Photoluminescence and phosphorescence of Mn2+ ion activated green phosphor Na2ZnSiO4:Mn2+ synthesized by self-reduction

Mn2+ activated phosphors are vital for lighting and displays, whereas the multivalent states characteristics of Mn made that reducing atmosphere (such as H2, CO, H2/N2) is generally required in the synthesis processes. Herein, a Mn2+ doped silicate green phosphor Na2ZnSiO4:Mn2+ was synthesized by an unconventional self-reduction of Mn7+/Mn4+/Mn3+ to Mn2+ under air atmosphere. Upon 260 nm excitation, an intense green photoluminescence band centered at 515 nm and the phosphorescence after stoppage of the excitation source can be observed in this phosphor. The photoluminescence and phosphorescence properties, self-reduction processes and mechanism in Na2ZnSiO4:Mn, as well as the phase transformations of the different Mn sources (MnCO3, Mn2O3, MnO2) at various temperatures were investigated systematically. Based on these investigations, together with the density functional theory (DFT) calculations, a self-reduction mechanism of Mn7+/Mn4+/Mn3+ to Mn2+ based on zinc vacancies VZn'' has been proposed. This work provides not only a new luminescent material, but also new insights into the Mn valence states controlling and luminescence tuning.