Oxygen hole states in zirconia lattices: quantitative aspects of their cathodoluminescence emission

3D-Architected Alkaline-Earth Perovskites

3D ceramic architectures are captivating geometrical features with an immense demand in optics. In this work, an additive manufacturing (AM) approach for printing alkaline-earth perovskite 3D microarchitectures is developed. The approach enables custom-made photoresists suited for two-photon lithography, permitting the production of alkaline-earth perovskite (BaZrO3 , CaZrO3 , and SrZrO3 ) 3D structures shaped in the form of octet-truss lattices, gyroids, or inspired architectures like sodalite zeolite, and C60 buckyballs with micrometric and nanometric feature sizes. Alkaline-earth perovskite morphological, structural, and chemical characteristics are studied. The optical properties of such perovskite architectures are investigated using cathodoluminescence and wide-field photoluminescence emission to estimate the lifetime rate and defects in BaZrO3 , CaZrO3 , and SrZrO3 . From a broad perspective, this AM methodology facilitates the production of 3D-structured mixed oxides. These findings are the first steps toward dimensionally refined high-refractive-index ceramics for micro-optics and other terrains like (photo/electro)catalysis.

The Role of Lattice Defects on the Optical Properties of TiO2 Nanotube Arrays for Synergistic Water Splitting

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. X-ray photoelectron spectroscopy measurements were used to support the change in the surface chemical bonding and electronic valence band position in TiO2. Electron paramagnetic resonance spectra confirmed the presence of OVs in the TiO2-x sample. The prepared TiO2-x NTAs show an enhanced photocurrent for water splitting due to pronounced light absorption in the visible region, enhanced electrical conductivity, and improved charge transportation.

120 MeV swift Au9+ion induced phase transition in ZrO2: monoclinic to tetragonal and cubic to tetragonal structure

This study reports the effect of 120 MeV swift Au⁹⁺ion irradiation on the structures of monoclinic, tetragonal and cubic ZrO₂, probed through x-ray diffraction (XRD) and Raman spectroscopy. Three phases of ZrO₂were prepared using the solution combustion method. The tetragonal and cubic phases of ZrO₂were stabilized at room temperature by adding 6% and 10% of yttrium ions, respectively. Both the XRD and Raman results confirm the partial phase transition from monoclinic to tetragonal, which was approximately 74%. Tetragonal ZrO₂is stable under 120 MeV Au⁹⁺ion irradiation. Interestingly, a phase transition from cubic to tetragonal ZrO₂was observed under 120 MeV Au⁹⁺ion irradiation. The roles of transient temperature, defects and strain in the lattice induced by swift heavy ions are discussed. This study reveals the structural stability of different phases of ZrO₂under swift heavy ion irradiation and should be helpful in choosing potential hosts for various applications such as inert fuel matrix inside the core of nuclear reactors, oxygen sensors and accelerators, and radiation shielding.

Investigation of multi-timescale processing phenomena in femtosecond laser drilling of zirconia ceramics

Femtosecond lasers have been applied to machining of zirconia (ZrO₂) ceramics because of their ultrashort pulse duration and high peak power. However, an unclear understanding of the ultrafast laser-material interaction mechanisms limits the achievement of precision processing. In this study, a pump-probe imaging method comprising a focusing probe beam integrated with a high-speed camera was developed to directly observe and quantitatively evaluate the multi-timescale transient processing phenomena, including electron excitation, shockwave propagation, plasma evolution, and hole formation, occurring on the picosecond to second timescales, inside a ZrO₂ sample. The variation mechanism in the shapes, lifetimes, and dimensions of these phenomena and their impacts on the drilling performance under different laser parameters were explored. The clear imaging and investigation of the above phenomena contribute to revealing the ultrafast laser-material interaction mechanisms and precision processing in the laser-drilling of zirconia ceramics.

Annealing-Induced Off-Stoichiometric and Structural Alterations in Ca2+- and Y3+-Stabilized Zirconia Ceramics

In the current study, high-temperature stability was investigated in two types of zirconia ceramics stabilized with two different additives, namely, calcia and yttria. The evolutions of structure and oxygen-vacancy-related defects upon annealing in air were investigated as a function of temperature by combining X-ray diffractometry with Raman, X-ray photoelectron and cathodoluminescence spectroscopies. We systematically characterized variations in the concentration of oxygen vacancies and hydroxyl groups during thermal treatments and linked them to structural alterations and polymorphic transformation. With this approach, we clarified how the combined effects of different dopants and temperature impacted on structural development and on the thermal stability of the oxygen-vacancy-related defect complex.

Oxygen Vacancy-Related Cathodoluminescence Quenching and Polarons in CeO2

We used cathodoluminescence (CL) spectroscopy to characterize the oxygen vacancies (V_O) in ceria (CeO₂). The effects of the processing atmosphere and thermal quenching temperature on the nature and distribution of the intrinsic defects and on the spectroscopic behavior were investigated. The presence of polarons and associates of the polarons with the oxygen vacancies such as (V_O ^••-Ce_Ce ^')^• is demonstrated. CL intensity quenching above a critical concentration of V_O has been shown. Even though the emission centers in all samples are the same, their concentration changes with the oxygen partial pressure of the processing atmosphere. Deconvolution of the observed CL spectra shows that the emissions originating from the F⁰ centers prevail over those of F⁺ centers of V_O when the defect concentration is high.

The influence of intense ultrasound applied during pressing on the optical and cathodoluminescent properties of conventionally sintered YSZ ceramics

The aim of the present work was to investigate the effect of the ultrasonic treatment on the optical and cathodoluminescent properties of translucent ZrO₂-8 mol.% Y₂O₃ (YSZ) ceramics obtained by conventional sintering of the pressed compacts. Treatment by intense ultrasound during dry pressing of the YSZ nanopowder leads to an increase in the relative density, a decrease in the pore size and an increase in the grain size of the sintered ceramics. It was shown that when the ultrasonic treatment is applied, the optical absorption cutoff wavelength of the sintered material is shifted to longer wavelengths, while the optical density of the material increases over the whole measurement spectrum. Samples subjected to ultrasonic treatment during pressing show higher intensity of luminescence than those obtained without the use of ultrasound, the shape of the luminescence spectra remaining unchanged. A correlation was obtained between the integral intensity of cathodoluminescence and the vacancy concentration in the sintered YSZ.