Ion-implanted silver nanoparticles for metal-enhanced fluorescence

Abstract

Metal Enhanced Fluorescence (MEF) has promising applications in the field of optical displays, bio-sensing and photodynamic therapy. In this work, we exploit the plasmons of embedded silver nanoparticles (Ag NPs) fabricated by ion implantation to enhance the fluorescence of Coumarin515 dye (C515) via MEF. Ion Implantation of 70 keV Ag ions in quartz matrix at different fluences was carried out to synthesize Ag nanoparticles inside quartz matrix. The formation of Ag NPs is characterized by the optical absorption measurements and approximate sizes of Ag NPs was obtained from the fitting of the optical absorption spectra with Mie theory calculations. Rutherford Backscattering Spectrometry (RBS) measurement was used to obtain the depth profile and concentration Ag within the substrate. From the RBS results, it was determined that front edge of the layer containing Ag was formed at an average depth of 16 nm below the surface, which closely agreed with Stopping and Range of Ions in Matter (SRIM) calculations. Increase in the size of the NPs is observed as the fluence of the Ag within the substrate is increased. The MEF of drop casted C515 dye was studied using steady-state emission and excitation spectra measurements. Fluorescence enhancement factor ranging from 1.0 to 2.1 with a maximum enhancement for the largest size NP was obtained. The observed MEF was ascribed to a combination of plasmon enhancement with larger nanoparticles and to increased plasmonic hot spots.