Rare-earth-free Li5La3Ta2O12:Mn4+ deep-red-emitting phosphor: Synthesis and photoluminescence properties

Li 5 La 3 Ta 2 O 12 :Mn 4+ (LLTO:Mn 4+ ) phosphors are prepared in air via high-temperature solid-state method and investigated for their crystal structures and luminescence properties. LLTO:Mn 4+ phosphor under excitation at 314 nm shows deep-red emission peaking at 714 nm due to the 2 E→ 4 A 2 transition of Mn 4+ ion. The excitation bands in the range 220 - 570 nm are attributed to the Mn 4+ - O 2- charge-transfer band and the 4 A 2g → 4 T 1g , 2 T 2g , and 4 T 2g transitions of Mn 4+ , respectively. The optimal Mn 4+ ion concentration is ~0.4 mol%. The concentration quenching mechanism in LLTO:Mn 4+ phosphor is electric dipole-dipole interaction. The luminous mechanism and temperature quenching phenomenon are explained by the Tanabe-Sugano energy level diagram and the configurational coordinate diagram of Mn 4+ in the octahedron, respectively. The experimental results indicate that LLTO:Mn 4+ phosphor has a potential application prospect as candidate of deep-red component in light-emitting diode (LED) lighting.