Photoluminescence properties and pump-saturation effect of Er3+/Yb3+ co-doped Y2Ti2O7 nanocrystals

The Er3+/Yb3+ co-doped Y2Ti2O7 phosphors were synthesized by the sol–gel method. XRD, TEM, and photoluminescence spectra of samples were measured and studied. The results demonstrate that the Y2Ti2O7 would transform from the amorphous to nanocrystalline at about 750 °C. The mechanism of both upconversion and near infrared (NIR) photoluminescence and their changes with annealing temperature were analyzed. What is more, the pump-saturation effect of NIR emission and the anomalous slopes of the fitted straight line in the double-logarithmic plots for upconversion emissions were found in the nanocrystalline samples, which can be ascribed to domination of upconversion over linear decay for the 4I11/2 and 4I13/2 state and the saturation of 4I13/2 state in Er3+ ions largely owing to the energy back-transfer process. They are induced by high pump power and Yb3+ ions concentration.