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Thermometry of thermal barrier coatings (TBCs) is essential for designing effective thermal management systems and prolonging the service life of components in aeroengines and gas turbines. However, conducting on-line thermometry in these systems is challenging because it requires physical or optical access to components during operation. A promising alternative is off-line thermometry, in which phosphorescent thermal-history sensors are used to record exposure temperatures after operation. In this study, we synthesized europium (III)-ion-doped barium aluminate (BaAl 2 O 4 :Eu3+) via a solid-state reaction and confirmed its ability to function as a thermal history sensor. Subsequently, we developed a new thermal-sensing strategy based on the self-reduction of Eu3+ to Eu2+ in a BaAl 2 O 4 :Eu3+ phosphor exposed to high temperatures (900–1300 °C) in ambient air. The Eu3+ concentration decreased as the heat exposure temperature increased due to self-reduction of Eu3+ to Eu2+, which irreversibly changed the phosphorescence of BaAl 2 O 4 :Eu3+, i.e., its spectra, the ratio of the phosphorescence intensities of Eu3+ and Eu2+, and the lifetime of Eu3+. As the heat exposure temperature increased, the ratio of the phosphorescence intensities of Eu3+ and Eu2+ monotonically decreased due to self-reduction, whereas the phosphorescence lifetime of Eu3+ initially gradually increased until the heat exposure temperature reached 1000 °C because of the degeneration of concentration quenching, and then decreased as the temperature exceeded 1000 °C because of the degeneration of lattice distortions. This demonstrates that heat exposure temperatures exceeding 1000 °C can be quantitatively evaluated through off-line analysis of Eu3+ and Eu2+ phosphorescence intensity ratios and Eu3+ lifetime at room temperature. Thus, BaAl 2 O 4 :Eu3+, a self-reducing phosphor, is a potential sensor for off-line thermometry of TBCs. [ABSTRACT FROM AUTHOR]

The advancement of bioimaging and theranostics necessitates the development of highly biocompatible multifunctional agents. Here, we introduce a potential multimodal agent based on nanosized hydroxyapatite (HAp) co-doped with europium(III) and gadolinium(III) (Eu3+ and Gd3+) ions. The study presents a detailed characterization of the HAp:Eu3+/Gd3+ nanoparticles synthesized via the co-precipitation method. The structure and morphology were analyzed using X-ray powder diffraction (XRPD), transmission electron microscopy (TEM), and Fourier transform infrared (FT-IR) spectroscopy. The study of spectroscopic properties (emission, excitation, emission kinetics) as a function of optically active ions was carried out. Moreover, various dopant ratio combinations were studied to optimize the optical and magnetic properties. HAp:Eu3+/Gd3+ demonstrates tunable PL intensity with different concentrations of Eu3+ and Gd3+ ions and increased magnetization with higher doping with Gd3+ ions. Furthermore, co-doping with Gd3+ ions results in an enhancement of Eu3+ emission intensity, rendering HAp:Eu3+/Gd3+ a potentially promising candidate for bioimaging applications. [ABSTRACT FROM AUTHOR]

In this paper, we report on fabricating optical fibers with a controlled process of crystallization core during the drawing process. The research and synthesis of the core material of silica-germanium-antimony oxide glass were discussed. We also investigated the optical and luminescence properties were in relation to concentrating Eu 2 O 3 and P 2 O 5. Based on this investigation, we selected the most promising material for optical fiber core. In the next step, we drew optical fibers using a well-known rod-in-tube method. After drawing, we examine the optical fibers for luminescence shape changes. We observed a promising similarity between optical fibers and heat-treated samples with confirmed nanocrystals. Finally, XRD and TEM measurements confirm EuPO 4 nanocrystals at the core of the optical fiber. Highlighting the successful control of crystallization in the one-step method used to draw optical fibers. [ABSTRACT FROM AUTHOR]

Functional materials exhibiting polymorphism serve as excellent candidates for various optical applications since the properties can be tuned to the desired target/application by modifying the structural features. Herein, we explored the synthesis of Eu3+ doped gadolinium oxyfluoride systems via a green microwave-assisted hydrothermal method, and phase controllability was established by varying the O2− to F- ratio. The phase evolution and crystal structure of the Eu3+ doped oxyfluoride analogs were examined using Rietveld refinement studies, and the results were consistent with the site symmetries unveiled by the photoluminescence spectra of Eu3+. The low phonon energy of all the phosphors, calculated from the Raman spectra, suggested the possibility of these groups of materials as excellent host matrices for optical applications. Further, a drastic variation in the morphology of studied oxyfluorides at different phases is evidenced by the electron microscopic analysis. The highly asymmetric rhombohedral sites enhanced the color purity, lifetime, and quantum yield of the red phosphor, making it an excellent red component for the fabrication of UV-excitable red as well as white light-emitting diodes for lighting and display device functionalities. [ABSTRACT FROM AUTHOR]

