Novel visible phosphors based on MgGa2O4-ZnGa2O4 solid solutions with spinel structure co-doped with Mn2+ and Eu3+ ions

Abstract

Photoluminescence excitation and emission spectra of Mg1-xZnxGa2O4 solid solutions (x = 0; 0.25; 0.5; 0.75; 1.0) co-doped with 0.05mol% Mn2+ and 4mol% Eu3+ ions have been investigated at room temperature. Polycrystalline samples were synthesized using high-temperature solid-state reaction technique. XRD measurements confirmed that all ceramic samples are compounds of a spinel structure. Lattice parameter follows linear dependence on composition that confirms Vegard's law for a Mg1-xZnxGa2O4 solid solution system. Complex broad luminescence band ranging from 350 to 475nm ascribed to emission from host defects was found at the excitation in "band-to-band" spectral region. Noticeable intense matrix luminescence in ceramic samples with x = 0.25 and 0.5 was observed. Emission of Mn2+ ions is presented by an intense band with a maximum around 505 nm and shifts at different compositions. Intense excitation of Mn2+ ions was found around the fundamental absorption edge. Complex excitation nature of Mn2+ ions was suggested. The charge transfer band and f-f excitation lines were found in excitation spectra of Eu3+ ions. Luminescence of Eu3+ ions is represented by a number of sharp f-f lines in the 575–650nm spectral region. Composition changing from MgGa2O4 to ZnGa2O4 leads to suppression of Eu3+ ions emission which shows a maximum at x = 0.25. Maximum of matrix luminescence and emission of Mn2+ ions were found at x = 0.50. Further increase of zinc amount in Mg1-xZnxGa2O4 solid solution leads to suppression of intensity of all luminescence bands. The influence of excitation wavelength and composition on the visible range luminescence intensity has been shown. Commission Internationale de l'Eclairage chromaticity diagrams are presented for different compositions and excitation conditions.