Localized surface plasmon absorption features arise at high doping levels in semiconductor nanocrystals, appearing in the near-IR range. The surface plasmons of Sn-doped In oxide nanocrystal films can be dynamically and reversibly tuned by postsynthetic electrochem. modulation of the electron concn. Without ion intercalation and the assocd. material degrdn., a textgreater1200 nm shift in the plasmon wavelength and a factor of nearly 3 change in the carrier d. was induced.