Tunable near-infrared localized surface plasmon resonances of djurleite nanocrystals: effects of size, shape, surface-ligands and oxygen exposure time

Colloidal djurleite nanocrystals exhibit a well-defined and strong localized surface plasmon resonance absorption in the near-infrared region, which arises from the excess free holes in the valence band. The near-infrared localized surface plasmon resonance absorption wavelength of the as-obtained djurleite nanocrystals can be modulated by varying their size and shape, which are controlled through the variation of the reaction conditions during the synthesis. For a given size, the plasmonic behavior of the spherical nanocrystals exhibits an obvious surface-dependent shift due to the different electron-donating abilities of the surface ligands, which leads to the change of hole density. Moreover, the plasmonic band of the djurleite nanocrystals shifts to a shorter wavelength upon exposure to air for longer time, during which no crystal structure is altered, and this blue-shift may be attributed to the increasing density of copper vacancies. The experimental results of the near-infrared plasmonic behavior are in good agreement with the calculated results based on the Mie–Drude model.