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2,460 results on '"Yoshikawa, Akira"'

8. Shape-controlled crystal growth of Y$_3$Al$_5$O$_{12}$:Ce single crystals with application of micro-pulling-down method and Mo crucibles, and their scintillation properties

Author

Yoshino, Masao, Kotaki, Atsushi, Yokota, Yuui, Horiai, Takahiko, and Yoshikawa, Akira

Subjects
Condensed Matter - Materials Science, Physics - Instrumentation and Detectors, Physics - Optics
Abstract

The technology to grow single crystals of the required shape directly from a melt has been researched extensively and developed in various industries and research fields. In this study, a micro-pulling-down method and a Mo crucible were applied to the shape-controlled crystal growth of Y$_3$Al$_5$O$_{12}$:Ce (YAG:Ce). Three types of Mo crucibles with different die shapes were developed. Stable crystal growth in the same shape as the die was achieved, and scintillation properties that are comparable with those of the previously reported YAG:Ce were obtained., Comment: 15 pages, 8 figures, submitted to Journal of Crystal Growth

Published
2021

9. Temperature dependence and quenching characteristics of (La, Gd)$_2$Si$_2$O$_7$ scintillators at various Ce concentrations

Author

Yoshino, Masao, Horiai, Takahiko, Takasugi, Tatsuki, Jary, Vitezslav, Nikl, Martin, Yokota, Yuui, Kamada, Kei, Shoji, Yasuhiro, Kucerkova, Romana, and Yoshikawa, Akira

Subjects
Condensed Matter - Materials Science, Physics - Instrumentation and Detectors, Physics - Optics
Abstract

We investigated the thermal stability of scintillation and the luminescence performances of (La, Gd)${}_{2}$Si${}_{2}$O${}_{7}$ single crystals at various Ce concentrations. We prepared (La${}_{0.25-x}$, Ce${}_{x}$, Gd${}_{0.75}$)${}_{2}$Si${}_{2}$O${}_{7}$ (x = 0.0001, 0.001, 0.005, 0.01, 0.02, 0.05, and 0.1; unit: molar concentration) single crystals by the Czochralski and micro-pulling-down methods. With increasing Ce concentration, the photoluminescence emission and photoluminescence excitation spectral bands shifted to low energies and the activation energy $\mathrm{\Delta }E$ for thermal quenching decreased. For Ce $\mathrm{<}$ 0.5 at.% samples, the photoluminescence emission background value calculated in the exponential approximation started to increase at temperatures greater than 320 K, which is probably because of Ce${}^{3+}$ 5$\textit{d}$ excited-state ionization. However, the effect was weaker for the Ce $\ge $ 0.5% samples, which may indicate a comparatively larger contribution from other nonradiative relaxations. Thus the main reason for the thermal quenching of the Ce${}^{3+}$ emission in (La, Gd)${}_{2}$Si${}_{2}$O${}_{7}$ is the combination of the 5$\textit{d}$1 excited-state ionization and nonradiative relaxation via thermally excited crossover from the 5$\textit{d}$ excited state to the 4$\textit{f}$ ground state. The temperature dependence of the scintillation light yield was similar irrespective of the Ce concentration, with Ce 1.0% exhibiting the best performance within the temperature range 300 K to 450 K., Comment: 27 pages, 11 figures

Published
2021

16. Crystal growth and optical properties of Ce-doped (La,Y)$_2$Si$_2$O$_7$ single crystal

Author

Horiai, Takahiko, Paterek, Juraj, Pejchal, Jan, Jarosova, Marketa, Rohlicek, Jan, Kurosawa, Shunsuke, Hanada, Takashi, Yoshino, Masao, Yamaji, Akihiro, Toyoda, Satoshi, Sato, Hiroki, Ohashi, Yuji, Kamada, Kei, Yokota, Yuui, Yoshikawa, Akira, and Nikl, Martin

Subjects
Physics - Optics, Condensed Matter - Materials Science
Abstract

We have grown Ce-doped (La,Y)$_2$Si$_2$O$_7$ single crystal by micro-pulling-down method and investigated its optical and scintillation properties. We have successfully prepared the single crystal with (Ce$_{0.015}$La$_{0.600}$Y$_{0.385}$)$_2$Si$_2$O$_7$ composition. The observed thermal quenching process could be characterized by the quenching temperature (T50%) of 526 K and its activation energy was determined to be 0.62 eV. Further considering the thermal quenching factors, it was found that the thermal quenching was caused by at least the thermal ionization and maybe also by classical thermal quenching. The light output and scintillation decay time were evaluated to be ~12,000 photons/MeV and ~42 ns, respectively. These results indicate that (Ce$_{0.015}$La$_{0.600}$Y$_{0.385}$)$_2$Si$_2$O$_7$ has a great potential for application in scintillation materials.

