Concentration effects on spectra and persistent hole-burning of porphyrin-doped Langmuir—Blodgett films

Abstract

The influence of impurity concentration on excitation and emission spectra, fluorescence decay rates and persistent spectral hole-burning parameters is reported for porphyrin dye molecules in a Langmuir—Blodgett film host. A shift of the fluorescence band and non-exponential radiative decay in heavily doped samples provide evidence of energy transfer. Hole widths in the heavily doped samples are strongly dependent on wavelength, becoming broader with higher excitation energy. No wavelength dependence of hole width and depth is observed for weakly doped samples. An analysis of the effect of Förster energy transfer on hole width and depth rules out this mechanism as being the whole explanation for the concentration and wavelength dependence. The effect of impurity aggregation is also inconsistent with our results.