Double-shelling AgInS₂nanocrystals with GaS/ZnS to make them emit bright and stable excitonic luminescence

This paper presents the successful synthesis of AgInS₂nanocrystals (NCs) double-shelled with GaSand ZnS for emitting bright and narrow excitonic luminescence from AgInS₂core NCs. Additionally, the AgInS_2/GaS/ZnS NCs with a core/double-shell structure have demonstrated high chemical and photochemical stability. The AgInS_2/GaS/ZnS NCs were prepared via three steps: (i) synthesis of AgInS₂core NCs by solvothermal method at 200 °C for 30 min, (ii) shelling GaSon AgInS₂core NCs at 280 °C for 60 min to produce the AgInS₂/GaScore/shell structure, and (iii) the outermost ZnS shelling at 140 °C for 10 min. The synthesized NCs were characterized in detail by using appropriate techniques such as x-ray diffraction, transmission electron microscopy, and optical spectroscopies. The luminescence evolution of the synthesized NCs is as follows: from the broad spectrum (peaking at 756 nm) of the AgInS₂core NCs to become the narrow excitonic emission (at 575 nm) prominent beside the broad one after shelling with GaS, then only the bright excitonic luminescence (at 575 nm) without broad emission after double-shelling with GaS/ZnS. The double-shell has made the AgInS₂/GaS/ZnS NCs not only remarkably enhance their luminescence quantum yield (QY) up to ∼60% but also maintain the narrow excitonic emission stably for a long-term storage over 12 months. The outermost ZnS shell is believed to play a key role in enhancing QY and protecting AgInS₂and AgInS₂/GaSfrom certain damage.