Eu3+ doped-Oxyfluorophosphate glasses with a general composition 75 NaPO 3 - (25-x) CaO – x CaF 2 (with x ranging from 0 to 25 mol%) were prepared and their spectroscopic changes induced by the addition of fluorine and when applying a thermal treatment in order to grow crystals in the glasses were investigated. The addition of CaF 2 at the expense of CaO reduces Ω 2 and Ω 4 parameters indicating that the Eu3+ ions are located in less covalent and well separated sites in oxyfluorophosphate glasses. An increase in the CaF 2 content at the expense of CaO also leads to an increase in the absolute thermometric sensitivity from (4.2 × 10−4) K−1 to (17.6 × 10−4) K−1 at 523 K while decreasing the relative thermometric sensitivity from 3.0% to 1.4%. The heat treatment leads to the precipitation of crystals, the composition of crystal phase depends on the glass composition. For the glasses with x = 0 and 10, the thermal treatment increases Ω 6 while reducing Ω 4 , as a result of an enhanced stiffness and reduced covalency of dopant's environment due to the precipitation of various crystals. As Ω 2 remains unchanged, the Eu3+ are suspected to remain mainly in the amorphous part of the glass-ceramics in agreement with the lack of sharp peaks in the emission spectrum. For the glasses with x = 20 and 25, Ω 2 increases indicating a change in the site symmetry of Eu3+ resulting from the dopant entering the CaF 2 crystalline phase. Due to the changes in the Eu3+ sites in the heat treated glasses, the heat treatment of the glass increases the absolute thermal sensitivity, but reduces the relative thermal sensitivity. The oxyfluorophosphate glass-ceramic with x = 25 exhibits high absolute thermometric sensitivity compared to oxyfluorophosphate glass, but also comparatively low relative sensitivity of 0.5% K−1. [ABSTRACT FROM AUTHOR]

Materials doped with the luminescent Eu3+ ion are attracting an ever-increasing amount of attention due to their potential applications in solid-state lighting, display devices, solar cells, or bioanalytics. But, why Eu3+? Unlike other lanthanides, its electronic features make the calculation of some physicochemical parameters quite straightforward, since they can be extracted directly from the emission spectrum. Highly appreciated for its reddish emission, the luminescent ion has also been widely used as a site-sensitive structural probe. With this in mind, this paper aims to offer easy guidance with helpful advice on how to interpret measurements of the emission spectra. It also presents the most useful tools for saving time, and gives a focused and practical explanation of the theoretical concepts involved. [Display omitted] [ABSTRACT FROM AUTHOR]

In the recent decade, various potential applications of the luminescence of nanosized ZrO 2 :Eu3+ have been demonstrated. However, the particle size effect on the luminescence properties of ZrO 2 :Eu3+ still requires intensive investigation. To this end, a series of tetragonal ZrO 2 :Eu3+ nanopowders with the europium concentration of 4 wt% and particle size of 3.0 ± 0.7 to 12.0 ± 4.8 nm was synthesized by laser vaporization. It was shown that the dominant role in the optical properties of ZrO 2 :Eu3+ nanoparticles belongs to OH groups, oxygen vacancies, and Eu3+ ions. It was found that a decrease in the particle size is accompanied by a significant increase in the emission intensity in the region of ∼440 nm. Based on the results of thermal analysis, IR and UV–vis DR spectroscopies, it was concluded that this luminescence is due to the emission of adsorbed OH groups. At the same time, a decrease in the number of vacancies with a decrease in the particle size leads to a change in the absolute quantum yield QY from ∼7 to 3.5%. In addition, despite the overall decrease in the intensity of the red luminescence of Eu3+, a decrease in the particle size leads to the appearance and increase in the emission intensity of the surface Eu3+. Thus, changing the particle size from 12.0 to 3.0 nm leads to a twofold decrease in the luminescence efficiency of ZrO 2 :Eu3+ and a shift in the color of its emission from pink-red (0.36, 0.26) to blue (0.19, 0.10). The results obtained are expected to be useful for further optimization of the luminescence properties of nanosized ZrO 2 :Eu3+ in numerous applications. [ABSTRACT FROM AUTHOR]

