Narrow-Line-Width Room-Temperature Single-Photon Emission from Multinary Copper-Based Quantum Dots.

Colloidal quantum dots are promising scalable quantum light sources, yet leading systems typically rely on toxic heavy metals and often exhibit spectral instability and photoluminescence intermittency. Here, we demonstrate room-temperature single-photon emission from individual Ga-doped multinary CuInS2/ZnS core-shell quantum dots, a cadmium-free alternative with low toxicity and tunable emission. Hanbury Brown-Twiss measurements show pronounced photon antibunching with a minimum g2(0) of 0.06, corresponding to a single-photon purity of 94%. The emitters also exhibit a remarkably narrow emission line width of 35 meV and strongly suppressed blinking, remaining predominantly in a bright state under low excitation. Combining single-particle spectroscopy with phasor-based lifetime analysis directly resolves emissive-state dynamics without multiexponential fitting, revealing competing radiative and nonradiative pathways involving charged excitons and Auger-assisted recombination. These results establish multinary CuInS2/ZnS quantum dots as environmentally benign colloidal quantum emitters for scalable room-temperature quantum photonic technologies.