Lifetimes and radiation patterns of luminescent centers close to a thin metal film.

The width d of an air gap between a 10-nm-thick luminescent europium benzoyltrifluoroacetone chelate film on a glass substrate and a 35-nm-thick layer of gold evaporated onto the base of a hemicylindrical high-index prism was varied between d >> lambda and d = 0. Thus the coupling of the luminescent centers (Eu(3+) ions, emission wavelength lambda = 612 nm) to the surface plasmons of the metal was varied. The luminescence lifetime decreased from tau = 520 microsec for d >> lambda to tau = 120 microsec for d = 0. By comparison of measured and calculated radiation patterns, i.e., of the angular distributions of the luminescent light emitted into the prism, the air gap d can be determined.