title: Rare-earth-free red-emitting K2Ge4O9:Mn(4+) phosphor excited by blue light for warm white LEDs.
abstract: A series of novel K2Ge4O9:Mn(4+) phosphors with red emission under blue light excitation have been synthesized successfully by traditional high-temperature solid-state reaction. The structure of K2Ge4O9 has been investigated by high-resolution transmission electron microscopy, scanning electron microscopy and X-ray powder diffraction with Rietveld refinement. The PL properties have been investigated by measuring diffuse reflection spectra, emission spectra, excitation spectra, decay curves and temperature-dependent spectra. The KGO:0.1% Mn(4+) phosphor can emit red light peaking at 663 nm under UV or blue light excitation. The critical quenching concentration of Mn(4+) was about 0.1 mol%. The concentration quenching mechanism could be a d-d interaction for the Mn(4+) center. The CIE chromaticity coordinates and FWHM are (0.702, 0.296) and 20 nm, which demonstrated that the K2Ge4O9:Mn(4+) has a high color purity. By tuning the weight ratio of yellow and red phosphors, the fabricated white LEDs, using a 455 nm InGaN blue chip combined with a blend of the yellow phosphor YAG:Ce(3+) and the red-emitting KGO:Mn(4+) phosphor driven by a 40 mA current, can get white light with chromaticity coordinates (0.405, 0.356) and CCT 3119 K. These results indicated that K2Ge4O9:Mn(4+) is a potential red phosphor to match blue LED chips to get warm white light.
authors.affiliation: Key Laboratory of Special Function Materials and Structure Design, Ministry of Education, Department of Materials Science, School of Physical Science and Technology, Lanzhou University, Tianshui South Road No. 222, Lanzhou, Gansu 730000, P. R. China. wyh@lzu.edu.cn.
authors.forename: Xin
authors.initials: X
authors.lastname: Ding
authors.affiliation: Key Laboratory of Special Function Materials and Structure Design, Ministry of Education, Department of Materials Science, School of Physical Science and Technology, Lanzhou University, Tianshui South Road No. 222, Lanzhou, Gansu 730000, P. R. China. wyh@lzu.edu.cn.
authors.forename: Qian
authors.initials: Q
authors.lastname: Wang
authors.affiliation: Key Laboratory of Special Function Materials and Structure Design, Ministry of Education, Department of Materials Science, School of Physical Science and Technology, Lanzhou University, Tianshui South Road No. 222, Lanzhou, Gansu 730000, P. R. China. wyh@lzu.edu.cn.
authors.forename: Yuhua
authors.initials: Y
authors.lastname: Wang