JPH0651872B2 - Method for producing rare earth oxybromide phosphor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a rare earth oxybromide phosphor, and more specifically, it relates to a rare earth oxybromide phosphor using cerium as an activator. The present invention relates to a method for producing a rare earth oxybromide phosphor in which the rare earth element is lanthanum and gadolinium, and both are solid-dissolved in a specific ratio to improve brightness and moisture resistance.

2. Description of the Related Art Rare earth oxybromide phosphors using cerium as an activator show high-intensity blue light emission under the excitation of energy rays such as X-rays, γ rays, electron beams, ultraviolet rays and neutron rays. It is useful as a phosphor for conversion screens, a phosphor for γ-ray conversion screens, a phosphor for cathode ray tubes, a phosphor for lamps and a phosphor for neutron conversion screens.

The rare earth oxybromide as a phosphor has a composition ratio of LnOBr: C as disclosed in JP-A-53-131987.
A phosphor represented by e (however, Ln is at least one selected from the group consisting of yttrium, lanthanum, and gadolinium) is known, and in the example, GdOBr: Ce phosphor, LaO
Br: Ce phosphors and YOBr: Ce phosphors are disclosed. Japanese Patent Publication No. 54-38996 discloses an intensifying screen using a LaOBr: Ce phosphor.

Among these phosphors, the GdOBr: Ce phosphor has extremely high brightness, but has extremely poor moisture resistance, and even if left in the air for a short time, the brightness is lower than those of the other phosphors. Causes degradation, while LaOBr: Ce phosphor and YOB
The r: Ce phosphor has extremely high humidity resistance as compared with the GdOBr: Ce phosphor, but has a low level of less than half in terms of brightness.

In order to solve the problem of such GdOBr: Ce phosphor, various researches to improve the moisture resistance of the phosphor have been vigorously carried out in various fields, but they are worth practical use. It has not been put to practical use until now because it cannot be made moisture resistant. In addition, various blue-emitting phosphors have been studied to substitute for GdOBr: Ce phosphors, but it has been discovered that GdOBr: Ce phosphors emit light with high brightness, which is equivalent to or close to that of GdOBr: Ce phosphors. Absent.

In view of the above points, the inventors of the present invention include a GdOBr: Ce phosphor with improved moisture resistance, which is equivalent to or similar to this phosphor, in order to obtain a blue light emitting phosphor, about GdOBr: Ce phosphor. As a result of various studies, lanthanum and gadolinium were dissolved at a specific ratio in (La, Gd) OBr: Ce phosphor,
Extremely high brightness and sufficient moisture resistance, which cannot be predicted from the approximate value (arithmetic mean value) expected for each composition ratio from the effects of both (LaOBr: Ce phosphor, GdOBr: Ce phosphor) The present invention has been accomplished by finding the range in which

Means for Solving the Problem Using the cerium of the present invention as an activator, the matrix is (La _1-x , G
d _x ) OBr (where x is a value in the range of 0.05 ≦ x ≦ 0.55) is a composition formula (La _1-x , Gd _x ) ₂ O. ₃ :
Cerium-doped lanthanum and gadolinium oxides (in the present specification, oxidation) in an amount satisfying Ce (where x is a value in the range of 0.05 ≦ x ≦ 0.55; the same applies hereinafter). A mixture of lanthanum and gadolinium oxide or a solid solution of lanthanum oxide and gadolinium oxide will be referred to as "lanthanum and gadolinium oxide"), and an approximately stoichiometric amount of ammonium bromide with respect to the lanthanum and gadolinium oxide. Mixed with (NH ₄ Br), 400
After baking at ˜600 ° C., ammonium bromide (NH ₄ Br) is further added to the obtained baked product, and the baking product is baked at 1000 to 1200 ° C. in a reducing atmosphere.

The phosphor of this system has many patents including various treatments for moisture resistance, and as described above, as a general formula, LnOBr: Ce phosphor is known, but the present invention It is not known at all that an unexpected effect is produced when lanthanum and gadolinium are solid-solved in a specific ratio by the manufacturing method of 1), and there is no actual case where both are solid-solved. Furthermore, a fluorescent substance generally has the characteristics of a solid solution in a homologous element,
Y, La, and Gd, which are almost the same as the arithmetic mean value in each composition ratio, and which are the typical base materials among rare earth elements
Are generally abbreviated as Ln, and it is understood that each is substitutable and does not cause unexpected effects between each other. Therefore, it is expected for those skilled in the art that a remarkable effect as described in detail below can be obtained in a (La, Gd) OBr: Ce phosphor in which lanthanum and gadolinium are dissolved in a specific ratio. It is a surprising effect that cannot be done.

