Positron Annihilation Lifetime Spectra Research Articles

High adsorption of Cu(II) in novel thiacalix[4]arene/acrylic polymer/diatomite fast fabricated by electron beam irradiation: Controllable microstructures, adsorption performance and mechanism

Chemical grafting of calix[4]arene is a common method to prepare high-performance calix[4]arene adsorbents for heavy metals, however, the chemical grafting process consumes much time and a large amount of heating energy due to the tedious steps. Herein, a thiacalix[4]arene/acrylic polymer/diatomite (TC4A/PAA/diatomite) adsorbent was fast fabricated by electron beam irradiation induced grafting, polymerization and crosslinking technique only in one-pot for the removal of Cu(II) as an important form of heavy metal pollution. Characterization by Fourier transform infrared (FTIR) spectra, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), diffuse reflectance UV–visible spectra and positron annihilation lifetime spectra (PALS) disclosed that the eco-friendly and low-cost TC4A/PAA/diatomite irradiated at 90 kGy namely TC4A/PAA/diatomite (90 kGy) with strong complexing ability owing to many functional groups such as carboxyl, hydroxyl etc in it. The effects of electron beam irradiation dose, initial solution pH, and initial concentration of Cu(II) on the adsorption performance of TC4A/PAA/diatomite were investigated. The isotherm adsorption data of Cu(II) in TC4A/PAA/diatomite (90 kGy) are more suitable for the Langmuir model with the maximum adsorption capacity of 123.30 mg/g. In addition, the bifunctional TC4A/PAA/diatomite (90 k Gy) can efficiently remove Cu(II) and display excellent reusability properties. The adsorption mechanism was further analyzed by FTIR, SEM, X-ray photoelelctron spectroscopy (XPS), diffuse reflectance UV–visible spectra and PALS. This study provides a fast, efficient and eco-friendly synthesis method of calix[4]arene adsorbent, conducing to the design of material innovation. Meanwhile, TC4A/PAA/diatomite (90 kGy) has potential application prospects in the treatment of practical Cu(II) contaminated wastewater.

Positron annihilation spectroscopic investigation of pillared clay-based catalytic hybrid nanocomposites

Positron annihilation lifetime spectra for pillared montmorillonite clay (PILC), as encapsulated with chitosan (CS) chains, supported with Pd nanoparticles, fresh and recovered PILC-CS@Pd heterogeneous catalysts, along with the starting montmorillonite clay (MC) were measured. After pillaring modification, as the interlayer nano-space expanded, the sub nanometer level free-volume nanohole size increases obviously from 0.182 nm (MC) to 0.246 nm (PILC). Then, as the CS chains and active Pd species encapsulated within the interlayer nano-space, the o-Ps lifetime (τ3) and intensity (I) undergo a continuous decrease, indicating the decrease of the free-volume nanohole size and concentration. Meanwhile, in practical catalytic application scenarios, it is found that the variations of the free-volume parameters show close correlation with the recycling aging behavior and catalytic performance decline of the catalytic nanocomposites. The decrease in density of sub nanometer level molecular stacking due to the leaching of Pd species and degradation of CS chains in the interlayer galleries nano-space of the recovered PILC-CS@Pd hybrid nanocomposite has been sensitively detected by the o-Ps probe.

Exploring the electrochemical properties of lithium-ion battery electrodes composed of vacancy-defective zinc-substituted magnetite nanocrystallites

