Synthesis of an efficient Mn4+-doped fluoride red phosphor with excellent fluorescence stability by green synthesis method for warm WLED

Currently, Mn4+-doped fluoride phosphors have become a research hotspot, which can help compensate for the missing red component in cold white light-emitting diodes (WLEDs). However, significant synthesis defects limit the development of such fluorescent powders due to the use of highly toxic solvent HF. To improve this situation, a simple green synthesis method should be explored to synthesize Mn4+-activated fluoride phosphor. In this study, a series of red-emitting Mn4+-activated BaTiF6 phosphors are successfully synthesized via the non-toxic reaction system (HNO3/HCl + NH4F). Its crystal structure, morphology, optical characteristics and thermal stability are systematically evaluated. Under blue light excitation, BaTiF6:Mn4+ exhibits a bright narrow-band red emission with exceptional correlated color temperature (3909 K) and color purity (90%). Additionally, the critical concentration of Mn4+ is determined to be 0.03 and the concentration quenching mechanism is also systematically discussed. By calculating the crystal field strength (Dq), Racah parameters (B and C) and nephelauxetic effect ratio parameter β1, it is confirmed that BaTiF6 host can provide a strong crystal field environment for Mn4+. Moreover, these results are compared with other matrix materials. Intriguingly, the optimal sample exists satisfactory thermal stability, whose fluorescence intensity at 423 K retains 49% of that at 298 K and the activation energy reaches up to 0.925 eV. In addition, the chromaticity shift and chromaticity coordinate variation are calculated as 17 × 10−3 and (−0.0063, 0.0063), respectively. Meanwhile, the feasibility of the as-fabricated WLEDs for interior illumination is examined. A high-performance warm WLED with low correlated color temperature (CCT = 4470 K) and high color rendering index (Ra = 88.3) is achieved by using BaTiF6:Mn4+ as a red-emitting material, moreover, WLED exhibits strong output stability under high driving current. The findings of this work provide a comprehensive understanding for rational design of high-performance Mn4+-activated fluoride red phosphors through a simple green synthesis method.