Red-to-near infrared persistent phosphors have attracted great attention because they are promising candidates for in vivo imaging. However, for most of the persistent phosphors that are activated only by ultraviolet (UV) light, the detection time is limited because persistent luminescence decays with time and UV excitation cannot be repeated due to the opacity of living tissues to UV radiation. Therefore, we have developed persistent phosphors with perovskite and garnet structures, which show 1) persistent luminescence at an optimum wavelength with high transparency for living tissue, 2) with brighter and longer persistent luminescence, and 3) with an additional function leading to long-term in vivo imaging capability.
Special Articles: The 71st CerSJ Awards for Academic Achievements in Ceramic Science and Technology: Review
The advent of advanced quantum beam sources and instrumentation makes it feasible to use quantum-beam (synchrotron X-ray and neutron) techniques to investigate the structure of disordered materials in a quantitative manner. In particular, a combination of quantum-beam measurements and advanced simulation techniques allows us to study structures at both the atomistic and electronic levels. In this article, some of the recent work on solving the structure of functional disordered materials, which do not contain a glass former, are reviewed to discuss the relationship between structure and glass-forming ability as well as the relation between atomistic and electronic structures and functions. Furthermore, we consider the use of other quantum-beam-based techniques and the introduction of descriptors for disordered matter to reveal the ordering hidden in correlation functions.
Crystal structure and electron-density distribution of the perovskite-type oxynitrides BaNbO2N and SrNbO2N have been analyzed by the synchrotron X-ray powder diffraction, Rietveld and maximum-entropy methods. In both BaNbO2N and SrNbO2N, the electron-density levels along the Nb–(O,N) bonds are significantly higher than those along the Ba–(O,N) and Sr–(O,N) bonds, which indicates higher covalency of the Nb–(O,N) bonds. The Nb–(O,N) bonds in SrNbO2N have higher electron-density levels than that in BaNbO2N, which suggests higher covalency of Nb–(O,N) bonds in SrNbO2N. The higher covalency of SrNbO2N cannot explain its wider band gap Eg than Eg of BaNbO2N. The wider Eg of SrNbO2N compared to BaNbO2N is attributable to the smaller Nb–(O,N)–Nb′ angles of SrNbO2N.
We report mechanoluminescence (ML) properties in the layered-structure compound Sr3Sn2O7:Sm3+. In this study, boric acid (H3BO3) was used as a flux in sintering process. By this step, we successfully enhanced the ML intensity of Sr3Sn2O7:Sm3+ to 6-times as large as that of the samples without using H3BO3. It was also found that the addition of H3BO3 leads to an anisometric shape of Sr3Sn2O7:Sm3+ particles, which may contribute the enhancement of ML intensity.
A non-destructive method is developed to determine the stress profile in double ion-exchanged lithium aluminosilicate glass. In this method, the steep compressive stress distribution from the surface to a depth of 10 µm is evaluated by the optical guided-wave method. The stress distribution from a depth of 50 to 413 µm is determined by the scattered light technique, where the scattered light intensity observed normal to an incident polarized beam is recorded and the phase shift is calculated from it. The stress profile combined with the optical guided-wave and the scattered light methods is presented and its comparison with the sodium and potassium concentration distributions and the Raman peak shift is discussed.
Upconverters that utilize two or more low energy photons to generate a single high energy photon are promising materials for solar energy conversion. Herein, we present a broadband-sensitive upconverter to utilize broad solar spectrum ranging from 1060 to 1650 nm which is not utilized by present crystalline Si (c-Si) solar cells. Our calculation shows that the broadband-sensitive upconverters designed can increase the efficiency of c-Si solar cell by ∼4.8%, considering the present value of ∼25% in the optimized c-Si solar cell. We used octahedrally oxygen-coordinated Ni2+ ions to harvest 1060–1500 nm photons and transferred the absorbed energies to the Er3+ ions. Those photons along with the 1450–1650 nm photons absorbed by the Er3+ ions themselves are upconverted to 980 nm, which is efficiently utilized by c-Si solar cells. We optimized the efficiency of the broadband-sensitive upconverters by monitoring host cations and active-ions (Ni2+ and Er3+) concentrations. Absorption and Stokes emission band positions of Ni2+ changed remarkably depending on the A-site cations in the ATiO3 (A = Mg, Ca, Sr, Ba) hosts making difference in the Ni2+ to Er3+ energy transfer efficiencies and hence the overall upconversion (UC) emission intensities. Further, absorption and emission intensities of the Ni2+ and Er3+ ions largely pronounced in the CaTiO3 host compared to the CaZrO3 due to more distorted nature of the CaTiO3 lattice. Intense Ni2+ emission with larger Stokes shift favored efficient Ni-to-Er energy transfer in the forward direction with minimum-energy back transfer making more intense Er3+ UC emission in the CaTiO3:Er3+,Ni2+ upconverter. Thus, to realize efficient broadband-sensitive UC, it is essential to design a host material with low symmetry lattice to confirm higher emission efficiency of Er3+ and controlled Ni2+ absorption and emission bands to suppress the energy back transfer while maintaining efficient energy transfer in the forward direction.
