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The role of lattice defects on the optical properties of TiO[sub]2 nanotube arrays for synergistic water splitting
Manel Machreki, Takwa Chouki, Georgi Tyuliev, Mattia Fanetti, Matjaž Valant, Denis Arčon, Matej Pregelj, Saim Emin, 2023, original scientific article

Abstract: In this study, we report a facile one-step chemical method to synthesize reduced titanium dioxide (TiO2) nanotube arrays (NTAs) with point defects. Treatment with NaBH4 introduces oxygen vacancies (OVs) in the TiO2 lattice. Chemical analysis and optical studies indicate that the OV density can be significantly increased by changing reduction time treatment, leading to higher optical transmission of the TiO2 NTAs and retarded carrier recombination in the photoelectrochemical process. A cathodoluminescence (CL) study of reduced TiO2 (TiO2–x) NTAs revealed that OVs contribute significantly to the emission bands in the visible range. It was found that the TiO2 NTAs reduced for a longer duration exhibited a higher concentration of OVs. A typical CL spectrum of TiO2 was deconvoluted to four Gaussian components, assigned to F, F+, and Ti3+ centers.
Keywords: TiO2 nanotubes, defects, cathodoluminescence
Published in RUNG: 13.12.2023; Views: 327; Downloads: 7
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Optical response of plasmonic Bi2Se3 topological insulator nanoplatelets investigated by cathodoluminescence microscopy
Blaž Belec, Mattia Fanetti, 2022, published scientific conference contribution abstract

Keywords: microscopy, cathodoluminescence, topological insulator
Published in RUNG: 02.06.2022; Views: 1287; Downloads: 0
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Spectroscopic investigation of oxygen vacancies in CeO[sub]2 : dissertation
Thanveer Thajudheen, 2021, doctoral dissertation

Abstract: A unique material, ceria (CeO2), which is widely applied in automobile exhaust catalysts, is functional due to presence of defects in its crystal structure. Furthermore, the structural defects dictate electrical and chemical properties of ceria. The creation of intrinsic oxygen vacancies in ceria is responsible for oxygen-ion conductivity in solid oxide fuel cells. This unfolds the keen interest in ceria defects. Using the analytical technique cathodoluminescence spectroscopy (CLS) we can characterize ceria for its band gap and the defect states within the band gap. Since CLS has a high spatial resolution, high sensitivity to low concentration of defects and ability to obtain depth resolved information it is an obvious technique of choice. The first part of the thesis is an introduction to the topic and description of the experimental techniques. Importance of ceria as a multifaceted material finding applications in areas spanning from energy production and conversion to biomedical applications is detailed. CLS as a tool to understand defect-related optical properties and advancement in the CL detection systems are discussed. To study the relationship between local structure and its impact on CL emission spectra, an X-ray absorption spectroscopy techniques were used. The X-ray absorption near edge structure (XANES) and the Extended x-ray absorption fine structure (EXAFS) techniques are summarized. The second part discusses CL emission from ceria. Initially, CL emission from reduced ceria and its dependence on oxygen vacancy concentration are presented. The origin of emission was attributed to different configurations of the oxygen vacancies and polarons. The recent F center description in ceria was adopted here. The intriguing observation of CL emission quenching as a function of oxygen vacancy concentration was explained on the basis of a relative change in population of F centers in ceria. This demonstrated the relevance of local structure for the CL emission in ceria. In order to have a better understanding of the system, La-doped ceria was proposed as a model system. A precise control over the stoichiometry helped to achieve a desired oxygen vacancy concentration. The CL emission behavior, as observed in reduced ceria, was replicated in the case of La-doped ceria and the analysis revealed that F+ centers favor CL emission whereas F0 centers are disadvantageous. The local structure investigation using EXAFS analysis of both cations Ce and La (K-Edge) showed distortion from the fluorite symmetry and corroborated the F center description of oxygen vacancies in ceria. Our results provide an experimental evidence for F center description involving oxygen vacancies and polarons.
Keywords: ceria, cathodoluminescence spectroscopy, local structure distortion, EXAFS analysis, La doped ceria, luminescence quenching, F centers, dissertations
Published in RUNG: 25.11.2021; Views: 2439; Downloads: 104
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