Core Nanoparticle Engineering for Narrower and More Intense Band-Edge Emission from AgInS(2)/GaS(x) Core/Shell Quantum Dots

Highly luminescent silver indium sulfide (AgInS(2)) nanoparticles were synthesized by dropwise injection of a sulfur precursor solution into a cationic metal precursor solution. The two-step reaction including the formation of silver sulfide (Ag(2)S) nanoparticles as an intermediate and their conversion to AgInS(2) nanoparticles, occurred during the dropwise injection. The crystal structure of the AgInS(2) nanoparticles differed according to the temperature of the metal precursor solution. Specifically, the tetragonal crystal phase was obtained at 140 °C, and the orthorhombic crystal phase was obtained at 180 °C. Furthermore, when the AgInS(2) nanoparticles were coated with a gallium sulfide (GaS(x)) shell, the nanoparticles with both crystal phases emitted a spectrally narrow luminescence, which originated from the band-edge transition of AgInS(2). Tetragonal AgInS(2) exhibited narrower band-edge emission (full width at half maximum, FWHM = 32.2 nm) and higher photoluminescence (PL) quantum yield (QY) (49.2%) than those of the orthorhombic AgInS(2) nanoparticles (FWHM = 37.8 nm, QY = 33.3%). Additional surface passivation by alkylphosphine resulted in higher PL QY (72.3%) with a narrow spectral shape.