fulltext33 - Excitation Energy Transfer and Trapping in...

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Unformatted text preview: Excitation Energy Transfer and Trapping in Dye-Loaded Solid Particles H ERN ´ AN B. R ODR ´ IGUEZ AND E NRIQUE S AN R OM ´ AN INQUIMAE/DQIAYQF, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina 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 en- ergy 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, fluores- cence 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. Key words: solid particles; energy trapping; dye aggregation; quenching radius Introduction The photophysical and photochemical study of dyes in heterogeneous media is relevant to different fields. The development of photosensitizers, 1 photo- catalysts, 2 nanosized reactors, 3 and visible light–driven solar cells, 4 among other real or foreseeable applica- tions, either require or are advantageously driven in constrained environments. In general, light collection efficiency is a key for the development of useful pho- toactive materials. Accordingly, high dye concentra- tions are needed to afford substantial absorption of incident light. Moreover, energy transfer among dif- ferent dyes may be a suitable strategy to broaden the excitation spectrum and/or to canalize the excitation energy to accomplish the desired objective. High lo- cal concentrations, however, give rise to deactivation processes either by the formation of dye aggregates or enhanced energy trapping. In general, a compromise has to be found between the large dye concentrations needed for substantial light absorption and excited- state deactivation due to dye-to-dye interactions at such concentrations. Frequently, the cited applications are carried out in systems composed of particles or particle aggregates of micrometer size, adding complexity to the study Address for correspondence: Enrique San Rom´an, Ciudad Universi- taria, Pabell´on II, C1428EHA Buenos Aires, Argentina. Voice: ++ 5411- 4576-3358; fax: ++ 5411-4576-3341. [email protected] as compared with experiments carried out in solution or nanoparticle suspensions. Several factors have to be taken into account in this case: 1) interactions be- tween dyes and the surface; 2) reabsorption and reemis- sion processes present at high overall concentrations; 3) multiple light scattering; 4) formation of ground- state aggregates; and 5) other interactions leading to...
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fulltext33 - Excitation Energy Transfer and Trapping in...

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