Upconversion luminescence enhancement of the composite films by coupling local surface plasmon effect and photonic crystals effect

Noble metal surface plasmon resonance or photonic crystals (PCs) effect is a novel and effective method for improving upconversion luminescence (UCL). UCL can be effected by the size, thickness of the noble metal film and the photonic band gap (PBG) of the PCs. So it is important to improve UCL by coupling surface plasmons resonance (SPR) with PCs effect. In this work, the PCs/Ag/UC composite films were fabricated to improve the upconversion emission of NaGdF 4 :Er 3+ /Yb 3+ /Al 3+ nanocrystals, and the influence of the Ag layer thickness on spectral properties was investigated. Studies reveal that the Ag layer thickness and morphology have a major impact on the Ag nanoparticles (NPs) plasma resonance and UCL intensity of NaGdF 4 :Er 3+ /Yb 3+ /Al 3+ nanocrystals for PCs/Ag/UC composite films. The highest enhancement factors of the red and green emissions were found to be 43 and 42 under 980 nm excitation, respectively. That is attributed to the coupling effect of the Ag NPs local SPR and PCs Bragg reflection, the local electromagnetic field enhancement produced by the excitation wavelength overlapping with the photonic band gap and strong plasmon resonance band overlapping with emission wavelength.