Optical Properties of Tellurite Glasses Embedded with Gold Nanoparticles

Abstract

Three series of samarium-doped sodium tellurite glass embedded with gold nanoparticles (Au NPs) in the compositions (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%), and (80-x)TeO2-20Na2O-xAuCl3 (x = 0.2, 0.4, 0.6, 0.8, 1) were prepared using conventional melt quenching technique. The homogeneous distribution and growth of spherical and non-spherical Au NPs (average size ~3.36 ± 0.076 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 nine 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 and ~590 nm. The infrared to visible frequency downconversion 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 downconversion emission intensity of both green and red bands was 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. The enhancement was mainly ascribed to the highly localized electric field of Au NPs positioned in the vicinity of Sm3+ ion. The enhancement of downconversion emission was understood in terms of the intensified local field effect due to gold NPs.