Up conversion luminescence of Yb3+–Er3+ codoped CeO2 nanocrystals with imaging applications

The effects of Yb3+ doping on up conversion in Yb3+–Er3+ co-doped cerium oxide nanocrystals are reported. Green emission around 545 and 560 nm attributed to the 2H11/2, 4S3/2→4I15/2 transitions and red emission around 660 and 680 nm due to 4F9/2→ 4I15/2 transitions under 975 nm excitation were studied at room temperature. Both green and red emission intensities increase as the Yb3+ concentration increases from 0%. Emission strength starts to decrease after the Yb3+ concentration exceeds a critical amount. The green emission strength peaks around 1% Yb3+ concentration while the red emission strength peaks around 4%. An explanation of competition between different decay mechanisms is presented to account for the luminescence dependence on Yb3+ concentration. Also, the application of up converting nanoparticles in biomedical imaging is demonstrated.