Ab initio study of the electronic structure and band gaps of Eu-doped LaSi3N5 phosphors: A role of oxygen atom

Ab initio calculations of the electronic structure and band gap of Eu-doped LaSi3N5 were carried out using HSE06 functional. The calculated band gaps of Eu3+- and Eu2+-doped LaSi3N5 are 0.68 eV and 3.28 eV respectively, with electronic transition p → 4f for the former and 4f → 5d for the latter system. In the case of Eu2+-doped LaSi3N5 the charge balance caused by La3+/Eu2+ substitution was compensated by N3−/O2−substitution. The band gaps of Eu2+-doped LaSi3N5 were also calculated as a function of the EuO distance. The band gap decreases from ∼3.3 eV to ∼2.9 eV with the increase of the EuO distance from ∼2.5 Å to ∼3.9 Å. Moreover, the oxygen content was increased by creation of La vacancy compensated by three N3−/O2− substitutions. The calculations showed that with increasing oxygen and vacancy content in the cell of LaSi3N5 and Eu3+ or Eu2+-doped LaSi3N5 the band gaps decreased by 0.2–0.6 eV.