Photoluminescence Intensity Enhancement and Stability in CdTe/SiO2 Quantum Dots through Water Molecule Adsorption and Trap Passivation

The study of the luminescence photostability for colloidal nanocrystals is an important task since the understanding of the corresponding physical processes advances new electronic devices based on semiconductor nanoparticles as well as other important applications such as biomarkers. In this paper, we provide the first study and comprehensive analysis of the photostability of the luminescent properties for colloidal CdTe/SiO2 core/shell quantum dots prepared by an aqueous-based method. The quantum dots were exposed to continuous laser radiation during two time intervals with prolonged break in between. The photoluminescence intensity of the quantum dots increased over time under continuous laser irradiation. Also, some processes occurred in the quantum dots in the dark (during the break), leading to a further increase in the photoluminescence intensity after turning on the laser radiation in the second time interval. The observed continuous photoluminescence intensity enhancement of the CdTe/SiO2 quantum dots was attributed to adsorption of water molecules on the surface of the nanocrystals and, as a consequence, to a decrease in the probability of nonradiative transitions. The positions of the photoluminescence intensity maximum and the colorimetric characteristics have been found to be stable against prolonged laser irradiation. This has been explained by the fact that for the CdTe core capped with a large-bandgap SiO2 shell (with respect to the bandgap of CdTe), photocorrosion, which is often responsible for the PL blueshift, is a slow process. The results of our work can be used in the development of optoelectronic and nanophotonic devices based on colloidal CdTe/SiO2 nanostructures.