Optical properties of samarium and ytterbium doped sodium tellurite glasses

Abstract

Interests in rare earth doped/co-doped inorganic binary lasing glasses with enhanced efficiency are ever-growing. Optimizing the rare earth concentrations to achieve significant optical performance is becoming more challenging. Two series of Sm3+/Yb3+ co-doped sodium tellurite glasses of composition (79.5-x)TeO2-20Na2OxSm2O3- 0.5Yb2O3 with 0 = x = 2.0 mol% and (79.5-y)TeO2-20Na2O-0.5Sm2O3- yYb2O3 with 0 = y = 2.0 mol% were synthesized using melt quenching technique. The influence of co-dopants on structural and optical properties of these glasses was determined. XRD pattern confirmed the amorphous nature of the glasses. Density, molar volume and the refractive index were found to be highly influenced by codopants. The temperature for glass transition, crystallization and melting were determined from DTA thermogram. The observed thermal stability in the range of 104 to 232 oC verified wide and stable range of glass formation. FTIR spectra revealed different modes of vibration with increasing transmission bands shift from 616 to 651 cm-1 which corresponds to stretching vibration mode of TeO4. Conversely, the Raman shift in intensity was found to decrease around 681-690 cm-1 and increase around 756-758 cm-1 due to the change in composition. These observations are ascribed to the structural changes between the stretching vibration mode of TeO4 trigonal bipyramid and TeO3 trigonal pyramid and the bending vibration mode within the Te-O-Te linkages through the creation of non-bridging oxygen atoms. The sizable alteration in the structure is evidenced due to co-dopants. The UV-VIS-NIR absorption spectra display eight prominent absorption peaks centered at 470, 948, 1086, 1238, 1386, 1492, 1550 and 1588 nm corresponding to transitions from ground state to various excited states. The absorption data was further complemented with the calculation of Judd-Ofelt intensity parameters K2, K4 and K6. The variation in K2 showed covalent nature of bonding and the spectroscopic quality factor was found to be around 171-251. The room temperature emission spectra for both glasses exhibited four peaks with enhanced intensity up to certain concentrations of co-dopants and quenching thereafter which was understood using partial energy level diagram. The maximum values of stimulated emission crosssection, gain band width and optical gain for 4G5/2 ? 6H9/2 transitions were observed to be 23.09×10-22 cm2, 28.54×10-28 cm3 and 12.51 cm2 s-1, respectively. A correlation was established between the Sm3+/Yb3+ co-doping and modification in structural and optical properties of the studied glasses. The excellent features of these results suggest that these glasses may be nominated as potential candidate for solid state lasers and other photonic devices.