Excitation energy transfer and trapping in dye-loaded solid particles.

The photophysics of several systems composed of a single dye or pairs of dyes attached to solid particles has been studied in the dry solid state at high dye concentrations taking into account light scattering and inner filter effects. Interaction among dye molecules and singlet-singlet energy transfer are relevant in these conditions, as has been demonstrated for pairs of dyes with suitable spectral overlap. For single dyes, after correction for radiative energy transfer, fluorescence quenching is observed as the surface concentration increases. This effect is explained by two different trapping models. Irrespective of the nature of the traps, concentration quenching may be of static (trap absorption) and dynamic (energy transfer) nature. The unraveling of energy trapping mechanisms is a key to the development of efficient photoactive solid materials.