Simultaneous construction of impermeable dual-shell stabilizing fluoride phosphors for white light-emitting diodes

The traditional strategy to improve material stability is to cover the surface with a shell to resist adverse environmental factors. For the red-emitting fluoride materials with easily hydrolyzed Mn4+ on the surface, many strategies have been reported with limited effectiveness. In this work, simultaneous construction of an impermeable dual-shell on Mn4+-doped fluoride is proposed to solve the instability problem by a simple pyruvic acid (PA) treatment. The internal quantum efficiency of the K2SiF6:Mn4+ with dual-shell can be optimized up to 99.71%, the photoluminescence intensity can maintain 88.5% of the original intensity after soaking in water for 360 h, and the body color is not changed even in boiling. The reduction effect of the PA solution builds a hard fluoride shell by removal of the surface Mn4+, and the hydrogen bonding effect of PA molecular leads to the formation of a soft organic shell. The dual-shell can effectively block the damage of fluoride by external water molecules and achieve a significant improvement in water stability. The dual effect of PA is derived from its special molecular structure containing α-ketone carbonyl and carboxyl groups. This hypothesis is supported by the results of the moisture resistance of fluoride-treated with a variety of solvents similar in molecular structure to PA. In addition, DFT calculations simulated various hydrogen bond structures that may be formed between PA molecules and fluoride surface atoms.