The rare earth oxybromide phosphor represented by the above composition of the present invention is produced, for example, by the production method described below.

The oxides of lanthanum and gadolinium satisfying the composition formula (La _1-x , Gd _x ) ₂ O ₃ : Ce are individually dissolved, or a mixture of both oxides is dissolved and each of them is dissolved in aqueous ammonia. The pH of the solution is adjusted, and predetermined cerium nitrate is added thereto. An oxalic acid solution is added to this to coprecipitate the rare earth oxalate. Then heated decompose the oxalates, the oxides of lanthanum and gadolinium doped cerium _{[(1-x) La 2 O} 3: Ce and _xGd 2 _O 3: C
e] or solid solution oxide of lanthanum and gadolinium [(La
_1-x , Gd _x ) ₂ O ₃ : Ce is obtained. In addition, (La _1-x , G
d _x) 2 _{O 3:} When you get _Ce is previously limited the composition ratio coprecipitation according to the phosphor composition ratio corresponding to the purpose. The cerium-doped rare earth oxide (La
_{When 2} O ₃ : Ce and Gd ₂ O ₃ : Ce are used, an approximately stoichiometric amount of ammonium bromide is added to a stoichiometric mixture of the amounts according to the composition of the target phosphor. The mixture is mixed, filled in a quartz crucible, covered with a lid, and fired at 400 to 600 ° C. for 1 to 2 hours. Ammonium bromide is further added to the fired product, mixed, and fired at 1000 to 1200 ° C. for 1 to 3 hours using the crucible. At the time of this firing, it is necessary to keep a reducing atmosphere in the crucible by coexisting with a reducing agent such as activated carbon in order to make the activator Ce trivalent. The amount of activated cerium is generally in the range of 0.1 to 10 mol%.

Thus, the (La _1-x , Gdx) OBr: Ce phosphor of the present invention was obtained.

The well-known LaOBr: Ce phosphor obtained by the same manufacturing method had a measured initial luminance of 125, and the GdOBr: Ce phosphor had a measured initial luminance of 250. Curve 1 in Figure 1 is (La _1-x , Gdx)
OBr: Ce phosphor with zero x value (LaOBr: Ce)
1 (GdOBr: Ce) and when the arithmetic mean value of both, which is a so-called generally predicted effect obtained by connecting the two, is set to 100, It is a curve which shows the relative value of the brightness | luminance which each fluorescent substance which made the solid solution of the lanthanum and gadolinium obtained by the manufacturing method show.

As is apparent from the curve 1 in FIG. 1, the lanthanum and gadolinium obtained by the production method of the present invention were solid-dissolved (L
The a1 _-x , Gdx) OBr: Ce phosphor showed a value (25% to 40% or more high brightness value) far exceeding the value predicted from the conventional well-known technology. From this figure, the preferable range of the solid solution range at the initial luminance is 0.03 ≦ x ≦ 0.55,
A more preferable range is 0.05 ≦ x ≦ 0.45.

On the other hand, as described above, since the GdOBr: Ce phosphor has extremely poor moisture resistance, the brightness is reduced to half or less even if it is left in the air for more than 10 hours. Practically, the time left for the production of fluorescent films and the production of fluorescent films such as intensifying screens, and products obtained by kneading with an organic binder such as intensifying screens are practically in the order of several years in air. Since it is used, practically, leaving it in the air for more than a dozen hours is optimal for predicting the deterioration of the fluorescent substance when the product is used.
By the way, when the manufactured phosphor is left in the air for 15 hours, the measured brightness of the LaOBr: Ce phosphor is 120, and the measured brightness of the GdOBr: Ce phosphor is 50.

The curve 2 in FIG. 1 shows the case where the x value of the (La _1-x , Gdx) OBr: Ce phosphor is 0 when left for 15 hours.
And the so-called generally expected effect obtained by connecting both of them is 10
When 0 is set, it is a curve showing the relative value of the luminance shown after leaving the respective phosphors in which the lanthanum and gadolinium obtained by the above-described manufacturing method are solid-dissolved for 15 hours with respect to this predicted value.

As is clear from the curve 2 in FIG. 1, when the (La _1-x , Gdx) OBr: Ce phosphor obtained by the production method of the present invention is put into practical use, the value significantly exceeds the expected value (about 30% to about 75% or more high brightness value) is in a very specific range. From this figure, the preferable solid solution range after the moisture resistance deterioration test is 0.05 ≦ x ≦ 0.
55, and a more preferable solid solution range is 0.2 ≦ x ≦ 0.
45.