Published
2021
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31. Circularly symmetric nanopores in 3D femtosecond laser nanolithography with burst control and the role of energy dose

Author

Paz-Buclatin Franzette, Esquivel-González Marcos, Casasnovas-Melián Alfredo, de Varona Omar, Cairós Carlos, Trujillo-Sevilla Juan Manuel, Kamada Kei, Yoshikawa Akira, Rodríguez-Ramos Jose Manuel, Martin Leopoldo Luis, and Ródenas Airan

Subjects
3d laser writing, 3d nanofabrication, 3d nanolithography, 3d nanophotonics, laser nanostructuring, nanofabrication, Physics, QC1-999
Abstract

The fabrication of three-dimensional (3D) nanostructures within optical materials is currently a highly sought-after capability. Achieving nanoscale structuring of media within its inner volume in 3D and with free design flexibility, high accuracy and precision is a development yet to be demonstrated. In this work, a 3D laser nanolithography technique is developed which allows producing mm-long hollow nanopores inside solid-state laser crystals and with a high degree of control of pore cross-sectional aspect ratio and size. We report an in-depth study on the formation of pores both within the non-thermal regime at which temperature is fast dissipated after each laser pulse, and for a thermally controlled regime using pulse-bursts which facilitate the formation of pores with highly circular shapes down to 1.1. We demonstrate this process for a wide range of speeds, pulse repetition rates and pulse energies, thus opening the door to a much more useful nanofabrication technique for nanophotonics. Finally, we also report the change in index of refraction that is produced at the nanoscale obtaining a positive index contrast of ∼3%. The work therefore provides a promising path towards reliable 3D nanostructuring of solid-state laser media for the flexible fabrication of large and complex structures with features sizes from the nanoscale up to the mm-scale. Moreover, due to the embedded, seamless, and monolithic nature of this technology, and since YAG crystals can sustain temperatures of up to 1900 °C and are highly chemically inert and erosion resistant, we anticipate its direct application in harsh environments.

Published
2023
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34. High-light-yield calcium iodide (CaI2) scintillator for astroparticle physics

Author

Iida, Takashi, Kamada, Kei, Yoshino, Masao, Kim, Kyoung Jin, Ichimura, Koichi, and Yoshikawa, Akira

Subjects
Physics - Instrumentation and Detectors
Abstract

A high light yield calcium iodide (CaI2) scintillator is being developed for an astroparticle physics experiments. This paper reports scintillation performance of calcium iodide (CaI2) crystal. Large light emission of 2.7 times that of NaI(Tl) and an emission wavelength in good agreement with the sensitive wavelength of the photomultiplier were obtained. A study of pulse shape discrimination using alpha and gamma sources was also performed. We confirmed that CaI2 has excellent pulse shape discrimination potential with a quick analysis., Comment: 5 pages, 5 figures, Proceeding of the 15th Vienna Conference on Instrumentation (VCI2019)

Published
2019
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35. Pulse-shape discrimination potential of new scintillator material: La-GPS:Ce

Author

Mizukoshi, Keita, Iida, Takashi, Ogawa, Izumi, Shimizu, Kensei, Kurosawa, Shunsuke, Kamada, Kei, Yoshino, Masao, and Yoshikawa, Akira

Subjects
Physics - Instrumentation and Detectors, High Energy Physics - Experiment, Nuclear Experiment
Abstract

(Gd,La)$_2$Si$_2$O$_7$:Ce (La-GPS:Ce) is a new scintillator material with high light output, high energy resolution, and fast decay time. Moreover, the scintillator has a good light output even at high temperature (up to 150$^\circ$C) and is non-hygroscopic in nature; thus, it is especially suitable for underground resource exploration. Particle identification greatly expands the possible applications of scintillator. For resource exploration, the particle identification should be completed in a single pulse only. The pulse-shape discrimination of the scintillator was confirmed. We compared two methods; a double gate method and a digital filter method. Using digital filter method (shape indicator), F-measure to evaluate a separation between $\alpha$ and $\gamma$ particles was obtained to be 0.92 at 0.66 MeVee., Comment: 9 pages, 9 figures

Published
2019
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40. Micro-Inclusion Engineering via Sc Incompatibility for Luminescence and Photoconversion Control in Ce3+-Doped Tb3Al5−xScxO12 Garnet

Author

Bartosiewicz, Karol, primary, Tomala, Robert, additional, Szymański, Damian, additional, Albini, Benedetta, additional, Zeler, Justyna, additional, Yoshino, Masao, additional, Horiai, Takahiko, additional, Socha, Paweł, additional, Kurosawa, Shunsuke, additional, Kamada, Kei, additional, Galinetto, Pietro, additional, Zych, Eugeniusz, additional, and Yoshikawa, Akira, additional

Published
2024
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