Designed Synthesis of Solid and Hollow Cu_2–<i>x</i>Te Nanocrystals with Tunable Near-Infrared Localized Surface Plasmon Resonance

Abstract

Solid and hollow structures of Cu_2–<i>x</i>Te nanocrystals are synthesized by the injection of a Te–TOP solution at different reaction times. Both types of Cu_2–<i>x</i>Te nanocrystals exhibit an intense absorption peak (localized surface plasmon resonance (LSPR)) in the near-infrared region, arising from excess holes in the valence band, and high molar extinction coefficients of 2.6 × 10⁷ M^–1 cm^–1 at 1150 nm and 8.1 × 10⁷ M^–1 cm^–1 at 1200 nm are demonstrated for the solid-type and hollow-type Cu_2–<i>x</i>Te nanocrystals, respectively. The experimentally observed extinction spectra and calculated extinction spectra based on the electrostatic approximation are studied. The LSPR responses in the near-infrared (NIR) region for both solid and hollow Cu_2–<i>x</i>Te nanocrystals are affected by the refractive index of the medium, whereas the NIR resonance shift is more obvious in the hollow-type Cu_2–<i>x</i>Te nanocrystals. Furthermore, the localized surface plasmon band of the Cu_2–<i>x</i>Te nanostructures can be tuned by post processing via oxidation and reduction methods (controlling their degree of copper deficiency)