| Quantum confined semiconductors (e.g. Si, CdSe) remain widely studied materials due to their potential application in a number of optical and optoelectronic devices such as LEDs, lasers, and photodiodes. Despite the large body of literature, the mechanism for luminescence in these materials remains poorly understood, particularly in the case of luminescent porous silicon. Specifically, it is not known whether emission is due to a spatial confinement of an optical exciton or simply a result of surface molecules or low lying defects in the nanocrystalline structure. We apply single molecule spectroscopic techniques to probe the luminescence of individual Si nanoparticles, eliminating the effects of spatial averaging, and uncovering previously unforeseen photo-physics such as: resolved vibronic structure, luminescence intermittency, random spectral wandering, and coupling between adjacent chromophores. Our results confirm the efficacy of the quantum confinement model in porous silicon, indicate the influence of oxide surface species on the emission, and show that the low bulk quantum efficiency is a result of a small number of highly efficient emitters.; The application of a quantum optical technique based on the Hanbury-Brown-Twiss two photon autocorrelation experiment will also be reported. This technique takes advantage of the non-classical nature of photoemission to probe the number radiative states present in a small excitation volume. The observation of photon anti-bunching from single CdSe quantum dots, a system with similar optical properties to porous silicon, at room temperature will be presented. Apart from providing a direct evidence for a solid state nonclassical light source (deterministic single photon emitter), this result proves that a single QD acts like an artificial atom, with a discrete anharmonic spectrum. In addition, the relative size of the anti-bunching signature can be used to determine the number (n = 1, 2 or 3) of emitting species present in an individual nanoparticle or an aggregate of nanoparticles. |
