optic transmission lines.