Investigation into chemical function in a Mn4+-activated Li-phase cryolite synthesis for green synthetic design

Abstract

Herein, a series of obstinate Mn4+-activated Li-phase cryolites Li3GaF6:Mn4+ have been newly synthesized and optimized via solvent composition regulation at traditional co-precipitation reaction. The phase purity, morphology, luminescence property and white light-emitting diode application of as-synthesized phosphor have been carefully investigated. Under 460 nm excitation, Li3GaF6:Mn4+ emits sharp lines at 633 nm with color purity of 99.75%. Notably, more than 15 times emission increment is realized based on partial replacement of toxic HF by CH3COOH (HAc) and little addition of H2O from the pure HF reaction system. The specific functions of chemicals in synthesis process are systematically studied via step-by-step synthesis optimization with single alteration in solvent compositions. It is disclosed that HF was used to dissolve insoluble reagents, provide H+ and F− ions; HAc offered weaker acidity; moderate H2O stimulated the ionization of weak acids. Besides, efficient Li3GaF6:Mn4+ tends to be formed in weaker acid environment with enough F− ions. Importantly, the employment of HAc and H2O immensely reduces the toxicity of reaction system. These findings on chemical function confirmation might enlighten the HF-free green co-precipitation synthesis of Mn4+-doped fluorides by using suitable raw material and solvent combinations.