Enhanced red upconversion emission of Er³⁺-doped ZnO by post-annealing

In this paper, we synthesized Er³⁺-doped Zinc oxide nanocrystals by conventional sol-gel method under 800 °C, and further mesoporous-like structure was obtained through post-annealing procedure at 1300 °C. Upconversion intensity was significantly enhanced by post-annealing, and the emission color was turned into relatively high purity red color (ratio of red to green emission is over 10). In addition, the mechanisms of post-annealing and upconversion luminescence were discussed in detail on the basis of the structural and spectral measurements.