Ultra-low-temperature nucleation for high-efficiency Zn0.5Cd0.5S white quantum dots

Quantum dots (QDs) are nanomaterials with high luminous efficiency and tunable wavelengths, suitable for applications in lighting, displays, and solar cells. White light QDs feature both band-edge and surface-state emissions, with a broad full width at half maximum (FWHM), making them suitable for lighting applications. However, challenges persist in commercialization due to the low quantum yield (QY, <86%) and low device efficacy (approximately 11 lm/W). To address these issues, we utilized unsaturated fatty acid oleic acid (OA) and a non-coordinating solvent, 1-octadecene (ODE), to synthesize Zn_0.5Cd_0.5S QD at low temperatures, effectively preventing surface defect passivation. A significant finding in this study is the successful preparation of Zn_0.5Cd_0.5S white light QDs at low temperatures (120°C to 180°C). At 150°C, the band-edge and surface-state emission wavelengths were 411 nm and 525 nm, respectively, achieving a remarkable relative quantum yield (QY) of up to 175%, marking the highest relative QY among the white QDs. These QDs exhibit a broad emission, enabling single-material encapsulation. This simplifies the process and prevents color shifts in light-emitting diode (LED) caused by varying lifespans of QDs. The encapsulated QDs resulted in a warm white LED with CIE coordinates of (0.37, 0.40), a correlated color temperature (CCT) of 4298 K, a color rendering index (CRI) of 79, and the luminous efficacy of 14.7 lm/W. This research confirms the successful synthesis of QDs in low-temperature oil phases and their application in solid-state lighting.