Fig. 1: Characterization of the TTB crystals.

a Structure projection of CSBN crystal along the c-direction. b, c Distorted NbO6 octahedra at the B1 and B2 sites. d Refined XRD pattern of the Ce:CSBN crystal. e iDPC-STEM image of the Ce:CSBN crystal along the c-direction. f, g Observed atomic arrangements of the Ce:CSBN crystal along the c- and a-directions. h iDPC-STEM image of the Ce:CSBN crystal along the a-direction. i Elemental mapping of Ce, Ca, Sr, Ba, Nb, and O in the Ce:CSBN crystal.