Narrow Red Emission Band Fluoride Phosphor KNaSiF₆:Mn⁴⁺ for Warm White Light-Emitting Diodes

Red phosphors AMF₆:Mn⁴⁺ (A = Na, K, Cs, Ba, Rb; M = Si, Ti, Ge) have been widely studied due to the narrow red emission bands around 630 nm. The different emission of the zero-phonon line (ZPL) may affect the color rendering index of white light-emitting diodes (WLED). The primary reason behind the emergence and intensity of ZPL, taking KNaSiF₆:Mn⁴⁺ as an example, was investigated here. The effects of pressure on crystal structure and luminescence were determined experimentally and theoretically. The increase of band gap, red shift of emission spectrum and blue shift of excitation spectrum were observed with higher applied pressure. The angles of ∠FMnF and ∠FMF­(M = Si, Ti, Ge) were found clearly distorted from 180° in MF₆^2– octahedron with strong ZPL intensity. The larger distorted SiF₆^2– octahedron, the stronger ZPL intensity. This research provides a new perspective to address the ZPL intensity problem of the hexafluorosilicate phosphors caused by crystal distortion and pressure-dependence of the luminescence. The efficacy of the device featuring from Y₃Al₅O₁₂:Ce³⁺ (YAG) and KNaSiF₆:Mn⁴⁺ phosphor was 118 lm/W with the color temperature of 3455 K. These results reveal that KNaSiF₆:Mn⁴⁺ presents good luminescent properties and could be a potential candidate material for application in back-lighting systems

High Color Rendering Index of Rb₂GeF₆:Mn⁴⁺ for Light-Emitting Diodes

High Color Rendering Index of Rb₂GeF₆:Mn⁴⁺ for Light-Emitting Diode