Quantitative X-ray absorption and emission spectroscopies: electronic structure elucidation of Cu2S and CuS

Cu2S and CuS have been under intense scrutiny, with the aim of understanding the relationship between their electronic structures and their commercially important physical properties. Here, X-ray absorption and emission spectroscopic data have been analyzed using a quantitative, molecular orbital (MO) based approach to understand the electronic structure of these two complex systems. Cu2S is shown to have a significant amount of Cu2+ sites and therefore Cu0 centers. The presence of low-valent Cu is correlated with the electrical conductivity of Cu2S, especially at high temperatures. CuS is shown to have tetrahedral Cu2+ and trigonal Cu1+ sites, with crystal planes that have alternating high and low charge on the Cu centers. This alternating charge density may contribute to internal energy transitions required for photoluminescence properties. The in-depth electronic structure solutions presented here not only solve a complicated much-debated problem, but also demonstrate the strength of a quantitative MO based approach to X-ray spectroscopies.