Temperature dependence photoluminescence properties of ZnSe-based core-shell quantum dots

Abstract

Heavy metal-free ZnSe-based core-shell quantum dots (QDs) are promising emitting material for achieving violet-blue luminescence. Investigating the temperature-dependent variations in the photoluminescence (PL) properties of ZnSe-based QDs will enhance our understanding of the intrinsic factors that influence their diverse luminescence characteristics. Here we select the optimally synthesized ZnSe core QDs with three diameters (4.1, 5.2, and 8.3 nm) and ZnSe/ZnS core-shell QDs to study their temperature-dependent photoluminescence properties. As the sample temperature is increased, the PL intensity decreases, the emission energy redshifts, and the spectral become broader. We observe a reduction in the exciton- longitudinal optical (LO)-phonon coupling constant from 21.7 meV to 16.1 meV as the diameter of ZnSe core QDs increased from 4.1 nm to 8.3 nm. This decrease is associated with a narrower homogeneous broadening of the emission spectrum. Besides, the epitaxial growth of a ZnS wide bandgap shells onto the ZnSe core QDs can effectively isolate the photogenerated excitons away from the inorganic-organic interface, thus reducing the PL peak width and increasing the exciton binding energy of the QDs. Our research provides a valuable addition to the existing studies on the photoluminescence properties of ZnSe-based core-shell QDs.