Narrow-band red-emitting Mn4+-doped hexafluoride phosphors: synthesis, optoelectronic properties, and applications in white light-emitting diodes

White light-emitting diodes (LEDs), including a blue-chip and yellow-emitting phosphor, are regarded as the new-generation of lighting sources because of their low energy consumption, long lifetime, and environmentally friendliness. Red-emitting fluoride phosphors improve the color reproducibility of white LEDs and have been given significant research interest because of their excellent optical properties, thermal stability, and low cost. This review focuses on recent advances in the development of A(I, II) M(IV) F-6: Mn4+ non-rare-earth luminescent materials for solid-state lighting applications. The numerous approaches for synthesizing fluoride phosphors, optoelectronic characterization, waterproof properties, and device performance are discussed. Several related recent research directions are also addressed in this article.