Emission features of Ho 3+ ion in Nb 2O 5, Ta 2O 5 and La 2O 3 mixed Li 2O–ZrO 2–SiO 2 glasses

Abstract

Li 2O–ZrO 2–SiO 2: Ho 3+ glasses mixed with three interesting d-block elemental oxides, viz., Nb 2O 5, Ta 2O 5 and La 2O 3, were prepared. Optical absorption and photoluminescence spectra of these glasses have been recorded at room temperature. The luminescence spectra of Nb 2O 5 and Ta 2O 5 mixed Li 2O–ZrO 2–SiO 2 glasses (free of Ho 3+ 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 Ta 5+ and Nb 5+ ions in the glass network. The Judd–Ofelt theory was successfully applied to characterize Ho 3+ spectra of all the three glasses. From this theory various radiative properties, like transition probability A, branching ratio β r and the radiative lifetime τ r, for 5S 2 emission levels in the spectra of these glasses have been evaluated. The radiative lifetime for 5S 2 level of Ho 3+ ions has also been measured and quantum efficiencies were estimated. Among the three glasses studied the La 2O 3 mixed glass exhibited the highest quantum efficiency. The reasons for such higher value have been discussed based on the relationship between the structural modifications taking place around the Ho 3+ ions.