CuInS2-Doped ZnS Quantum Dots Obtained via Non-Injection Cation Exchange Show Reduced but Heterogeneous Blinking and Provide Insights into Their Structure–Optical Property Relationships

Cadmium-free CuInS2-doped ZnS quantum dots (QDs) are synthesized through a two-step non-injection synthetic method. The resulting QDs are small (∼8 nm or less) and relatively isotropic with photoluminescence quantum yields (PL QY) up to almost 70% and emission peaks in the 560–600 nm window, depending on the amount of the Zn precursor added. The results indicate that small CuInS2 clusters within a zinc blende ZnS lattice are the radiative recombination centers in the nanoparticle. Interestingly, higher ensemble photoluminescence quantum yields (PL QY) result when cation exchange is less extensive (∼80% ZnS composition), while a reduction in blinking is observed when ZnS composition exceeds 99%. A wide heterogeneity in blinking behavior from QD to QD is evident, and a subpopulation statistical analysis shows that the on state dwell times change from multiexponential (or inverse power law) behavior toward monoexponential behavior for particles that spend more of their time in the on state. These results indicate that as the number of CuInS2 emitting centers is reduced, the number of pathways leading to the off state decreases, and a model is proposed to relate this behavior to the QD structure. These results provide a novel route toward CuInS2-doped visible-light-emitting ZnS QDs with high quantum yield and reduced blinking and provide insights into how the composition of the dopant and host matrix affects the radiative recombination mechanisms in single particles.