Scalable synthetic approach for superior performance of thermoelectric (TE) materials is a crucial step for the TE technology progress. Herein, reduced graphene oxide (RGO), carbon nitride (g-C 3 N 4) and europium (Eu) are utilized as additives to bismuth telluride (Bi 2 Te 3) matrix to prepare various novel nanocomposites (NCs): (RGO@Bi 1.8 Te 3 Eu 0.2) and (RGO-g-C 3 N 4 @Bi 1.8 Te 3 Eu 0.2) with an enhanced TE performance. The novel NCs were synthesized via solvothermal method, physiochemically characterized and consolidated into pellets of 1 mm thickness to measure their TE properties. The new additives potentially affected the physicochemical and TE properties of Bi 2 Te 3. Nanostructured hexagonal nanoplatelets with 12.5 nm thickness were observed by scanning and transmission electron microscopy (SEM and TEM) of the synthesized Bi 2 Te 3. This thickness shrinked to 5.7 and 5.2 nm upon the formation of (RGO@Bi 1.8 Te 3 Eu 0.2) and (RGO-g-C 3 N 4 @Bi 1.8 Te 3 Eu 0.2) NCs, respectively. Energy dispersive X-ray Spectroscopy (EDS) of NCs proved the existence of Bi, Te, C, Eu and N atoms. Raman and Fourier-transform infrared (FT-IR) spectra confirmed the NC formation that led to narrowing the energy band gap of Bi 2 Te 3 as displayed by UV–Vis spectra. Brunauer–Emmett–Teller showed specific surface area expansion of Bi 2 Te 3 from 6.78 to 19.00 and 16.75 m2g-1 of (RGO@Bi 1.8 Te 3 Eu 0.2) and (RGO-g-C 3 N 4 @Bi 1.8 Te 3 Eu 0.2) NCs, respectively. The electrical conductivity of Bi 2 Te 3 rose by 56 and 69 times, whereas its thermal conductivity significantly dropped by 1.6 and 1.7 times upon (RGO@Bi 1.8 Te 3 Eu 0.2) and (RGO-g-C 3 N 4 @Bi 1.8 Te 3 Eu 0.2) NCs formation. Owing to extra channels of carrier transfer and phonon scattering induced by NCs heterointerfaces. Novel combination of carbon-based materials and Eu with Bi 2 Te 3 matrix boosts its TE performance resulting in a worthy candidate for power generation applications at room-temperature. [Display omitted] • Novel RGO@Bi 1.8 Te 3 Eu 0.2 and RGO-g-C 3 N 4 @Bi 1.8 Te 3 Eu 0.2 NCs were solvothermally fabricated. • NCs heterostructure enhanced Bi 2 Te 3 physicochemical and TE properties. • Extra channels of carrier transfer and phonon scattering were provided by NCs heterointerfaces. • The electrical conductivity of the NCs potentially rose by 56 and 69 times. • NCs thermal conductivity significantly dropped by 1.6 and 1.7 times. [ABSTRACT FROM AUTHOR]

