Alloyed multi-shell quantum dots with tunable dual emission

In this work, we synthesized ZnxCd1-xSe/ZnS/ZnyCd1-ySe/ZnS dual emission-alloyed QDs for the first time. Through introducing a ZnS barrier layer, we avoid exciton diffusion to realize dual emission. By adjusting the composition of the core and the quantum well (QW) layer, the emission wavelength can be effectively tuned from 550 to 710 nm and 500 to 550 nm, respectively. The photoluminescence (PL) intensity of the QW layer can also be adjusted by changing the annealing time and the thickness of the outmost ZnS layer, which was the result of reduction of the defects of the QW layer. The highest quantum yield (QY) was over 50% for the dual emission-alloyed QDs. Moreover, this material also exhibited high photostability, and even being exposed to 365 nm Hg lamp irradiation for 12 h, the QY was still maintained at about 85% of the unirradiated level. The energy transfer efficiency between the core and the QW is calculated to be 48% using time-resolved PL spectra.