A universal HF‐free synthetic method to highly efficient narrow‐band red‐emitting A₂XF₆:Mn⁴⁺ (A = K, Na, Rb, Cs; X = Si, Ge, Ti) phosphors

Abstract

Mn4+‐activated fluoride red‐emitting narrow‐band phosphors have been successfully used in wide color‐gamut white LEDs for liquid crystal display (LCD) backlights. However, highly concentrated and toxic HF is usually used in their synthesis, causing environment and safety issues. In this work, we proposed a HF‐free green method, that is, using NH4F/HCl instead of HF, to synthesize a series of A2XF6:Mn4+ (A = K, Na, Rb, Cs; X = Si, Ge, Ti) phosphors. The microstructure, photoluminescence (PL) properties, thermal quenching, and applications of the synthesized phosphors were investigated. Using the proposed approach, the phosphors generally showed a pure phase, a particle size ranging from 5 to 45 μm, and some characteristic sharp emission lines of Mn4+ in the red spectral range. The internal quantum efficiency was varied in a broad range of 69%‐94% under the 460 nm excitation, depending on the composition of the fluoride host. Among these compositions, K2XF6:Mn4+ (X = Ge and Ti) phosphors even had a similar external quantum efficiency (>60%) with commercial ones. By combining K2GeF6:Mn4+ (narrow‐band red) and β‐sialon:Eu2+ (narrow‐band green) with a blue LED, a white light‐emitting diode (wLED) backlight with a color gamut of 87.7% National Television System Committee Standard, color temperature of 8423 K, and a luminous efficacy of 110.8 lm/W was demonstrated. These results indicate that the synthetic method proposed in this work is universal for preparing highly efficient fluoride phosphors used in wLEDs.

Combinations of Superior Inorganic Phosphors for Level‐Tunable Information Hiding and Encoding

“…The phase‐pure K 2 TiF 4 red phosphor doped with 8% Mn 4+ manifests high IQE and EQE of 92% and 44% under the excitation of 460 nm, respectively. [ 207 ]…”

“…The phasepure K 2 TiF 4 red phosphor doped with 8% Mn 4+ manifests high IQE and EQE of 92% and 44% under the excitation of 460 nm, respectively. [207] For the CDs, with a great effect of functional groups on CDs surface, most of the CDs have low QEs, especially for longwavelength emissions. [208,209] The two methods including selection of special precursors and heteroatom doping are often adopted to achieve high QEs.…”

HF‐Free Microwave‐Assisted Synthesis of Nano‐Micro‐Sized K2SiF6:Mn4+ for MicroLED Color Conversion

“…Mn 4+ doped fluoride compound phosphors, A 2 XF 6 :Mn 4+ (A = Li, Na, K, Rb, Cs; X = Si, Ti, Ge, etc. ), [ 10 ] as a representative of a class of narrow‐band red‐emitting phosphors, it is expected to construct MicroLED display devices with a wide color range and high efficiency. Compared with quantum dots, K 2 SiF 6 : Mn 4+ also has strong light absorption in the blue region, but has low toxic chemical composition, excellent thermal stability, and 630 nm red emission is sensitive to human eyes.…”

Mechanochemical Fabrication of a Mn4+-Activated Inorganic Rb2KTiOF5 Perovskite Red Phosphor for White Light-Emitting Diodes

“…Olchowka et al used Mn 4+ -doped A 2 SiF 6 (A = Li, Na, K, Rb, or Cs) under microwave radiation . Xie et al proposed a green method for fabricating A 2 XF 6 :Mn 4+ phosphors with the NH 4 F/HCl medium. , These methods are still performed in solutions, which surely can cause a certain degree of environmental pollution. Therefore, a dry manufacturing process will be environmentally friendly compared to the wet ones mentioned above.…”