Effect of heat treatment on the structural and optical properties of tellurite glasses doped erbium

The 75TeO2–20ZnO–4Na2CO3–1Er2O3 (in molar ratio) glass system was prepared by the conventional melt-quenching method. As such, the samples prepared were investigated by differential scanning calorimetry (DSC), X-ray diffractrometry (XRD), Raman spectroscopy and infrared luminescence. DSC analyses were carried out on our glass at different heating rates between 5 and 20 °C/min. The result of the annealing temperature on the spectroscopic properties of Er3+ in tellurite glasses was discussed. The activation energy, for surface crystallization, was determined graphically from a Kissinger-type plot and had a value about 897.2 kJ/mol. Crystalline phases for both α-TeO2, γ-TeO2 and Zn2Te3O8 system were determined by the XRD method and were confirmed by Raman spectroscopy characterizations after heat treatment. The effect of heat treatment on absorption spectra and luminescence properties in the tellurite glass was also investigated. With heat treatment, the ultraviolet absorption edge presented a redshift. As a result, the Judd–Ofelt (J–O) intensity parameters (Ω2, Ω4, Ω6) were determined. The spontaneous emission probabilities of some relevant transitions, the branching ratio and the radiative lifetimes of several excited states of Er3+ were predicted using intensity J–O parameters. The near infrared emission that corresponds to Er3+: 4I13/2→4I15/2 can be significantly enhanced after heat treatment. Notably, it is found that the luminescence lifetime in the present system is much longer than that in most other glasses and glass ceramics. A comparative study on luminescence performance suggests that the obtained glass ceramic is a promising material for Er3+ doped fiber amplifiers.