A highly efficient red emitting phosphor with enhanced blue-light absorption through a local crystal field regulation strategy

Mn4+-doped oxide phosphors with emission in deep-red region are promising for the application of plant cultivation lighting. However, it remains a great challenge to synthesize these phosphors with high blue-light absorption efficiency, which is pivotal for their practical commercial applications. Herein, we conducted a local crystal field regulation strategy to notably improve the luminescent property of the Mg14Ge5O24:Mn4+ phosphor. For instance, by introducing F- ions into the host, the absorption efficiency in blue-light region increased remarkably from 13% to 28%. By further substitution of Ti4+ for Ge4+ ions, the absorption efficiency further increased to 50%. Meanwhile, the achieved internal photoluminescence quantum yield is up to 92% for the Mg28Ge5.42Ti2O38F10:Mn4+ phosphor under 422 nm blue-light excitation. Besides, the phosphor exhibits excellent photoluminecence thermal stability, i. e., the emission intensity at 423 K retained 96% of that at room temperature. By means of X-ray absorption near-edge structure and extended X-ray absorption fine structure analysis, the effect of introducing F- and Ti4+ ions on the local coordination and valence of Mn ions in the hosts and the luminescent property of the phosphors are discussed in detail. Finally, LEDs were packaged by combining blue diode chips and Mg28Ge5.42Ti2O38F10:Mn4+ phosphor, and their validity for promoting growth of plants were successfully demonstrated.