Ag–Ga–S quantum dots (QDs) are obtained by colloidal synthesis in aqueous solutions with glutathione ligands at mild conditions. The QDs can be assigned to metastable orthorhombic, rhombohedral, or rocksalt-type phases, assuming a significant internal pressure within crystallites, while the conventional tetragonal AgGaS₂ phase is less likely formed. Similarly to these metastable phases, the QDs reveal a relatively narrow indirect bandgap contrary to the wide and direct bandgap of tetragonal AgGaS₂. Size-selected fractions of the colloidal solutions are separated by repeated centrifuging with addition of 2-propanol. The QD size is evaluated from atomic force microscopy, while the crystallite size determined using the Scherrer formula is underestimated. X-ray photoemission spectroscopy reveals that the QD composition changes from nearly stoichiometric for the fraction with the largest QDs toward Ag deficient and S rich for smaller QDs. The synthesized QDs are characterized by the absorption edge blueshift with decreasing QD size. A blueshift of the photoluminescence (PL) peak with decreasing QD size is observed as well as a nonmonotonous size dependence of the PL intensity. Raman spectra of the Ag–Ga–S QDs are discussed compared to those of bulk crystals and a strong contribution of surface phonons is revealed.

中文翻译：

---

Ag-Ga-S量子点的合成及光学性质

Ag-Ga-S 量子点 (QD) 是通过在温和条件下与谷胱甘肽配体在水溶液中进行胶体合成获得的。假设微晶内有显着的内部压力，QD 可以分配给亚稳态正交、菱面体或岩盐型相，而传统的四方 AgGaS ₂相不太可能形成。_{与这些亚稳相类似，QD 显示出相对窄的间接带隙，这与四方 AgGaS 2}的宽而直接的带隙相反. 通过添加 2-丙醇重复离心分离胶体溶液的大小选择部分。QD 尺寸是通过原子力显微镜评估的，而使用 Scherrer 公式确定的微晶尺寸被低估了。X 射线光电子能谱表明，QD 组成从具有最大 QD 的部分的接近化学计量变化为对于较小的 QD 缺乏 Ag 和富含 S。合成的量子点的特征在于吸收边蓝移随着量子点尺寸的减小。观察到随着 QD 尺寸减小的光致发光 (PL) 峰的蓝移以及 PL 强度的非单调尺寸依赖性。与块状晶体相比，讨论了 Ag-Ga-S QD 的拉曼光谱，并揭示了表面声子的强大贡献。