JPH0412752B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a phosphor that emits light when stimulated by X-rays, and is mainly applicable to X-ray intensifying screens, X-ray fluorescent screens,
The present invention relates to phosphors used in fluorescent films such as the input surface of linear fluorescence multiplier tubes.

[Conventional technology]

Terbium-activated rare earth oxysulfide phosphors that emit light when stimulated by X-rays are primarily used in X-ray intensifying screens. An X-ray intensifying screen is used in medical radiography for the purpose of medical diagnosis, in close contact with an X-ray film in order to improve the sensitivity of the imaging system. In recent years, due to the demand for reducing the radiation exposure of examinees, high-sensitivity intensifying screen systems using terbium-activated rare earth oxysulfide phosphors, which have a large amount of X-ray absorption and high light conversion efficiency, have come into use. Ta. By the way, these high-sensitivity systems have the disadvantage that although the sensitivity is improved, the graininess is deteriorated. Deterioration of graininess reduces image quality in radiography,
Decrease the degree of discrimination. Deterioration of graininess is a phenomenon that tends to occur with high-sensitivity intensifying screens, but this is because high-sensitivity intensifying screens reduce the number of X-ray particles by reducing the incident It is explained that this is caused by fluctuations in the A technique has been proposed in which a pigment that absorbs a specific wavelength spectrum is attached to the surface of a phosphor (Japanese Patent Application Laid-Open Nos. 107692-1982, 75641-1980,
and Special Publication No. 58-2640). These phosphors have improved granularity by allowing pigment particles on the surface of the phosphor to absorb a portion of the emitted light from the phosphor. Furthermore, phosphors with absorption bands in the blue or green spectral region have also been developed (Japanese Patent Laid-Open No. 1983-
110780). This phosphor is ball milled and
Alternatively, the body color may be changed by means such as pressurization. In addition to graininess, sharpness is also important in order to achieve good image quality in radiography. It is explained that sharpness is reduced due to light scattering on the phosphor surface as well as crossover effects. In other words, the sharpness decreases due to light scattering.As shown in Figure 1, when the X-ray 1, which has passed through a lead plate slit and is focused into a narrow beam, excites the phosphor 2, the phosphor emits less light. The light emitting output (curve A in the figure) spreads out in all directions and spreads out from the incident X-ray flux (image information), centered on point 3 on the extension line of the incident X-rays, due to mutual reflection, absorption, and refraction of the phosphor particles. It is explained that it is used to expose a film to form an X-ray image.

[Problem to be solved by the invention]

The phosphor disclosed in the above publication in which pigment particles are attached to the surface allows the pigment particles on the surface to absorb light in the blue to green region, reducing the amount of light reflected between the phosphor particles. , light emitted from a long path reaching a part away from point 3 is attenuated before reaching the film surface, narrowing the width of the spread of the light emitting output (curve B in the figure) and improving sharpness. These phosphors have pigment particles attached to their surfaces to prevent sharpness from decreasing due to crossover effects. FIG. 2 illustrates so-called crossover light that blurs the X-ray image. In normal X-ray photography, an intensifying screen system is used in which a film having emulsion layers A on both sides of a film base D is arranged in a sandwich structure between two intensifying screens F and B as shown in Figure 2. used. in this case,
The light emitted from intensifying screens F and B (a in the figure) exposes the emulsion layer on the side of each intensifying screen (b in the figure), and then passes through the film base to expose the emulsion layer on the opposite side (in the figure). b′). Furthermore, the light reflected by the intensifying screen (crossover light) exposes the emulsion layer (c in the figure) and passes through the film again to expose the emulsion layer on the light-emitting side (c' in the figure). . In this way, there is a difference between the image produced by light perpendicular to the film surface (b, b' in the figure) and the image produced by crossover light reflected by the intensifying screen on the opposite side of the light emitting side (c, c' in the figure). Because of the lack of alignment (restry), the image becomes wider and its sharpness decreases. Conventional phosphors with pigments attached to the surface absorb light in the short wavelength range by the pigments attached to the surface. This reduces image sharpness due to crossover effects. That is, conventional phosphors have improved granularity and image sharpness due to the pigment particles attached to the surface. However, even though pigmented phosphors achieve the above-mentioned features, it is not only difficult to maintain uniformity of coloration over the entire surface of the phosphor layer due to "peeling off of the pigment," but also due to problems with the phosphor and the pigment. This method inevitably has the drawback of complicating the manufacturing process of photosensitive paper. Furthermore, ball-milled or pressurized colored phosphors can only slightly reduce the reflectance in the blue region. In other words, it has the disadvantage that the absorption rate in the blue region can only be slightly increased. The present invention was developed with the aim of putting into practical use a phosphor that has even more excellent features without losing its conventional features.An important objective of the present invention is to make the rare earth oxysulfide phosphor itself available during firing. By adding color to the body of the phosphor, a part of the emitted light from the phosphor is absorbed by the body color of the phosphor itself, reducing light scattering and reducing X-ray quantum noise, thereby improving X-ray image characteristics. It is an object of the present invention to provide a phosphor which can improve the uniformity of coloring in addition to improving coloring, and which can be easily manufactured as a phosphor and an X-ray intensifying screen. Another important object of the present invention is to add CdS to the phosphor.
In order to add color to the phosphor, a small amount of
The object of the present invention is to provide a phosphor that can be colored with CdS, reduce deterioration of the original characteristics of the phosphor, and improve image quality.

