J.H. Oh, K.N. Lee, S. Kim, S. Lee, Y.R. Do
Keywords: quantum dots, LEDs
Summary:This study introduces innovative exothermic reaction assisted synthetic method for highly efficient green emitting ZnAgInS-ZnInS/ZnS quantum dots (QDs) by simply adding excess amounts of Zn precursors (Zinc acetate dehydrate, ZAD) and application for down-converted light emitting diodes (LEDs). The ZnAgInS-ZnInS/ZnS QDs were synthesized using multi-step hot-injection method: Ag-In-S core growth, Zn-Ag-In-S core-alloy, Zn-In-S inner-shell, Zn-S outer-shelling. We compared low and high concentration of ZAD in order to make different reaction conditions during formation of ZnAgInS-ZnInS/ZnS QDs. We found when we use high concentration of ZAD, ZnInS inner-shell was successfully synthesized between ZnAgInS core-alloy and ZnS shell and photoluminescence quantum yield (PLQY) of QDs was increased by the exothermic reaction. The PLQY of QDs using high concentration of ZAD (86%) shows 1.43 times higher than that of QDs using low concentration of ZAD (60%). Dominant wavelength of QDs using high concentration of ZAD (511 nm) show blue shift about 15 nm compared to QDs using low concentration of ZAD (536 nm). Finally, we realized down-converted LEDs using 450 nm emitting blue LED and highly efficient green emitting QDs. The maximum luminous efficacy of down-converted LED shows 136 lm/W with the 1931 CIE color coordinates of (0.299, 0.392) at rated current of 60 mA. The highly efficient ZnAgInS-ZnInS/ZnS QDs can be a good candidate for color converting materials in the field of LED lightings and displays.