Synthesis, Structure, and Performance of Efficient Red Phosphor LiNaGe 4 O 9 :Mn 4+ and Its Application in Warm WLED s

For phosphor‐converted warm white light‐emitting diodes ( WLED s), it is essential to find highly efficient red oxide phosphors, which are better chemically stable and benign to environment and can be prepared in a much milder condition. Here, we report a red phosphor LiNaGe 4 O 9 :Mn 4+ with a quantum yield up to 78% after systematic optimization in synthesis temperature, dopant concentration of Mn 4+ , and sintering time. Best performance of the phosphor can be reached when it is synthesized in a mild reaction condition, that is, at 850°C for 3 h in air. The integrated emission intensity is more than four times stronger than commercial red phosphor 3.5MgO·0.5MgF 2 ·GeO 2 :Mn 4+ ( MFG :Mn 4+ ) under a blue light excitation at 470 nm. Crystal structural analysis reveals that the high efficiency Mn 4+ exhibits in the compound is mainly due to the well separation of GeO 6 groups from each other by GeO 4 tetrahedra in the neighborhood and the ideal substitution of octahedral Ge 4+ site by Mn 4+ in view of both size and charge matches. The high performance of the phosphor encourages us to apply the blue absorbing red phosphor to WLED , which is based on combination of a blue LED chip and YAG :Ce 3+ , and the warm perception WLED is therefore achieved with a color temperature of 3353 K.