Electronic energy transfer at semiconductor interfaces. I. Energy transfer from two-dimensional molecular films to Si(111)

The fluorescence decays from submonolayers of pyrene separated from Si(111) by Xe spacer layers are measured as a function of spacer thickness (17–200 Å), pyrene coverage, and emission wavelength. The results are explained in terms of two decay channels: energy transfer and trapping among the molecules in the two-dimensional pyrene overlayer, and excitation of electrons from the valence to the conduction band in the Si(111) by the dipole near field of the electronically excited pyrene molecule. The intralayer energy transfer is modeled using the Kohlrausch equation N(t)=N0 exp(−t/τ)α, in which α is related to the distribution of pyrene molecules in energy. Energy transfer from the molecule to the semiconductor is modeled using the classical image dipole theory. The classical model is used to calculate the energy transfer rates from a dipole to Si and GaAs as a function of dipole–semiconductor separation, and as a function of dipole emission wavelength.