Investigation of physical and spectroscopic properties of WO3 doped zinc-lithium-dysprosium borotellurite glasses

Abstract

Abstract A set of WO3 doped zinc-lithium-dysprosium-borotellurite glasses in the compositions, (B2O3)0.2–(TeO2)0.3-x–(ZnO)0.28 –(Li2CO3)0.2 –(Dy2O3)0.02–(WO3)x; x = 0.02 to 0.12 (labeled as W1, W2, W3, W4, W5 and W6 respectively) have been synthesized. Amorphous nature of the samples has been confirmed and density measured. Molar volume, oxygen packing density and field strength were determined. Optical absorption spectra were recorded. Band gap values are found to increase with WO3 content up to 0.08 mol fractions and decreases for further amounts of WO3. Urbach energy behaved in the opposite fashion to that of band gap with WO3 content. These results are attributed to bonding defects and the number of non-bridging oxygen. Refractive index, molar refractivity, molar electronic polarizability, reflection loss, metallization ratio, oscillator strengths and Judd-Ofelt (J-O) intensity parameters have been determined. Based on the observed trends of JO intensity parameters, lasing ability of the glasses and their optical quality has been discussed. Photoluminescence (PL) spectra have been recorded and they exhibited three bands namely, 4F9/2 → 6H15/2 (blue), 6H13/2 (yellow) and 6H11/2 (red). The observed ratio of intensity of yellow to blue band inferred that asymmetry around rare earth ions decreases with increase of WO3 content. Using PL decay profiles, the lifetime (τexp) for yellow emission has been determined. Using the values of τexp and estimated radiative lifetime (τR), the quantum efficiency (η) has been determined and for 4F9/2 → 6H13/2 transition and, it is found to be in the range from 43% to 67% for the present glasses. Based on JO parameters, quantum efficiency and other radiative parameters, W4 glass is proposed for lasing in yellow region. For the first time, effect of WO3 on the optical properties of zinc-lithium-dysprosium-borotellurite glasses has been thoroughly investigated.