Single phase Zn2+-substituted magnetite nanocrystallites are synthesized via co-precipitation method and used as lithium-ion battery electrodes. The structural properties and vacancy distribution of nanoparticles are evaluated by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and positron annihilation lifetime spectroscopy (PALS). The Rietveld refinement of the X-ray diffraction patterns shows that the lattice constant increases with Zn2+ content from 8.392 Å for magnetite to 8.448 Å for Zn0.2Fe2.8O4. The XPS measurements show that cation vacancies increase with Zn content on the surface of nanoparticles. Positron annihilation lifetime spectra suggest more concentration of monovacancies and larger size of vacancy clusters in the Zn0.1Fe2.9O4 sample compared with the other two samples, Fe3O4 and Zn0.2Fe2.8O4. Electrochemical measurements show better reversibility, higher initial discharge capacity, and lower electrochemical impedance for the Zn0.1Fe2.9O4 electrode, which are attributed to the higher concentration of vacancy defects in its nanocrystallites. The electrochemical impedance spectroscopy (EIS) shows that the Li+ diffusion coefficient (DLi+) increases with Zn2+ doping from 1.51 × 10–15 cm2s–1 for Fe3O4 to 3.25 × 10–13 cm2s–1 for Zn0.1Fe2.9O4, and 1.43 × 10–13 cm2s–1 for Zn0.2Fe2.8O4. The initial discharge capacities of the samples found to be about 1345.04 mAh g−1 for Fe3O4, 1435.82 mAh g−1 for Zn0.1Fe2.9O4, and 1063.72 mAh g−1 for Zn0.2Fe2.8O4 electrodes, respectively. During first few cycles, the discharge capacity decline faster as Zn content increases. The discharge capacity of the Zn0.2Fe2.8O4 electrode is stable at 410 mAhg−1 from the 60th to the 200th cycle, which is higher than the Fe3O4 electrode (150 mAhg−1) and the Zn0.1Fe2.9O4 electrode (270 mAhg−1). This variance is explained by the cation vacancy concentration and the lattice constant of the samples. The impedance of the electrodes is also affected by the vacancy defects formed during the sample preparation.

Development of novel positron lifetime measurement system for potential liquid material inspection

β+-γ coincidence method and anti-coincidence method have great potential in positron annihilation lifetime (PAL) measurements of liquid material. Based on anti-coincidence method with the advantage of better picking out positron annihilation events in the sample, a novel PAL spectrometer, which can isolate the sample from the positron source and is suitable for liquid material inspection, is developed. The influences of the measuring geometry and the signal processing on the anti-coincidence effect are systematically studied. By comparing the PAL spectra of well annealed pure iron acquired by the new system with that acquired by the conventional system, the performance of system is evaluated. The analysis results of PAL spectra at different distances from the sample to the source and precise measurement of PAL in liquid water show that reliable values are obtained for liquid material inspection at an adjustable distance of less than 1.0 mm. This system is expected to be applied to liquid scintillators, oils or other special materials, which could easily contaminate the positron source.

Artificial neural network as an effective tool to calculate parameters of positron annihilation lifetime spectra

The paper presents the application of the multi-layer perceptron regressor model for predicting the parameters of positron annihilation lifetime spectra using the example of alkanes in the solid phase. Good agreement of calculation results was found when the approach is compared with the commonly used methods, e.g., LT. The presented method can be used as an alternative quick and accurate tool for the decomposition of positron annihilation lifetime spectroscopy (PALS) spectra in general. The advantages and disadvantages of this new method are discussed. We show the preliminary results where the trained network can give better outcomes than the results yielded by programs based on an analysis of a single PALS spectrum.

Thermal aging mechanism of PBT energetic elastomer based on the evolution of microstructure

