Physical characterization and optical spectroscopy of Er3/Yb3-doped multicomposition tellurite glass for broadband amplifiers

The erbium ion doped (Er3+)-tellurite glasses have been extensively studied in recent decades as a potential host material for broadband applications at 1.5 µm band. As compared to other host glasses they possess variety interesting physical and optical properties which further can be exploited especially in optical communications. Therefore continuous investigation of appropriate glass compositions is very important in order to synthesis high performance tellurite glass.In this dissertation, series of selected oxide based tellurite glasses (TeO2) were synthesized and characterized. Three ternary TeO2-AmOn-BmOn; TZT:TeO2-ZnOTiO2,TTB:TeO2-TiO2-Bi2O3, TPB: TeO2-PbO- Bi2O3 and two multicomposition TeO2-AmOn-BmOn-CmOn-DmOn-EmOn (more than three components); TZPTiN:TeO2-ZnO-PbO-TiO2-Na2O (with difference PbO concentration) tellurite glasses were studied (AmOn, BmOn, CmOn, DmOn, EmOn represent the oxide components,m,n=integer). Selected batch composition was chosen as a ‘host’ glass for Er3+/Yb3+doping by substituting selected batch component with the rare earth oxide dopants Er2O3/Yb2O3. All oxide components were above 99.9% purity and a quantitative glass batching procedure based on mol% formulation calculation was performed. A standard melt-quenching technique around 1000 oC for an hour and followed by annealing at 250 oC was done for all glass batches. The physical characterization of the glass samples involved X-Ray diffraction (XRD), thermal analysis, density,molar volume and refractive index while the spectroscopic properties were obtained through Fourier Transform Infra Red spectroscopy, Ultraviolet-Visible-Near Infra Red absorption spectroscopy, Raman spectroscopy and fluorescence spectra of the visible upconversion and near infra red emission under 980 nm laser diode (LD) excitation. All measurement were performed at room temperature. The non distinguishable intensity peaks with broad ‘halo’ diffraction of the XRD spectrogram confirmed the amorphous nature of the selected host glasses. The density of the glasses was observed higher with the incorporation of heavier mass component of PbO and Bi2O3 in both TTB and TPB glasses where higher n values were obtained in both glasses. All host glasses TZT, TTB, TPB, TZPTiN and TZPTiN indicated higher n > 2. The FTIR analysis revealed higher transmission infra red cut-off beyond 6m with distinct water (OH-) absorption between 2000-3500 cm- 1 in most of the studied glass samples. The optical absorption edge analysis in most samples showed an appreciable formation of non-bridging oxygen with respect to the calculated optical energy gap trend. This was clearly supported by the obtained intensity parameters values t(t=2,4,6) through the Judd-Ofelt analysis. The reduction of 2 and 6 values were strongly associated with enhancement of the symmetrical behaviour at the Er3+ site with the creation of higher electron density on the oxygen ligand ion; as consequences strong Er-O covalency are formed with the increasing of Er3+ doping concentration. In addition this factor has also contributed structural deformation of TeO2 by transformation of [TeO4] trigonal bypiramid to [TeO3] trigonal pyramid via [TeO3+1] polyhedral units which was confirmed through the Raman spectroscopy analysis with obtained maximum phonon vibration energy lies between 730-750 cm-1 slightly lower than reference TeO2 glass value at 780 cm-1. The upconversion spectra exhibited significant both green and red emission upon 980 nm LD excitation especially in Er3+-TZT and Er3+/Yb3+-TZPTiN glasses where indicated by two or/and three photon absorption processes. Intense with broad near infra red 1.5 m emission above 70 nm width and gain bandwidth within (500-1300) x 10-28 cm3 were obtained in most Er3+/Yb3+-doped glass samples. These characteristics suggest that the synthesized multicomposition tellurite glass is a potential optical material for the future broadband telecommunication technology.

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