The enhancement of photoluminescence ͑PL͒ is demonstrated from silicon nanocrystals ͑Si-ncs͒ by strong coupling of excitons to surface plasmon polaritons ͑SPPs͒ supported by a Au thin film. SPPs excited via excitons in Si-ncs were Bragg scattered to photons by one-or two-dimensional gratings, and strong and directional PL was obtained. From the angular dependence of PL spectra, dispersion relations of electromagnetic modes involved in the light emission process were obtained. The overall

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... nt between experimentally obtained and theoretically calculated dispersion relations confirmed that the strong and directional PL is mediated by SPPs. The PL decay rate of Si-ncs increased by placing a Au thin film on top and the wavelength dependence of the rate enhancement agreed well with that of the calculated SPP excitation rate. This suggests that the observed PL enhancement is due to efficient energy transfer from excitons to SPPs followed by efficient scattering of SPPs to photons, resulting in the enhancement of luminescence quantum efficiency.