Titanium dioxide nanoparticles mediated surface plasmon resonance assisted optical properties of erbium-doped tellurite glass

Abstract

Low emission and absorption cross-section of rare earth (RE) ion doped tellurite glasses that limit them from making solid state lasers needs further improvement. Combination of metal nanoparticles (NPs) with RE ions in the glass is proven to be prospective for overcoming such limitations. Via tuneable surface plasmon resonance (SPR) of metal NPs, an alteration in the optical properties of such glasses is feasible. In this view, present thesis takes an attempt to determine the mechanism of metal NPs SPR mediated modification in the optical properties of Erbium (Er3+) ions by embedding Titanium dioxide (TiO2) NPs into the tellurite glass. Five glass samples are prepared using melt-quenching technique with the composition (69-x)TeO2-20ZnO-10Na2O-1Er2O3-xTiO2, where x = 0.1, 0.2, 0.3, 0.4 mol%. Prepared samples are thoroughly characterized using X-ray diffraction (XRD), transmission electron microscope (TEM), energy dispersive X-ray (EDX), Fourier transform infrared (FTIR), Raman, ultraviolet-visible-near infrared (UV-Vis-NIR) and photoluminescence (PL) measurements. XRD pattern of achieved transparent glass samples confirmed their amorphous nature and TEM images revealed the existence of TiO2 NPs with average size between 16 to 22 nm. EDX spectra displayed the presence of Ti element in the sample together with other appropriate elemental traces. FTIR and Raman spectra showed different vibration modes of Te-O bond (bending, asymmetric and symmetric stretching) in the structural unit of TeO4 and TeO3. Glass containing 0.4 mol% of TiO2 NPs displayed an enhancement in the Raman signal by a factor of 1.56 to 3.58 for the bands centered at 388, 495, 673, 758 and 845 cm-1. This intensity enhancement is mainly attributed to the TiO2 NPs SPR assisted effects. Meanwhile, UV-Vis-NIR spectra exhibited ten absorption bands centred at 407, 444, 452, 489, 522, 552, 653, 800, 976 and 1532 nm. Absorption spectra of TiO2 NPs manifested two plasmon bands at 552 (transverse mode) and 580 nm (longitudinal mode). PL spectra demonstrated three prominent bands centred at 525, 545 and 660 nm, which are allocated to the Er3+ ion transition from the excited levels (2H11/2, 4S3/2 and 4F9/2) to the ground level (4I15/2). Furthermore, glass containing 0.2 mol% of TiO2 NPs revealed PL intensity enhancement by a factor of 30.00, 28.57 (for green bands) and 19.60 (for red band). This observation is ascribed to the SPR effect of TiO2 NPs which created strong local electric field in the vicinity of Er3+ ion. Green emission showed the highest enhancement due to its appearance in the immediate proximity of plasmon band. It is asserted that the incorporation of TiO2 NPs in the glass produced plasmonic effect and thereby altered the UV-Vis-NIR absorbance and improved the emission intensity of the samples. A correlation between SPR effect and surface enhance Raman scattering (SERS) is established. Present functional glass composition may be useful for device applications especially in photovoltaic and solid state laser.