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Abstract:

We report up-conversion emission from an aqueous solution of YVO 4:Yb3+,Er3+ nanocrystals synthesized by an original method that produces nanoparticles with excellent crystallinity and no porosity. We show that these YVO4:Yb3+,Er3+ nanocrystals are not very sensitive to nonradiative relaxations, leading to a high green-to-red emission ratio of 6.3. Using a comparison with YVO 4:Eu3+ particles, we determined the quantum yield of the up-conversion emission of the aqueous YVO4:Yb3+,Er 3+ dispersion to be 0.09 ± 0.04% for an excitation intensity of only 0.55 kW•cm-2 at 970 nm. Furthermore, single YVO 4:Yb,Er particles with an estimated size down to 10 nm can be detected using a wide-field microscope under a 970 nm, 8 kW•cm-2 excitation. Because of their unexpectedly high up-conversion emission without intermittency, their water dispersibility, and their photostability, YVO 4:Yb3+,Er3+ nanoparticles are highly appropriate both for single-biomolecule and for in vivo imaging. © 2010 American Chemical Society.

Abstract:

We have investigated the optical properties of GaN nanorods with different diameters by using micro- and time-resolved photoluminescence measurements. Donor-bound and free exciton peaks are observed in GaN nanorods with diameters larger than 100 nm. While the relative magnitude of the free exciton emission gradually increases with decreasing nanorod diameter, there is a relative decrease in the emission from the donor bound exciton. Using time-resolved photoluminescence, the diameter dependence of the decay times for these exciton peaks is measured to be a few tens of ps. With decreasing diameter, the decay time decreases due to surface recombination.