Effect of the [Ba2BO3F] Layer on the Band Gap: Synthesis, Characterization, and Theoretical Studies of BaZn2B2O6·nBa2BO3F (n = 0, 1, 2)

Two new zincoborate fluorides with the common formula BaZn2B2O6·nBa2BO3F (n = 1, 2) have been successfully synthesized for the relationship study between the band gaps and crystal structures in zinc-containing borate fluorides. Ba3Zn2B3O9F with n = 1 in the common formula belongs to the orthorhombic space group Pnma (No. 20), and Ba5Zn2B4O12F2 with n = 2 in the common formula crystallizes in the monoclinic space group C2/c (No. 62). They can both be seen as compounds with the n[Ba2BO3F] (n = 1 or 2) layer inserted in the structure of BaZn2B2O6. UV–vis–near-IR diffuse-reflectance spectra show that the band gaps of BaZn2B2O6·nBa2BO3F (n = 0, 1, 2) gradually increase with more [Ba2BO3F] layers inserted. The first-principles calculation indicates that the inserted n­[Ba2BO3F] layers play a positive effect in increasing the band gaps of zincoborate fluorides. Furthermore, the IR spectra, thermal behaviors, and refractive indices of these compounds are also studied.