SITE-SELECTIVE FLUORESCENCE SPECTROSCOPY IN DYE-DOPED POLYMERS .1. DETERMINATION OF THE SITE-ENERGY DISTRIBUTION AND THE SINGLE-SITE FLUORESCENCE-SPECTRUM

Laser-induced fluorescence spectra have been measured, including narrow resonance fluorescence lines appearing at the same energy as the exciting light, for dye molecules doped in polymer films at low temperatures. This has been made possible by the combination of short light pulses from a cw mode-locked laser for the excitation and a time-correlated single-photon counting method for the detection. The distribution of the number of the molecules as a function of the energy of the zero-phonon line in the sample has been obtained from the excitation profile of the resonance fluorescence line. The fluorescence spectra of dye molecules in a single site have also been determined by making use of the saturation effect of the laser-induced fluorescence. The procedures of the experiment and analysis are reported in detail.