Excitation Energy Dependence of Dye Fluorescence Lifetime in the Presence of Metal Nanoparticles

Abstract

The controlled manipulation of fluorescence properties of fluorophoreshas openedup new applications in biomedical fields1. Presence of metal nanoparticles willalter the fluorescence properties of dye molecules due to surface plasmons 2-9. We have investigated the fluorescence spectra, emission intensities and lifetimes of Rhodamine B dye molecules attached to silver nanoparticles, excited by ultrafast (100 fs) laser pulses, employing a fast (2 ps resolution) streak camera. Resonant and non-resonant energy coupling to the surface plasmons leads to fluorescence intensity quenching and enhancement, respectively. Interestingly, we also observe a systematic variation of fluorescence lifetime with excitation laser power: the lifetime is reduced from 2.5 ns to 1.8 ns when the laser power is increased from 0.1 mJ to 0.3 mJ. Results from this novel observation are analyzed and discussed in detail.