[Means to solve the problem]

The present invention is based on a new idea that is further advanced from the conventional technical concept of secondary attenuation of fluorescence intensity using a colored film filter or a pigment filter. This method directly and temporarily attenuates part of the fluorescence emitted by the fluorescent light. Conventional Tb used in high-sensitivity intensifying screens for X-rays
The activated rare earth oxysulfide phosphor has a white body color, so it emits blue light (416 nm) that sensitizes the film.
And yellow-green (545 nm) fluorescence is emitted without being absorbed by the phosphor itself. The phosphor of the present invention contains CdS in the phosphor composition in order to impart color to the phosphor. CdS
is known as cadmium yellow and is famous as a yellow to orange pigment. In the phosphor of this invention, CdS is not attached as a pigment to the surface of the phosphor. CdS is added during the firing process and is included in the matrix of the phosphor, giving the phosphor its yellow color. Phosphors that have a body color due to the CdS they contain do not change color due to ``pigment peeling''. CdS can be included in the phosphor during the firing process for synthesizing the phosphor. That is, when a mixture of a rare earth oxide, sulfur, a flux, etc. is fired into a rare earth oxysulfide, a rare earth oxysulfide containing CdS can be synthesized by simultaneously adding and mixing CdS or cadmium and sulfur. Although the amount of CdS contained is quite small, the degree of coloration is remarkable. CdS, which gives the body color to the phosphor, becomes darker as the content increases, but if it is too much, the luminous efficiency decreases. Therefore, considering the required body color and luminous efficiency, CdS is usually 2 times smaller than the phosphor.
×10 ⁻⁶ to 0.3 mol, preferably 2×10 ⁻⁴ to 1×
Contains 10 ^-2 mol.

