JPS6352077B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for producing a rare earth orthophosphate phosphor with improved luminous efficiency.

[Prior art]

Conventionally, terbium-activated lanthanum orthophosphate and cerium phosphors have been known as rare earth orthophosphate phosphors. This phosphor can be activated by ultraviolet excitation.
It emits green light with an emission peak at 543 nm, and its emission spectrum is linear with a narrow spectral width, so it is a three-wavelength fluorescent lamp that uses phosphors that emit light in three colors: blue, green, and red. It has high practical value as a green component. Since the luminous efficiency of the green phosphor has a large effect on the total luminous flux of this three-wavelength band type fluorescent lamp, it is highly desirable to improve the luminous efficiency of terbium-activated lanthanum orthophosphate and cerium phosphors. ing.

JP-A-54-56086 discloses this terbium-activated lanthanum orthophosphate, cerium phosphor, and its manufacturing method involves mixing a rare earth oxide and diammonium phosphate and firing this mixture. It is shown. Further, JP-A-57-23674 describes a method of firing a rare earth phosphate obtained by reacting a rare earth carbonate with an aqueous phosphoric acid solution.

However, according to the former method, secondary ammonium phosphate decomposes thermally during firing and evaporates into phosphorus pentoxide, making it difficult to control the ratio of rare earth elements and phosphoric acid groups.
There is a drawback that a phosphor with stable high luminous efficiency cannot be manufactured. In addition, in the latter method, when carbonate is reacted with phosphoric acid, rare earth phosphate with extremely small particle size is generated, and since this is a high melting point compound, it is difficult to sinter even if it is fired, and in the end, it is difficult to sinter even if it is fired. Since it becomes a phosphor, it also has the disadvantage that a phosphor with high luminous efficiency cannot be manufactured.

[Summary of the invention]

The purpose of this invention is to provide a method for manufacturing a phosphor with high luminous efficiency without the above-mentioned drawbacks,
A step of adding a boric acid oxide or an oxygen salt additive to a rare earth oxide obtained by firing a coprecipitated oxalate of lanthanum, terbium, and cerium, and reacting the rare earth oxide with phosphoric acid; It is characterized by comprising a step of drying the reaction product to form a powder, and a step of firing this powder. In other words, according to this method, phosphoric acid, which does not easily evaporate even at high temperatures, is reacted with rare earth oxide, whose particle size can be controlled, to form a powder, which is then fired, which eliminates the above-mentioned drawbacks of the conventional method and makes it stable. This makes it possible to produce a phosphor with high luminous efficiency.

[Embodiments of the invention]

Optimal embodiments of terbium-activated lanthanum orthophosphate and cerium phosphors will be described in detail below.

Terbium oxide [Tb ₄ O ₇ ] 9.18Kg, lanthanum oxide [La ₂ O ₃ ] 21.40Kg and cerium carbonate (containing 45% as cerium oxide [CeO]) 58.20Kg, with specific gravity
Prepare a rare earth nitrate aqueous solution at a temperature of 80℃ by dissolving 105.3Kg of concentrated nitric acid (1.38%) in a solution diluted with 360% pure water. Next, this rare earth nitrate aqueous solution is poured into an aqueous solution containing 75.0 kg of oxalic acid [HOCOCOOH.2H ₂ O] at a temperature of 80° C. and a volume of 400 to co-precipitate the rare earth nitrate. After coprecipitation, the precipitate is left to mature for 12 hours. After filtering and drying the obtained precipitate, it is calcined in air at 900°C for 1.5 hours to obtain a rare earth oxide. Rare earth oxide powder thus obtained
55.0Kg and potassium borate [K ₂ B ₄ O ₇・5H ₂ O] 204g
was added to 80°C of water at 90°C and stirred to form a slurry, and then 37.46 kg of 85% phosphoric acid [H ₃ PO ₄ ] was injected for reaction. During the reaction, 30 kg of 30% hydrogen peroxide solution [H ₂ O ₂ ] was injected little by little to accelerate the reaction. After the reaction is completed, the slurry is dried to obtain a powder.
Next, this powder is calcined in air at 1150°C for 2.0 hours, and the calcined product is cooled, pulverized, and passed through a 100-mesh sieve. The powder of the obtained fired product is fired again at 1250° C. in a mixed gas of nitrogen and hydrogen for 1.5 hours, cooled and pulverized to obtain a phosphor.

When a 40 watt straight tube fluorescent lamp was made using the phosphor thus produced, the total luminous flux at the initial stage of lighting was 5100 lumens. On the other hand, the phosphor produced using the above-mentioned known secondary ammonium phosphate has a luminance of 4,400 lumens, and the phosphor produced by reacting a rare earth carbonate with phosphoric acid has a luminance of only 4,700 lumen. The phosphor manufactured by the manufacturing method of this invention had better luminous efficiency.

In the above example, potassium borate was added, but this was added for the purpose of preventing thermal deterioration of the phosphor, and other compounds such as lithium borate [Li ₂ B ₄ O ₇・5H ₂ O] , alkali metal compounds such as boric acid [H ₃ BO ₃ ], alum [AlK(SO ₄ ) _{2.12H 2} O], lithium carbonate [Li ₂ CO ₃ ], borates,
A similar effect can be obtained by replacing it with an aluminum compound or the like. In addition, hydrogen peroxide is added to promote the solubility of poorly soluble tetravalent terbium oxide and tetravalent cerium oxide, and to increase the reactivity with phosphoric acid. A similar effect can be obtained by using -(+)-ascorbic acid [C ₆ H ₈ O ₆ ] or the like.

〔Effect of the invention〕

As explained above, this invention involves adding a boric acid oxide or an oxygen salt additive to a rare earth oxide obtained by firing a co-precipitated oxalate of lanthanum, terbium, and cerium. The process of reacting phosphoric acid, drying this reaction product to form a powder, and firing this powder has the effect of producing a rare earth orthophosphate phosphor with high luminous efficiency.

Claims (1)

[Claims] 1. Calculating the coprecipitated oxalate of lanthanum, terbium, and cerium to obtain a rare earth oxide, adding a boron oxide or oxyacid additive to the rare earth oxide, and adding the above rare earth oxide to the rare earth oxide. A method for producing a rare earth orthophosphorus salt phosphor, comprising the steps of: reacting the reaction product with phosphoric acid; drying the reaction product to form a powder; and firing the powder.