Fluorescent apparent quantum yields for excited molecules near dielectric interfaces

Fluorescence energy transfer from excited molecules to dielectric medium interfaces was modeled as a many-dipole system. A formula for the apparent quantum yield q , which expresses the ratio of the energy flux above the emitting dipoles to the total a 3 Ž . power emitted by these dipoles, was derived. The distances between Eu ions of europium III thenoyltrifluoroacetonate Ž . EuTTA and the dielectric interfaces were controlled with alumina spacers of varied thickness, and the distance-dependence of the fluorescence intensity of the Eu3 ions was measured. The q for 25 dielectric systems, where the emitting centers are a ̊ located in alumina at a distance of 20 A from the interfaces, was calculated. Comparison between the calculated and experimental q shows that the fluorescence energy transfer can be explained by the classical electromagnetic theory. At the a ̊ Ž . short distance 10 50 A , the fluorescence quenching is very strong for almost all materials. For example, the emitting centers ̊ within 20 A of a transparent conductor In O film surface will be quenched to below 1% of its normal fluorescence. Thus, the 2 3 calculated q may be considered as a characteristic parameter to evaluate materials for possible inclusion in diverse light-emitting a devices. 2001 Elsevier Science B.V. All rights reserved.