Preparation And Up-conversion Luminescence Of Er～(3+), And Er～(3+) And Yb～(3+) Doped TiO₂ Synthesized By Sol-gel Method

Er³⁺, and Er³⁺ and Yb³⁺ doped TiO₂ nanocrystal powders were prepared by sol-gel method, The influences of the sintering temperature and the Er³⁺-doping concentration on phase structure, crystal size of TiO₂ powder and up-conversion luminescence properties were systematically studied, and the effect of Yb³⁺ on enhanced upconversion luminescence was investigated.1.0 mol% Er³⁺:Ti02 nanocrystal powders were anatase phase when sintered at 500, 700 ℃, but rutile phase with a small quantity of Er₂Ti₂O₇ at 900℃. 3.0 mol% Er³⁺:TiO₂ and 1.0 mol% Er³⁺-(0.1-5.0) mol% Yb³⁺codoped TiO₂ nanocrystal powders sintered at 700℃ were anatase phase. The TiO₂ phase transition from anatase to rutile was evidently suppressed by doping the rare earth ions. Crystallization degree and average crystal size decreased with increasing the rare-earth-ion concentration, whereas increased with increasing the sintering temperature.Green emission and red emission at 552-567 and 678 nm were obtained in the Er³⁺:TiO₂ nanocrystals using 980 nm semiconductor laser as excitation source. The obviously effects of the crystal phase and average crystal size on upconverted emssion of Er³⁺ in TiO₂ nanocrystal powders were observed. Overall upconversion luminescence intensity (I_red+-I_green) of Er³⁺ in the bigger grain size powders was stronger than that in the smaller grain size powders with the same Er³⁺ concentration and TiO₂ phase structure, whereas for Er³⁺:TiO₂ nanocrystal powders with different phase structures, overall upconversion luminescence intensity of Er³⁺ in the anatase phase was enormously stronger than that in the rutile phase. The intensity of green emission was stronger than that of red emission for the Er³⁺:TiO₂ powders sintered at 700℃ from 0.1 to 3.0 mol% Er³⁺-doping concentration. The intensities of both green and red emission reached peak at 0.5 mol% Er³⁺ concentration, but decreased gradually above 0.5 mol%.In Yb³⁺ codoped 1.0 mol% Er³⁺: TiO₂ nanocrystal powders, the intensities of green and red emission was evidently enhanced due to the larger absorption section of Yb³⁺ at 980 nm than that of Er³⁺ and effective energy transfer from Yb³⁺ to Er³⁺. The intensity of red emission was weaker than that of green emission at less than 1.0 mol% Yb³⁺ concentration, while stronger at 1.0 mol% and more than 1.0 mol% Yb³⁺ concentration. The green emission intensity increased slightly, but red emission intensity increased remarkably with increasing the Yb³⁺ concentration. The upconversion luminescence intensities dependence on pumppower confirmed that both green and red emission in Er3+, and Er3+ and Yb3+ doped nanocrystals were two-photon absorption upconversion processes. The relative intensity ratio of red emission and green emission gradually increased in Er3+:TiC>2 nanocrystals, whereas slightly decreased in Er3+ and Yb3+ codoped TiC>2 nanocrystal powders, with the increase of pump power.