【Example】

The terbium-activated rare earth oxysulfide phosphor of the present invention can be manufactured, for example, by the manufacturing method described below. First, as phosphor raw materials, cadmium oxide, yttrium oxide, lanthanum oxide, terbium oxide, nitric acid or hydrochloric acid, oxalic acid, sulfur, a flux such as sodium carbonate, sodium sulfide, ammonium hydrogen phosphate, potassium hydrogen phosphate, etc., and cadmium sulfide are prepared. When manufacturing a phosphor, first, using the above raw materials, weigh them so that the relative ratio corresponds to the general formula stoichiometrically, dissolve them in nitric acid or hydrochloric acid, and add pure water to make a solution. Make (A). Next, solution (B), which is an oxalic acid solution, is added to (A) to co-precipitate the rare earth as an oxalate, and after washing and dehydrating, it is packed into a heat-resistant container such as a quartz tray or an aluminum crucible. Then, the oxalate is thermally decomposed in an electric furnace to form an oxide. The thus obtained oxide and cadmium sulfide are weighed in a relative ratio corresponding to the above general formula, mixed well with sulfur and solvent, and then filled into a closed container such as an alumina pot. , fired in an electric furnace. The appropriate firing temperature is in the range of 900°C to 1300°C, and the firing time varies depending on the filling amount of the phosphor raw material mixture and the firing temperature, but is generally 0.5°C.
Hours to 12 hours is appropriate. The sintered body obtained by the above firing is thoroughly washed with water, loosened into primary particles using a ball mill, etc., and then dried. By utilizing the manufacturing method described above, a terbium-activated rare earth oxysulfide cadmium sulfide phosphor can be obtained. Examples and comparative examples of the present invention are described below. However, these examples do not limit the present invention. Example 1 360.51 g of gadolinium oxide (Gd ₂ O ₃ ) and 2.06 g of terbium oxide (Tb ₄ O ₇ ) were dissolved in 940 ml of 10N hydrochloric acid, and 960 ml of distilled water was added to this hydrochloric acid solution and stirred well. Heat to °C (solution A). On the other hand, an oxalic acid aqueous solution prepared by dissolving 590 g of oxalic acid in 3 liters of distilled water is heated to 80°C (solution B). Solution B is added to solution A with stirring, and stirring is continued for an additional 30 minutes after the addition is complete. In this way, gadolinium and terbium oxalate are produced in the mixed solution and co-precipitated. Next, the solution containing the precipitate is allowed to cool, and then washed three times with distilled water by decantation, and the precipitate is filtered and swirled under suction. Fill this precipitate into a quartz container,
Oxalate is converted to oxide by heating and decomposing it in an electric furnace at 850°C for 3 hours. 362.57 g of the oxide thus obtained, 105.99 g of sodium carbonate, 64.12 g of sulfur, 18.13 g of ammonium hydrogen phosphate, 0.14 g of cadmium sulfide.
After thoroughly blending and mixing, the mixture was filled into an alumina crucible and fired at 1150°C for 7 hours. The sintered body thus obtained is washed with water, crushed in a ball miner, separated into solid and liquid, and then dried at 120°C. The general formula of the phosphor thus obtained is:
(Gd _0.9945 Tb _0.0055 ) ₂ O ₂ SCd _0.001 S _0.001 , and the reflectance of this phosphor at 416 nm and 545 nm is comparable to that of the conventional Tb-activated gadolinium oxysulfide phosphor, which has a white body color. In comparison, as shown in Table 1, they decreased by 12% and 2%, respectively. In other words, the absorption rate improved by 12% and 2%, respectively. Note that the reflectances in Table 1 and below are values with the reflectances of magnesium oxide at 416 nm and 545 nm taken as 100%. Also, the decrease in reflectance is, for example, 12%.
is the percentage when the comparative samples are unified to 100%, i.e.,
This means 100-(82÷93)×100=12, and this allows the effects of cadmium sulfide to be compared with each other. (Similar to Example 2 and below) Example 2 225.37 g of yttrium oxide (Y ₂ O ₃ ), 0.75 g of terbium oxide (Tb ₄ O ₇ ), 105.99 g of sodium carbonate (Na ₂ CO ₃ ), 64.12 g of sulfur (S), Potassium hydrogen phosphate (K ₂ HPO ₄ ) 64.12g, cadmium carbonate (CdCO ₃ )

