Abstract

Nanocrystallites of non-stoichiometric copper sulfides were synthesized via the reaction between [Cu(NH₃)₄]²⁺ and thiourea in sealed autoclaves at the low temperature of 60 °C for 3 h. Thiourea played a key role in the process of Cu₉S₈ nanocrystal formation. Through adjusting the redox atmosphere, Cu₇S₄ and CuS were obtained from the freshly formed Cu₉S₈ nanocrystals. The products were characterized by means of X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), FT-IR spectroscopy and transmission electron microscopy (TEM) techniques. The Cu ∶ S atomic ratios for Cu₉S₈ and Cu₇S₄ were 9 ∶ 8.08 and 7 ∶ 4.05, respectively, analyzed by inductively coupled plasma (ICP) spectroscopy. The possible mechanism of phase transformation among copper sulfides (Cu₉S₈, CuS, and Cu₇S₄) was discussed. The optical properties of the products were also recorded by means of UV–vis absorption, and photoluminescence spectroscopy.