Temperature-dependent photoluminescence properties of water-soluble CuInS2 and CuInS2/ZnS quantum dots

Although the photoluminescence (PL) of oil-soluble CuInS2 (CIS) quantum dots (QDs) has been widely investigated, the origin of PL in water-soluble CIS QDs is less well understood. Elucidation of the PL origin of water-soluble CIS QDs is an important issue in applications such as bioimaging and optical materials. Herein, we prepared CIS and CIS/ZnS QDs using a hydrothermal method and systematically investigated the temperature dependence of their PL properties. For both CIS and CIS/ZnS QDs, the temperature dependence of the PL intensity could be quantitatively understood by considering thermally activated nonradiative recombination processes. In contrast, the Stokes shift and PL decay time of the CIS/ZnS QDs showed a significantly different temperature dependence than those of the CIS QDs. This unusual temperature-dependent behavior of the CIS/ZnS QDs was attributed to carrier localization at the core/shell interface at low temperatures. The temperature dependence of the PL decay time of the CIS/ZnS QDs could be quantitatively explained using a phenomenological rate equation model that considered carrier localization at low temperatures.