Spectrally Narrow Blue-Light Emission from Nonstoichiometric AgGaS<sub>2</sub> Quantum Dots for Application to Light-Emitting Diodes
Makoto Tozawa, Shuto Ofuji, Mizuki Tanaka, Kazutaka Akiyoshi, Tatsuya Kameyama, Takahisa Yamamoto, Genichi Motomura, Yoshihide Fujisaki, Taro Uematsu, Susumu Kuwabata, Tsukasa Torimoto
Abstract
Luminescence color tuning of less toxic I–III–VI-based quantum dots (QDs) has been intensively investigated for application in wide-color-gamut displays. However, the emission peaks of these multinary QDs are relatively broad in the blue-light region compared to those in the green and red regions. Here, we report the synthesis of AgGaS 2 (AGS) QDs that show a narrow blue emission peak through nonstoichiometry control and surface defect engineering. While as-prepared AGS QDs with angular shapes primarily exhibited a weak green photoluminescence (PL) peak at 520 nm assigned to defect-site emission, treatment with chloride ions resulted in the appearance of a sharp band-edge PL peak at 442 nm, with the number of surface defect sites decreasing as a result of rounding off the angles of the QD shape. Further coating of the QDs with a gallium sulfide (GaS x ) shell selectively enhanced the band-edge PL peak at 446 nm with a narrow full width at half-maximum of 22 nm, where the defect-site emission was almost eliminated due to the removal of surface defect sites. The PL quantum yield (QY) significantly increased from 5.5% for chloride-treated AGS QDs to 12% for AGS core-GaS x shell QDs (AGS@GaS x ). QD light-emitting diodes fabricated with AGS@GaS x QDs exhibited a sharp emission peak at 450 nm, slightly red-shifted from that of the PL spectrum of the QD films, accompanied by the reappearance of a weak broad defect-site emission peak at around 560 nm.