The use of a single ammonium acidic salt towards simple green co-precipitation synthesis for Mn4+-activated fluorides

Abstract

Herein, a simple green co-precipitation route for Mn⁴⁺-activated fluorides has been realized via individually using the aqueous acidic salt NH₄HF₂ as a solvent. The systematic explorations of ionization, erosion, solvent concentration, solvency on reactants, and reaction with an extra weak acid disclosed that the near-saturated aqueous NH₄HF₂, ionizing into abundant HF₂⁻, H⁺, and F⁻ ions, exhibited large dissolving capacity and good stabilization on Mn⁴⁺ without obvious toxicity. The green synthesized example of Cs₂GeF₆:Mn⁴⁺ emitted a typical narrow band red light at 633 nm with normal optimal doping at ∼8 at%. Compared with its contrast prepared from the HF system, it experienced only ∼10% reduction in quantum efficiency and slight emission attenuation below 150 °C as the more humidity-sensitive weaker acid surface aroused lattice thermal vibration. The further action as red component fabricated a high-quality warm white light-emitting diode (W-LED) with a high color rendering index (Ra ∼ 91), high luminous efficacy (∼149 lm W⁻¹), low correlated color temperature (∼3211 K), and good color stability against the operating environment. Combined with the universal synthesis of A₂XF₆:Mn⁴⁺ (A = K, Rb, Cs; X = Si, Ge), our findings can probably open up a simple and feasible green synthetic strategy for efficient Mn⁴⁺-doped fluorides using acidic salts.