3,3-bis(azidomethyl) oxetane and tetrahydrofuran copolymer (PBT)-based thermosetting polyurethane is an ideal energetic elastic matrix for high-energy, low-smoke, and insensitive solid propellants used in the field of aeronautics and aerospace. Its aging during long-term storage will cause deterioration of the mechanical properties of the propellant, which will bring serious security risks when working. To explore the thermal aging mechanism, the PBT elastomer was prepared and then aged at 40 °C, 60 °C, and 70 °C. Starting from characteristic structures that affect the mechanical properties of elastomer, active groups, hydrogen bonds, chemical crosslinking, free volume, crystallization, microphase separation, and mechanical properties of the PBT elastomer during thermal aging were analyzed by fourier transform-infrared (FT-IR) spectroscopy, swelling method, positron annihilation lifetime spectrum (PALS), X-ray diffraction (XRD), dynamic mechanical analysis (DMA), and uniaxial tensile test, respectively. Here, we found that the thermal aging of the PBT elastomer was a coupling process of several aging effects and showed a segmented feature. Destruction of hydrogen bonds, degradation of urethanes and oxidative crosslinking between polyether backbones successively dominated the thermal oxidation process of the PBT elastomer. This work is of great significance for the development of antiaging technologies for the PBT propellant and lays the foundation for the establishment of a mechanical property deterioration model based on microstructure evolution.

Super high counting rate of positron annihilation lifetime spectrometer achieved via multiple detectors

Positron annihilation lifetime (PAL) spectroscopy has long been considered as a powerful approach to characterize atomic-scale vacancy-type defects and supermicropores, which affect the macroscopic properties of materials. In standard PAL measurements, several million annihilation events are required to achieve accuracy. For a conventional PAL spectrometer which consists of two scintillation detectors and analytical electronics, the two detectors are usually perpendicularly positioned to diminish spectra distortions (caused by backscattering and pileup). The perpendicular placement of detectors leads to a counting rate of 100 – 300 counts/second (cps) while using a 30 μCi 22Na source (3.3 – 10 cps/μCi). Consequently, collecting one PAL spectrum with total counts of one million takes several hours. The long time limits its potential to observe changes in the microstructure. To increase the counting rate of PAL measurements, we propose a novel multi-detector PAL spectrometer, which includes three or four detectors, a digital oscilloscope, and an algorithm for any detector to record both start and stop signals. The spectrometer achieves a high counting rate of around 2144 cps (71.5 cps/μCi) with four detectors, which is about ten times that of a conventional one with two detectors perpendicularly positioned. This work enables us to perform in-situ PAL measurements to disclose the minute-scale evolution of microstructure more precisely during fast physical and chemical processes in the future.

A SiPM-based dual and triple coincidence system for positron annihilation lifetime measurement

Positron annihilation lifetime (PAL) spectroscopy is a powerful non-destructive method to study defects in materials. Silicon photomultipliers (SiPMs) have emerged as promising photodetector alternatives for PAL systems. However, further research is needed to fully optimize SiPM arrays for PAL applications. In this study, a dual and triple coincidence system has been developed based on four 1 × 4 SiPM arrays with resistor-chain readout, and initial results of PAL measurement have been obtained. A pixel-by-pixel time shift correction method was proposed and successfully applied using triple γ coincidence for summing 128 PAL spectra in one measurement. The system provides position, timing, and energy information for both 1275 and 511 keV γ-rays. The use of SiPM arrays and the pixel-by-pixel time shift correction method have enabled precise and reliable measurements of PALs in single-crystal silicon and yttria-stabilized zirconia samples. The developed SiPM-array-based PAL system also offers a technical solution to measure angular correlations of positron annihilation radiation, with the potential for further improvements.

Evaluation of a resistor-chain-based SiPM detector for positron annihilation lifetime measurement

Silicon photomultipliers (SiPMs) have great potential to replace photomultiplier tubes (PMTs) and exceed their performance in positron annihilation parameter-measurement systems. However, due to the limited active area of a single SiPM, it only covers a small γ-ray emission acceptance range and provides position information over a very small region. Using a SiPM array is a good way to overcome these problems. In this study, a resistor-chain-based SiPM detector was designed and evaluated for positron annihilation lifetime (PAL) measurements. This detector uses a 1 × 4 scintillator array, a 1 × 4 SiPM array, and a resistor-chain readout circuit to obtain position, energy, and timing information about 1275 and 511 keV γ-rays, with the readout pulses serving as both the position, energy, and timing signals. A comprehensive evaluation was conducted to assess the detector in terms of position profile, energy resolution, and time resolution. The position profiles showed that all the crystal elements in the lutetium fine silicate scintillator array were clearly resolved. The detector had an energy resolution of 11.3±0.9% and a time resolution of 198±9 ps. A total of 32 PAL spectra were obtained using two SiPM array detectors. The PAL in yttria-stabilized zirconia (YSZ) sample was accurately verified using the summed PAL spectrum. The developed SiPM detector provides good performance for PAL measurements and could be used to build a high-performance PAL spectrometer.

