Approaching the structure of REBaB9O16 (RE = rare earth) by characterization of a new analogue Ba6Bi9B79O138

Understanding structure-property relationships are key to the rational design of superior materials. The series of well-known photoluminescent hosts with the chemical formula REBaB9O16 (RE = La-Lu, Y) have been extensively studied but no structural details have been reported. We prepared a new analogue Ba6Bi9B79O138 (BBBO) and proved the isomorphism by X-ray diffraction studies, in spite of the fact that they possess different cationic compositions. In addition, we successfully prepared complete solid solutions of Ba-6(Bi1-xEux)(9)B79O138 (0 <= x <= 1). Single crystal XRD characterizations on a suitable crystal of BBBO indicated an ordered structure model with the noncentrosymmetric space group R3. It possesses a layered-type structure composed of BO4-BiO6-BO4 sandwiched layers and polyborate inter-layer groups. Ba2+ atoms are located in the inter-layer cavities. There are three and two independent Bi and Ba atoms, respectively. In other words, we have taken a step forward in understanding the structure of REBaB9O16 by analysing a new analogue. We believe this will help the further interpretation and development of REBaB9O16-based optical materials.