Plasmon-tuned upconversion luminescence in silanized NaYF4:Yb,Er nanocrystals via ultra-thin gold film

Abstract Plasmonic enhancement of the upconversion luminescence (UCL) via ultra-thin gold film was rarely investigated so far and the photophysical mechanism was not completely clear, although the noble metal nanoparticles or nanorods have been used to enhance the UCL of upconverting nanophosphors. Two types of sandwich geometry involving gold film and silanized nanophosphors were designed and facilely fabricated. Both intensified and quenched UCL were observed under the excitation of 980 nm NIR laser. Based on the steady state spectra and the UCL decay data, the coupling of the excitation energy with the surface plasmon resonance (SPR) absorption band of ultrathin gold film with significant roughness surface could be responsible for the UCL enhancement. Results indicated that employing the SPR effect on the rough surface of gold film could be a promising strategy to achieve efficient and tunable UCL, which makes it more practical for the widespread applications.