A new rare-earth borate K₃LuB₆O₁₂: crystal and electronic structure, and luminescent properties activated by Eu³⁺

Abstract

A new potassium lutetium borate, K₃LuB₆O₁₂, was synthesized by a flux method and the crystal structure was determined by the single crystal X-ray diffraction. It crystallizes in non-centrosymmetric space group R3₂ and features a three-dimensional framework that is composed of B₅O₁₀, KO₆, KO₈, LuO₆ and (K|Lu)O₆ groups. Band structure calculations by the density functional theory method indicate that K₃LuB₆O₁₂ has direct bond gap of about 2.84 eV. The optical absorption can be mainly ascribed to the charge transitions from the O-2p states to the Lu-6s and Lu-5d states. Moreover, Eu-doped phosphor K₃Lu_0.95Eu_0.05B₆O₁₂ was synthesized by a solid-state reaction and its photoluminescence properties were studied. Under near-UV excitation (393 nm), K₃Lu_0.95Eu_0.05B₆O₁₂ exhibits an intense red emission centered at around 611 nm with the CIE coordinate of (0.641, 0.357), which can be assigned to the electric dipole ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions. We think that K₃Lu_0.95Eu_0.05B₆O₁₂ may be used as a good red phosphor pumped by near UV light LED chips.