Optical Properties of Dy$^{\mathrm{3+}}$ Doped Calcium Bismuth Borate and Barium Bismuth Borate Glasses

The optical properties of dysprosium ions (Dy$^{\mathrm{3+}})$ in calcium and barium bismuth borate glasses were analyzed as a function of the glass composition with Bi$_{\mathrm{2}}$O$_{\mathrm{3\thinspace }}$content varying from 29.5 to 59.5mol{\%}. These glasses were prepared using the melt-quench method. Refractive index was measured using a Brewster's angle set up. Absorption and fluorescence spectra were then recorded using a Cary 5g UV-VIS-NIR spectrometer and a CCD spectrometer, respectively. The absorption edge was analyzed for glasses with and without Dy$^{\mathrm{3+}}$ ions to calculate the optical band gap of the glasses. Absorption spectra of Dy$^{\mathrm{3+}}$ ions were then analyzed using the Judd-Ofelt theory. The intensity of an absorption band can be expressed in terms of the oscillator strength. Using the oscillator strength for each transition, we obtained the intensity parameters which represent changes in the asymmetry of the ligand field at the Dy$^{\mathrm{3+}}$ ion site (due to structural changes) and to changes in Dy-O covalency. Radiative transition probabilities, the radiative lifetime of the excited states and the branching ratios are then obtained from these intensity parameters. The compositional dependence of these parameters are discussed.