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Influence of energy transfer on the structure of site-selection spectra of molecules

1986; Taylor & Francis; Volume: 57; Issue: 3 Linguagem: Inglês

10.1080/00268978600100441

1362-3028

R. Avarmaa, Raivo Jaaniso, Koit Mauring, Indrek Renge, Raivo Tamkivi,

Spectroscopy and Laser Applications

The influence of the excitation energy transfer on the selectively-excited fluorescence spectra of impurity centres is treated theoretically. The introduced model takes into account the Förster-type homotransfer in conditions of large inhomogeneous spectral broadening, whereas the transfer rate is assumed to be preaveraged over distances. The integral equation, describing the transfer processes via phonon wing overlap at a T → 0 limit, is solved numerically for different transfer rate values and excitation frequencies. It is shown that as a result of energy transfer the relative intensity of the nophonon line is drastically decreased for excitation in the high-energy part of the inhomogeneous band, while the decrease is less considerable at the ‘red’-edge excitation. The influence of the transfer rate on the observable Debye-Waller factors in the fluorescence and excitation spectra is also considered. The results of model calculations are compared with the experimental data obtained for chlorophyll-α and pheophytin-α in frozen organic solvents at T = 5 K at concentrations up to 7 × 10-3 M under selective laster excitation.