| 研究実績の概要 |
In this year, the subject is composed of two parts: (i) Optical probes for excitation-free brain imaging; (ii) Ceramic persistent phosphors toward efficient flicker suppression in alternating current (AC)-wLEDs. For (i), Fluorescence based optical imaging using NIR light is a noninvasive imaging technique, which possesses the possibility to acquire real-time data at a high speed, and allows for the time-resolved detection of in vivo dynamic processes with high spatial and temporal resolution. The wavelength region longer than 1.0um in SWIR; the 2nd (NIR-II, 1.0-1.35um) and 3rd (NIR-III, 1.5-1.8um) windows, is highly advantageous over the shorter NIR-I one because of lower scattering coefficient result in improved contrast quality, higher spatial resolution. Inspired by the energy levels of lanthanoid and transition metal ions in host matrix like garnets or perovskites, we realized long persistent luminescence (over 10 hours after ceasing external excitation) in the NIR-III window utilizing the persistent energy transfer from Cr3+ to Er3+ in GAGG garnet structure, and Cr3+ to Nd3+ LaAlO3 perovskite structure in the NIR-II window. For (ii), based on the research result in garnet-based persistent phosphors, by modifying the Ga3+ substitution in Ce3+-Cr3+ co-doped GAGG garnets, yellow persistent phosphors have been fabricated able to generate intense initial persistent luminescence to suppress the flicker effect of AC-driven LEDs. The best sample exhibits obvious flicker suppression, with flicker ~26.15% and index ~0.07 for the sinusoidal waveform.
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