Tuning local surface plasmon resonance of silver and photoluminescence intensity enhancement by adding copper

Abstract

In order to match the local surface plasmon resonance (LSPR) frequency of Ag with the frequency of light that needs enhancement, the relationship between the free carrier concentration and LSPR frequency must be considered in order to design noble alloy nanoparticles (NPs) to substitute for pure Ag. In this study, Ag, Cu, and Ag-Cu continuous films were prepared by magnetron sputtering to investigate the relationship between the free carrier concentration and LSPR wavelength, which were tested with a Hall effect detector and ultraviolet-visible spectrophotometer, respectively. Ag and Ag-Cu NP films were deposited by short-time magnetron sputtering on an organic-YAG:Ce3+ substrate to test and compare their effects on the photoluminescence (PL) intensity. The thickness of the metal films was determined using an optical thin film analysis system. The morphology was observed for the continuous and NP films by scanning electron microscopy. Compared with the pure Ag films, the Ag-Cu films had a lower free carrier concentration and longer peak wavelength, which was closer to the emission wavelength of YAG:Ce3+. The enhancement ratio for the PL intensity reached a maximum of 1.16 with the Ag NP films. By contrast, for the Ag-Cu NP films with a shorter deposition time, the PL enhancement ratio reached 1.125, where the optimal ratio of Ag to Cu for the product of sputtering power and time was 2:1. The addition of Cu to Ag is beneficial for industrial production because the cost of the materials and the preparation time for Ag-Cu alloy NP films are more than 50% lower compared with pure Ag NP films.