New highly efficient green phosphor for LEDs

To develop a highly energy-efficient white light sources, one needs to design highly efficient yellow, green and red phosphors, which are able to absorb excitation energy of blue LEDs and generate emissions. In this paper, results on production of a new green multiphase thiogallate phosphor {SrGa ₂S₄ + MgGa₂O₄}: Eu²⁺ with improved luminescence properties have been presented. The detailed XRD analysis, Raman spectroscopy and PL study have been carried out in order to enlarge the understanding of the radiative processes in {SrGa₂S ₄+ MgGa₂O₄}:Eu²⁺, based on two different crystallographic phases {SrGa₂S₄} and {MgGa ₂O₄}, prepared by solid state reaction at 900-1000°C during 4 h with a carbon reduction atmosphere. A model of 4f-5d optical transitions with due account for the electron-vibrational interaction is discussed. An approximate simple expression for the shape function of the broad vibronic bands with allowance for the terms corresponding to the emission (absorption) from both ground and first excited vibrational levels is given. Within this approximation we analyze the room temperature experimental data on the 4f-5d transitions in thiogallates doped with Eu²⁺ ions. The vibronic coupling parameters, Stokes shift and nephelauxetic effect for systems under study are estimated. The theoretical results are in a good agreement with the experimental data.