Electronic Spectra of $Pr^3^+$ Doped Mixed Alkali Borate Glasses

An investigation of the optical absorption spectra of 1 mol% $Pr_2O_3$ in mixed alkali borate glasses of the type $xNa_2O.(30-x)K_2O.69B_2O_3.1Pr_2O_3$ (x=5, 10, 15, 20 and 25) is presented. The glasses were obtained by quenching melts consisting of $Na_2CO_3, K_2CO_3, H_3BO_3 and Pr_2O_3 $(850-1000 Deg C, 1.5-2 h) between brass plates. Spectroscopic parameters like Racah $(E^1, E^2 and E^3)$ and spin orbit ( \xi 4f) interaction parameters and Judd-Ofelt intensity parameters (\Omega 2,\Omega4 and \Omega 6) have been calculated as a function of x in the glass matrix. Radiative and nonradiative transition rates $(A_T and W_M_P_R)$, radiative lifetimes $( \tau _R)$, branching ratios (\beta) and integrated absorption cross sections (\Sigma) are reported for certain excited states of $Pr^3^+$ in all glasses studied. Variations of these parameters as a function of composition are discussed in terms of covalency and of changes into the crystal field around the $Pr^3^+$ ions caused by structural changes of the glass matrix.