Structural and spectroscopic properties of zinc-tellurite doped samarium glass embedded with gold nanoparticles

Abstract

Modification in the structural, thermal and optical properties of samarium ions (Sm3+) doped zinc-tellurite glass with gold nanoparticles (Au NPs) embedment was studied. In this regard, two series of zinc-tellurite glass systems with composition (80-y)TeO2-20ZnO-ySm2O3, where 0.0 = y = 2.0 mol% and (79- x)TeO2-20ZnO-1Sm2O3-xAuCl3, where 0.00 = x = 0.10 mol% were prepared using melt quenching technique. Sm3+ ions and Au NPs concentration dependent structural, thermal and optical properties of these glass samples were determined. Structural characterizations were made using X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopy. Thermal properties were measured by differential thermal analyzer (DTA). The existence, size, and morphology of Au NPs in the glass matrix were examined via transmission electron microscopy (TEM). Optical properties of glass samples were determined using UV-Vis-NIR absorption and photoluminescence (PL) spectroscopy. The occurrence of broad hump in the XRD patterns verified the amorphous nature of glass samples. FTIR spectra exhibited three major bands which were allocated to the TeO3, TeO4 units and bending vibrations of Te-O-Te linkages or Zn-O vibrations. Raman spectra showed the bending vibrations mode of Te-O-Te and stretching vibration modes of nonbonding oxygen linked to the TeO4 and TeO3 units. TEM images manifested the existence of Au NPs of average diameter 17.12 nm. Both glass systems exhibited thermal stability and glass forming ability which was increased from 80 °C to 143 °C and from 0.37 to 1.03, respectively with the increase of Au NPs contents. The absorption spectra displayed ten prominent peaks corresponding to the transitions from the ground state (6H5/2) to various excited states of Sm3+ ions. Surface plasmon resonance (SPR) bands of Au NPs were detected at 652 and 715 nm. The bonding parameters of the prepared glass samples that were calculated from the absorption spectra revealed the covalent/ionic nature of the rare earth-ligand (Sm-O) bond. Optical band gap energies and the Urbach energy values were determined. The ligand field parameters estimation showed that the crystal field strength and the degree of covalency between ions were increased. Besides, the interelectronic f-f repulsion Racah parameters were decreased with increasing NPs contents. The room temperature PL spectra disclosed four prominent emission bands centered at 562 nm (green), 600 nm (orange), 644 nm (red) and 709 nm (red) which were assigned to the 4G5/2 ? 6H5/2, 4G5/2 ? 6H7/2, 4G5/2 ? 6H9/2 and 4G5/2 ? 6H11/2 transitions, respectively. Overall, the structural, thermal and optical properties of the studied tellurite glass system were strongly influenced by the embedment of Au NPs in the glass matrix. The alteration in the overall properties was attributed to the mediation of Au NPs surface plasmon, radiative transitions and cross-relaxation effects. The improvement in the properties of these glasses may be beneficial for different optical applications.