Enhanced thermoelectric properties of SnTe through core-shell structures and band engineering

The energy filtering effect is an effective method to improve the thermoelectric performance, and the core-shell structure with more interfaces and various potential barriers can introduce a stronger energy filtering effect. In this article, Ag2S@SnS core-shell structure is introduced into SnTe thermoelectric materials by incorporating Ag2S. When the concentration of Ag2S reaches 5%, the carrier concentration decreases by 41% compared with the undoped sample at room temperature,and the Seebeck coefficient increases to 140 μV K−1 at 800 K. Positron annihilation lifetime spectra show that the addition of Ag2S alloy reduces the vacancy concentration in SnTe, which leads to the weakening of ionized impurity scattering and the increase of mobility. This makes up for the reduced mobility due to the presence of the core-shell structure and the secondary phases. The core-shell structure, the secondary phase formed by the diffusion of small Ag2S particles and the binding of elements in SnTe and point defects, all of these unique hierarchical microstructures greatly reduce the lattice thermal conductivity of the samples over a wide temperature range. On this basis, In is doped into the material to introduce resonance levels and point defects, resulting in the lowest lattice thermal conductivity of 0.68 W m−1K −1 at 800 K. Moreover, The ZTave value obtained after In doping is 100% higher than that of single-alloyed Ag2S. The ZTmax value of Sn1.02In0.01Te-5%Ag2S increases to 1.02 at 800 K. This work provides a new idea for regulating thermoelectric performance.

Interaction of lanthanide and actinide with BaHfO3 perovskite: A case study with cerium and uranium

AbstractSpeciation of actinide (An) and lanthanide (Ln) in technologically important ceramics is very important from both fundamental as well as technological aspects. The intrinsic structural flexibility of perovskite containing AO6 and BO12 polyhedra makes them suitable and rich hosts for An and Ln. In this work, emphasis was given to deciphering information such as oxidation state, local dopant site, charge compensating defects, excited state kinetics, and so forth in BaHfO3 (BHO) related to dopant uranium (BHO‐U) and cerium (BHO‐Ce). Several spectroscopic techniques namely, time‐resolved photoluminescence (TRPL), positron annihilation lifetime spectra (PALS), and thermoluminescence (TL) spectroscopy coupled with density functional theory (DFT) were employed to probe the same. Ce and U though are distributed at both Ba and Hf sites, Ce prefers the former, while U prefers the latter site. Uranium on the other hand stabilizes as U6+ in the form of octahedral uranate ion giving green emission. PALS suggested the formation of defects in BHO‐Ce and BHO‐U with oxygen vacancies predominating in the former whereas BHO‐U perovskites are loaded with cation vacancies and vacancy clusters. These cation vacancies are responsible for lower TL output in BHO‐U. TL measurements also suggested cerium doping leads to a higher density of deeper traps in BHO‐Ce compared to uranium doping in BHO‐U which is in concurrence with DFT results and may have implications in designing afterglow phosphors based on perovskite. We believe this work would have a long‐term impact on exploring the potential of perovskite for nuclear waste host and afterglow phosphors applications.

