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

Europium doped zinc-tellurite glasses modified with LiF, Na2O + Li2O and Na2O+ Li2O+ 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 degrees Cmin(-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 D-5(0) level of Eu3+ ions in these glasses. The relative luminescence intensity ratio (R) of D-5(0)-> F-7(2) to D-5(0)-> F-7(1) 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 D-5(0)-> F-7(1) 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 C-2v 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 D-5(1) 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.