CHANGES IN FLUORESCENCE LIFETIMES INDUCED BY VARIATION OF THE RADIATING MOLECULES OPTICAL ENVIRONMENT

We report results of experiments with about 30 nm thick evaporated layers of an europium-chelate fluorescing at λ = 612 nm: i.) For layers on different substrates S1 in air the lifetime decreases with increasing refractive index n1 of S1. ii.) For a layer on a substrate S1 the lifetime decreases when the width d of an air gap between the layer and a second plate S2 is reduced from d å λ to d = 0. Theoretically, we derived analytic expressions for the spontaneous emission rates of electric and magnetic dipole transitions taking place in an atomic system embedded in a very thin layer of refractive index n0 and optical thickness n0d0 « λ/8, which is sandwiched between two dielectric loss-free media of refractive indices n1 and n2. Comparison of theory and experiment allows to determine the absolute quantum efficiency of the emitting state. © 1979.