• nanoparticles;
  • surface activation;
  • femtosecond spectroscopy;
  • UV-vis spectroscopy;
  • hydrodynamic size;
  • proximity length


Most of the optical properties of nanoparticles (NPs) depend on a nonadditive effect, where there is a maximum (or optimum) value at a specific distance from the NP surface (proximity length). However, knowledge on the relation between the specific surface layer and light responsiveness of NPs is limited. In this study, surface properties of NPs are modulated by electron beam (e-beam) treatment together with ionic control of the NP surface and dispersing media. The surface modification in terms of the proximity length is found to be critical to the selective enhancement of light absorbance in the ultraviolet-visible (UV-vis) and terahertz (THz) regions. In particular, the non-temporarily electron-activated NPs absorb short wavelength UV-vis light, rendering them particulary advantageous for solar energy use. The control over the physical properties of general light-responsive NPs is a new approach to designing solar-energy-based technologies.