Precise Control of Copper-Localized Surface Plasmon Resonance in the Near Infrared Region for Enhancement of Up-Conversion Luminescence

The surface plasmon resonance of copper in the near infrared region provides a novel method for enhancement of up-conversion luminescence compared to using gold and silver, as the former grants significant cost savings. In this study, we made a flat Cu film covered TiO2 to enhance the up-conversion fluorescence intensity. The results show that the deposition of copper/TiO2 dioxide nanocomposite film prepared via spin-coating has no effect on the structure of NaGdF4:Er3+, Yb3+. The absorption wavelength of the copper film moved from the original visible wavelength (~600 nm) range to the infrared wavelength after covering TiO2, and most obviously, the copper film covered two layers of TiO2 by about 16 nm; the peak of the absorption appeared at 835 nm due to the enhanced excitation field. The behavior of the nanocomposite film with NaGdF4:Er3+ and Yb3+ under 980 nm excitation was investigated; it provides a novel way for studying mental-enhanced fluorescence. Besides, the peaks of the fluorescence spectrum show different emissions at 542 nm and 660 nm, respectively. The copper nanoparticles-covered TiO2 layer can obviously enhance the fluorescence intensity, and the maximum enhancement factors of emission of NaGdF4:Er3+ and Yb3+ nanoparticles are 3.1 and 1.9 on the nanocomposite film, respectively.