Saman Qadir Mawlud / Physics Department
Five series of samarium doped sodium tellurite glass embedded with gold nanoparticles (Au NPs) in the composition (80-x) TeO2-20Na2O-xSm2O3 (x=0, 0.3, 0.6, 1, 1.2, 1.5 mol%), (79-x)TeO2-20Na2O-1Sm2O3-xAuCl3 (x=0, 0.2, 0.4, 0.6, 0.8, 1 mol%), (80-x)TeO2-20Na2O-xAuCl3 (x=0.2, 0.4, 0.6, 0.8, 1), 78.6TeO2-20Na2O-1Sm2O3-0.4AuCl3 (Heat treated at 300 oC, 325 oC, 350 oC, 375 oC) and 78.6TeO2-20Na2O-1Sm2O3-0.4AuCl3 (Heat treated for 3h, 6h, 12h, 24h), were prepared using conventional melt quenching technique and characterized by X-ray diffraction (XRD), differential thermal analyzer (DTA), transmission electron microscopy (TEM), Raman spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, absorption spectroscopy, and emission spectroscopy. The amorphous nature of the glass was confirmed using the X-ray diffraction method. The increase in Tg from 265.6 to 270.9 °C as revealed by DTA analysis attributed to the arrangement of Au NPs in the glass matrix. The homogeneous distribution and growth of spherical and non-spherical Au NPs (average size ~3.36±0.076 nm to ~10.62±0.303 nm) in the glassy matrix was evidenced from the transmission electron microscopy (TEM) analysis. The UV-Vis-NIR absorption spectra showed 9 bands corresponding to transition bands from ground state 6H5/2 to excited states 6P3/2, 4I11/2, 6F11/2, 6F9/2, 6F7/2, 6F5/2, 6F3/2, 6H15/2 and 6F1/2 in which the most intense bands were 6F9/2, 6F7/2, 6F5/2 and 6F3/2. The absorption spectrum of Sm3+ ions free glass sample containing Au NPs displayed two prominent surface plasmon resonance (SPR) band located at ~550 nm and ~590 nm. The infrared to visible frequency down conversion emission under 404 nm excitation showed four emission bands centered at 577 nm, 614 nm, 658 nm and 718 related to the transitions 4G5/2→6H5/2, 4G5/2→6H7/2, 4G5/2→6H9/2 and 4G5/2→6H11/2,respectively, corresponding to Sm3+ transitions. An enhancement in down conversion emission intensity of both green and red bands were observed in the presence of gold NPs either by increasing annealing time or by NPs concentration. For glass series II, the enhancement in photoluminescence (PL) intensity of glass containing 0.4 mol% AuCl3 showed the maximum enhancement by a factor of 1.90:1.82:1.97:2.25 times for all transitions bands. For glass series IV, the enhancement in PL intensity of glass with heat treatment at 325 °C showed the maximum PL intensity with enhancement factor of 1.88:1.33:1.54:2.16 for those four bands. For glass series V, the enhancement in PL intensity of glass with heat treatment at 325 oC and annealing time 6 h showed the maximum PL intensity with enhancement factor of 1.54:1.76:1.68:1.45 for those four bands. The enhancement was mainly ascribed to the highly localized electric field of Au NPs positioned in the vicinity of Sm3+ ion. FTIR spectra show the vibrational Na-O bonds units, Te-O bond in TeO3 trigonal pyramidal (tp) and TeO4 trigonal bipyramidal (tbp) units and the hydroxyl groups. Raman spectra show the presence of Sm-O bond, Na-O bond, Te-O-Te bridging configurations and with higher oxygen coordination, anti-symmetric vibrations of Te-O-Te bonds and stretching modes of non-bonding oxygen found on the TeO3 and TeO3+1 unit. The enhancement of down conversion emission was understood in terms of the intensified local field effect due to gold NPs. For Series I and Series II of samples, the Judd-Ofelt parameters (, λ= 2, 4, 6) were calculated and used to estimate the important parameters such as total: radiative transition probability (), stimulated emission cross-section (), radiative lifetime () and branching ratio () for the excited levels of Sm3+ ions in the glass. The values of for the 4G5/2 emission transition are in order of 6H7/2 > 6H9/2 > 6H11/2 > 6H5/2. It was found that 4G5/2→6H7/2 transition has maximum value 12.51×10-22 cm2 for TNSA3 glasses. The maximum value of gain bandwidth 17.55×10-28 cm3 was obtained for TNSA3 glass corresponding to 4G5/2→6H7/2 transitions. Similarly, the maximum optical gain corresponding to 4G5/2→6H7/2 transition was 0.63×10-25 cm2 s-1 obtained. Furthermore, the values of for the studied glasses were found to be higher than that of glasses reported in the literature. These relatively higher values of reflect low symmetry and high covalency around the Sm3+ ions. Authors assert that these tellurite glass nanocomposites can be used for developments of the solid-state lasers and nanophotonics applications.