One-step synthesis of white-light-emitting quantum dots at low temperature.

Alloyed Zn(x)Cd(1-x)Se quantum dots (QDs) have been successfully prepared at low temperatures by reacting a mixture of Cd(ClO(4))(2) and Zn(ClO(4))(2) with NaHSe using 3-mercaptopropionic acid as a surface-stabilizing agent. The optical properties and composition of the alloyed QDs were highly dependent on the molar ratio of Zn(2+) to Cd(2+). With an increase in the Zn content, a systematic blue shift in the first exciton absorption and band-edge emission indicated the formation of the alloyed QDs. Moreover, X-ray diffraction peaks of the alloyed QDs systematically shifted to larger angles as the Zn molar fraction of the Zn(x)Cd(1-x)Se QDs was increased. This systematic shift further confirmed the appearance of alloyed QDs. Interestingly, among these alloyed QDs, the Zn(0.93)Cd(0.07)Se QDs exhibited white-light emission with quantum yields of 12%. In addition, we discovered that we could adjust the Zn(0.93)Cd(0.07)Se QD intensity ratio of the band-edge (431 nm) to trap-state (499 nm) emissions by controlling the reaction time. Careful control of the reaction time allowed us to balance the relative strength of the band-edge and trap-state emissions, thereby attaining white-light-emitting QDs. The Zn(0.93)Cd(0.07)Se QDs offer unique advantages, including one-step synthesis, tunable white-light emission, easy manipulation, a low-temperature requirement, and low fabrication costs.