2016 Fiscal Year Annual Research Report
| Project/Area Number |
16J05936
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| Research Institution | Tohoku University |
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Principal Investigator |
温 大尉 東北大学, 工学研究科, 特別研究員(DC2)
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| Project Period (FY) |
2016-04-22 – 2018-03-31
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| Keywords | LED / Phosphor / Crystal structure / Photoluminesence / Rare earth |
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| Outline of Annual Research Achievements |
In this year, new white phosphors Ca3Ln(AlO)3(BO3)4:Ce3+,Tb3+,Mn2+ (Ln = Y and Gd), red phosphors Sr4.1+xCe2.7Ln1.2-xZnO12.3-0.5x were successfully developed.
The anomalous site occupancy phenomenon which smaller ions prefer to occupy the high coordinate number sites, was investigated. For Ca3Ln(AlO)3(BO3)4:Ce3+ and Ca3Ln(AlO)3(BO3)4:Mn2+, large Ce3+ preferred to occupy the smaller sites while small Mn2+ occupied the larger sites, which was interpreted by the space hindrance. White light emission was generated by blue, green and red components from Ce3, Tb3+ and Mn2+ ions, respectively. The forbidden f-f and d-d transitions of Tb3+ and Mn2+ were sensitised by Ce3+ through energy transfer. White light emission with desirable IQE of 54% and 43% for CYAB:5%Ce3+,20%Tb3+,2%Mn2+ and CGAB:5%Ce3+,20%Tb3+,2%Mn2+ was realized by adjusting the Ce3+, Tb3+ and Mn2+ emission and energy transfer.
Novel red phosphors Sr4.1+xCe2.7Ln1.2-xZnO12.3-0.5x were developed and the crystal structure was determined by single crystal X-ray diffraction. The phosphors can be excited by 250-450 nm due to the charge transfer of O2--Ce4+ and the red emission is originated from f-f transitions of Eu3+. The long wavelength excitable properties is originated from the relatively long bond length of Ce-O.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
In this stage, two new phosphors were developed and the crystal structure were analyzed.
The internal quantum efficiency of the Ca3Ln(AlO)3(BO3)4:Ce3+,Tb3+,Mn2+ (Ln = Y and Gd) white phosphors were 58% and 47% for Ln = Y and Gd, respectively. However, the thermal quenching properties were 70% and 65% of the room temperature, which is still improvable.
The Sr4.1+xCe2.7Ln1.2-xZnO12.3-0.5x can be optimized to be Sr4.3Ce2.7La0.4Eu0.6ZO12.2, which has a internal quantum efficiency of 49% and the thermal quenching property was not very promising: the emission intensity was 40% of the room temperature in 423K. As the first NUV/Vis light excitable Ce4+ based phosphor, that is a good beginning.
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| Strategy for Future Research Activity |
In the future, we plan to investigate the relationship between the crystal structure and the thermal quenching properties to enhance the thermal resistance. The band gap as well as the rigidity of the host lattice will be emphatically focused.
To further understand the thermal quenching due to the photoionization, the energy difference between the excitation state of luminescence and the conduction band will be investigated.
Materials of high ordering structure will be chosen as phosphors because of the high rigidity. In addition, it is possible to increase the degree of ordering of the known phosphors to further enhance their thermal quenching performance.
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