Rapid surface treatment to realize non-polar solvent soluble and bright ammonium sulfide-coated colloidal quantum dots

The surface composition of colloidal quantum dots (CQDs) influences their performance across various applications. To date, most highly emissive CQDs are cation-terminated and coated with anionic ligands, while reports on highly emissive anion-terminated CQDs are rare. This study presents a strategy to achieve highly emissive (photoluminescence quantum yield > 80%) ammonium sulfide-coated CdSe/CdS core/shell CQDs within 30 min at room temperature. A facile prepared ammonium polysulfide was used to react surface metal salts in non-polar solvent. The polysulfide was then reduced to sulfide by trioctylphosphine and passivated by ammonium. Although alkyl ammoniums with varying numbers of alkyl groups provide similar colloidal stability, primary ammonium offers superior surface passivation due to its minimal steric hindrance. This strategy is applicable to CQDs with different ligands and compositions. These unique ammonium sulfide-coated, highly emissive CQDs serve as novel platforms for exploring new properties of CQDs and provide valuable experimental evidence for theoretical studies.