Single-step synthesis of hyperbranched, luminescent Mn2+-doped ZnSe1−xSx nanocrystals using dichalcogenide precursors

Abstract

Taking advantage of dichalcogenide precursors, a simple, single-step heat-up method for obtaining Mn²⁺-doped ZnSe_1−xS_x nanocrystals (NCs) is presented. Tuning the ratios of diselendide and disulfide precursors results in alloys with varying shape, size and composition. When diphenyldiselenide (Ph₂Se₂) is used, highly branched networks of small NCs form. Dimethydisulfide (Me₂S₂) induces formation of larger NCs with less branching. Mixtures of the two exhibit branching proportional to the amount of Ph₂Se₂vs. Me₂S₂, allowing formation of a series of branched Mn²⁺-doped NCs. Interestingly, these NCs exhibit photoluminescence (PL) characteristic of Mn²⁺, despite the large number of defects and unusual shapes they possess. This demonstrates Mn²⁺ can be successfully doped into NCs with several degrees of branching, in which it acts as an efficient radiative trap. Addition of thiol to the NCs led to a large enhancement in the Mn²⁺ PL. In organic solution, the sensitivity to thiol varied with the degree of NC branching, with hyperbranching NCs giving the most sensitive response. After transfer to aqueous solution, the Mn²⁺ PL of the hyperbranched NCs increased dramatically in response to μM concentrations of dithiothreitol (DTT).