A first-principles study of the electronic structure and mechanical and optical properties of Mn-doped K2SiF6

The lattice constants, electronic structures, mechanical and optical properties of non-doped and Mn4+-doped K2SiF6 (KSF:Mn4+) were investigated using first-principles calculations. The calculated results show that Mn4+ doping enlarges the lattice constant and cell volume of KSF. Around the Fermi energy level, there is a decrease in the peak of density of states, significantly weakening the electron localization property. Mn4+ doping induces two impurity energy levels, causing a shift in the electronic states of KSF towards to the low-energy, thereby altering in the energy band structure. This alteration results in a narrower forbidden bandwidth, which reduces the photon energy required for electron transitions. Consequently, it increases the probability of electron transitions from the valence band to the conduction band, thereby enhancing the material's photocatalytic ability in the visible and ultraviolet regions. The pressure-volume relations are described using the Birch-Murnaghan's equation of state to calculate the bulk modulus of KSF and KSF:Mn4+, which is associated to the hardness of a material under particular conditions. This study provides a theoretical basis for a better understanding of the effects of Mn4+ doping on the mechanical properties, electronic structure and optical properties of KSF.