Synthesis of the high-pressure polymorph β-TmB3O6 at ambient pressure through the combination of Bi3+-doping and seed-assisted sol-gel method

Most members of β-REB3O6 (RE ​= ​Y, Nd–Lu) were prepared under high temperature and high-pressure conditions with two exceptional cases of Tb and Dy, which were grown from molten salt at ambient pressure. In literature, a successful strategy of -Bi3+-doping -was applied to prepare β-RE1-xBixB3O6 (RE ​= ​Y, Sm–Er) at ambient pressure. However, the Tm, Yb, Lu-analogues were not obtainable with the same strategy. In this work, we prepared β-Tm0.875Bi0·125B3O6 at ambient pressure by further incorporating the seed-assisted sol-gel method. Transmission electron microscopy with elemental mapping and powder XRD confirmed the phase formation and the homogenous Bi3+-doping. Interestingly, Bi3+ possesses a site-preferential occupation behavior proved by Rietveld refinements. Additionally, Bi3+-dopant exhibits a broad band absorption centered at 287 ​nm along with the intense blue emission with the maximum at 426 ​nm.