title: Red emission generation through highly efficient energy transfer from Ce(3+) to Mn(2+) in CaO for warm white LEDs.
abstract: CaO:Ce(3+),Mn(2+) phosphors with various Mn(2+) concentrations were synthesized by a solid state reaction method. Efficient energy transfer from Ce(3+) to Mn(2+) was observed and it allows the emission color of CaO:Ce(3+),Mn(2+) to be continuously tuned from yellow (contributed by Ce(3+)) to red (by Mn(2+)) with an increase in Mn(2+) concentration and upon blue light excitation. The red emission becomes dominant when the Mn(2+) concentration is ≥0.014 with an energy transfer efficiency higher than 87% which can reach as high as 94% for a Mn(2+) concentration of only 0.02. A critical distance of 10.5 Å for the Ce(3+)-Mn(2+) energy transfer was determined. A faster decrease of Ce(3+) luminescence intensity in comparison with its lifetime was observed on increasing the Mn(2+) concentration. The analysis of this feature reveals that the Ce(3+) excitation energy can be completely transferred to Mn(2+) if the Ce(3+)-Mn(2+) distance is shorter than 7.6 Å. A warm white LED was fabricated through integrating an InGaN blue LED chip and a blend of two phosphors (YAG:Ce(3+) yellow phosphor and CaO:0.007Ce(3+),0.014Mn(2+) red phosphor) into a single package, which has CIE chromaticity coordinates of (x = 0.37, y = 0.35), a correlated color temperature of 3973 K and a color rendering index of 83.1. The results indicate that CaO:Ce(3+),Mn(2+) may serve as a potential red phosphor for blue LED based warm white LEDs.
authors.affiliation: State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, 3888 Eastern South Lake Road, Changchun, 130033, China. zhangjh@ciomp.ac.cn haozd@ciomp.ac.cn and Graduate School of Chinese Academy of Sciences, Beijing, 100039, China.
authors.forename: Leyu
authors.initials: L
authors.lastname: Feng
authors.affiliation: State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, 3888 Eastern South Lake Road, Changchun, 130033, China. zhangjh@ciomp.ac.cn haozd@ciomp.ac.cn.
authors.forename: Zhendong
authors.initials: Z
authors.lastname: Hao
authors.affiliation: State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, 3888 Eastern South Lake Road, Changchun, 130033, China. zhangjh@ciomp.ac.cn haozd@ciomp.ac.cn.
authors.forename: Xia
authors.initials: X
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, 3888 Eastern South Lake Road, Changchun, 130033, China. zhangjh@ciomp.ac.cn haozd@ciomp.ac.cn.
authors.forename: Liangliang
authors.initials: L
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, 3888 Eastern South Lake Road, Changchun, 130033, China. zhangjh@ciomp.ac.cn haozd@ciomp.ac.cn.
authors.forename: Guohui
authors.initials: G
authors.lastname: Pan
authors.affiliation: State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, 3888 Eastern South Lake Road, Changchun, 130033, China. zhangjh@ciomp.ac.cn haozd@ciomp.ac.cn.
authors.forename: Yongshi
authors.initials: Y
authors.lastname: Luo
authors.affiliation: State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, 3888 Eastern South Lake Road, Changchun, 130033, China. zhangjh@ciomp.ac.cn haozd@ciomp.ac.cn.
authors.forename: Ligong
authors.initials: L
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, 3888 Eastern South Lake Road, Changchun, 130033, China. zhangjh@ciomp.ac.cn haozd@ciomp.ac.cn.
authors.forename: Haifeng
authors.initials: H
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, 3888 Eastern South Lake Road, Changchun, 130033, China. zhangjh@ciomp.ac.cn haozd@ciomp.ac.cn.
authors.forename: Jiahua
authors.initials: J
authors.lastname: Zhang