This paper presents for the first time the systematic synthesis of AgInS2 (AIS) nanocrystals (NCs) with different sizes of 2.6 – 6.8 nm just by controlling only the reaction temperature. The synthesis of AIS core NCs was carried out in 2 steps: (i) synthesis of Ag2S NCs and then (ii) partial exchange of Ag+ with In3+ in the template Ag2S NCs. For step (i), Ag2S NCs of different sizes were synthesized by reaction of the Ag and S precursors at different temperatures of 30 oC to 130 oC, for the same reaction time of 30 min. For step (ii), AIS NCs were created by the exchange of Ag+ with In3+ at 120 oC for 60 min. Finally, GaSx was shelled on AIS core NCs to produce the AgInS2/GaSx core/shell structures. The synthesized AIS/GaSx NCs demonstrate the clear excitonic absorptions and strong, narrow excitonic luminescence peaking at 530 – 606 nm depending on the size of AIS core NCs.

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