When nanomaterials with antibacterial properties were sent to the infected area, it was predicted that infection and related complications could be prevented. The nanoparticles can be designed to possess magnetic and luminescence (magneto-luminescent) properties to be effectively targeted and localized at the infection foci without dispersing into the body. Simultaneously, the magneto-luminescent characteristic of particles allows visualization and confirmation of localized particles at the desired area. In this regard, there are no studies on the use of antibacterial magneto-luminescent bioactive glass for orthopedic applications and the treatment of orthopedic device-related infections. In this study, antibacterial magneto-luminescent 58S bioactive glasses were synthesized by the modified Stöber using coupled with a layer-by-layer assembly approach to possess core/shell particle morphology. SPION/Bioactive glass nanoparticles had an average size of 50 nm and displayed superparamagnetic behavior. While the saturation magnetization value (σ s) of the undoped 58S sample was 25.32 emu/g, that of the co-doped sample (2% Eu, 2% Zn) was 21.74 emu/g; this showed that the doping slightly reduced the magnetization value. Europium (Eu) doping of SPION/Bioactive glass nanoparticles induced characteristic red emission originating from Eu emissions belonging to 5D 0 –7F J (J = 1–4) transitions and the strongest peak was at 612 nm (electric-dipole transition, 5D 0 –7F 2). Color chromaticity coordinates confirmed emission in the red region. XPS spectrum revealed the existence of Eu and Zn dopant elements in 58S bioactive glass. After soaking characteristic peaks at 31.74° and 45.43° belonging to the hexagonal hydroxyapatite phase were detected in the XRD data, confirming the SEM images. 2% Eu doped SPION/Bioactive glass nanoparticles had the highest osteoblast viability up to 7 days in vitro , while doping the samples with 2% zinc did not yield bone cell viability as high as the Eu doped ones. Importantly, Eu doped SPION/Bioactive glass nanoparticles inhibited gram-positive Staphylococcus aureus (S. aureus) and gram-negative Escherichia coli (E. coli) growth up to 48 h in vitro. The results showed that Eu doping of SPION/Bioactive glass nanoparticles increased osteoblast viability and inhibited bacterial growth, while possessing superparamagnetic properties and exhibiting red luminescence. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, the phosphorescence properties of Eu3+ and Er3+ co-doped yttria stabilized zirconia (YSZ: Eu3+, Er3+) as a function of oxygen partial pressure and temperature are investigated to explore the possibility of using this phosphor for pressure and temperature measurements at elevated temperature (up to 600 °C). The YSZ: Eu3+, Er3+ phosphors have a fixed Eu3+ concentration (1 mol%) and a varied Er3+ concentration (0.5–5 mol%). The phosphorescence intensity and lifetime of Eu3+ bands are sensitive to both oxygen partial pressure and temperature when temperature exceeds 400 °C. This oxygen/pressure sensitivity is related to the oxygen vacancy-induced non-radiative decay through charge transfer state (CTS), and is inversely correlated with Er3+ concentration. In contrast, the phosphorescence intensity and lifetime of Er3+ bands are temperature-sensitive but oxygen-insensitive, which is related to the dominant oxygen-independent 4S 3/2 → 2H 11/2 transition. Accordingly, two measurement strategies are proposed including an intensity ratio method and a lifetime method. The intensity ratio of the oxygen-sensitive Eu3+ bands and the oxygen-insensitive Er3+ reference bands is capable of 2D pressure measurement using a dual-camera system. But temperature-induced errors exist due to the temperature-sensitivity of intensity ratio. Simultaneous pressure and temperature measurements (point by point) can be achieved utilizing two PMTs that record the lifetimes of Eu3+ and Er3+, respectively. This method can resolve the issue of temperature sensitivity of Eu3+ and accurately correct the temperature-induced errors. The YSZ: Eu, Er phosphors show great potential for applications in high-temperature environment where the existing organic PSPs and TSPs cannot survive. [ABSTRACT FROM AUTHOR]

Tb3+ and Eu3+ doped La 4 GeO 8 multicolor emitting phosphors were synthesized. A systematic investigation was done into the photoluminescence properties of La 4 GeO 8 :Tb3+,Eu3+. Energy transfer from trivalent terbium to europium ions in La 4 GeO 8 results from quadrupole-quadrupole interaction. The variable temperature emission spectra ranging from 303 to 513 K were used to demonstrate the thermal stability of La 4 GeO 8 :0.07Tb3+,0.01Eu3+ phosphor. The obtained activation energies for trivalent terbium and europium ions were 0.186 eV and 0.187 eV, separately. By altering the content ratio of Eu3+ to Tb3+, the La 4 GeO 8 :Tb3+,Eu3+ phosphors can achieve multicolor luminescence and tunable chromaticity from green (0.3416, 0.5423) to red (0.6479, 0.349) under 265 nm light excitation. The findings suggest that La 4 GeO 8 :Tb3+,Eu3+ are promising phosphors for solid-state lighting application. [ABSTRACT FROM AUTHOR]

