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  2. Ema Kazuhiro

Ema Kazuhiro

  (江馬 一弘)

Profile Information

Affiliation
Professor, Faculty of Science and Technology, Department of Engineering and Applied Sciences, Sophia University
Degree
博士（工学）(東京大学)
Contact information
k-emasophia.ac.jp
Researcher number
40194021
J-GLOBAL ID
200901045168026490
researchmap Member ID
1000167951

1983-1986 Mechanical properties of optical glass fibers
1986-1991 Pulse-shape control of ultrafast optical pulses
1991-2002 Pulse propagation properties in excitonic resonant region
1991-present Nonlinear optics at exciton resonance in semiconductors
1994-present Generation and control of coherent phonons in semiconductors
1995-2001 Optical properties and nonlinear optics in polymers
1996-present Optical properties in organic-inorganic hybrid materials
2004-present Optical properties of photo-catalysis materials　　
2006-present Optical properties of semiconductor nanocolumns
2006-2010 Optical properties and nonlinear optics in a quantum-dot ensemble
2006-present Anderson localization of light and random lasing
2007-present Optical properties of nitride semiconductors

I study optical properties in semiconductors and organic materials by means of time-resolved and/or nonlinear spectroscopy with ultrafast optical pulses. Recently I mainly study optical properties of semiconductor nanostructures. For a carrier in education, I have been teaching lectures concerning optics and optical physics for more than ten years, such as “Electromagnetics II”, “Optical physics”, “Quantum optics”, and “Optical properties in solids”. Also I have been teaching a general educational lecture named “Physics in daily life” for more than ten years.

(Subject of research)
Ultrafast Optical Signal Processing
Excitonic Nonlinear Optics
Optical properties of inorganic-organic materials
Optical properties of Photocatalytic materials
Optical properties of semiconductor nanostructure
Light loclization and random lasing

Research Interests

 13

Research Areas

 4

Research History

 13
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Education

 3

Committee Memberships

 17
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Awards

 1

Papers

 209
  • Naoki Shimosako, Mizuki Kumamoto, Yui Muroga, Zihao Liu, Masato Sotome, Takashi Kondo, Hideyuki Kunugita, Kazuhiro Ema
    The Journal of Chemical Physics, 161(17), Nov 1, 2024  
    Metal halide perovskite materials (MHPs) are promising for several applications due to their exceptional properties. Understanding excitonic properties is essential for exploiting these materials. For this purpose, we focus on CsPbBr3 single crystals, which have higher crystal quality, are more stable, and have no Rashba effect at low temperatures compared to other 3D MHPs. We have estimated exciton energy positions, longitudinal-transverse splitting energy, and damping energy using low-temperature reflection spectra. Under high excitation intensity, two biexciton emissions (M-emission) and exciton–exciton scattering emission (P-emission) were observed. We assign the two M-emissions to the emission to the states of longitudinal and transverse excitons, i.e., ML and MT emissions. From the energy position of the MT emission, the biexciton binding energy has been estimated to be ∼2 meV. By analyzing P-emission obtained from the back side of the sample, we have estimated the exciton binding energy to be 17.8–23.7 meV. This estimation minimizes the influence of the wavenumber distribution in the scattering process. In addition, time-resolved transmittance measurements using pulsed white light have revealed the group velocity dispersion. Comparing experimental results with theoretical calculations using the Lorentz model clarifies that exciton dynamics in CsPbBr3 can be described with a simple Lorentz model. These insights enhance the understanding of exciton behavior and support the development of exciton-based devices using MHPs.
  • Yota Suzuki, Yuji Mizuta, Ayame Mikagi, Tomoyo Misawa-Suzuki, Yuji Tsuchido, Tomoaki Sugaya, Takeshi Hashimoto, Kazuhiro Ema, Takashi Hayashita
    ACS Sensors, Dec 20, 2022  Peer-reviewed
  • Ryohei Yoshinaga, Fuya Kojima, Kazuma Sugiyama, Hideyuki Kunugita, Takeshi Hashimoto, Takashi Hayashita, Kazuhiro Ema
    Analytical Sciences, Nov 27, 2022  Peer-reviewedLast authorCorresponding author
  • N. Shimosako, K. Kinjo, Y. Inose, T. Nakaoka, T. Oto, K. Kishino, K. Ema
    Journal of Applied Physics, 130(14), Oct 14, 2021  Peer-reviewedLast authorCorresponding author
    The parameters related to the localized states in green-emitting indium gallium nitride (InGaN) have been evaluated by considering the energy diagrams derived by five different methods: (1) the exponential tail of the low-energy side of photoluminescence (PL) spectra, (2) the photon energy dependence of PL decay time, (3) excitation energy dependence of the PL peak energy, (4) the PL excitation spectrum, and (5) the temperature dependence of PL peak energy. The results indicate that the energy diagram of InGaN is divided into four regions: deep localized states, migration region, transition region, and extended states. It is suggested that wider localized states and a narrower transition region are preferable in order to achieve higher PL efficiency. In addition, the dependence of carrier density on PL properties supports the fact of photo-generated carriers forming localized excitons in green-emitting InGaN, although the carriers do not form localized excitons in orange-emitting InGaN and instead exist as localized electrons and holes.
  • N. Shimosako, Y. Inose, K. Kinjo, T. Nakaoka, T. Oto, K. Kishino, K. Ema
    J. Appl. Phys., 128(13) 133102-1-133102-10, Oct 1, 2020  Peer-reviewedLast authorCorresponding author
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Misc.

 163

Books and Other Publications

 23
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Presentations

 82
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Professional Memberships

 4

Research Projects

 35
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Industrial Property Rights

 3

Other

 3
  • 1998
    文化系学生向けに，物理の考え方と面白さを，身近な題材を用いて講義している．90分の講義を3テーマくらいに分けて，30分程度で一つの話題に時間を抑えている．これは，もし興味の沸かないテーマだった場合にも切り替えが速いことで対応できること，および興味が沸いた学生にとっては，もっと深く知りたいと感じたところで終わり，自分で調べる意欲を沸かせるという教育上の効果を狙っている．
  • 1994
    すべての講義において，自作の補助教材を用意し，事前に学生に配布している．図表や細かい式などは，その教材に記載されているので，学生は講義の最中に長い式や複雑な図表のノート取りの必要はなく，講義の内容を聞くことに集中できる．また，動画を見た方がわかりやすいものは，ノートＰＣを使って動画を見せたり，わかりやすいスライドを見せることも行っている．
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