Effects of surface ligands on localized surface plasmon resonance and stabilization of Cu2−xSe nanocrystals

Cubic Cu2−xSe nanocrystals (NCs) exhibit a strong localized surface plasmon resonance (LSPR) absorption in the near-infrared (NIR) region, in which the LSPR wavelength and stability are significant for the NIR-region applications in photo-thermal therapy and photoacoustic imaging. Herein, we have systematically studied the effects of surface ligands with varying the feeding ratio of oleylamine (OM) to oleic acid (OA) on LSPR behavior and stabilization of Cu2−xSe NCs, which were synthesized by using a typical hot-injection method. The LSPR wavelength of the as-obtained Cu2−xSe NCs could be tuned from 1260 to 1030 nm with an increase of the feeding ratio of OM to OA. Furthermore, these Cu2−xSe NCs showed different LSPR stability with varying feeding ratios of OM to OA. For the Cu2−xSe NCs synthesized in the presence of only OM, the LSPR could keep stable basically after exposure to air for 60 days. However, in the feeding ratio of OM to OA of 7:3 and 5:5 cases, the LSPR extinction spectra showed an obvious blue-shift in the wavelength. The characterized results indicated the different surface ligands had significant effects on the LSPR behavior and stabilization, and the LSPR change was in good agreement with the calculated results based on the Mie-Drude model. This work provides a new research idea for tuning the LSPR behavior of copper chalcogenide NCs.