Preparation and Upconversion Emission Investigation of the YVO 4 :Yb 3+ :Er 3+ Nanomaterials and Their Coupling with the Au Nanoparticles

YVO4:Yb3+:Er3+ nanoparticles and their mixture with Au nanoparticles have been fabricated by a simple chemical method. With the excitation of a 975-nm laser, both samples had strong upconversion emissions at 2.18, 2.25, and 2.36 eV, which correspond to the transitions 4F9/2 → 4I15/2, 4S3/2 → 4I15/2 and 2H11/2 → 4I15/2 of Er3+ ions, while the emission at 2.36 eV has a large overlap with the resonant absorption energy, 2.34 eV, of the Au nanoparticles. With the coupling of the Au nanoparticles, the upconversion emission at 2.36 eV presents a strong quenching effect which is due to the energy transfer from the Er3+ ions to the Au nanoparticles. This depends on the energy difference between the emission of the Er3+ ions and the absorption of the Au nanoparticles. The upconversion power dependence shows that the slope factor of the power dependence is about 3 for a high pump power, which means that the upconversion process is a three-photon process for both samples.