Physical characteristics and infrared fluorescence properties of sol–gel derived Er3+–Yb3+ codoped TiO2

Er 3+ – Yb 3+ codoped TiO2 films were prepared on fused silica by sol–gel processes. The Yb3+ codoping effect on the physical characteristics and ∼1.54 μm photoluminescence (PL) properties of Er3+-doped TiO2 films was investigated. Maximum ∼1.54 μm PL intensity occurs in Er3+ (5 mol %)–Yb3+(30 mol %) codoped TiO2 samples annealed at 700 °C. However, when the concentration of Yb3+ ions is more than 30 mol %, the back energy transfer effect from Er3+ to Yb3+ will deteriorate the ∼1.54 μm PL efficiency. Extended x-ray absorption fine structure measurements show that the average spatial distance between Er3+ ions is slightly decreased due to the partial substitution of Yb3+ for Er3+ ions in the local structure. The Yb3+ ion in the Er3+–Yb3+ codoped TiO2 samples not only plays the role of disperser but is also a sensitizer of the Er3+ ion. This dual effect leads to larger PL intensity in the Er3+–Yb3+ codoped TiO2 system in comparison with Er3+–Y3+ codoped TiO2 samples. Compared with SiO2 films with Er3+ (5 mol %)–Yb3+ (30 mol %) codoped and annealed at optimal temperature of 985 °C, the Er3+–Yb3+ codoped TiO2 film obtains better PL properties at lower annealing temperature.