Fluorescent apparent quantum yields for excited molecules near dielectric interfaces

Fluorescence energy transfer from excited molecules to dielectric medium in terfaces was modeled as a many-dipole system. A formula for the apparent qu antum yield q(a), which expresses the ratio of the energy flux above the em itting dipoles to the total power emitted by these dipoles, was derived. Th e distances between Eu3+ ions of europium(III) thenoyltrifluoroacetonate (E uTTA) and the dielectric interfaces were controlled with alumina spacers of varied thickness, and the distance-dependence of the fluorescence intensit y of the Eu3+ ions was measured. The q(a) for 25 dielectric systems, where the emitting centers are located in alumina at a distance of 20 Angstrom fr om the interfaces, was calculated. Comparison between the calculated and ex perimental q(a) shows that the fluorescence energy transfer can be explaine d by the classical electromagnetic theory. At the short distance (10-50 Ang strom), the fluorescence quenching is very strong for almost all materials. For example, the emitting centers within 20 Angstrom of a transparent cond uctor In2O3 film surface will be quenched to below 1% of its normal fluores cence. Thus, the calculated q(a) may be considered as a characteristic para meter to evaluate materials for possible inclusion in diverse light-emittin g devices. (C) 2001 Elsevier Science B.V. All rights reserved.