Cation-deficient copper chalcogenide nanocrystals (NCs) as a typical degenerated semiconductor have attracted great attention owing to their unique properties. However, the association between band structures and localized surface plasmon resonance (LSPR) in such NCs has not been thoroughly studied. Moreover, the synthesis of the colloidal Cu2-xSeyS1-y NCs with diverse crystal phases remains a challenge to date. Hence, we developed a facile method to synthesize a range of Cu2-xSeyS1-y-alloyed NCs with disparate crystal phases. We elucidated the tunable band structures and LSPR shift, and the results indicated that the modulation of the valance band maximum (VBM) position by Se/S alloying and the overlapping of the valence band and the Fermi level (EF) dominate LSPR properties in alloyed NCs. Not only the variation of Cu vacancy along with the induced free carrier concentration but also the negative shift of VBM contribute to the LSPR shift toward higher energy.
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