Collective excitations in charged nanocrystals and in close-packed arrays of charged nanocrystals

We present self-consistent tight binding calculations of the dielectric response of charged semiconductor nanocrystals. We predict collective effects such as the oscillation in opposite phase of the additional electron and of the plasma of valence electrons near the resonance. In arrays of charged nanocrystals, the coupling between infrared light and collective excitations is shown to be strong, the real part of the dielectric constant becoming negative in some part of the spectrum. Transverse and longitudinal excitation modes obeying the Lyddane-Sachs-Teller equation are predicted.