Metal-enhanced fluorescence from thermally stable rhodium nanodeposits

Different density rhodium nanoparticulate substrates were fabricated by electron-beam physical vapor deposition in order to study the fluorescence of close-proximity fluorophores to the high thermally stable rhodium nanoparticles. We observed an apparently constant metal-enhanced fluorescence (MEF), when fluorophores were placed in close proximity to rhodium nanoparticles before and after autoclaving of the substrates. Fluorophores with different emission wavelength maxima and free-space quantum yields have also been studied and can undergo different enhancements, a 2.5-fold increase in far-field luminescence was observed from 15 nm Rh films for Tinopal, and up to a 10-fold enhancement was observed for fluorescein. Similarly, the near-field fluorescence enhancement values were estimated to be similar to 125 and 500 fold, respectively. Further, the electromagnetic field distributions around different size Rh nanoparticles were simulated using FDTD to understand the wavelength dependence of the e-field. Our findings show that the decay time of fluorophores was not reduced near to the rhodium substrates, suggesting only an enhanced electric field component is the mechanism for fluorescence enhancement.