Spectroscopic and structural implications of hosting Zn²⁺, Cd²⁺ and Hg²⁺ ions in the AgInS₂ quantum dots

This work address the issue of spectral implications provided by doping AgInS₂ QDs with Zn²⁺ and its higher homologues including Cd²⁺ and Hg²⁺. The impact of alloying AgInS₂ QD with IIB group atoms is here discussed in terms of comprehensive spectroscopic measurements as well as theoretical predictions performed within the Density Functional Theory. It is shown that each of the admixtures used induces a completely different spectral response including complete reversal character for Cd²⁺ and Hg²⁺ ions. Observed differences were here associated with changes in the native defects structure and possible relaxation pathways due to doping. It is shown that Zn²⁺ ions results in quite weak impact on the emission properties of the AgInS₂ QDs. Highest impact was found for Cd²⁺ and Hg²⁺ ions. Doping AgInS₂ QDs with Cd²⁺ results in successive deactivation of the relaxation pathways which were typical for pristine AgInS₂ QDs leading to significant shortening of the photoluminescence lifetime and partial band symmetrisation. Doping with Hg²⁺ ions was found to be of completely opposite character. It was found that mercury adatom has the lowest affinity to the AgInS₂ surface giving rise to formation of metallic Hg-Ag complexes on a surface which may be responsible for anomalous behaviour of Hg-doped AgInS₂ QDs.