Nanomilling-driven volumetric changes in multiparticulate As4S4-bearing nanocomposites recognized with a help of annihilating positrons

Employing positron annihilation lifetime (PAL) spectroscopy, nanomilling-driven volumetric changes driven are identified in multiparticulate nanocomposites of As4S4–ZnS–Fe3O4 system, considered in transitions between their respective hierarchical derivatives from triparticulate (1⋅As4S4/4⋅ZnS/1⋅Fe3O4) to biparticulate (1⋅As4S4/1⋅Fe3O4, 1⋅As4S4/4⋅ZnS) and monoparticulate (As4S4) ones. Unconstrained three-component PAL spectra of nanocomposites are parameterized in terms of positron-Ps trapping conversion obeying x3-x2-CDA (coupling decomposition algorithm). Coexistence of nanocrystalline nc-β-As4S4 and amorphous a-AsS phase is shown to be crucial feature of these nanocomposites, the latter being generated continuously due to reamorphization of initial disordered phase and/or vitrification of nc-β-As4S4 phase. The inverse positron-to-Ps trapping conversion prevails in transition from biparticulate (1⋅As4S4/1⋅Fe3O4) and monoparticulate (As4S4) nanocomposites (both dominated by trapping in As4S4-bearing sub-system) to triparticulate (1⋅As4S4/4⋅ZnS/1⋅Fe3O4) one, disappeared positron traps being vacancy defects in a-As–S matrix, and Ps-decay sites formed instead being triple junctions between amorphized nc-β-As4S4 grains. The normal Ps-to-positron-trapping conversion prevails in transition from biparticulate (1⋅As4S4/4⋅ZnS) nanocomposite dominated by positron trapping in ZnS sub-system to triparticulate (1⋅As4S4/4⋅ZnS/1⋅Fe3O4) one, disappeared Ps-decay sites being triple junctions between amorphized nc-β-As4S4 grains, and positron traps formed instead being vacancy-type defects in the packing of the finest ZnS crystallites (~ 2–3 nm).

Positron annihilation lifetime spectroscopic analysis of Nafion and graft‐type polymer electrolyte membranes for fuel cell application

AbstractThe subnano free‐volume hole features of Nafion‐212 and poly(styrene sulfonic acid) grafted poly(ethylene‐co‐tetrafluoroethylene) polymer electrolyte membranes are investigated by using the positron annihilation lifetime spectroscopic analyses with three‐ and four‐component models (i.e., one‐ and two‐ortho‐positronium [o‐Ps] components). The four‐component model provides a more adequate description of free‐volume hole features for both membranes, in which the longer o‐Ps lifetime is assigned to the larger free volume hole sizes in the mobile side chains, while the shorter o‐Ps lifetime is associated with the smaller free volume hole sizes within the backbones (the rigid amorphous fractions and the crystalline‐amorphous interfaces) and the interfaces between the main chains and the side chains. The o‐Ps annihilation is found to occur primarily in the side chains. The subnano volume hole features revealed by the positron annihilation lifetime (PAL) spectra suggest the primary water uptake and conductance in the side chains and the possible presence of water molecules in the rigid amorphous fractions and the interfaces. Note that the three‐component model as usually reported in the literature may underestimate the lifetime and intensity of ortho‐positronium annihilation.

Free‐Volume Extended Defects in Structurally Modified Ge–Ga–S/Se Glasses

Herein, transformation of free‐volume extended defects in selected chalcogenide glasses caused by thermal annealing for 10, 25, and 50 h is studied. For 80GeSe2–20Ga2Se3 as well as for GeS2–Ga2S3 glasses with different GeS2 and Ga2S3 contents (80GeS2–20Ga2S3, 82GeS2–18Ga2S3, 84GeS2–16Ga2S3), positron annihilation lifetime spectroscopy and Doppler broadening of annihilation radiation methods are applied. By analyzing the positron annihilation lifetime spectra decomposed into two components, it is shown that the observed changes in the second defect‐related component for the 80GeSe2–20Ga2Se3 glasses confirm the agglomeration of free volumes in the initial stage of annealing (10 h) with further fragmentation (25 h) and shrinkage (50 h). Increased content of Ge‐related subsystem in the GeS2–Ga2S3‐based glasses results in the agglomeration of free‐volume defects in the 82GeS2–18Ga2S3 glasses with their further expansion in the 84GeS2–16Ga2S3 matrix.

