Localized Surface Plasmon Resonance in CuGaS2 Nanoparticles Dictated by Crystal Phase

Localized surface plasmon resonance (LSPR) is widely applied in photo-functional technologies such as photocatalysis and solar cells. Research into LSPR materials has recently extended to semiconductor nanoparticles (NPs) because their composition and structure flexibility allow for tuning of optical properties. However, many of the crystallographic factors governing the LSPR of semiconductor NPs are not understood due to the difficulty of controlling the crystal structure of NPs. Here we report for the first time on the crystal structure and size-controlled synthesis of CuGaS2 (CGS) NPs which are typical I-III-VI semiconductors. Moreover, we investigate their LSPR properties to reveal the crystal structure dependence of LSPR extinction. Chalcopyrite and wurtzite CGS (c-CGS and w-CGS, respectively) dictate LSPR in the NIR region. The extinction coefficient of c-CGS was approximately 3 times larger than that of w-CGS because of the larger polarizability of c-CGS. Semiconductors with larger polarizability are better candidates as NIR light-harvesting materials for plasmon-based photocatalysis and solar cells. These results should significantly deepen our understanding of semiconductor plasmonics and serve as a foundation for developing highly efficient energy conversion systems.