Enhancement Effect of Illumination on the Photoluminescence of Water-Soluble CdTe Nanocrystals: Toward Highly Fluorescent CdTe/CdS Core−Shell Structure

A strong photoluminescence enhancement effect of illumination on CdTe nanocrystals stabilized by thioglycolic acid (TGA) was observed. Under optimized conditions, the fluorescence quantum yield of CdTe nanocrystals in aqueous solution reached 85% at room temperature. Optical measurements indicated that the photodegradation of TGA rather than NCs was the main reason for the PL enhancement effect since sulfide ions released from TGA during illumination coordinated with cadmium ions on the surface of CdTe and formed a shell structure of CdS there. X-ray photoelectron spectroscopic results further proved the formation of CdS shell on the CdTe core during illumination. The colloidal solution of CdTe/CdS core−shell nanocrystals with photoluminescence quantum yield higher than 80% turned out to be very stable. Therefore, the current investigations not only reveal the PL enhancement effect of illumination, but also provide a useful synthetic route for producing water-soluble and highly fluorescent CdTe/CdS core−shell nanocrystals