Synthesis and luminescence properties of NaAl11O17:Mn2+ green phosphor for white LEDs

Novel NaAl11O17:Mn2+ green phosphor is synthesized by solid-state reaction method in air. The emission band peaking at ~508 nm is observed owing to the 4T1→6A1(6S) transition of Mn2+ ion, and the chromaticity coordinates are (0.0725, 0.6468). The excitation band peaking at ~360, 382, 424, 450, and 490 nm are attributed to 6A1(6S)→4E(4D), 4T2(4D), [4A1(4G), 4E(4G)], 4T2(4G), and 4T1(4G) transitions of Mn2+ ion, respectively, which indicate that NaAl11O17:Mn2+ phosphor may be excited by (near) ultraviolet and blue LED chip. The luminous mechanism is explained by Tanabe-Sugano diagram of Mn2+ ion. The optimal Mn2+ doping concentration is ~3.5 mol%. The NaAl11O17:3.5%Mn2+ phosphor shows high quantum efficiency of ~67.84% with excitation 424 nm. The lifetime decreases from 6.72 to 6.0 ms with increasing Mn2+ concentration in the range of 0-4 mol%.