Variations in the Efficiency of Fluorescence Excitation in Anthracene

Abstract

The efficiency with which fluorescence is excited in single crystals of anthracene has been reported to vary considerably with both the excitation wavelength and the condition of the crystal. These variations are analyzed quantitatively in this paper. It is assumed that the variations are principally the effect of a layer of anthraquinone which forms when the crystal is abrased or aged in the atmosphere. A model which takes into account selective absorption of incident radiation in this surface layer of anthraquinone, specular reflectance by the bulk crystal, quenching of the fluorescence via nonradiative exciton decay at the surface, and the absorption characteristics of the bulk crystal (including reabsorption and re-emission of part of the fluorescence) is used to obtain a theoretical fluorescence excitation spectrum. This spectrum agrees very well with the corresponding experimental spectrum.