Hybrid functional study on optical properties of Sr2M2O7 xNx(M ¼ Nb, Ta) photocatalysts with perovskite-slab structures

We present the electronic, dielectric, and optical properties of layered perovskite pure and N-doped Sr2M2O7 (M ¼ Nb and Ta) based on density functional theory with the HSE06 approximation. The band gaps for pure Sr2M2O7 (M ¼ Nb and Ta) are consistent with the experimental data. Optical properties are obtained and compared with the experimental results. Pure Sr2Nb2O7 and Sr2Ta2O7 have broad applications in photocatalysis in the ultra-violet region. In contrast with Sr2Ta2O7, the absorption ability of Sr2Nb2O7 is slightly stronger. The N doping in Sr2Nb2O7 shifts the light absorption boundary into the visible region. The optical absorption effect of Sr2Nb2O5N2 is better than Sr2Nb2O6.5N0.5 in the visible region. The N doping in Sr2Ta2O7 reduces the band gap and produces visible light absorptions. Sr2Ta2O5N2 shows higher absorption effect in the visible light region than Sr2Ta2O6.5N0.5.