The effect of mixed alkalis on the absorption and fluorescence properties of Ho3+ ions in borate glasses

Spectroscopic properties of Ho3+ in 67B2O3·xLi2O ·(32- x)Na2O, 67B2O3·xLi2O ·(32- x)K2O and 67B2O3·xLi2O ·(32- x)Cs2O (where x = 8, 12, 16, 20 and 24) glasses were investigated on the basis of Judd-Ofelt theory. Various spectroscopic parameters (E1,E2,E3, ξ4f, α and β) and Judd-Ofelt intensity parameters (Ω2, Ω4 and Ω6) are calculated as a function of x in the three glass matrices. The obtained Judd-Ofelt intensity parameter Ω2 increases with the addition of a second alkali and also shows minima or maxima at x = 16-20 mol % in the above glasses. Using Judd-Ofelt intensity parameters (Ω2, Ω4 and Ω6), radiative transition probabilities (AT), radiative lifetimes (τR), branching ratios (β) and integrated absorption cross sections (Σ) have been calculated for certain excited states of Ho3+. The non-radiative transition rates of different excited states of Ho3+ are also estimated from 'energy gap law'. From the luminescence spectra, stimulated emission cross-sections (σp) have been obtained for the two transitions 5F5 →5I8 and 3K8 → 5I8 of Ho3+. The trend of all these parameters observed as a function of x in these glass systems have been discussed, keeping in mind the effect of mixed alkalis