Long range enhancement of molecular fluorescence by closely packed submicro-scale Ag Islands

Abstract

We found that closely packed submicro-scale Ag islands (each ∼370 nm across and ∼90 nm in height on the average) produced not only extremely short-range fluorescence enhancement for rhodamine dye (RhB) placed only ∼1 nm away from the metal surface, but also a novel, long-range enhancement for the same dye for the metal- molecule distance up to ∼50 nm. The net enhancement factor for the spin-coated RhB, with a fluorescence quantum yield of ∼2 % in the absence of Ag islands, was as high as ∼20-folds at the metal-molecule distance of ∼30 nm. We propose that strong interparticle surface plasmon interactions involving such large Ag islands play crucial roles for the long-range fluorescence enhancement. © 2009 The Surface Science Society of Japan.