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

Novel NaAl 11 O 17 :Mn 2+ green phosphor is synthesized by solid-state reaction method in air. The emission band peaking at ~508   nm is observed owing to the 4 T 1 → 6 A 1 ( 6 S) transition of Mn 2+ 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 6 A 1 ( 6 S)→ 4 E( 4 D), 4 T 2 ( 4 D), [ 4 A 1 ( 4 G), 4 E( 4 G)], 4 T 2 ( 4 G), and 4 T 1 ( 4 G) transitions of Mn 2+ ion, respectively, which indicate that NaAl 11 O 17 :Mn 2+ phosphor may be excited by (near) ultraviolet and blue LED chip. The luminous mechanism is explained by Tanabe–Sugano diagram of Mn 2+ ion. The optimal Mn 2+ doping concentration is ~3.5   mol%. The NaAl 11 O 17 :3.5%Mn 2+ phosphor shows high quantum efficiency of ~67.84% with excitation 424   nm. The lifetime decreases from 6.72 to 6.0   ms with increasing Mn 2+ concentration in the range of 0–4   mol%.