Regular papers

Fluorescence quenching and photobleaching in Au/Rh6G nanoassemblies: impact of competition between radiative and non-radiative decay

¹ Royal Institute of Technology, Division of Optics, 164 40 Kista, Sweden
² Royal Institute of Technology, Division of Functional Materials, 164 40 Kista, Sweden
³ Zhejiang University, Center for Optical and Electromagnetic Research, 310058 Hangzhou, China
⁴ Aalto University, Department of Applied Physics, 00076 Aalto, Finland
⁵ University of Eastern Finland, Department of Physics and Mathematics, 80101 Joensuu, Finland

^* lindong@kth.se

Received: 14 January 2011

Abstract

We report the study of fluorescence quenching from nanoassemblies formed by Rhodamine 6G and gold nanoparticles (Au NPs) of 2.6 nm radius. The presence of Au NPs induces long-term degradation of the photostability (photobleaching) of Rhodamine 6G used as a gain medium in a Fabry-Perot laser cavity. We found that the degradation gets profound when the Au NPs concentration is significantly increased. Calculation of the radiative rate and direct time-resolved measurement of the fluorescence decay indicates that both the decrease of radiative decay rate and increase of non-radiative decay rate are responsible for the fluorescence quenching and photostability degradation. An energy transfer from the dye molecules to gold nanoparticles is dominating within small distance between them and suppresses the quantum efficiency of Rhodamine 6G drastically. In a long time scale, the photobleaching rate was slowing down, and the laser output intensity reached a stabilized level which depends on the gold nanoparticles concentration.