AgInS2-ZnS (ZAIS) quaternary semiconductors nanocrystals are versatile cadmium-free luminescent nanomaterials. Their broad emission spectrum and strong absorption make them ideal for the development of new white-LED devices taking advantage of nano-optical phenomena. We recently found strategies to increase the photoluminescence quantum yield of ZAIS nanocrystals up to 80%. In a second step toward high efficiency luminescent materials, we aim at increasing the net conversion efficiency of ZAIS nanocrystals by coupling them with metallic nano-antennae. Indeed, by grafting ZAIS nanocrystals onto carefully chosen metal/dielectric core/shell nanoparticles, both the absorption and emission processes can be tuned and enhanced. A finite-element simulation based on the discrete dipole approximation (DDA) was used to predict the nano-optical behavior of silver@oxide@ZAIS nanostructures. Desirable combinations of materials and geometry for the antennae were identified. A chemical method for the synthesis of the simulated nanostructures was developed. The coupling of ZAIS nanocrystals emission with the plasmonic structure is experimentally observed and is in accordance with our predictions.
Detection of nanoparticles in solution is required to manage safety and environmental problems. Spectral transmission turbidity method has now been known for a long time. It is derived from the Mie Theory and can be applied to any number of spheres, randomly distributed and separated by large distance compared to wavelength. Here, we describe a method for determination of size, distribution and concentration of nanoparticles in solution using UV-Vis transmission measurements. The method combines Mie and Beer Lambert computation integrated in a best fit approximation. In a first step, a validation of the approach is completed on silver nanoparticles solution. Verification of results is realized with Transmission Electronic Microscopy measurements for size distribution and an Inductively Coupled Plasma Mass Spectrometry for concentration. In view of the good agreement obtained, a second step of work focuses on how to manage the concentration to be the most accurate on the size distribution. Those efficient conditions are determined by simple computation. As we are dealing with nanoparticles, one of the key points is to know what the size limits reachable are with that kind of approach based on classical electromagnetism. In taking into account the transmission spectrometer accuracy limit we determine for several types of materials, metals, dielectrics, semiconductors the particle size limit detectable by such a turbidity method. These surprising results are situated at the quantum physics frontier.
Luminescent nanocrystals of AgInS2-ZnS (ZAIS) and core-shell AgInS2-ZnS@ZnS (ZAIS@ZnS) nanostructures were synthesized with different compositions of the core AgInS2-ZnS solid solution. With this method, luminophores displaying a broad emission spectrum and a maximum emission tunable between 555 nm and 825 nm could be obtained. Their optical absorption and luminescence properties were studied in order to understand the evolution of their optical band gap, their photoluminescence quantum yield (PLQY) and the amount of defects. Ageing tests of the colloidal solutions of these nanocrystals under blue light excitation were also performed. We show that the high PLQY of ZAIS nanocrystals is correlated to the amount of defects they contain which explains the effect of both the composition and the
synthesis method on the PLQY. We also show that ZnS coated nanocrystals exhibit high photostability under blue light
excitation compared to their non-coated counterparts. These results emphasize the potential of ZAIS nanocrystals as
highly luminescent and stable luminophores for white-LED applications.
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