Enhanced up-conversion red light emission from rare earth titanium oxide nanocrystals with pyrochlore phase

A facile sol-gel method combined with the post-annealing process has been used to synthesize Yb3+/Er3+ co-doped TiO2 nanocrystals. It is found that the high Yb3+ concentrations can promote the formation of TiO2 nanocrystals with pyrochlore phase. An intense up-conversion (UC) red light emission (658 nm) has been achieved under 980 nm laser excitation, which is enhanced by 108 folds compared with the reference sample. Both the luminescence intensity and the red-to-green emission intensity ratio are dependent of the annealing temperature, which can be explained as the distribution of rare-earth ions and phase change of TiO2 nanocrystals.