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

Li5La3Ta2O12:Mn4+ (LLTO:Mn4+) phosphors are prepared in air via high-temperature solid-state method and investigated for their crystal structures and luminescence properties. LLTO:Mn4+ phosphor under excitation at 314 nm shows deep-red emission peaking at 714 nm due to the E-2 ->(4)A(2) transition of Mn4+ ion. The excitation bands in the range 220 - 570 nm are attributed to the Mn4+ - O2- charge-transfer band and the (4)A(2g)-> T-4(1g), T-2(2g), and T-4(2g) transitions of Mn4+, respectively. The optimal Mn4+ ion concentration is similar to 0.4 mol%. The concentration quenching mechanism in LLTO:Mn4+ 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 Mn4+ in the octahedron, respectively. The experimental results indicate that LLTO:Mn4+ phosphor has a potential application prospect as candidate of deep-red component in light-emitting diode (LED) lighting.