Hexagonal gadolinium Phosphate Hydrate doped with different europium amounts (Gd 1-x PO 4 :Eu x ·H 2 O; x = 0.01, 0.05, 0.10, 0.15, and 0.20) was synthesized by hydrothermal synthesis method and the obtained samples were analyzed giving the optimal dopant concentration. Furthermore, gadolinium was additionally replaced by Lanthanum Gd 0.85-y La y PO 4 :15%Eu (y = 0.25, 0.5, 0.75) in hopes of improving luminescence properties even more. This may be possible due to the fact that LaPO 4 exhibits a monoclinic crystal structure, which usually shows better luminescence properties. All of the synthesized compounds were analyzed by X-ray diffraction in order to investigate their crystal structure. SEM analysis was used to characterize the morphology of synthesized particles, while surface area and the pore size of Gd 0.85-x La x PO 4 :15%Eu samples were measured using Nitrogen adsorption by the BET method and BJH method. The luminescence properties were also characterized and discussed in detail. Lastly, the cytotoxicity study demonstrated that the replacement of gadolinium with lanthanum leads to a reduction in the toxicity of the samples. [ABSTRACT FROM AUTHOR]

Inorganic luminescent materials with special unidimensional morphologies have become one kind of highly promising materials in luminescence field. Here, CaGdAl 3 O 7 :Eu3+ unidimensional nanostructures containing nanofibers, nanobelts and hollow nanofibers are fabricated perfectly via facile mono-axial electrospinning technology combined with subsequent oxidation procedure. The formation mechanisms of CaGdAl 3 O 7 :Eu3+ unidimensional nanostructures have been put forward and a new technology of constructing the unidimensional nanostructures is given. The morphologies of nanofiber, nanobelt and hollow nanofiber can be easily modulated via regulating the components of spinning solution and spinning parameters. CaGdAl 3 O 7 :Eu3+ unidimensional nanostructures are tetragonal in structure with space group of P ‾ 42 1 m and possess perfect unidimensional morphologies. The unidimensional nanostructures show the predominant emissions at 590 and 619 nm under 256-nm ultraviolet light excitation, which result from 5D 0 →7F 1 and 5D 0 →7F 2 transitions of Eu3+ ions, respectively. The luminescence properties of the nanostructures can be adjusted by altering Eu3+ content, calcination temperatures and morphologies of the nanostructure. In brief, this work is of great significance for follow-up investigations of melilite group aluminates luminescence nanomaterials with distinct unidimensional morphologies. • CaGdAl 3 O 7 :Eu3+ one-dimensional nanostructures are first prepared via electrospinning. • Various one-dimensional structures are easily obtained by tuning spinning conditions. • CaGdAl 3 O 7 :Eu3+ nanofiber, nanobelt and hollow nanofiber emit excellent fluorescence. • Emitting color is tuned by tuning sintering temperature, morphology and Eu3+ content. • The technique is extended to prepare other aluminate one-dimensional nanostructures. [ABSTRACT FROM AUTHOR]

Europium (Eu3+)-doped heavy metal phosphate glass systems have been synthesized by melt-quench technique. Optical as well as spectroscopic characteristics are analyzed in detail. X-ray diffraction (XRD) pattern of synthesized samples confirms their glassy nature. Optical band-gap (E g) for the synthesized samples has been calculated using different methods. Refractive index and other parameters such as dielectric constant, molar refraction, reflection losses, and polarizability have also been determined for prepared glass samples. Photoluminescence properties are examined from the excitation as well as emission spectra and results revealed prominent emissions in red region. The optical band gap for the prepared samples has been evaluated using three different methods viz. Tauc's method, absorption spectrum fitting (ASF) method and differential absorption spectrum fitting (DASF) method. Similar results have been obtained by all the three methods. Judd-Ofelt (J-O) theory has been employed to emission bands of Eu3+ ions for determination of phenomenological intensity parameters i.e. Ω 2, Ω 4 and Ω 6 , radiative rate, branching ratio and radiative lifetime. J-O analysis revealed that the large value of Ω 2 parameter indicated high covalency between metal-ligand bonds along with the distortion among symmetric sites of Eu3+. Branching ratio (β R) is greater than 0.5 for 5D 0 →7F 2 (transition) indicating their prospective for usefulness in laser-based applications. High branching ratio values and color purity suggests the potential use of glass samples for red laser applications. [ABSTRACT FROM AUTHOR]

