Theoretical and experimental study on the electronic and optical properties of K0.5Rb0.5Pb2Br5: a promising laser host material

摘要

The data on the electronic structure and optical properties of bromide K _(0.5) Rb _(0.5) Pb _(2) Br _(5) achieved by first-principle calculations and verified by X-ray spectroscopy measurements are reported. The kinetic energy, the Coulomb potential induced by the exchange hole, spin-orbital effects, and Coulomb repulsion were taken into account by applying the Tran and Blaha modified Becke–Johnson function (TB-mBJ), Hubbard U parameter, and spin-orbital coupling effect (SOC) in the TB-mBJ + U + SOC technique. The band gap was for the first time defined to be 3.23 eV. The partial density of state (PDOS) curves of K _(0.5) Rb _(0.5) Pb _(2) Br _(5) agree well with XES K Ll and Br Kβ _(2) , and XPS spectra. The valence band (VB) is characterized by the Pb-5d _(3/2) and Pb-5d _(5/2) sub-states locating in the vicinities of ?20 eV and ?18 eV, respectively. The VB middle part is mainly formed by K-3p, Rb-4p and Br-4s states, in which the separation of Rb-4p _(3/2) and Rb-4p _(1/2) was also observed. The strong hybridization of Br-p and Pb-s/p states near ?6.5 eV reveals a major covalent part in the Br–Pb bonding. With a large band gap of 3.23 eV, and the remarkably high possibility of inter-band transition in energy ranges of 4–7 eV, and 10–12 eV, the bromide K _(0.5) Rb _(0.5) Pb _(2) Br _(5) is expected to be a very promising active host material for core valence luminescence and mid-infrared rare-earth doped laser materials. The anisotropy of optical properties in K _(0.5) Rb _(0.5) Pb _(2) Br _(5) is not significant, and it occurs at the extrema in the optical spectra. The absorption coefficient α ( ω ) is in the order of magnitude of 10 ~(6) cm ~(?1) for an energy range of 5–25 eV.