Crystal field optimization and fluorescence enhancement of a Mn-doped fluoride red phosphor with excellent stability induced by double-site metal ion replacement for warm WLED.

The effective double-site metal ion replacement strategy was adopted to optimize the crystal field environment of a Mn-activated fluoride phosphor. In this study, a series of KBaSiGeF:Mn phosphors with optimized fluorescence intensity, excellent water resistance, and outstanding thermal stability was synthesized. The composition adjustment includes two different types of ion substitution based on the BaSiF:Mn red phosphor: [Ge → Si] and [K → Ba]. X-ray diffraction and theoretical analysis revealed that Ge and K could be successfully introduced into BaSiF:Mn to form new solid solution KBaSiGeF:Mn phosphors. The emission intensity enhancement and slight wavelength shift were detected in different cation replacement procedures. Furthermore, KBaSiGeF:Mn with superior color stability performance possessed a negative thermal quenching phenomenon. Excellent water resistance was also found, which was more reliable than KSiF:Mn commercial phosphor. A warm WLED with low correlated color temperature (CCT = 4000 K) and high color rendering index ( = 90.6) was successfully packaged by using KBaSiGeF:Mn as the red light component, and it also exhibited high stability for different currents. These findings demonstrate that the effective double-site metal ion replacement strategy can open up a new avenue for designing new Mn-doped fluoride phosphors to improve the optical properties of WLEDs.