The up-conversion luminescent properties and silver-modified luminescent enhancement of YVO4:Yb3+, Er3+ NPs

In this paper, the unique up-conversion luminescence (UCL) properties of as-prepared and annealing YVO4:Yb3+, Er3+ nanoparticles (NPs, similar to 100 nm) and the corresponding YVO4:Yb3+, Er3+@Ag hybrids under 980 nm excitation were systemically studied through power-dependent, temperature-dependent emission spectra and dynamics. It is interesting to determine that the radiative transition rate of H-2(11/2)/S-4(3/2)-I-4(15/2) for Er3+ ions in YVO4 is about an order of magnitude faster than that in the other hosts due to the wave function coupling with the 3d orbital of V5+ and, thus, the up-conversion (UC) green emissions of YVO4:Yb3+, Er3+ NPs is efficient. In addition, efficient novel UC broad band centering around 630 nm (1.97 eV) was observed in YVO4:Yb3+, Er3+ powders, which was attributed to defect emissions related to oxygen vacancies near V5+ sites in the lattices of YVO4. In as-prepared YVO4:Yb3+, Er3+@Ag hybrids colloids, more than one order UCL enhancement than YVO4:Yb3+, Er3+ was observed. Powder and the annealing samples lead the UCL enhancement effect to disappear. The main UCL enhancement mechanism of YVO4:Yb3+, Er3+@Ag hybrids colloids was attributed to prevent YVO4:Yb3+, Er3+ interaction with the solution, instead of surface plasmon enhancement (SPE) effect.