【table】

【table】

【table】

[Table] 0.34 g was weighed and produced in the same manner as in Example 1 to obtain a phosphor having the general formula (Y _0.998 Tb _0.002 ) ₂ O ₂ SCd _0.002 S _0.002 . 416nm and 545n of this phosphor
The absorption rate of m was improved by 32% and 3%, respectively, compared to the conventional Tb-activated yttrium oxysulfide phosphor. (Table 2) Example 3 Gadolinium oxide (Gd ₂ O ₃ ) 324.80 g, yttrium oxide 22.58 g, terbium oxide (Tb ₄ O ₇ )
1.50g, sodium carbonate (Na ₂ CO ₃ ) 105.99g,
Weighed 64.12 g of sulfur (S), 18.13 g of ammonium hydrogen phosphate {(NH ₄ ) ₂ HPO ₄ }, and 0.58 g of cadmium sulfide (CdS), produced in the same manner as in Example 1, and obtained the general formula (Gd _0.896 Y _0.100 Tb _0.004 )
A phosphor with ₂ O ₂ SCd _0.004 S _0.004 was obtained. The absorption rate of this phosphor at 416 nm and 545 nm is 22% higher than that of a comparative product that does not contain cadmium sulfide, respectively.
Improved by 10%. (Table 3) Example 4 Lanthanum oxide (La ₂ O ₃ ) 324.84 g, terbium oxide (Tb ₄ O ₇ ) 1.12 g, sodium carbonate (Na ₂ CO ₃ ) 105.99 g, sulfur (S) 64.12 g, phosphoric acid 23.92 g of potassium hydrogen (K ₂ HPO ₄ ) and 5.17 g of cadmium carbonate (CdCO ₃ ) were weighed and produced in the same manner as in Example 1 to obtain the general formula (La _0.997 Tb _0.003 ).
A phosphor with ₂ O ₂ SCd _0.03 S _0.03 was obtained. The absorption rates of this phosphor at 416 nm and 545 nm were improved by 43% and 15%, respectively, compared to a comparative product that does not contain cadmium sulfide. (Table 4) As shown in Figures 3 and 4, the absorption rate in the short wavelength region decreases as the content of cadmium sulfide, which is contained in the phosphor and gives the body its color, decreases as the content increases. Along with this, the fluorescence output of the phosphor also decreases.
Therefore, the content of cadmium sulfide is usually 2 x 10 -6 to 0.3 mol, preferably 2 x 10 ^-6 to 0.3 mol per mol of the phosphor matrix, taking into account the required light absorption rate and fluorescence output. It is determined to be approximately ×10 ⁻⁴ to 1×10 ⁻² mol. However, when R in the composition formula is La, the content of CdS is preferably determined to be in the range of 2 x 10 ^-4 to 3 x 10 ^-2 moles. Furthermore, the activation amount of terbium is determined to be in the range of 5×10 ^-5 ≦x≦2×10 ^-2 in the above composition formula, since the fluorescence output will decrease if it is too large or too small. .

