Warm white LEDs with a high color rendering index and a low correlated color temperature have undergone rapid development. In this regard, red-emitting materials - such as fluoride phosphors, namely, A2MF6:Mn4+ (A = K, Na, and Cs; M = Si, Ge, Zr, Sn, and Ti) and XSiF6:Mn4+ (X = Ba or Zn), nitridoaluminate phosphor (Sr[LiAl3N4]:Eu2+), and nanocrystals of cesium lead iodide perovskite (CsPbI3) - have been extensively investigated recently. These compounds generate narrow emissions in the visible red spectral region that are highly perceived by the human eye and lead to excellent chromatic saturation of the red spectra. This paper describes the structure, luminescence properties, morphologies, thermal features, and moisture resistance of critical red components, as well as their limitations for practical applications. This Perspective also provides a basis for future development and scientific challenges in optical research.
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