The photophysical anisotropy and electronic structure of new narrow band gap perovskites Ln2AlMnO6 (Ln = La, Pr, Nd): An experimental and DFT perspective. Issue 13 (September 2020) - Halder, Saswata
Abstract: Perovskite oxides have exhibited multi-dimensional applications in light driven photophysical processes like optoelectronics and photocatalysis. A detailed first-principles density functional theory (DFT) approach is undertaken to explore the electronic structure and photophysical properties of new double perovskites La2 AlMnO6 (LAM), Pr2 AlMnO6 (PAM) and Nd2 AlMnO6 (NAM) crystallizing in monoclinic P2 1 /n symmetry. The optical band gap of the synthesized perovskites range between 1.28 and 1.77 eV which is promising for optimal photophysical performance. The investigated electronic structures reveal a direct band gap for LAM and PAM, in contrast to an indirect band structure for NAM. The direct nature of LAM and PAM facilitates a faster separation and recombination mechanism of electron-hole pairs as compared to the indirect nature of NAM. The linear optical properties of these compounds have been extracted to understand their applications as promising photophysical materials. The optical response functions exhibit an anisotropy which exists due to the preferential spatial polarization of the monoclinic structure of the perovskites. The calculations show that LAM and PAM show relatively higher birefringence (Δn ~ 0.2) than NAM (Δn ~0.05). The calculated optical properties result from predicted inter-band transitions between the O 2p and Mn 3d states constituting the band edges. The optical properties are compared to related experimental results of other well-known perovskites to demonstrate the applicability of LAM, PAM and NAM in photophysical applications.