Plasmon-Enhanced Upconversion Fluorescence in Er3+:Ag Phosphate Glass: the Effect of Heat Treatment

The melt quenching method is used to prepare erbium-doped silver nanoparticle (NP) embedded phosphate glass. The effect of annealing on the glass on the formation of silver NPs produced by the reduction of silver (Ag+ -->Ag-o) is studied. The glass samples are characterized by x-ray diffraction, UV-vis-NIR absorption, photoluminescence spectroscopy and transmission electron microscopy (TEM) imaging. The absorption spectra reveal not only the peaks due to Er3+ ions, but also the surface plasmon resonance band of silver NPs located around similar to 442 nm. The TEM imaging shows the homogeneous distribution of silver NPs of almost spherical shape with an average diameter of similar to 5 nm. Upconversion luminescence spectra show two major emissions at 550 and 638 nm, originating from the S-4(3/2) and F-4(9/2) energy levels of the Er3+ ions, respectively. The enhancement in the luminescence intensity of both the green and red bands is found to be due to the effective local field of the silver NPs as well as the energy transfer from the nanoclusters, comprised of centers with silver ions bound to silver atoms in dimers or trimers to Er3+ ions, whereas quenching occurred due to the energy transfer from erbium ions to silver NPs (Er3+ -->Ag-o).