【Effect of the invention】

The body color of the terbium-activated rare earth oxysulfide phosphor of the present invention is pale yellow to yellow depending on the CdS contained therein. Therefore, the phosphor itself partially absorbs fluorescence at terbium's main emission wavelengths of 416 nm and 545 nm. Therefore, by using this phosphor in the phosphor layer of an X-ray intensifying screen, it is possible to reduce the scattering of light on the surface of the phosphor and the crossover effect, thereby improving the sharpness of the X-ray image. It is possible to prevent deterioration of graininess due to X-ray quantum noise and improve the identification resolution of X-ray images. The phosphor of the present invention has a pale yellow or yellow body color, and is not colored by attaching a pigment to the surface. A high-quality intensifying screen system can be realized using the same intensifying screen manufacturing technology as when using phosphors, and phosphors can be manufactured by simply mixing metal sulfides with raw materials in the firing process. The manufacturing process for the phosphor is simple, and unlike conventional surface-adhering pigments, it does not require sophisticated technology to firmly and reliably adhere to the phosphor surface. Furthermore, the phosphor of the present invention, in which the body color of the phosphor is colored with CdS, does not have to worry about peeling off of the pigment, unlike conventional phosphors that are colored by attaching pigments to the surface. It can be colored uniformly and stably, and the above-mentioned image sharpness and resolution improvement effects are
This can be achieved reliably and stably under ideal conditions. Furthermore, CdS imparts color to the phosphor simply by mixing a small amount thereof, and the above-mentioned features can be achieved with less reduction in the luminous efficiency of the phosphor. Hereinafter, the features of the present invention will be explained in detail based on the drawings. FIG. 3 and FIG. 4 show the phosphors of the present invention (Gd _1-x Tb _x ) ₂ O ₂ S・Cd ₃ S ₃ and (Y _1-x Tb _x ), respectively.
It represents the spectral reflectance (400 nm to 560 nm) of ₂ O ₂ S・Cd ₃ S ₃ . From A to G in Figure 3 and from A to E in Figure 4, the value of the content y of CdS, which gives the body color to the phosphor, increases, and gradually the value of the content y of CdS in the vicinity of 400 to 550 nm increases. Reflectance is reduced. That is, as is clear from this figure, by controlling the y value indicating the CdS content, the intensity of the body color of the phosphor (reflectance in the blue and green regions) can be freely changed. For this reason, the terbium-activated oxysulfide cadmium sulfide phosphor of the present invention has a higher emission wavelength near 416 nm and 545 nm due to Tb, compared to the conventional white-colored terbium-activated oxysulfide phosphor (shown by curve A). The amount of light absorbed increases. Therefore, when the phosphor of the present invention is used in an X-ray fluorescent film, for example, an X-ray intensifying screen,
As mentioned above, the light transmission coefficient in the intensifying screen is reduced, and it is possible to prevent deterioration of graininess caused by statistical fluctuations of X-ray quanta accompanying a decrease in the amount of incident X-rays during imaging. In addition, the phosphor of the present invention has a pale yellow to yellow body color and absorbs the light emitted from the phosphor, so as shown in FIG. However, the negative effect of reducing sharpness due to reflection from surrounding phosphors is eliminated. That is, Fig. 1 2
Compared to the conventional phosphor whose body color is white, as shown by curve A in FIG. The sharpness of images can be improved. Regarding the crossover effect, the phosphor of the present invention having a body color absorbs a part of the phosphor emission, so as shown in FIG. It is possible to significantly reduce the amount of reflection caused by the image, and effectively prevent a decrease in image sharpness due to the crossover effect. As described above, the phosphor of the present invention has superior features when used, which are comparable to those of phosphors with pigments attached to the surface. It has a unique composition and is a technical concept that cannot be imagined using conventional phosphor concepts.In other words, by incorporating CdS into the phosphor composition, the body color of the phosphor changes from white to pale yellow or yellow. This was realized using a ground-breaking technology. Therefore, compared to the conventional method in which pigments are attached to the surface of the phosphor, the phosphor of the present invention can achieve excellent effects that reliably and stably achieve the above-mentioned excellent properties.

[Brief explanation of drawings]

Fig. 1 is a reference diagram showing the state in which light emitted when stimulated by X-rays is scattered, Fig. 2 is an explanatory cross-sectional view showing the crossover effect, and Figs. 3 and 4 show the effects of the present invention on the CdS content. It is a graph showing the reflectance of a phosphor.

Claims (1)

[Claims] 1. Contains CdS by mixing and firing raw materials containing sulfur and cadmium.
It is a terbium-activated rare earth oxysulfide phosphor that emits light due to X-ray excitation and exhibits a body color that absorbs blue light due to CdS, and its compositional formula is (R _11-x Tb _x ) ₂ O ₂ S・yCdS. , in the above composition formula, R is Y, La,
It is a type of element selected from the group of Gd and Lu, and the value of x is in the range of 5×10 ^-5 ≦x≦2×10 ^-2 , and the value of y is in the range of 2×10 ^-6 ≦y≦0.3. A phosphor characterized by: 2. The phosphor according to claim 1, wherein R is Gd and 2×10 ⁻⁴ ≦y≦1×10 ⁻² . 3. The phosphor according to claim 1, wherein R is Y and 2×10 ⁻⁴ ≦y≦1×10 ⁻² . 4. The phosphor according to claim 1, wherein R is La and 2×10 ⁻⁴ ≦y≦3×10 ⁻² . 5 R is Gd and Y, and 2×10 ^-4 ≦y≦1×
10 ^-2 phosphor according to claim 1.