New red phosphor Na₃EuB₈O₁₅ with an open-window tubular structure

A new rare-earth polyborate, trisodium europium octaborate, Na₃EuB₈O₁₅, was prepared using the high-temperature molten-salt method and structurally determined by single-crystal X-ray diffraction analysis. It crystallizes in the triclinic space group P-1 and contains a one-dimensional [B₈O₁₅]_∞ tube structure that is constructed from BO₃ and BO₄ polyhedra. The Eu³⁺ and Na⁺ cations reside in this structure to ensure cohesion and neutrality. The excitation spectra, emission spectra, decay time and Commission Internationale de l'Éclairage (CIE) chromaticity index of Na₃EuB₈O₁₅ were studied. Under near-UV light excitation (393 nm), the polyborate shows an intense red emission, which mainly originates from the highest intensities of the ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transitions.