Research

Physical Chemistry of Excited States Induced by Light and Ionizing Radiation

We develop optical materials applied to radiation sensors through the control of electron excited states produced by photons and ionizing radiations. The developed radiation sensors are anticipated to be applied to detectors in the medical field, such as nuclear medical diagnosis and radiotherapy for cancer, and those in basic science, such as synchrotron radiation science and particle physics experiments. The materials we develop are classified into the following two types.

Scintillators

Scintillators are materials that show luminsecence immediately after ionizing radiation. When the scintillators combine with appropriate photodetectors, they operate as the real-time radiation detector. We have develop materials for radiation measurements with higher accuracy or for various measurement targets. For example, we have develop materials with higher light yields of immediate fluorescence (scintillation) after ionizing radiation, shorter scintillation decay time, or higher interaction probability with high-energy photons and neutrons.

Dosimeters

Dosimeters are materials that enable to record radiation dose during a certain period of time. These materials store the energy produced by ionizing radiation in the form of metastable chemical molecules or separated electron–hole pairs, and the stored energy in some form is read out in in any kind of way to obtain radiation dose information. For example, radiation dose can be measured through fluorescence (called thermoluminescence and optical stimulated luminescence, respectively) produced by thermal or photo stimulations after ionizing radiation, or through photoluminescence generated after ionizing radiation (called radiophotoluminescence). Additionally, the radiation dose is measured based on color change after ionizing radiation (called radiochromism). Dose distribution images can also be obtained devising readout methods.

Our laboratory uses various materials systems, such as inorganic single crystals, glasses, organic materials, or organic–inorganic hybrid materials to achieve high performances in the above mentioned materials. We also control various excitation states involved in fluorescence, such as the ionic internal excitations and inner-shell holes as luminescent centers, charge-transfer states, Wannier and Frenkel excitons, or self-trapped excitons.

Our laboratory is collaborating with many universities and research institutes to develop materials, evaluate their performance, or elucidate their fundamental processes. The institutions where we have co-authored papers and conference presentations recently are Akita University, National Institutes for Quantum Science and Technology (Takasaki Advanced Radiation Research Institute, National Institute of Radiological Sciences), Kyushu University, High Energy Accelerator Research Organization, National Institute of Advanced Industrial Science and Technology (Tsukuba Center, Kansai Center), Tokyo Metropolitan University, Shizuoka University, the University of Tokyo, Yokohama National University, Nagoya University, Nagoya Institute of Technology, Nara Institute of Science and Technology, Kanazawa Institute of Technology,　Osaka University, Hiroshima University, and the French Alternative Energies and Atomic Energy Commission.

Synthesis Equipments

  • Muffle furnace (~1500℃)

  • Tube furnace (~1200℃)

  • Vertical Bridgman furnace (~1100℃)

  • Synthesis reactor (−20–160℃, −30–200℃)

Evaluation Equipments

  • Powder X-ray diffractometer

  • Spectrophotometer (transmittance, absorbance, diffuse reflection, diffuse transmission)

  • Fluorescence spectrometer (200 to 750 nm)

  • Fluorescence quantum yield spectrometer (250 to 900 nm)

  • Fluorescence lifetime spectrometer( 10 K to room temperature, photoluminescence spectrum measurement also available)

  • Thermal fluorescence glow curve measurement system (10 K to room temperature, room temperature to 670 K)

  • Thermal fluorescence spectrum measurement system (10 K to 670 K)

  • Scintillation spectrum measurement system (10 K to room temperature)

  • Scintillation decay measurement system

  • Scintillation pulse height spectrum measurement system

  • Photoacoustic spectrum measurement system

  • X-ray-induced acoustic spectrum measurement system

Others

  • X-ray irradiation equipment (1 mGy/min~700 Gy/min)

  • Nitrogen gas generating apparatus

  • Gas burner (for processing quartz tubes)

  • Large format printer (mainly for printing posters with A0 size)

In addition to the above, common equipment in the department can be used

ex.) ESR, SEM-EDS, FTIR, XRF, XPS, TEM, ICP-MAS, Raman, etc. http://www.tech.eng.tohoku.ac.jp/sosiki/goudou/index.html