Designing Band-Edge Emissive AgInS2 Nanocrystals via Composition and Structure Control

Colloidal semiconductor nanocrystals (NCs) of ternary I–III–VI compounds are promising luminescent materials for photonic and optoelectronic applications. However, defect-induced broad trap emission dominates, and achieving band-edge photoluminescence (PL) without appropriate shell coating remains challenging. This study introduces a synthesis route and optical characterization results of weakly quantum-confined In-rich AgInS₂ NCs, which exhibit spectrally narrow band-edge PL in the red spectral range. Leveraging precursor stoichiometry and growth condition optimization, band-edge emissive AgInS₂ NCs with mitigated defect emission are realized. Structural analysis of the NCs reveals a stoichiometric AgInS₂ core surrounded by an In-enriched surface layer, facilitating efficient exciton radiative relaxation pathways. With NC diameters approaching the exciton Bohr diameter of the bulk semiconductor, the PL peak energies of AgInS₂ NCs align closely with the bulk bandgap (2.0 eV), and these NCs exhibit spectrally pure emission with reduced batch-to-batch variation for red emission. The band-edge PL properties are remarkably improved by coating a GaS_x shell that effectively suppresses the residual trap emission and reduces nonradiative recombination, thereby enhancing the overall emission efficiency. These findings provide new insights into composition-controlled optical property regulation of ternary semiconductor NCs and underscore their potential for photonic and optoelectronic applications.