Some solid phosphates show high protonic conductivity in the intermediate temperature range at 150–250°C. Although the conductivity of crystalline phosphate materials, such as CsH2PO4 and CsHSO3, is high at intermediate temperature, it decreases significantly below phase transition temperature. In order to quench the structure of the high temperature phase with high conductivity, non-crystalline ultraphosphate glasses without phase transition in the wide temperature range at 25–250°C were evaluated. In the present work, the valency effects of cation dopant on protonic conductivity and glass structure were investigated. The P–O bonding was strengthened by doping trivalent La, which decreased proton conductivity. On the other hand, orthophosphate and end phosphate structures were formed by doping univalent Cs. The conductivity of 30Cs2O–70P2O5 glass was 1.7 × 10−3 S/cm at 200°C. However, the production of free orthophosphoric acid deteriorated the chemical stability for Cs-doped phosphate glasses. The 30ZnO–70P2O5 glass has a potential as an electrolyte of intermediate temperature fuel cells, since a maximum power density of 1.2 mW/cm2 was obtained at 200°C.
The performance of Ni-based trimetallic alloy cermet anodes, Ni0.8−xCu0.2Mx (M = Fe and Co; x = 0.1, 0.2, and 0.3)/Ce0.8Sm0.2O1.9 (SDC), was investigated for intermediate-temperature (500–700°C) solid oxide fuel cells (IT-SOFCs), using humidified (3% H2O) model syngas with a molar ratio of H2/CO = 3/2 as the fuel. Though doping Fe or Co 10 mol % into the Ni0.8Cu0.2/SDC anode led the cell performance to the increase, the cell performance decreased as Fe or Co content increased further. On the one hand, doping Fe or Co into the Ni0.8Cu0.2/SDC anode further effectively inhibited carbon deposition owing to CO on the anode. Our results suggest that the Ni0.7Cu0.2Fe0.1/SDC and Ni0.7Cu0.2Co0.1/SDC anodes are more promising materials than Ni0.8Cu0.2/SDC anode for syngas fuel in IT-SOFCs.
This study aims to characterise the freeze–thaw resistance of concrete incorporating carbonated coarse recycled concrete aggregate (C-CRCA) at partial or full replacement rates of coarse natural aggregate (CNA). Experimental work is conducted for C-CRCA with varying CO2 curing time (0 day, 3 day, 7 day) and C-CRCA weight replacement percentages (0, 20, 50, 100%) for concrete production. Weight loss, relative dynamic modulus of elasticity (RDME) and residual compressive strength were monitored after 300 freeze–thaw cycles. Pore size distribution and crack volume variation were also measured via nuclear magnetic resonance to investigate changes in the microstructure of the concrete interior. The compressive strength of concrete decreases with the replacement percentage of CNA by the C-CRCA. The internal freeze–thaw resistance of concrete with C-CRCA was higher or equal to those of concrete with CRCA and CNA. The total replacement of CNA by C-CRCA led to the highest RDME, and 50% replacement of CNA by C-CRCA led to the highest residual compressive strengths after the freeze–thaw cycles. However, the weight loss was more severe with the increasing replacement of CNA by C-CRCA. Increasing CO2 curing time improved the frost resistance of C-CRCA concrete. The analyses of concrete mesostructure based on pore size distribution and crack volume variation agreed with the results of RDME and the compressive strength of concrete.
This paper describes the joining of aluminum and alumina by using polymethylphenylsiloxane, which is a type of polysiloxane. The polymethylphenylsiloxane that was coated on alumina formed an interlayer through a heat reaction involving aluminum, alumina, and polymethylphenylsiloxane. Scanning electronic microscopy and transmission electronic microscopy showed that the alumina and aluminum were joined together through the interlayer without any cracks or exfoliation, and the thickness of the interlayer was approximately 100 nm. The interlayer formed at temperatures of 873 K and higher. The X-ray diffraction pattern and energy dispersive X-ray spectroscopy suggested that the interlayer consisted of aluminum silicate. The average bending strength of the joined samples was 232 MPa. Although the strength of the samples decreased during a thermal cycling test under conditions of alternating exposure to heating at 423 K and cooling at 233 K, the strength maintained a value of at least 160 MPa, despite the number of thermal cycles exceeding 100 times.
Edited and published by : The Ceramic Society of Japan Produced and listed by : Komiyama Printing Co., Ltd.(Vol.115 No.1344-Vol.116 No.1351, Vol.118 No.1376-) Letterpress Co., Ltd.(Vol.116 No.1352-Vol.118 No.1375)