Er3+ local structure and its optical properties in ZnO–PbO tellurite glasses

Tellurite glasses are important in optical applications because of their high refractive index. Optical spectroscopy and X-ray Absorption Fine Structure spectroscopy (XAFS) studies allows us to report on optical properties and structural parameters of Erbium-doped lead tellurite (TZPE) glasses [(70TeO2 - (30-x)ZnO - xPbO)]0.99 (Er2O3)0.01, where x = 5, 10, 15, 20. The structural information by EXAFS for the first shell of oxygen atoms around Er3+ give a constant distance of 2.34 Å, while coordination number (N) and Debye Waller factor (DW) were found to be ~6.5 and ~0.015 Å2 respectively, slightly increasing for x >= 10. Next nearest shells are difficult to quantify, due to high static disorder, indicating the absence of preferential bonds. Optical spectroscopy shows that the transition intensities of Er3+ ions decrease with increase of PbO content. We have performed the Judd-Ofelt (JO) analysis to correlate the local structure of Er3+ with its influence on the radiative properties. The JO analysis shows that the local asymmetry and basicity of Er3+ ions in these glasses decreases with increase of PbO content, correspondingly with the observed reduction in transition intensities of Er3+ ions. This decreasing intensity of characteristic erbium transitions shows that the oscillator (electric dipole transition) strength reduces as the PbO content increases.