Effect of Al₂O₃ concentration on fluorescence intensity ratio of Er³⁺/Yb³⁺ co-doped tellurite glasses for optical temperature sensors under 375 nm and 980 nm excitation

Alumina (Al₂O₃) is one of the most important ceramic materials. It has been used as a property modifier in different silica or tellurite glasses but its effect on the luminescent properties or on the fluorescence intensity ratio of Er³⁺/Yb³⁺ co-doped tellurite glasses has not been fully studied. In this work, the effect of the alumina on the structural, thermal and optical properties of tellurite glasses co-doped with Er³⁺ and Yb³⁺ ions was studied. It was observed that all the samples exhibit an amorphous structure but the glass transition temperature, thermal stability and band gap values increase with the alumina addition. Moreover, the luminescence behavior was studied in dependence of the temperature and specific attention was paid to the fluorescence intensity ratio (FIR) between ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 transitions. The results indicate that the addition of alumina increases the rate of change of FIR versus temperature.