Further, when the x value is determined based on the relationship between the data shown in FIG. 1 and the absolute luminance, it is 0.15 ≦ x ≦ 0.55, more preferably 0.2.
≦ x ≦ 0.55. Furthermore, the well-known moisture resistance treatment and the moisture resistance treatment with the fluoride, phosphate, carbonate and sulfate previously proposed by the applicant (Japanese Patent Application Laid-Open No. 61-62585-625).
88, 61-73788, 61-76586) and (La _1-x , Gdx) OBr: Ce phosphor in combination, x
When the value is 0.2 ≦ x ≦ 0.55, a good effect is exhibited, and particularly when 0.25 ≦ x ≦ 0.55 is very good, and among these, 0.
Practical use is recommended in the range of 25 ≦ x ≦ 0.5.

As described above, according to the present invention, a rare earth oxybromide phosphor having high brightness and excellent moisture resistance was obtained.

When the fluorescent light obtained by the production method of the present invention is excited by radiation, the fluorescent light absorbs well and exhibits high-intensity light emission, and is suitable for a fluorescent material for intensifying screens. In particular, the intensifying screen using the phosphor obtained by the production method of the present invention has a photographic sensitivity several times higher than that of the conventional CaWO ₄ phosphor when used in combination with a regular type radiographic film having blue sensitivity. Show.

A detailed description will be given below with reference to examples.

Example: 122 g of La ₂ O ₃ : Ce, 45 g of Gd ₂ O ₃ : Ce and 100 g of ammonium bromide (NH ₄ Br), each having a doping amount of Ce of 1.1 mol% with respect to lanthanum and gadolinium, were thoroughly mixed by a ball mill, and then a quartz crucible. And cover with 400 ℃ 1
Burned for hours. Next, 50 g of NH ₄ Br was added to the baked product and mixed. In the same manner as above, a quartz crucible was filled with this, and a quartz cloth was sprinkled on the quartz crucible. In order to keep the inside of the crucible in a reducing atmosphere, 50 g of activated carbon was filled and the lid was capped. Of the present invention (La _0.75 Gd _0.25 ) OBr: Ce
A fluorescent substance (Ce / (La _0.75 Gd _0.25 ) = 1.1 mol%) was obtained. The average particle size was about 10 μm.

In addition, as a result of obtaining the lattice constant by X-ray diffraction of this phosphor,
Lattice constant ratio (c / a =) between LaOBr: Ce and GdOBr: Ce
1.83) is shown, and it is clear that it is a solid solution of La and Gd.

In addition, a luminance of 220 is obtained by measuring the luminance of the fluorescent substance by the following method.
showed that. As shown in FIG. 1, this value was 42% higher than the arithmetic mean value (curve 1), and 78% higher than the arithmetic mean value after the humidity resistance test (curve 2). The phosphors of the respective compositions of the present invention obtained by the same manufacturing method are shown in FIG.

〔Measuring method〕

1 Method for measuring the luminance of the fluorescent substance The fluorescent substance to be measured is filled in a smooth container so that the amount of the fluorescent substance is about 500 mg / cm ² , and the same amount of known calcium tungstate fluorescent substance is simultaneously irradiated with X-rays. The light emitted by the X-ray excitation is received by a photomultiplier tube, and the fluorescence intensity of the sample is measured by comparing it with the emission intensity of a relatively known equal amount of calcium tungstate phosphor. The irradiation X-rays have an X-ray tube voltage of 60 KV, an X-ray tube current of 1 mA, and an X-ray tube-sample distance of 1 m.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the composition ratio (x value) and the specific emission intensity of the phosphor of the present invention as relative intensity with respect to the arithmetic mean value.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Etsuo Shimizu 1060 Narita, Odawara-shi, Kanagawa Kasei Optonix Co., Ltd. Odawara factory (56) Reference JP-A-61-19688 (JP, A)

Claims (1)

[Claims] 1. A composition formula (La _1-x , Gd _x ) ₂ O ₃ : Ce.
The amount of lanthanum and gadolinium doped with cerium and the oxide of lanthanum and gadolinium which are in an amount satisfying (where x is a value in the range of 0.05 ≦ x ≦ 0.55) are almost the same. Stoichiometric amount of ammonium bromide (N
H ₄ Br) and mixed and baked at 400 to 600 ° C., and then the obtained baked product is further subjected to ammonium bromide (NH ₄ B).
1000 to 120 under reducing atmosphere with addition of r)
Baking at 0 ° C., using cerium as an activator, and a matrix of (La _1-x , Gd _x ) OBr (where x is a value in the range of 0.05 ≦ x ≦ 0.55) ) A method for producing a rare earth oxybromide phosphor represented by: