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

Abstract

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 GaSx 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.