Concentration dependent structural, thermal and luminescence properties in Er3+/Tm3+ doped tellurite glasses

Tellurite glasses with compositions (70-x)TeO2-20ZnO-5Na(2)O-4.8Bi(2)O(3)-0.2Er(2)O(3)-xTm(2)O(3) (x = 0, 0.2, 0.4, 0.6 and 0.8 mol%) in fixed Er3+ and variable Tm3+ doped concentrations were synthesized by using conventional melt-quenching technique, and the concentration dependent structural nature, thermal stability and near-infrared band luminescent property were investigated. Under the excitation of 808 nm laser diode (LD), the Er3+/Tm3+ codoped tellurite glasses produced a broad near-infrared band fluorescence emission ranging from 1350 to 1650 nm, which completely covers the telecommunication window of WDM transmission system. The full width at half-maximum (FWHM) of this broadband emission contributed by the Er3+:I-4(13/3) -> I-4(15/2) and Tm3+:H-3(4) -> F-3(4) radiative transitions increased with the decrease of Er3+/Tm3+ doped concentration ratio, and reached to a value of about 148 nm in the 0.2 mol% Er2O3 and 0.8 mol% Tm2O3 codoped tellurite glass sample. The quantitative analyses of energy transfers between the Er3+/Tm3+ ions as well as the fluorescence decaying behavior of Er3+ were carried out to elucidate the observed broadband luminescent phenomena. Judd-Ofelt analysis was presented and some important spectroscopic parameters such as the spontaneous radiative transition probability, fluorescence branching ratio and radiative lifetime were estimated to reveal the potential luminescent properties. Meanwhile, the amorphous structural nature of the synthesized tellurite glasses with different doped concentrations was confirmed by the X-ray diffraction (XRD) patterns, the presence of functional vibrations assigned to the tellurite network was clarified by the Raman spectra and the good thermal stability of glass host was revealed by the differential scanning calorimeter (DSC) analyses. Also, the optical band gap energy corresponding to the direct and indirect allowed transitions was derived. The obtained results indicate that Er3+/Tm3+ codoped tellurite glass might be a promising candidate material for the development of near-infrared broadband fiber amplifiers.