Absorption and emission features of Ho3+ ion in Nb2O5 mixed Lithium zirconium silicate glasses

Abstract

Li2O–ZrO2–SiO2: Ho3+ glasses mixed with Nb2O5 were prepared. Optical absorption and photoluminescence spectra of these glasses have been recorded at room temperature. The optical absorption spectra of all glasses recorded at room temperature in the wavelength region 300-2000 nm exhibited several absorption bands all from the ground state 5I8 to 5G5, 5G6, 5F1, 5F3, (5F4+5S2), 5F5, 5I5, 5I6, 5I7. The luminescence spectra of all the glasses recorded at room temperature in the visible and NIR regions exhibited the following prominent emission bands 5F3 → 5I8, 5S2 → 5I8, 5G4 → 5I6, 5K8 → 5I7, 5F5 → 5I8 ,5G5 → 5I6, 5F4 →5I7, 5G5 → 5I5, 5F2 → 5I6, 5F3 → 5I6, 5I5 → 5I8 (Visible region) and ,5I7 → 5I8 (NIR region). The luminescence spectra of Nb2O5 mixed Li2O–ZrO2–SiO2 glasses (free of Ho3+ ions) have also exhibited broad emission band in the blue region. This band is attributed to radiative recombination of self-trapped excitons (STEs) localized on substitutionally positioned octahedral Nb5+ ions in the glass network. The Judd–Ofelt theory was successfully applied to characterize Ho3+ spectra of all the glasses. From this theory, various radiative properties like transition probability A, branching ratio βr, the radiative lifetime τr, for 5S2 emission levels in the spectra of these glasses has been evaluated. The radiative life time for 5S2 level of Ho3+ ions has also been measured and quantum efficiencies were estimated.