Highly luminescent water-soluble quaternary Zn–Ag–In–S quantum dots and their unique precursor S/In ratio-dependent spectral shifts

Quaternary I–II–III–VI semiconductor quantum dots (QDs) containing less toxic elements are receiving increasing attention because of their promising applications in solar cells, light-emitting diode (LED), and biological labeling. Despite its advantages, the quaternary system is more complex than the binary and ternary analogues. This is reflected in the difficulty to control the size, size distribution, elemental composition, and optical properties of quaternary I–II–III–VI QDs, especially in aqueous medium. In this work, we have synthesized new aqueous quaternary Zn–Ag–In–S (ZAIS) QDs with tunable photoluminescence (PL) for the first time, giving the highest PL quantum yield (QY) of 30%, which is close to those of the conventional well-developed aqueous II–VI QDs. Most importantly, three unique spectral shifts depending on precursor S/In ratio were observed in this quaternary system. The spectral were characterized by diverse analytical methods to systematically establish distinct features of the quaternary nanomaterials. The results demonstrate the potential utility of this new water-soluble system in fundamental and applied researches with quaternary QDs.