Green synthesis and luminescence characteristics of ZnSe-ZnS core-shell quantum dots

Abstract

The core-shell quantum dots of ZnSe-ZnS were synthesized in aqueous solution using glutathione (GSH) in an environmentally friendly way. The effects of the concentration of GSH, the synthesis temperature and the NaOH concentration (pH) on the microstructural and optical properties of the prepared core-shell systematically were investigated. Analysis of the XRD patterns and TEM particle images confirmed that the round-typed ZnSe-ZnS quantum dots of size 3 to 5 nm were formed. Comparing to the single core ZnSe, the core-shell ZnSe-ZnS showed an increase in photoluminescence (PL) emission intensity up to 130%. In addition, the core-shell quantum dots showed a good long-term stability maintaining their high PL intensity for at least 84 days. The synthesis process optimization was discussed in detail. The light emission intensities of the quantum dots were dependent on the GSH concentration. The optimum GSH concentration for the core-shell synthesis was found to be around 0.1 mmol. High temperature above 70 C for the core-shell synthesis generally improved the optical properties. However, light discharge characteristics were correlated with the core-shell synthesis temperature and the pH in solution. At the high temperatures of 70 °C and 90 °C, the emission intensities were degraded with high pH of 13 due to the dissociation of the ligand were accelerated. The optimized ZnSe-ZnS quantum dots showed high color purity emitting blue fluorescence light of 378 nm with the narrow full width at half maximum (FWHM) less than 20 nm. Optimization of synthesis parameters showed the possibilities of the simple and eco-friendly manufacture of long term stable and efficient ZnSe-ZnS core-shell quantum dots in aqueous solutions for display applications.