Red-Emitting Quantum Dots for Solid-State Lighting

Abstract

Red emitters that can be excited with blue InGaN LEDs are essential for warm white LEDs for solid-state lighting (SSL). Current red phosphors do not satisfy all of the criteria for SSL. Red-emitting CdTe-based quantum dot (QD) heterostructures meet several of these criteria, such as narrowband emission, broad blue absorption, high quantum yield (QY), and high luminous efficacy of radiation. This paper describes the synthesis of CdTe, CdTe/2CdSe, CdTe/2CdSe/CdS, and CdTe/2CdSe/CdS/5ZnS QDs and their photoluminescence. The growth of two CdSe shells on the CdTe core increases the QY to 95.5%. The shells reduce the thermal quenching above room temperature. CdTe cores that were aged for one year, exhibited thermal quenching of 73% at 100°C, whereas the aged CdTe/2CdSe and CdTe/2CdSe/CdS QDs had thermal quenching of 39% and 38%, respectively at 100°C. After cooling to room temperature, the QDs retained ∼92% of their initial QYs. CdTe-based QDs have substantially less thermal quenching than CdSe/ZnSe QDs, which exhibit an 87% reduction in the QY and thermal degradation at 100°C. Aging the various QDs for one year resulted in blue-shifts of the absorbance and PL emission by ∼5–11 nm; broadening of the FWHM by ∼0.7–4 nm; and an increase in the PL lifetimes.