Yuuki Kitagawa 교수

Magnesium tetraborate, MgB4O7, is an attractive host material for dosimetry due to the two characteristics: its low effective atomic number (Zeff = 8.4) and high neutron capture cross-section of the 10B isotope. Particularly, Ce3+ and Li+ ions co-doped MgB4O7 has shown optically stimulated luminescence (OSL) signal comparable to that of Al2O3:C, which is a well-known OSL dosimetry material. In this work, for further improvement of the dosimetric properties, a new synthesis route for MgB4O7:Ce3+-

Trivalent europium (Eu³⁺) ions show red luminescence with sharp spectral lines owing to the intraconfigurational 4f-4f transitions. Because of their characteristic luminescence properties, various Eu³⁺-doped inorganic compounds have been developed to meet the demands of optoelectronic devices. Regardless of shielding by the outer 5s and 5p orbitals, the properties of the Eu³⁺:4f-4f transition depend on the local environment, such as the shapes of the coordination

Eu3+-doped YSiO2N phosphor was synthesized, and its crystal structure was analyzed by single-crystal X-ray and neutron powder diffraction techniques. The new crystal structure of YSiO2N with the monoclinic lattice (space group C2/c) composed of nonequivalent [YO6N2] dodecahedra was identified, and, in this structure, five different Y3+ sites take Ci or Cn symmetry. Based on the experimentally determined crystal structure, we characterized the luminescence properties of the Eu3+ ions with site-se

The photoluminescence spectra and luminescence lifetimes of Eu3+-doped oxyhalides, YOX:Eu3+ (X = Cl or Br), and their temperature dependence on different halide species of mixed-anion coordinations were investigated and analyzed. In terms of the ionic and covalent nature of bonding, Eu3+ ions form different coordination polyhedra in the isostructural YOCl and YOBr hosts: a ninefold [Eu3+O4Cl5] and an eightfold [Eu3+O4Br4] polyhedra. The Judd–Ofelt Ω2 parameter for YOCl:Eu3+ takes a very large va

In Pr 3+ -doped Y 3 Al 5 O 12 , the blue-to-UV upconversion luminescence is significantly more affected by concentration quenching than the UV Stokes luminescence, which is due to cross-relaxation involving the upconversion intermediate states 3 P J and 1 D 2 .

By estimating the trap depth from the relative position of the zigzag curve of divalent lanthanoid ions and conduction band bottom, the YSiO 2 N:Ce 3+ ‐based blue persistent phosphors are developed, and their persistent luminescence and thermoluminescence properties are characterized to identify the electron trap distributions. Taking the nephelauxetic effect caused by covalent nitrogen into account for the vacuum referred binding energy diagram, it is predicted that Tm 3+ and Sm 3+ ions with th

The valence state of Eu ions doped in inorganic compounds is easily influenced by the synthesizing conditions. In this study, X-ray absorption spectroscopy revealed that almost half of Eu ions incorporated in the YSiO₂N host were reduced into the divalent state through the sintering process at 1600 °C under a N₂ gas atmosphere without any annealing processes. The prepared Eu^2+/3+-doped YSiO₂N sample showed anomalous deep-red to near-infrared luminescen

Abstract Recently, an ionic decision-maker (IDM) was developed to efficiently process information by using nanoionic phenomena within Nafion polymer electrolytes. Whereas a Nafion-IDM is able to solve multi-armed bandit problem (MBP), it has an inherent drawback that is unsuitable for high integration: it requires an insertion of Pt/C-nanograins dispersion film to the electrode/Nafion interface in order to increase the effective electrode/electrolyte interface area, otherwise such electrode/Nafi

Charge transfer (CT) luminescence of different types of polyhedra, [WO₅]^4- in Ca₃WO₅Cl₂ and [WO₆]^6- in Ca₃WO₆, is characterized by spectroscopic experiments and <i>ab initio</i> calculations. According to the geometry optimization, W⁶⁺ ions form five-fold [WO₅]^4- square pyramids in Ca₃WO₅Cl₂ because of a large interatomic distance be

The increasing demand for ultraviolet (UV) sterilization requires the development of new luminescent materials in the UVC region (100-280 nm). In this study, to obtain blue-to-UVC upconversion (UC) luminescence, fluorophosphate glasses doped with various Pr³⁺ concentrations were prepared by using the melt-quenching method, and their optical properties were evaluated. Absorption bands attributed to the 4f¹5d¹ → 4f² and 4f² → 4f² tr

This paper discusses the theory and experiments of heating and air cooling of battery modules. Heating mechanism is shown first, and cooling of a single battery is examined. Optimum air flow speed is discussed. Then, similar discussion is made for a battery module of six serial cells.