Substitution disorder and photoluminescent property of a new rare-earth borate: K3TbB6O12

A new rare-earth borate K3TbB6O12 has been prepared using the high temperature molten salt method and was structurally determined by single crystal X-ray diffraction analyses. The structure features a three-dimensional (3D) framework which is composed of isolated B5O10, KO6, KO8 and TbO6 groups. An atom site in the 3(2) screw axis is shared by K and Tb atoms with the molar ratio of 1:1. The self-activated photoluminescence (PL) property of K3TbB6O12 was studied. Under the excitation of 378 nm, the emission spectrum exhibits an intense green emission centered at 543-548 nm with the chromaticity coordinates (0.342, 0.590), which can be assigned to the D-5(4)-> F-7(5) transition of Tb3+. The excitation spectra cover a wide range from 330 to 385 nm, which suggests that the K3TbB6O12 phosphors can be effectively excited by a near-UV light source. One may expect that compound K3TbB6O12 can be used as a green phosphor pumped by near-UV LED chips.