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

Abstract

This paper presents the successful synthesis of AgInS₂nanocrystals (NCs) double-shelled with GaS_xand ZnS for emitting bright and narrow excitonic luminescence from AgInS₂core NCs. Additionally, the AgInS_2/GaS_x/ZnS NCs with a core/double-shell structure have demonstrated high chemical and photochemical stability. The AgInS_2/GaS_x/ZnS NCs were prepared via three steps: (i) synthesis of AgInS₂core NCs by solvothermal method at 200 °C for 30 min, (ii) shelling GaS_xon AgInS₂core NCs at 280 °C for 60 min to produce the AgInS₂/GaS_xcore/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_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 AgInS₂and AgInS₂/GaS_xfrom certain damage.

Keywords: AgInS2; AgInS2/GaS x; AgInS2/GaS x /ZnS; exciton; luminescence; nanocrystals.