Method of making EU2+ activated inorganic red phosphor

A method of manufacturing an Eu2+ activated inorganic red phosphor, comprising:

• (i) providing a firing container having an internal surface defining a cavity;
• wherein the internal surface is a virgin material selected from the group consisting of molybdenum, tungsten, tantalum, niobium, chromium, platinum, titanium, zirconium, lanthanum, yttrium, cerium and alloys thereof;
• (ii) providing a mixture of starting materials for the preparation of the Eu2+ activated inorganic phosphor, wherein the mixture of starting materials includes an initial source of Eu2+ cations;
• (iii) loading the mixture of starting materials from step (ii) into the firing container, wherein the mixture of starting materials contacts the internal surface of the firing container;
• (iv) placing the loaded firing container from step (iii) into a furnace;
• (v) firing the mixture of starting materials under a reducing atmosphere in the furnace at a temperature of 1300 to 2000° C. for a period of 2 to 36 hours, then removing the firing container from the furnace;
• (vi) removing and grinding the contents of the firing container to provide a ground material, loading the ground material back into the firing container, and placing the reloaded firing container back into the furnace;
• (vii) firing the ground material under the reducing atmosphere in the furnace at a temperature of 1300 to 2000° C. for a period of 2 to 36 hours, then removing the firing container from the furnace;
• (viii) repeating steps (vi) through (vii) zero to three times;
• (ix) removing and grinding the contents of the firing container from step (viii) to provide an intermediate, providing an additional source of Eu2+ cations, mixing the ground intermediate and the additional source of Eu2+ cations to provide an intermediate mixture, and loading the intermediate mixture into the firing container;
• (x) placing loaded firing container containing the intermediate mixture into the furnace, firing the intermediate mixture under the reducing atmosphere in the furnace at a temperature of 1300 to 2000° C. for a period of 2 to 36 hours, and then removing the firing container from the furnace;
• (xi) removing and grinding the contents of the firing container to provide a ground substance;
• (xii) optionally, providing a further source of Eu2+ cations;
• (xiii) mixing the ground substance from step (xi) with any further source of Eu2+ cations from step (xii) to provide a substance mixture, loading the substance mixture back into the firing container from step (xi), placing the firing container containing the substance mixture into the furnace, firing the substance mixture under the reducing atmosphere in the furnace at a temperature of 1300 to 2000° C. for a period of 2 to 36 hours, and then removing the firing container from the furnace;
• (xix) repeating steps (xi) through (xiii) zero to three times;
• (xx) removing and grinding the contents of the firing container from step (xix) to provide an Eu2+ activated inorganic red phosphor;
• wherein the mixture of starting materials provided in step (ii) and the firing conditions in steps (v) through (viii) are selected such that the intermediate in step (ix) is an inorganic luminescent compound represented by formula (I)
• M(I)icM(II)iaSi5NixCiyOiz:Eu2+ib (I)
• wherein M(I) is a monovalent species selected from the group consisting of Li, Na, K, F, Cl, Br and I;
• wherein M(II) is a divalent cation selected from the group consisting of at least one of Mg, Ca, Sr and Ba;
• wherein 1.7≦ia≦2;
• 0<ib≦0.1;
• 0≦ic≦0.1;
• 5≦ix≦8;
• 0≦iy≦1.5;
• 0≦iz≦5;
• wherein the intermediate exhibits an intermediate emission spectrum, iES455, upon excitation with monochromatic light having a wavelength of 455 nm;
• wherein the intermediate emission spectrum, iES455, is resolvable into an intermediate first Gaussian emission curve and an intermediate second Gaussian emission curve;
• wherein the intermediate first Gaussian emission curve has an intermediate first Gaussian emission curve peak, iP1;
• wherein the intermediate first Gaussian emission curve peak, iP1, has an intermediate peak 1 height, iHP1, at an intermediate peak 1 peak wavelength, iPλP1;
• wherein the intermediate second Gaussian emission curve has an intermediate second Gaussian emission curve peak, iP2;
• wherein the intermediate second Gaussian emission curve peak, iP2, has an intermediate peak 2 height, iHP2, at an intermediate peak 2 peak wavelength, iPλP2;
• wherein iPλP1<iPλP2;
• wherein the intermediate emission spectrum, iES455, has an intermediate peak ratio, iPR, of >1 as determined by the following equation
• iPR=iHP1/iHP2;
• wherein the intermediate mixture provided in step (ix), the further source of Eu2+ cations provided is step (xii), if any, and the firing conditions in steps (x) through (xix) are selected such that the Eu2+ activated inorganic red phosphor provided comprises an inorganic compound represented by formula (II)
• M(I)pcM(II)paSi5NpxCpyOpz:Eu2+pb (II)
• wherein M(I) is a monovalent species selected from the group consisting of Li, Na, K, F, Cl, Br and I;
• wherein M(II) is a divalent cation selected from the group consisting of at least one of Mg, Ca, Sr and Ba;
• wherein 1.7≦pa≦2;
• 0<pb≦0.3;
• 0≦pc≦0.1;
• 5≦px≦8;
• 0≦py≦1.5;
• 0≦pz≦5;
• wherein the Eu2+ activated inorganic phosphor exhibits a phosphor emission spectrum, pES455, upon excitation with monochromatic light having a wavelength of 455 nm;
• wherein the phosphor emission spectrum, pES455, is resolvable into a phosphor first emission curve and a phosphor second emission curve, wherein the phosphor second emission curve has a phosphor full width at half max, pFWHMP2, of <100 nm.