Optical spectra and exciton-light coupled modes of a spherical semiconductor nanocrystal

The structures of optical spectra of a semiconducting sphere are studied over a wide range of radius. The calculation is based on a microscopic nonlocal theory and we reformulate the theory to simplify the procedure. The nonlocal theory enables us to analyze correspondences between spectral peaks and exciton states directly, decompose a scattered field into an exciton contribution and the Mie scattering, and provide complex eigenenergies of the exciton-light coupled modes. The imaginary part of the eigenenergy gives the radiative decay width of the mode, and for each mode there exists an optimal radius to enhance the width. When the Mie scattering becomes comparable to the scattering by exciton, there appears a dip structure in the optical spectra around the energy of the exciton-light coupled mode.