Controllable energy transfer in fluorescence upconversion of NdF3 and NaNdF4 nanocrystals

The synthesized Nd fluoride nanocrystals exhibited different upconversion behaviors as dispersed and aggregated samples due to the different energy transfer mechanisms. When they were dispersed in water, the NaNdF4 nanocrystals exhibited similar to 400 times stronger upconversion fluorescence than the NdF3 nanocrystals. Remarkable upconversion behaviors were found when the nanocrystals were aggregated in the films. For the NdF3 nanocrystals, the energy transfer processes I-4(13/2)<- F-4(3/2)->(4)G(7/2) in the films generated avalanche upconversion emissions with a high slope of similar to 12.0, which could be due to the large avalanche cross relaxation rates and spectral broadening effect. In contrast, the spectral broadening effect in the NaNdF4 NCs films increased the energy transfer I-4(15/2)<- F-4(3/2)->(4)G(5/2) of the Nd3+ ions, and induced a new upconversion emission at similar to 680 nm with the slope increased from 1.0 to 3.2. (C) 2010 Optical Society of America