TECHNICAL FIELD

The present disclosure is related generally to light emitting diodes (LEDs) and more specifically to coated fluoride phosphors for LED applications.

BACKGROUND

Manganese-activated, red-emitting fluoride phosphors have recently emerged as an important class of LED down-converters due to their narrow-band spectral emission, high photoluminescence efficiency, and low thermal quenching. When incorporated into LED components, these phosphors can enhance the performance of both lighting and display products. Of this class of materials, manganese-activated potassium fluorosilicate (KSF:Mn) is the most notable, having become commercially available in the past few years.

For lighting applications, KSF:Mn enables warm-white LED components with high luminous efficacy (Im/VV) while preserving a high color rendering index (CRI), typically greater than 90. The phosphor's narrow red emission band results in less “wasted” light emitted into the far-red and infrared when compared to conventional phosphors. In displays, KSF:Mn enables a wider color gamut due to its saturated narrow band emission.

Yet the wide-spread commercial adoption of KSF:Mn in solid state lighting has been limited, in part, by the reliability of the material, which is sensitive to moisture, high temperature, and high blue-flux density. When exposed to water, for example, the manganese activator can rapidly discolor, resulting in a dramatic decline in performance. Furthermore, the fluorosilicate host can generate corrosive fluoride species which pose a threat to the various sensitive materials found in LED components.

BRIEF SUMMARY

A stabilized fluoride phosphor for light emitting diode applications includes particles comprising manganese-activated potassium fluorosilicate and an inorganic coating on each of the particles. The inorganic coating comprises a silicate.

A stabilized salt includes particles comprising a water-soluble salt and an inorganic coating on each of the particles. The inorganic coating comprises a silicate.

A method of making a stabilized fluoride phosphor includes forming a reaction mixture that includes particles comprising a manganese-activated potassium fluorosilicate; a reactive silicate precursor; a catalyst; a solvent; and water in an amount no greater than about 10 vol. %. The reaction mixture is agitated to suspend the particles therein. As the reactive silicate precursor undergoes hydrolysis and condensation in the reaction mixture, an inorganic coating comprising a silicate is formed on each of the particles. Thus, a stabilized fluoride phosphor is formed.

A method of making a stabilized salt includes forming a reaction mixture that includes particles comprising a water-soluble salt; a reactive silicate precursor; a catalyst; a solvent; and water in an amount no greater than about 10 vol. %. The reaction mixture is agitated to suspend the particles therein. As the reactive silicate precursor undergoes hydrolysis and condensation in the reaction mixture, an inorganic coating comprising a silicate is formed on each of the particles. Thus, a stabilized salt is formed.

