Thermal, structural and optical properties of Eu3+-doped zinc-tellurite glasses

Abstract

Europium doped zinc-tellurite glasses modified with LiF, Na2O + Li2O and Na2O + Li2 O + Nb2O5 were prepared by the conventional melting procedure and their thermal, structural and optical properties were investigated. Differential thermal analysis curves in the temperature range 30–1200 °C at a heating rate of 10 °C min−1 were used to determine the thermal properties such as glass transition, crystallization and melting temperature. FT-IR spectra were used to analyse the glass structure. The spectroscopic properties including absorption and emission spectra and fluorescence lifetime of Eu3+ ions were measured. A strong red fluorescence is observed from the 5 D0 level of Eu3+ ions in these glasses. The relative luminescence intensity ratio (R) of 5D0 → 7F2 to 5D0 → 7F1 transitions has been evaluated to estimate the local site symmetry around the Eu3+ ions. The emission spectra of these glasses show a complete removal of degeneracy for the 5 D0 → 7F1 transition of Eu3+ ions. Based on the energy level data obtained from the absorption and emission measurements, free-ion energy level analysis has been carried out. Second rank crystal-field parameters have been calculated together with the crystal-field strength parameter by assuming the C2v symmetry for the Eu3+ ions in these glasses. The crystal-field parameters are found to be higher in binary zinc-tellurite glasses. The trend of variation of crystal-field strength with glass composition is found to be more or less opposite to that of R in the present glasses. The effect of temperature on the luminescence from 5D1 level is studied. The decay from the 5D0 level is found to be exponential and the lifetime is shorter than those found in Eu3+-doped borate, phosphate and fluoride based glasses.