2016 Fiscal Year Annual Research Report
Fabrication and optical properties of transparent ceramic persistent phosphors based on band-gap engineering
| Project/Area Number |
16J09849
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| Research Institution | Kyoto University |
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Principal Investigator |
許 健 京都大学, 人間・環境学研究科, 特別研究員(DC2)
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| Project Period (FY) |
2016-04-22 – 2018-03-31
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| Keywords | transparent ceramics / persistent phosphors / garnet / perovskite / band-gap engineering / energy transfer / optical property / rare earths |
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| Outline of Annual Research Achievements |
In the fiscal year of 2016, based on the vacuum referred binding energy (VRBE) diagram of garnet host and energy transfer mechanism among lanthanide ions, different kinds of lanthanide-chromium doped yttrium aluminum gallium garnet (YAGG) (transparent) ceramics have been successfully developed. The emitting wavelength region of these persistent phosphors can be tunable from ultraviolet (UV) to near-infrared (NIR) light with bright radiance and long duration.
[1] The stability of hole traps at the ground states of Pr3+, Nd3+, Tb3+, Dy3+ ions and the possibility to collaborate with Cr3+ electron traps to induce persistent luminescence (PersL) in the YAGG host are discussed. The energy gaps between the ground states of Pr3+/Tb3+ and the top of the valence band are large enough so that Pr3+/Tb3+ ions can form stable hole traps. The duration of the persistent luminance of the YAGG:Pr-Cr and YAGG:Tb-Cr samples due to Pr3+ (orange) and Tb3+ (light green) transitions could reach over 8 h and 12 h, respectively.
[2] By utilizing efficient persistent energy transfer from Ce3+ to Er3+, a novel YAGG:Er-Ce-Cr persistent phosphor was prepared, which exhibited long (>10 h) NIR PersL in the broad range from 1450 to 1670 nm due to the typical Er3+ transition in garnet. The NIR PersL bands of Er3+ match well with the third bio-imaging window and the response curve of InGaAs detectors. I also gave the first PersL imaging by a commercial InGaAs camera monitoring Er3+ emission indicating that this material can be a promising candidate for in vivo bio-imaging in the NIR-III window.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
Till the end of 2016 FY, in one garnet host (YAGG), I have developed several bright (transparent) ceramic persistent phosphors with tunable emission wavelength from UV to NIR, and most of them are reported for the first time in the world. Considering the cubic isotropic structure of the garnet host and its high tolerability of three different cation sites for different doping ions (i.e. the larger dodecahedral sites are ideal for lanthanide ions while the smaller octahedral sites are of the appropriate size for Cr3+ ions), versatile doping strategies can be utilized to obtain different and considerable optical properties.
[1] UV/Orange (Pr3+), light green (Tb3+), green (Ce3+), yellow (Ce3+), deep-red (Cr3+) transparent ceramic persistent phosphors have been successfully fabricated using conventional one-step solid-state reaction method and vacuum sintering technology. These important ceramic plates will be further combined with InGaN blue LED chips to generate white light with high luminous efficacy, high color rendering and high quantum efficiency (QE)
[2] The emission wavelengths of garnet persistent phosphors were further extended to NIR region due to typical transitions of Nd3+ (1.06 μm) and Er3+ (1.53 μm), which match well with the second (1000-1350 nm) and third (1500-1800 nm) biological windows. Therefore, multi-functional applications not only in the in vivo bio-imaging but also in the drug delivery and cancer treatment can be expected in the near future by using these ceramic materials as a nano-sized bio-probe.
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| Strategy for Future Research Activity |
Based on the research results in the 2016 FY, the whole project will be mainly divided into two targets in the 2017 FY:
[1] The main target will be focused on combination of InGaN blue LED chips and proper garnet transparent ceramic plates to generate bright white light. The luminous efficacy, color rendering and quantum efficiency of the novel wLED device will be carefully measured and evaluated. Especially, compared with commercial ceramic powders, the superior thermal conductivity of transparent ceramic plates is considered to be the key point to obtain high power wLED devices with high thermal stability.
[2] On the other hand, considering the important priority I took for the NIR PersL working in the second and third biological windows, it is definitely important to shift the luminescent wavelength of the optical probe from the first biological window (650-950 nm) to the second (1000-1350 nm) and third ones (1500-1800 nm) with improved optical resolution quality and deep tissue penetration depth. The performance and evaluation of NIR persistent luminescent nano-particles (PLNPs), although not the main target of this project, still worth to try and will be continually studied.
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| Remarks |
田部研究室ホームページ
http://www.talab.h.kyoto-u.ac.jp/index.html
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