Double-shelling AgInS2 nanocrystals with GaSx/ZnS to make them emit bright and stable excitonic luminescence

Abstract

This paper presents the successful synthesis of AgInS2 nanocrystals (NCs) double-shelled with GaS x and ZnS for emitting bright and narrow excitonic luminescence from AgInS2 core NCs. Additionally, the AgInS2/GaS x /ZnS NCs with a core/double-shell structure have demonstrated high chemical and photochemical stability. The AgInS2/GaS x /ZnS NCs were prepared via three steps: (i) synthesis of AgInS2 core NCs by solvothermal method at 200 °C for 30 min, (ii) shelling GaS x on AgInS2 core NCs at 280 °C for 60 min to produce the AgInS2/GaS x core/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 AgInS2 core NCs to become the narrow excitonic emission (at 575 nm) prominent beside the broad one after shelling with GaS x , then only the bright excitonic luminescence (at 575 nm) without broad emission after double-shelling with GaS x /ZnS. The double-shell has made the AgInS2/GaS x /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 AgInS2 and AgInS2/GaS x from certain damage.