Multi-photon upconversion luminescence of Er3+-doped Y2O3 nanocrystals

Visible upconversion emission intensities are investigated in Er3+-doped Y2O3 nanocrystals. We also find that the upconversion intensity varies nonlinearly with the excitation power with a threshold of 110 mW, which indicates that the green and red emissions would be photon avalanche upconversion when the excitation power exceeds the threshold.