Enhancing the color rendering index for phosphor-converted white LEDs using cadmium-free CuInS₂/ZnS QDs

CuInS2 (CIS) I-III-VI-type quantum dots (QDs) were synthesized under different growth times by the facile solvothermal method. Emission wavelengths showed a deep red region (630-650 nm) with low quantum yields (QYs). The core CIS was effectively passivated by the coating layer of ZnS, thereby remarkably increasing the QYs (48% and 82%) and causing the blue shift of the emission band (580-623 nm). Red-emitting CIS/ZnS QDs that were blended with Y ₃Al₅O12:Ce³⁺ phosphor-based white light-emitting diodes (LEDs) were further demonstrated. The color rendering index of white LEDs was improved (Ra = 86) by using red-emitting CIS/ZnS QDs with broader spectra. The optical properties were evaluated under various forward currents; these properties included the electroluminescence spectra and luminous efficiency of CIS/ZnS QDs-assisted white LEDs. These results clearly showed that CIS/ZnS QDs are promising candidates for application in white LEDs.