Blue Light Emitting Defective Nanocrystals Composed of Earth‐Abundant Elements

Copper-based ternary (I-III-VI) chalcogenide nanocrystals (NCs) are compositionally-flexible semiconductors that do not contain lead (Pb) or cadmium (Cd). Cu-In-S NCs are the dominantly studied member of this important materials class and have been reported to contain optically-active defect states. However, there are minimal reports of In-free compositions that exhibit efficient photoluminescence (PL). Here, we report a novel solution-phase synthesis of approximately 4 nm defective nanocrystals (DNCs) composed of copper, aluminum, zinc, and sulfur with approximately 20 % quantum yield and an attractive PL maximum of 450 nm. Extensive spectroscopic characterization suggests the presence of highly localized electronic states resulting in reasonably fast PL decays ( approximately 1 ns), large vibrational energy spacing, small Stokes shift, and temperature-independent PL linewidth and PL lifetime (between room temperature and approximately 5 K). Furthermore, density functional theory (DFT) calculations suggest PL transitions arise from defects within a CuAl5 S8 crystal lattice, which supports the experimental observation of highly-localized states. The results reported here provide a new material with unique optoelectronic characteristics that is an important analog to well-explored Cu-In-S NCs.