Localized surface plasmon resonances and its related defects in orthorhombic Cu3SnS4 nanocrystals

Abstract

Orthorhombic Cu3SnS4 nanocrystals (NCs) possessing obvious localized surface plasmon resonances (LSPR) in the near-infrared region (NIR) frequencies are prepared. In Cu3SnS4 NCs, valence state of Cu remains close to +1, indicating Cu+ occupies positions originally belong to Cu2+ in a similar way as Cu+ replaces Zn2+ to form Cu-Zn antisites in Cu2ZnSnS4. The increase of Cu/Sn ratio results in slightly red-shifted and weakened NIR absorption. Moreover, LSPR is also verified in wurtzite Cu2SnS3 NCs, although the observed peak maximum is red-shifted comparing to the LSPR band of Cu3SnS4 NCs. But the calculated free carrier concentration for Cu2SnS3 by Drude model is on the same order of magnitude with Cu3SnS4 in which sulfur vacancies acting as compensation centers could reduce hole density to some extent. Whereas Cu2ZnSnS4 presents almost no absorption due to its relatively lower hole concentration.