Preparation of highly stability ZnxCd1-xS white light quantum dots by silica coating

In this study, colloidal ternary ZnxCd1-xS (x=0.5 and 0.8, named as Zn-0.5 and Zn-0.8) white light quantum dots (WQDs) were prepared, which have the characteristics of band edge and surface state emissions, resulting in emitting white light. However, the low stability of device limits the application in solid state lighting (SSL). In order to solve the above problem, WQDs is coated with SiO2 to protect and passivate the surface. The results show that emission intensity of powder-typed Zn-0.8 and Zn-0.5 WQDs reduces to 40 % after four months at room temperature. On the other hand, the emission intensity of silica coating samples increase twice times compared to as-prepared sample. The luminous efficacy of as-prepared Zn-0.8-based and Zn-0.8@SiO2-based white light emitting diode (WLED) are 4.1 and 0.2 lm/W, respectively. The luminous efficacy of as-prepared Zn-0.5-based and Zn-0.5@SiO2-based white light emitting diode (WLED) are 8.1 and 6.2 lm/W, respectively. Moreover, the luminous efficacy of as-prepared Zn-0.5-based WLED only maintains for one week, while the Zn-0.5@SiO2-based devices can maintain for more than two weeks. These results confirm that coating SiO2 on the surface enhances the stability of WQDs and white light devices.