Upconversion luminescence dynamics in Er3+/Yb3+ codoped nanocrystalline yttria

The upconversion luminescence and dynamics in Er3+/Yb 3+ codoped nanocrystalline yttria (7-65 nm) are studied under 980-nm pulsed laser excitation. It is found that the red emission of 4F 9/2-4I15/2 and the green emission of 2H11/2/4S3/2 in nanoparticles with lower concentration of Yb3+ result from a two-photon excitation. In nanocrystals with higher Yb3+ concentration, the red emissions from a two-photon excitation, while the green emissions from a three-photon excitation. The luminescence dynamics indicates that as the particle size decreases, both the rise and the decay time constants become shorter. As the size decreases to several nanometres, the rise process nearly disappears, suggesting that the upconversion luminescence originates mainly from self-excitation of Er3+, instead of the energy transfer of Yb 3+ → Er3+. © 2005 Chinese Physical Society and IOP Publishing Ltd.