Plasmon-enhanced luminescence of samarium doped sodium tellurite glasses embedded with gold nanoparticles: Judd-Ofelt parameter

Abstract

A series of samarium doped sodium tellurite glass embedded with gold nanoparticles (Au NPs) in the composition (79-x)TeO2−20Na2O-1Sm2O3-xAuCl3 (x=0, 0.2, 0.4, 0.6, 0.8, 1 mol%) are prepared using conventional melt quenching technique. The UV–Vis–NIR absorption spectra shows 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 are 6F9/2, 6F7/2, 6F5/2 and 6F3/2. The homogeneous distribution of spherical and non-spherical Au NPs (average size ~3.36±0.076 nm) in the glassy matrix is evidenced from the transmission electron microscopy (TEM). The absorption spectrum of Sm3+ ions free glass sample containing Au NPs displays a 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 shows 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 is observed in the presence of gold NPs either by increasing annealing time or by NPs concentration, the enhancement in photoluminescence (PL) intensity of glass containing 0.4 mol% Au (as to be compared with glass without Au) shows the maximum enhancement by a factor of 1.90:1.82:1.97:2.25 times for all transitions band. The enhancement is mainly ascribed to the highly localized electric field of Au NPs positioned in the vicinity of Sm3+ ion. The enhancement of down conversion emission is understood in terms of the intensified local field effect due to gold NPs. The Judd-Ofelt parameters (Ωλ, λ= 2, 4, 6) are calculated that is used to estimate the important parameters such as total radiative transition probability (AT), stimulated emission cross-section (σpE), radiative lifetime (τR) and branching ratio (βR) for the excited levels of Sm3+ ions in the glass. Furthermore, the value of Ω2 for the studied glasses is found higher than that of glasses reported in the literature. These relatively higher values of Ω2 reflect low symmetry and high covalency around the Sm3+ ions. We assert that these tellurite glass nanocomposites can be used for developments of the solid-state lasers and nanophotonics applications.