Study on Upconversion and Thermal Properties of Tm3+/Yb3+ Co-Doped La2O3-Nb2O5-Ta2O5 Glasses

The effect of Yb3+ ions on upconversion luminescence and thermal properties of Tm3+/Yb3+ co-doped La₂O₃-Nb₂O₅-Ta₂O₅ glasses has been studied. Glass transition temperature is around 740 °C, indicating high thermal stability. The effect of Yb3+ ions on the thermal stability is not obvious. Both the glass forming ability and the upconversion luminescence first increase and then decrease with the increase of Yb3+ ions. The glasses perform low glass forming ability with ΔT around 55 °C. Blue and red emissions centered around 477, 651, and 706 nm are obtained at the excitation of 976 nm laser. The upconversion luminescence mechanism is energy transfer from Yb3+ to Tm3+ mixed with two- and three- photon processes. The thermal kinetic Differential Thermal Analysis (DTA)-analysis indicates that the average activation energy first increases and then decreases with the increase of Yb3+ ions. This result can be introduced in order to improve upconversion luminescence of glasses by crystallization in the future. Tm3+/Yb3+ co-doped La₂O₃-Nb₂O₅-Ta₂O₅ glasses with good upconversion and thermal properties show promising applications in solid-state laser, optical temperature sensing.