Publication date: 15th December 2025
To date, II–VI colloidal semiconductor nanocrystals are the most extensively studied materials for achieving optical gain because of their superior amplification properties and high quantum yield¹. However, the toxicity of II–VI NCs remains a major concern due to the presence of heavy metals such as Cd, Pb, and Hg. As a result, emerging non-toxic alternatives, namely I–III–VI quantum QDs composed of elements such as Ag, Cu, In, Ga, and S—have gained increasing attention. Studies on population inversion or amplified spontaneous emission (ASE) in I–III–VI QDs are still limited. Investigating population inversion in these NCs is particularly compelling. We have performed fluence-dependent photoluminescence measurements on highly luminescent, densely packed AgInS₂ QD films2 of various sizes and observed a very narrow emission ASE resonance. Transient absorption and time-resolved PL measurements indicate that the optical gain is biexcitonic in nature. Furthermore, we applied a polymer coating to the QD films to enhance their stability; the films show consistent performance for several hours under continuous illumination. This work represents a step forward toward achieving lasing from non-toxic nanocrystals.
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