Enhancement of the upconversion radiation in Y2O3:Er3+ nanocrystals by codoping with Li+ ions

We report on an innovative route to increase the upconversion (UC) green radiation by two orders of magnitude in Y2O3:Er3+ nanocrystals through tailoring Er3+ ions' local environment with Li+ ions under diode laser excitation of 970 nm. Theoretical investigations based on the steady-state rate equations indicate that such enhancement arises from a combining effect of the tailored lifetime of the intermediate I-4(11/2)(Er) state, the suppressed cross relaxation H-2(11/2)(Er)+I-4(15/2)(Er)-> I-4(9/2)(Er)+I-4(13/2)(Er) process, and the enlarged nanocrystal size induced by the Li+ ions. The proposed route here may constitute a promising step to solve the low efficiency problem in UC materials. (C) 2008 American Institute of Physics.