In this study, colloidal ternary Zn_xCd_1-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 Zn0.8- 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 Zn0.5-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.

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Yun-Xuan Huang and Shu-Ru Chung, "Preparation of highly stability ZnxCd1-xS white light quantum dots by silica coating," Proc. SPIE 11085, Low-Dimensional Materials and Devices 2019, 110850H (Presented at SPIE Nanoscience + Engineering: August 12, 2019; Published: 12 September 2019); https://doi.org/10.1117/12.2529040.