A new digital positron annihilation lifetime spectrometer for a single piece of micron-thickness film

Positron annihilation lifetime (PAL) spectroscopy is a unique method to study defects and supermicropores in solid materials. Traditionally, the pulsed slow positron beam (accelerator system included) was used to measure the PAL spectrum for a single film with a thickness of several microns, which is more complicated, expensive, and has worse time resolution than a conventional PAL spectrometer. In this paper, we developed a new PAL spectrometer to measure a single piece of micron-thickness film using two lanthanum bromide (LaBr3) detectors, a specially designed plastic scintillator detector, and a fast digitizer, at a cost equivalent to that of a conventional PAL spectrometer. The reliability and time resolution (around 210 ps, comparable to that of a conventional PAL spectrometer) of this spectrometer were verified by testing samples with thicknesses range from 15 to 60μm. Due to the successful construction of the new PAL spectrometer, PAL spectroscopy can now be applied to a single piece of micron-thickness film for the first time without building an accelerator system.

Correlation of adsorbed and embedded palladium species in chitosan composite nanofibers with their catalytic activities for Suzuki reactions

Heterogeneous palladium catalysts play an important role in the synthetic organic chemistry. Palladium species have been adsorbed on the surface of solid matrices or embedded inside solid matrices to prepare recyclable heterogeneous catalysts. Due to the different surrounding environment, these two type palladium species had different electronic properties and catalytic performances. In this study, we fabricated three series of chitosan composite nanofibers with adsorbed and embedded palladium species. Their fiber morphologies and chemical structures were characterized by SEM and FT-IR, respectively. Positron annihilation lifetime spectra (PALS) showed that the intensities (I3) of o-Ps annihilations were all linearly decreased with the increase of palladium contents in the chitosan composite nanofibers. Moreover, compared with the palladium adsorbed chitosan composite nanofibers, the palladium embedded chitosan composite nanofibers had stronger o-Ps annihilation ability, which could be ascribed to the stronger electron donating property of embedded palladium species and higher crosslinking of chitosan molecules by embedded palladium species. At last, the I3 values were successfully correlated with the rate constants of chitosan supported palladium composite nanofibers catalyzed Suzuki reactions of iodobenzene with phenylboric acid. Therefore, we have developed a facile method to distinguish the adsorbed and embedded palladium species by PALS, which can be further related with their catalytic performance.

Effects of Peroxide Initiator on the Structure and Properties of Ultralow Loss Thermosetting Polyphenylene Oxide-Based Composite.

Although thermosetting polyphenylene oxide- (PPO) based composites with excellent dielectric properties have been widely accepted as superior resin matrices of high-performance copper clad laminate (CCL) for 5G network devices, there has been limited information regarding the composition–process–structure–property relationships of the systems. In this work, the effects of peroxide initiator concentration on the structure and dielectric properties of a free radical cured ultralow loss PPO/Triallyl isocyanate (TAIC) composite system were studied. As expected, the glass transition temperature (Tg) and storage modulus increased with the advancing of crosslinking, whereas the dielectric loss showed an “abnormal” rise with the increase in crosslink density. Extensive studies were carried out by varying the initiator contents and characterizing the structure with spectroscopy, thermal analysis, and positron annihilation lifetime spectrum (PALS) techniques. The results show that the competition of polarity, crosslink density, free volume, and free TAIC are the key factors determining the dielectric properties of the composites.

