Excited-state dynamics of Er3+ in Gd2O3 nanocrystals

The temperature-dependent lifetime of the green emission from Er3+ ions in 40-50 nm Gd2O3 nanocrystals has been measured and analyzed. The luminescence decay from the S-4(3/2) state of Er3+ shows nonexponential characteristics when excited directly to the thermally coupled H-2(11/2) from 10 to 300 K, indicating energy transfer to defects in the nanocrystals. The intrinsic lifetime of the S-4(3/2) state was determined by utilizing the efficient energy transfer from Gd3+ to Er3+. It is shown that, on the basis of a simplified thermalization model, multiphonon nonradiative relaxation from S-4(3/2) to F-4(9/2) plays a leading role in the observed temperature dependence of the intrinsic lifetime. Furthermore, a reciprocity method has been successfully extended to the calculation of the room-temperature emission spectrum of the H-2(11/2)-I-4(15/2) transition according to the measured excitation spectrum. Unusual phonon side bands in the laser excitation spectrum are observed in the hypersensitive transitions of Er3+. The origin of the phonon side bands is ascribed to the M process that involves the infrared-active lattice modes.