Revealing mechanisms of PL properties at high and low temperature regimes in CdSe/ZnS core/shell quantum dots

Abstract

Here, we report on the strong temperature dependence of PL properties in CdSe/ZnS core/shell quantum dots, within a broad temperature range of 80–500 K. Our results demonstrate different PL quenching mechanisms in high and low temperature ranges. In the low temperature range of below 320 K, PL quenching is proved to be dominated by thermally activated carrier escape. While in the high temperature range of above 320 K, PL undergoes additional quenching because of surface trapping by the thermally created surface defects, which is calculated and proved by the rapidly decreasing PL lifetime. Our calculating result proves that the model of thermally activated carrier escape is also responsible for PL quenching in the high temperature range. However, the red-shifted PL peak energy and the broadened FWHM with increasing temperature follow the same mechanisms in the whole temperature range. The former is due to the temperature-dependent band-gap shrinkage and the latter is due to the exciton scattering with acoustic and longitudinal-optical phonons.