A four-channel coincidence digital positron annihilation lifetime spectrometer

Positron annihilation lifetime (PAL) spectrometer is an effective tool to investigate material microstructures. Commonly used PAL spectrometers are conventional PAL spectrometer based on nuclear instrument modules (NIMs) and digital PAL spectrometer based on ultra-high-speed digitizer. Limited by the detection efficiency of the detectors, the coincidence count rate of the PAL spectrometer is always low, causing long time consumption of measurement. To solve this problem, a multi-channel coincidence method based on the ultra-high-speed digitizer was proposed. However, the ultra-high-speed digitizer is usually excessively expensive for research institutes. In this paper, we introduce a four-channel coincidence digital PAL spectrometer. Through the improvement of the timing and trigger circuit, all channels can act as start and stop channels during one measurement. Hence the coincidence count rate can be increased by an order of magnitude. The time measurement shows good linearity and high resolution with a full width half maximum (FWHM) at a level of several tens picoseconds. The effective number of bits (ENOB) of the analog-to-digital converter (ADC) reaches 10.72 bits. The energy resolution of the 511 keV photopeak reaches 4.16% when using LaBr 3: 5% Ce3+ scintillator, better than 4.62% of the conventional spectrometer. The time resolution of our PAL spectra when one channel receives start signals and one channel receives stop signals reaches 193.7 ps, better than that of the conventional spectrometer (212.8 ps). The FWHMs of the lifetime spectra of the two and four channel coincidence measurements are 205.8 ps and 212.4 ps respectively. Moreover, the coincidence count rate of our system increases significantly by using the four-channel coincidence method, which can be 10 times higher than the conventional spectrometer.

Luminescence Properties of Ho2O3-Doped Y2O3 Stabilized ZrO2 Single Crystals

Single crystals of Ho2O3-doped Y2O3 stabilized ZrO2 (YSZ) with different Y2O3 and Ho2O3 contents were grown by the optical floating zone method. XRD and Raman spectra were measured and showed that crystal samples all had tetragonal structures. Measurements of positron annihilation lifetime spectra indicated that the increase in Y2O3 concentration led to the increases of defects and mean positron lifetime, which enhanced the scattering of light and reduced the luminous intensity and the quantum yield (QY) of the crystal. Under the excitation at 446 nm, photoluminescence (PL) spectra of Ho2O3-doped YSZ crystals showed emission peaks at 540, 551, 670, and 757 nm corresponding to Ho3+ transitions from 5S2, 5F4, 5F5, and 5I4 excited states to the 5I8 ground state, respectively. At low Ho2O3-doped concentrations (0.10–0.50 mol%), the overall emission intensity increased with Ho2O3 contents, reached the maximum value at 0.50 mol%, then decreased with higher Ho2O3 contents, probably as a result of increased non-radiative relaxation caused by increased interactions between Ho3+ ions. Quenching of the PL occurred at Ho2O3 concentrations > 0.5 mol% and due to the electric dipole–dipole interaction. The calculated chromaticity coordinates (CIE) were approximately (0.307, 0.683) and the color purity achieved 99.6%. The results showed that Ho2O3: YSZ crystals were suitable for green light-emitting devices.

Influence of different preparation method on the microstructure and physical properties of CuFeO2

The single-phase CuFeO2 multiferroics material were achieved in crystal and ceramic forms successfully prepared by the optical floating zone with a low growth rate of 0.5 mm/h and high temperature solid state methods, respectively. All samples are delafossite structure. X-ray photoelectron spectroscopy spectra showed that there were different in the state of Cu iron. Positron annihilation lifetime spectra showed a decrease in the open volume of vacancy type defects in the crystal along with an increase in their concentration and the local electron density at the lattice was also changed compared to the ceramic sample. Raman spectra results proved that the vibration of the CuO bond was affected. Magnetic properties measurements indicated that the stability of antiferromagnetism and the interaction between magnetic domains of CuFeO2 are closely related to its internal defects, and the difference in internal defects reduces the transition temperature TN1 from 15.9 K in ceramic to 15.5 K in crystal.