Study of electronic, magnetic and optical properties of KMS₂ (M  =  Nd, Ho, Er and Lu): first principle calculations

Wide band gap magnetic semiconductors made of lanthanide compounds have a wide range of applications in opto-magneto-electronic industry and electro (photo) luminescence devices. We have carried out a systematic study of electronic, magnetic and optical properties of rare earth potassium sulfides KMS₂ (M  =  Nd, Ho, Er, and Lu) using density functional theory (DFT) with full potential linearized augmented plane wave method (FP-LAPW). Different exchange and correlation approximations are employed such as generalized gradient approximation (GGA), GGA  +   U and TB-mBJ. It is inferred that the GGA  +   U approach correctly predicts the localized behavior of 4 f electrons in lanthanide atoms for the calculation of band gaps, electronic, magnetic and optical properties. All compounds are stable in ferromagnetic phase except KLuS₂, while KLuS₂ is a non-magnetic semiconductor because there is no unpaired f -electron. Band gaps of KMS₂ are estimated and these materials are found to be wide band gap semiconductors. These materials absorb mainly ultraviolet (UV) radiations, which make them good photoluminescent materials with a strong dependence on the direction of the polarization of incident photons. (paper)