A correlation between piezoelectricity and photoluminescence is investigated for europium doped (Na 0.41 K 0.09 Bi 0.5)TiO 3 ceramic. An optimum piezoelectric and dielectric response is observed for 1.0 at.% Eu doped (Na 0.41 K 0.09 Bi 0.5)TiO 3. For doping concentration higher than 1.0 at.% a gradual fall in the piezoelectric response is observed which is associated to the amphoteric nature of Eu3+ ion. On the contrary, the photoluminescence intensity increases monotonically with the increase in Eu concentration. On application of an electric field, although there is no noticeable shift in the position and shape of the photoluminescence line, a quenching of hypersensitive 5D 0 → 7F 2 transition is observed. The quenching effect is more evident for lower doping concentration (less than 2.0 at.%) of europium. The emergence of irreversible tetragonal phase, after application of the electric field, is attributed to the quenching of 5D 0 → 7F 2 transition. Based on these investigations it is concluded that the piezoelectric and photo-luminescence lack one-to-one correlation. The PL response is associated to the local site symmetry around Eu3+ and it is independent of the development of long-range ordering. [ABSTRACT FROM AUTHOR]

Four Li–Al–Si– O -based ceramic compounds with varying Si to Li ratios were synthesized via a high-temperature reaction route and characterized by X-Ray diffraction, scanning electron microscopy, and photoluminescence techniques. Eu was used as an activator in these four compositions namely, LiAlSiO 4 , LiAlSi 2 O 6 , LiAlSi 3 O 8 , and LiAlSi 4 O 10 , and the radiative properties were evaluated. The activator concentration was optimized in all these samples to 2 mol%. The photoluminescence emission intensity and decay time values increased with the Si to Li ratio. The relative intensities of the emission spectra and the lifetime values indicated that the rare earth ion stabilizes itself at interstitial positions in the lattice having approximately C 2v symmetry. The chromaticity indices for the four ceramic samples doped with Eu were calculated that showed near red emission for all. To get an idea about their commercial utility, color purity, quantum efficiencies for the phosphors were evaluated. The emission profile of the prepared samples was compared with a commercial sample. The Judd-Ofelt parameters, transition probabilities, branching ratios, and quantum efficiencies were also calculated for these systems. It was observed that the metal-ligand bond covalency decreased with an increase in the Si to Li ratio which was responsible for the increase in the emission intensities and luminescence decay time values. [ABSTRACT FROM AUTHOR]

Tin oxide (TO), F-doped SnO 2 (FTO), and Eu/F-codoped SnO 2 (EFTO) films were deposited by spray pyrolysis. Additionally, for the DFT calculations, different superstructures were considered as models for TO (SnO 2), FTO (Sn 36 O 71 F), and EFTO (EuSn 35 O 70 F 2). Electrical and optical measurements showed that the EFTO films maintain the characteristics of a transparent conducting oxide (TCOs), i.e., high optical transparency and low electrical resistivity (ρ). The plasma wavelength for EFTO thin films was red-shifted when compared to FTO, which is related to the diminishing of free electron density (n e) and the increase of ρ; such effects were promoted by the incorporation of Eu impurities which act as electron acceptors. Photoluminescence (PL) studies revealed that the EFTO films did not show electronic transitions related to Eu states in the visible part of the spectra (vis). On the other hand, the DFT calculations confirmed the experimental results related to the incorporation of Eu/F impurities in TO, such as cell expansion, the creation of direct bandgap TCOs, the appearance of the Burstein-Moss effect, the absence of emission lines in the vis, and the diminishing of n e due to the presence of Eu acceptor states. [ABSTRACT FROM AUTHOR]

Ln 2 (Hf 2-x Ln x)O 7-x/2 (Ln = Sm, Eu; x = 0.1) pyrochlores have been prepared via mechanical activation of oxide mixtures, followed by heat treatment for 4h at 1450 and 1600 °C, respectively. According to the ESR data, the Eu cations on the Hf site in the Hf 1-x Eu x O 6 octahedra in pyrochlore Eu 2 (Hf 2-x Eu x)O 7-x/2 (x = 0.1) are most readily oxidized and reduced. Oxidation at 840 °C for 24h in air reduces the total conductivity of the Ln 2 (Hf 2-x Ln x)O 7-x/2 (Ln = Sm, Eu; x = 0.1) by a factor of 2.5–6, due to the decrease in the concentrations of oxygen vacancies and Ln2+ ions as a result of the oxidation. The anomalous low-frequency behavior of the permittivity of the Eu 2 (Hf 2-x Eu x)O 7-x/2 (x = 0.1) at ~800 °C can be understood in terms of the changes in the oxygen sublattice of the pyrochlore structure as a result of the oxidation of divalent europium and partial filling of oxygen vacancies at this temperature. [ABSTRACT FROM AUTHOR]