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 H-2(11/2), S-4(3/2)-> I-4(15/2) transitions and red emission around 660 and 680 nm due to F-4(9/2) -> I-4(15/2) 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 Vb(3+) concentration. Also, the application of up converting nanoparticles in biomedical imaging is demonstrated. (C) 2011 Elsevier B.V. All rights reserved.