Concentration dependent structural and spectroscopic properties of Sm3+/Yb3+ co-doped sodium tellurite glass

Tuning the optical and structural behaviors of tellurite glasses with controlled dopants is the key issue in solid state lasers and amplifiers. Sm3+/Yb3+ co-doped sodium tellurite glasses are prepared by the melt quenching technique and characterized using XRD, FTIR and DTA, optical absorption and luminescence techniques. The XRD spectra reveals the amorphous nature of glasses and the presence of functional groups such as Te-O bond in trigonal bipyramids (TeO4), Te-O bending vibration of the trigonal pyramids (TeO3) and non-hygroscopic nature of the glasses are confirmed from FTIR spectra. The DTA measurement shows the thermal stability lies in the range of 106-123. The UV-vis-NIR spectra exhibit eight absorption bands corresponding to the transition from ground level 6H5/2 to the various excited state of Sm3+ ions and the broad absorption band in the range of ~825-1100 nm is ascribed to the large contribution of the absorption from 2F7/2→2F5/2 transition of Yb3+ ion. The experimental oscillator strengths calculated from the absorption spectra are used to evaluate three phenomenological Judd-Ofelt (J-O) intensity parameters Ωλ (λ=2, 4 and 6). Emission spectra consist of four bands 4G5/2→6H7/2 (moderate green) 4G5/2→6H5/2 (intense orange), 4G5/2→6H7/2 (moderate orange-yellow) and 4G5/2→6H11/2 (feeble red). The J-O parameters are employed to calculate radiative parameters such as transition probability (AR), branching ratio (BR), effective bandwidth (λeff) and stimulated emission cross-section σ(λp) of these emission transition of trivalent samarium ion. The optical band gap energy value (Eopt) and Urbach energy values (ΔE) are calculated and compared. The concentration dependent spectroscopic behavior of Sm3+-doped and Sm3+/Yb3+co-doped glasses is understood. Our systematic study may contribute towards the development of optical device fabrication.