Phosphine-free synthesis of Ag–In–Se alloy nanocrystals with visible emissions

Abstract

As promising heavy metal-free emitting materials, Ag–In–Se nanocrystals (NCs) are conventionally synthesized using organic phosphine agents and exhibit near-infrared emissions. In this work, we demonstrate a rapid phosphine-free approach for synthesizing Ag–In–Se alloy NCs with the emissions tunable to the visible region on the basis of the phosphine-free dissolution of Se powder. At room temperature, Se powder is reduced by dodecanethiol and dissolved in oleylamine to produce a Se precursor. The resultant Se precursor is highly active, which permits rapid synthesis at a relatively low temperature, such as at 90 °C for 150 s. By optimizing the size, structure, and composition, the photoluminescence quantum yield of the as-synthesized Ag–In–Se NCs is enhanced to up to 10%. The growth of the Ag–In–Se NCs involves composition and phase transition, which strongly depend on the reaction temperature. The Ag₂Se nuclei form first, and the Ag–In–Se NCs are produced by doping In³⁺ into the preformed Ag₂Se nuclei. Tetragonal phase Ag–In–Se is obtained below 170 °C, while the orthorhombic phase appears over 190 °C. The potential of Ag–In–Se NCs as red emitting phosphors for lighting-emitting diodes is further demonstrated.