PbLnB₇O₁₃ (Ln = Tb or Eu): a new type of layered polyborate with multi-colour light emission properties

Two new lead rare-earth polyborates, PbTbB₇O₁₃ and PbEuB₇O₁₃, have been successfully synthesized via a high temperature molten salt method. Single crystal X-ray diffraction analysis reveals that they are isostructural and feature a 2D layer structure that contains alternating layers of [B₇O₁₃]_∞ and [Tb]_∞. The [B₇O₁₃]_∞ layer is constructed of BO₃ and BO₄ groups with the fundamental building block of B₇O₁₇ (3Δ4□: <Δ2□>Δ<Δ2□>). Solid solutions of PbTb_1-xEu_xB₇O₁₃ (x = 0-1) were prepared via a solid state reaction and the photoluminescence properties were studied. The results show that under UV or near-UV excitation, the luminescence colour of samples of PbTb_1-xEu_xB₇O₁₃ (x = 0-1) can be tuned from green through yellow to red by simply adjusting the relative Eu³⁺ and Tb³⁺ concentrations, because of the Tb³⁺ → Eu³⁺ energy transfer mechanism.