Synthesis and luminescence properties of rare-earth free narrow band green emitting Na2ZnSiO4:Mn2+ phosphor for white LEDs

Novel rare-earth free green-emitting phosphor Na2ZnSiO4:Mn2+ was prepared by conventional high temperature solid state reaction method in the carbon reducing atmosphere at 900 degrees C. The crystal structure was confirmed by X-ray diffraction (XRD) and the structure information was refined by the Rietveld method. The luminescence properties of Na2ZnSiO4:Mn2+ phosphors as a function of Mn2+ concentrations were investigated. The excitation band peaking at similar to 359, 383, 427, 449, and 467 nm are attributed to ground level (6)A(1)(S-6) to excited levels E-4(D-4), T-4(2)(D-4), [(4)A((4)G), E-4((4)G)], T-4(2)((4)G), and T-4(1)((4)G) transitions of Mn2+ ion, respectively, which indicates that Na2ZnSiO4:Mn2+ phosphor may be excited by (near) ultraviolet and blue region light-emitting diode chip. The narrow emission band peaks at similar to 515 nm generated by T-4(1)((4)G) ->(6)A(1)(S-6) transition of the Mn2+ can exhibit strong green emission. The luminescence mechanism was explained by the Tanabe-Sugano diagram. The optimum Mn2+ doping concentration was 0.5 mol%. The critical distance between Mn2+ was calculated to be 33.7 A. The concentration quenching mechanism can be interpreted by the dipole-dipole interaction of Mn2+ ions. With the Mn2+ doping concentration increasing in the range of 0.2-0.8 mol%, the lifetime of this phosphor decreased from 7.51 to 7.39 ms. These phosphors also possessed good thermal stability at high temperature, and the emission intensity at 125 degrees C was about 74.9% of that at 25 degrees C. The present work suggests that Na2ZnSiO4:Mn2+ phosphor is a kind of potential green-emitting phosphor to provide a bright green component in the red/green/blue tri-color system w-LEDs.