Nanoparticles: doped metal oxides

Degenerately doped metal oxide nanoparticles with carrier densities in the range of 1021 cm‑3 are characterized by localized surface plasmon resonances in the NIR.  The order of magnitude lower carrier density of these materials relative to noble metals and the large number of acceptor states in their conduction band (CB) make them very amenable to plasmon manipulation. The addition of charge carriers to their CB upon post-synthetic capacitive charging (electrochemistry or photo-doping) currently finds relevance for electrochromic applications. In the photo-doping process, light with energy larger than the optical bandgap (typically in the UV/vis) excites an electron from the valence band (VB) to the CB. The hole is scavenged leaving only the electron behind, charge balanced by a positive cation at the NC surface. In this way, the additional electrons remain in the NC tracked as a stronger and blue-shifted plasmon resonance. Thus, This an optically driven nano-manipulator is created.