Study on Upconversion and Thermal Properties of Tm/Yb Co-Doped La₂O₃-Nb₂O₅-Ta₂O₅ Glasses.

The effect of Yb ions on upconversion luminescence and thermal properties of Tm/Yb co-doped La₂O₃-Nb₂O₅-Ta₂O₅ glasses has been studied. Glass transition temperature is around 740 °C, indicating high thermal stability. The effect of Yb 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 Yb 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 Yb to Tm 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 Yb ions. This result can be introduced in order to improve upconversion luminescence of glasses by crystallization in the future. Tm/Yb co-doped La₂O₃-Nb₂O₅-Ta₂O₅ glasses with good upconversion and thermal properties show promising applications in solid-state laser, optical temperature sensing.