Time-resolved fluorescence spectra were measured for two kinds of permethyldecasilanes, Me(SiMe2)(10)Me and Ph(SiMe2)(10)Ph, in fluid solutions at room temperature, in frozen solutions and in vacuum-deposited thin films. Time-dependent red-shifts were clearly observed in fluid solutions but not in dilute frozen solutions, which was discussed in terms of conformational relaxation in the excited states. In concentrated frozen solutions, significantly red-shifted, long-lived fluorescence bands appeared, indicating the formation of molecular aggregates. Temperature dependence of fluorescence lifetimes as well as peak wavelengths for films were discussed with respect to exciton migration followed by trapping in localized sites.