Spectroscopic studies of samarium-doped sodium tellurite glass containing silver nanoparticles

Abstract

Samples of samarium doped tellurite glass containing Ag nanoparticles with molar composition (74.5 – x) TeO2 + 25 Na2O + 0.5 Sm2O3 + x Ag where, 0.5 mol% = x = 2.0 mol% have been successfully made by melt quenching technique. The amorphous nature of the glasses has been confirmed using X-ray Diffraction and the presence of Ag nanoparticles in the glass samples is verified using Transmission Electron Microscopy (TEM). It is found that the nanoparticles are almost spherical in shape with an average diameter of 31.2 nm. In this study, the effects of adding various concentrations of Ag nanoparticles into the glass samples to the thermal, structural, optical and emission properties of the glass are investigated. The thermal parameters, such as the glass transition temperature Tg, crystallization temperature Tc, melting temperature Tm and thermal stability (Tc -Tg) of the glass have been investigated using Differential Thermal Analysis (DTA) technique. It is found that the introduction of Ag nanoparticles in the glass network has increased the network rigidity and therefore increases the glass thermal stability. The vibrational spectrum of the glass has been studied using Fourier Transform Infrared (FTIR) spectroscopy. The spectra exhibit four absorption bands around 609.69 cm-1, 736.76 cm-1, 1636.0 cm-1 and 3434.56 cm-1. The presence of Sm3+ ions and Ag nanoparticles however did not give any significant change to the infrared spectra. From the UV-Vis-NIR spectra, eight absorption peaks have been observed around 398 nm, 471 nm, 947 nm, 1085 nm, 1238 nm, 1386 nm, 1492 nm and 1546 nm, which correspond to the transitions from ground state of 4I15/2 to the excited state of 6F1/2, 6F3/2, 6F5/2, 6F7/2, 6F9/2, 6F11/2, 4I3/2, and 6P5/2 respectively. The values of the optical band gap Eopt of the glass systems lie between 2.806 eV to 2.878 eV and these values are slightly shifted towards higher energies as the Ag nanoparticles content is increased; probably due to the increase of non-bridging oxygen in the glass samples. The Urbach energy Etail is found to lie between 0.230 eV to 0.268 eV. The effect of embedding nanoparticles to the luminescence properties of the glass has been investigated through photoluminescence measurements. The photoluminescence spectra at 406 nm excitation wavelength revealed four emission bands at 562 nm, 599 nm, 645 nm and 705 nm corresponding to 4f-4f transitions; 4G5/2?6H5/2, 4G5/2?6H7/2, 4G5/2?6H9/2 and 4G5/2?6H11/2 respectively. Incorporation of Ag nanoparticles enhances the intensity of these emission bands and the enhancement increases with the increase in the content of Ag nanoparticles. The luminescence enhancement is due to energy transfer from silver plasmon band to Sm3+ ion.