Syntheses, band structures and optical properties of Zn3B2O6 and KZn4B3O9

Two compounds Zn3B2O6 and KZn4B3O9 were synthesized by high temperature solution reaction with different experiment routes from references. The crystal structure of Zn3B2O6 was refined and it crystallizes in monoclinic space group C2/c with cell dimensions a=23.826Å, b=5.4033Å, c=8.3826Å, β=102.912, V=981.8Å3 and Z=8, μ=14.494cm−1, Dcalcd=4.245g cm−3. The UV-vis DRIS (ultraviolet-visible diffuse reflection integral spectrum), fluorescent spectra of two compounds have been studied. The calculated results of crystal energy band structure by the DFT method show that the solid state compounds of both Zn3B2O6 and KZn4B3O9 are isolators with direct band gaps. The calculated total and partial density of states indicate that the top valence bands are contributions from the mixings of O-2p, B-2p and Zn-3d states and low conduction bands mostly originate from Zn-4s states. The BO bonds are pure covalence and ZnO bonds are mostly ionic interactions, and the ionic interaction strength is stronger between the KO than between the ZnO in KZn4B3O9. The calculated optical response functions expect that these two compounds have width light transmission from the near ultraviolet (UV) to infrared (IR) light zone, and the average refractive index are 1.41 and 1.39 for Zn3B2O6 and KZn4B3O9 crystals, respectively.