No abstract

Water-soluble CuInS2 (CIS) quantum dots (QDs) were hydrothermally prepared in the presence of N-acetyl-L-cysteine (NAC) as a stabilizer, and the optimal hydrothermal synthetic conditions for NAC-capped CIS QDs were investigated. The photoluminescence (PL) quantum yield (QY) of the CIS QDs synthesized under optimal conditions was 4%, which was comparable with the highest QY reported for water-soluble CIS core QDs. The introduction of a ZnS shell produced CIS/ZnS core/shell QDs and further increased the PL QY to 30%. Furthermore, bilayer structures consisting of Au nanoparticles and CIS/ZnS QDs were fabricated using a layer-by-layer method to enhance the PL of the CIS/ZnS QDs on the basis of the localized surface plasmon resonance of Au nanoparticles.

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.

The donor–acceptor pair emission is the underlying mechanism of the PL of the hydrothermally-synthesized water-soluble CIS QDs.