Alloyed ZnxCd1-xSe quantum dots (QDs) have been successfully prepared at low temperatures by reacting a mixture of Cd(ClO4)2 and Zn(ClO4)2 with NaHSe using cysteine as a surface-stabilizing agent. The photoluminescence (PL) spectra of the alloyed QDs are determined on the basis of the Zn2+/Cd2+ molar ratio, reaction pH, intrinsic Zn2+and Cd2+ reactivities toward NaHSe, concentration of NaHSe, and the kind of thiols. A systematic blue shift in emission wavelength of the alloyed QDs was found with the increase in the Zn mole fraction. This result provides clear evidence of the formation of ZnxCd1-xSe QDs by the simultaneous reaction of Zn2+ and Cd2+ with NaHSe, rather than the formation of separate CdSe and ZnSe nanocrystals or core-shell structure CdSe/ZnSe nanocrystals. The size and inner structure of these QDs are also corroborated by using high-resolution transmission electron microscopy and X-ray powder diffraction. To further understand the formation mechanism, the growth kinetics of Zn0.99Cd0.01Se was studied by measuring the PL spectra at different growth intervals. The results demonstrated that, in the initial stage of growth, Zn0.99Cd0.01Se has a structure with a Cd-rich core and a Zn-rich shell. The post-preparative irradiation of these QDs improved their PL properties, resulting in stronger emission.

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.

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