Preparation and upconversion emission enhancement of SiO_2 coated YbPO_4: Er^3+ inverse opals with Ag nanoparticles

Abstract

The rare earth ions doped up-converting inverse opals exhibited application potential in the fields of biosensors and optic–electronic devices. However, there are two major factors which have limited their applications. One is the parity forbidden characters of 4f-f transitions of rare earth ions. Another factor is their low upconversion luminescence efficiency caused by the surface defects. In the present work, the SiO2 shell was coated on the skeleton surface of YbPO4:Er3+ inverse opals to protect the luminescent ions, and about a 10-fold enhancement of upconversion luminescence was obtained. Additionally, the localized surface plasmon resonance from Ag nanoparticles was used to enhance the upconversion luminescence of SiO2 coated YbPO4:Er3+ inverse opals. The green and red upconversion luminescence of inverse opal was enhanced selectively. Finally, the green and red upconversion luminescence are enhanced by about 50 and 30 folds by coupling effect of SiO2 coating and Ag nanoparticles, respectively. The selective enhancement mechanism of upconversion luminescence was investigated.