Compositional dependence of optical properties of praseodymium (Pr³⁺) ions in binary and ternary bismuth borate glasses

We studied the compositional effects on Pr³⁺ absorption and fluorescence properties in binary bismuth borates and ternary bismuth boro-tellurite glasses. Addition of TeO₂ can significantly affect the optical properties of Pr³⁺ ions doped in bismuth borate glasses.  We used a modified Judd-Ofelt analysis to obtain the intensity parameters from the optical absorption spectra. With increase in bismuth oxide content, an increase in the covalency of the Pr-O bond in the binary glasses and a more pronounced variation in the ternary glasses is observed.  Optical band gap decreases with increase in bismuth content in both binary and ternary glasses. Fluorescence spectra show peaks in the blue and red region characteristic of Pr³⁺ ions. We carried out a phonon side band analysis which suggests that the energy levels of Pr³⁺ responsible for the intense red emission are populated through a cross-relaxation mechanism instead of a multi-phonon decay process.  The blue transition of Pr³⁺ shows significant enhancement for the stimulated emission cross-section in ternary system containing TeO₂ compared to the binary system. Our glass samples also possess high spectroscopic quality factors compared to similar systems doped with Pr³⁺ ions which make them suitable for optical applications.