Excited states of tetrahedral single-core ${\mathrm{Si}}_{29}$ nanoparticles

We dispersed bulk crystalline Si into identical hydrogenated nanoparticles with negligible impurities and defects, which provide the opportunity for detailed comparison between measurement and theory. The UV photoluminescence of a dispersion of 1 nm silicon particles was studied. Distinct bands appear in the emission spectra with the lowest peaks in wavelength identified to be at 400, 360, and 310 nm with optimal excitation at 3.7, 4.0, and 4.6 eV, respectively. The multiple photoluminescence bands are analyzed in terms of the molecularlike energy levels of one bulklike and two nonbulklike reconstruction configurations of the filled fullerene single-core ${\mathrm{Si}}_{29}{\mathrm{H}}_{24},$ calculated by quantum Monte Carlo calculations and by time-dependent density functional theory. The measured bands are in close agreement with the excited states of the ideal bulklike configuration. However, there is a possibility that some of the observed bands might originate from the nonbulklike reconstructions. The Stokes shifts are discussed in terms of radiative relaxation via the molecularlike states versus charge carrier relaxation via the underlying continuum states.