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

Europium doped zinc-tellurite glasses modified with LiF, Na2 O+L i 2O and Na2 O+L i2 O+N b 2O5 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 ◦ Ca t 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 Eu 3+ ions were measured. A strong red fluorescence is observed from the 5 D0 level of Eu 3+ ions in these glasses. The relative luminescence intensity ratio (R )o f 5 D0→ 7 F2 to 5 D0→ 7 F1 transitions has been evaluated to estimate the local site symmetry around the Eu 3+ ions. The emission spectra of these glasses show a complete removal of degeneracy for the 5 D0→ 7 F1 transition of Eu 3+ 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 Eu 3+ 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 5 D1 level is studied. The decay from the 5 D0 level is found to be exponential and the lifetime is shorter than those found in Eu 3+ -doped borate, phosphate and fluoride based glasses.

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