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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.

Abstract:

Cavities embedded in photonic crystal waveguides offer a promising route toward large scale integration of coupled resonators for quantum electrodynamics applications. In this letter, we demonstrate a strongly coupled system formed by a single quantum dot and such a photonic crystal cavity. The resonance originating from the cavity is clearly identified from the photoluminescence mapping of the out-of-plane scattered signal along the photonic crystal waveguide. The quantum dot exciton is tuned toward the cavity mode by temperature control. A vacuum Rabi splitting of ∼140 μeV is observed at resonance. © 2010 American Institute of Physics.

Abstract:

To enable the study of cavity quantum electro-dynamical effects in nitride systems, it is essential to be able to fabricate high quality cavity structures that exhibit large Q-values of the order of several thousands. A promising candidate for such a realisation is based around the micro-pillar distributed Bragg reflector (DBR) cavity. The growth of nitride stacks is problematic due to such material issues as lattice mismatch and dislocation propagation which seem to be more pronounced when compared to similar arsenide structures. In this paper we report on our efforts to characterize the homogeneity of our first generation planar DBR structures through both reflectivity measurements using the broadband output of a photonic crystal fiber (PCF) and cryogenic photoluminescence under ultraviolet (UV) excitation. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.