Holmium concentration dependent structural and optical properties of zinc tellurite glass

Abstract

This thesis examined the effects of Ho2O3 dopant concentration variation on the physical, optical, thermal and structural properties of zinc tellurite glass system. Glass with composition of (80 x) TeO2 20ZnO xHo2O3, where x = 0.0, 0.5, 1.0, 1.5 and 2.0 mol% were prepared using melt quenching method. Samples were characterized by X-ray diffraction (XRD) measurement, Energy-dispersive X-ray (EDX) spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, Raman spectroscopy, Differential Thermal Analysis (DTA), Archimedes Method, UV-Visible-NIR (UV-Vis-NIR) spectrometer and Photoluminescence (PL) spectrometer. XRD pattern verified the amorphous nature of prepared sample. EDX spectra detected the presence of appropriate elements in the glass. FTIR spectra showed all the functional group such as Zn O, TeO4 and TeO3 in the range of 443 – 487, 654 – 675 and 760 – 763 cm-1 . Raman spectrum showed three bands at 463, 530 and 676 cm-1 of Te–O–Te linkages, TeO4 and TeO3 respectively. The DTA thermogram showed the peak for glass transition temperature, Tg (367 °C), melting temperature, Tm (632 °C) and crystallization temperature, Tc (458 °C). The density, ? and molar volume, Vm of the prepared glass sample was varied respectively in the range of 5.554 5.580 g cm-3 and 26.088 27.270 cm3 mol-1 with increase of Ho2O3 concentration. The absorption spectra showed seven bands centered at 418, 454, 480, 541, 646, 894 and 1155 nm which assigned to the transitions from the ground state to the excited 5G5, 5G6, 5 F3, 5 F4 + 5 S2, 5 F5, 5 I5 and 5 I6 levels of Ho3+. The indirect band gap energy, direct band gap energy and Urbach energy were varied from 3.31 – 3.36, 3.21 – 3.30 and 0.17 – 0.21 eV respectively with the changes of holmium concentration. The PL spectra displayed two peaks at 657 nm (red region) and 753 nm (NIR region) for 5 F5 5 I8 and 5 S2 5 I7 transitions.