Investigation of optical and thermal properties in Er3+-doped Ga2O3-La2O3-Ta2O5 glasses fabricated by containerless solidification

55Ga2O3-(35-x)La2O3-10Ta2O5-xEr2O3 transparent and bulk glasses were successfully synthesized by a containerless processing method. The effects of Er3+ concentration on thermal stability and optical properties were studied in detail. The prepared glasses exhibited high glass-transition temperature (Tg> 798 °C) and goodo resistance to crystallization (ΔT > 134 °C) by differential thermal analysis (DTA). Moreover, the detailed crystallization kinetics of 33La2O3-55Ga2O3-10Ta2O5-2Er2O3 glass was investigated, and the activation energy (E) and the frequency factor (v) of crystallization were gained by means of Kissinger method. The refractive indices were higher than 1.94 as well as the Abbe numbers were greater than 31. The transmittance spectra showed a wide transparent window ranging from 280 nm to 7.5 µm and the prepared glasses performed high infrared transmittance of nearly 80.5%. Two intense emissions centered at 1535 nm and 2700 nm could be observed when the glasses were excited by a 980 nm laser, corresponding to the Er3+ ions: 4I13/2→4I15/2, 4I11/2→4I13/2 transitions, respectively. By fitting the decay curves, the highest lifetime of 4I13/2 level could be evaluated to be 7.49 ms. Finally, a reasonable luminescence mechanism of down-conversion was proposed systematically.