Enhancement of down- and upconversion intensities in Er3+/Yb3+ co-doped oxyfluoro tellurite glasses induced by Ag species and nanoparticles

Abstract New oxyfluoro-tellurite glasses co-doped with Er 3+ /Yb 3+ and containing silver species and nano particles (NPs) were prepared using the conventional melt quenching technique. The X-ray diffraction patterns obtained in this work do not reveal any crystalline phase in the glass. Heat treatment at 290 °C, for about 6 h, of an Er 3+ /Yb 3+ co-doped oxyfluoro-tellurite glass containing 1.0 mol% AgNO 3 yielded well-dispersed, nearly spherical Ag NPs, as verified by transmission electron microscopy. The observed surface plasmon resonance (SPR) band was observed around 490 nm for heat treated glasses containing only silver. Upon off resonance (375 nm) and in resonance (486 nm) excitation of SPR band, the intense visible (520, 540 and 650 nm) and NIR (0.98 µm and 1.53 µm) downconversion emission bands were observed and further enhanced with the increase of Ag concentration and heat treatment duration up to 6 h. An intensity drop was observed by further heat treatment (up to 9 h). In addition, enhancement of upconversion emissions, in the green and red, as a function of Ag concentration and heat treatment time, has also been verified. The intensity was found to be enhanced by increasing the Ag concentration and heat treatment time up to 3 h. However, further increase in the heat treatment time duration (up to 9 h) resulted in reduced intensities. Enhancement in the luminescence intensity was discussed in terms of the surface plasmon resonance whereas the quenching was attributed to the intense absorption of photons, emitted from RE ions, by larger Ag NPs.