Electronic Structure Engineering in ZnSe/CdS Type-II Nanoparticles by Interface Alloying

Abstract

We report the synthesis and characterization of type-II ZnSe/CdS semiconductor nanocrystals that exhibit strong charge separation, high photoluminescence quantum yields, low optical gain thresholds, and alloyed core–shell interfaces. Shell growth rates and the degree of alloying both depend strongly on the shelling temperature. The core–shell NCs exhibit band edge PL with emission wavelengths spanning the blue to orange region of the electromagnetic spectrum (380–562 nm). Fluorescence quantum yields up to 75% can be obtained by deposition of an additional ZnS layer. Transient absorption spectroscopy reveals that the population of the first two exciton states (1Se–1Sh, 1Se–2Sh) in the type-II structures can be controlled by alloying. Increased alloying leads to a greater population of the 2S hole state exciton.