Effect of TiO2 and Al2O3 on energy transfer and upconversion in Ho-Yb co-doped sol-gel silica glass

Holmium (Ho3+) and Ytterbium (Yb3+) co-doped in sol-gel silica glasses are prepared and the effect of incorporating TiO2 and Al2O3 are also studied. Photoluminescence studies using 450 nm excitation show that both TiO2 and Al2O3 improves luminescence but through different mechanisms. The observations are in support of the increased energy transfer between Ho3+ and Yb3+ in the presence of TiO2. Upconversion is also observed with 980 nm excitation showing emission in the green and red regions. Upconversion intensity is also enhanced by TiO2 and Al2O3 but comparison of the intensity ratio of the green and red emissions shows significant back transfer in presence of TiO2.The power dependence study reveals the F-5(5) -> I-5(8) transition of Ho3+ involves a two-step process. [GRAPHICS] .