Optical bandgap evaluation of rare earths doped ZnO materials obtained by electrospinning
Pericle Varasteanu1, Dumitru Manica1, Petronela Pascariu1,2, Cosmin Romanitan1, Oana Brincoveanu1, Cristina Pachiu1, Mirela Petruta Suchea1,3*, Emmanouel Koudoumas1,3*
1 National Institute for Research and Development in Microtechnologies - IMT Bu-charest, 126A, Erou Iancu Nicolae Street, 077190, Voluntari-Bucharest, ROMANIA;
2 ”Petru Poni” Institute of Macromolecular Chemistry, 41A Grigore Ghica Voda Alley, 700487, Iasi, Romania;
3 Center of Materials Technology and Photonics, School of Engineering, Hellenic Mediterranean University (HUM), 71410 Heraklion, Crete, Greece;
Abstract:
Zinc oxide (ZnO), a wide bandgap (aprox. 3.3 eV) II-VI semiconductor with a large exciton binding energy, is a versatile material attracting considerable interest for its use in optoelectronics, photocatalysis, sensors, and energy devices. Its inherent high electron mobility, thermal stability, and biocompatibility can position it as a key material in nanotechnology. The wide electronic bandgap of undoped ZnO restricts its photoabsorption performances to the UV range, which constitutes a limited portion of the solar irradiance, thereby hindering its use in applications which require visible light activation. To overcome this limitation, the introduction of dopant species, with a particular focus on rare earth (RE) ions, has emerged as a significant strategy for modulating ZnO's optoelectronic characteristics and enabling photoresponse within the visible region. Rare earth (RE) elements, characterized by their unique 4f electronic configurations, exhibits exceptional optical and catalytic properties. When introduced into the ZnO lattice, RE ions introduce intermediate energy states within the bandgap, modify defect chemistry, and induce lattice distortions. Usually, all these effects collectively lead to bandgap modification, enhanced light absorption, and modified charge carrier dynamics.
The electrospinning-calcination technique offers a powerful route for synthesizing rare earth (RE)-doped zinc oxide (ZnO) semiconductor nanostructures. By carefully controlling parameters such as the precursor solution properties (viscosity, concentration), applied electric field, and flow rate, one can achieve fine-tuned control over the morphology of the resulting nanofibers, ensuring uniform incorporation of pure and doped ZnO based nanocrystalline semiconductor material in a sacrificial polymeric matrix that will be removed by calcination. This level of control is important for tuning the optoelectronic properties of doped ZnO materials for specific applications. This work is focused on the study of morpho-structural modifications of pure and RE doped ZnO materials and its bandgap modification when different RE dopants are used. Several characterization techniques were employed to obtain a complete picture of the materials such as X Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Raman spectroscopy, UV-vis spectroscopy and diffuse reflectance. This work emphasizes the effect of different types of RE dopants on bandgap modification of RE doped ZnO materials obtained by electrospinning calcination technique.
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