JPH01165690A - Phosphor and x-ray intensifying screen prepared by using the same - Google Patents

Abstract

PURPOSE:To prepare a phosphor capable of providing an X-ray intensifying screen which emits light upon being excited by X-radiation and is excellent in the sensitivity of the intensifying screen, sharpness of image quality and graininess characteristics, by incorporating dysprosium in a terbium-activated rare earth oxysulfide phosphor. CONSTITUTION:Dysprosium is incorporated as a coactivator in an amt. of 0-2.0mol%, pref. 0.1-1.0mol% based on 1mol of a terbium-activated rare earth oxysulfide phosphor to prepare a phosphor having a compsn. of the formula (wherein Ln is Y, Gd, La or Lu; 5X10<-5=x<=2X10<-2>; 0<y<=2X10<-2>).

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 an X-ray intensifying screen using the same, and particularly relates to a rare earth oxysulfide-based fluorophore. btl to the body and an X-ray intensifying screen using it.

[Prior Art and its Problems] Generally, in medical radiography or industrial radiation radiography, intensifying screens closely attached to both sides of the X-ray film are used to increase the sensitivity of the X-ray film. In recent years, various high-sensitivity intensifying screen systems that provide a small amount of X-ray exposure have been widely used based on the demand for reducing the X-ray exposure dose of subjects. In the high-sensitivity intensifying screen system, the X-ray film is 400n
550 nm with decreasing sensitivity in the blue region around m
It has increased sensitivity in nearby areas. In these high-sensitivity intensifying screens, terbium-activated rare earth V sulfide phosphors, which have a large amount of X-ray absorption and high light conversion efficiency, are often used in their phosphor layers.

By the way, it is generally well known that in an intensifying screen, there is a reciprocal relationship between the sensitivity of the intensifying screen and the sharpness of the image quality. That is, as the sensitivity of the intensifying screen increases, there is a problem in that the sharpness of the image quality decreases, and this problem is particularly important in high-sensitivity intensifying screens.

Sharpness is an important factor along with graininess in order to obtain good image quality in a radiographic system.

It is generally explained that sharpness is reduced due to light scattering on the surface of the phosphor and crossover effects.

In other words, the decrease in sharpness due to light scattering is caused by the fact that when X-rays focused into a narrow beam passing through a lead plate slit excite a phosphor, the light emitted by the phosphor spreads in all directions, causing the phosphor particles to interact with each other. This is said to be done to expose the X-ray film with a light emitting output that is wider than the human tJ1x ray flux as image quality information, centering on a point on the extension line of the human 01x ray, through reflection, absorption, and refraction, and to form an X-ray image. There is.

Further, the decrease in sharpness due to crossover light is explained as follows. In the case of the double-sided emulsion type double intensifying screen that is commonly used, an X-ray film is inserted between the two front and back intensifying screens, and this X-ray film is connected to the film base.
This film base has emulsion layers on both sides. In such a high-sensitivity intensifying screen system with a sandwich structure sandwiching an X-ray film, the emitted light from the intensifying screen exposes the emulsion layer on each side of the intensifying screen, and then passes through the film base to reach the emulsion on the opposite side. Also expose the layers. Furthermore, the light reflected by the intensifying screen (crossover light) exposes the emulsion layer and passes through the film again to expose the emulsion layer on the light-emitting side. In this way, the image formed by the light perpendicular to the film surface is mismatched with the image formed by the crossover light reflected by the intensifying screen on the opposite side to the light emitting side, so that the image spreads and the sharpness decreases.

Special Publication No. 58-2640 as a technology to improve sharpness
As shown in Japanese Patent Laid-Open No. 62-45682, by attaching a pigment to the surface of the phosphor, or by adding a color to the phosphor itself as shown in Japanese Patent Application Laid-Open No. 62-45682, A part of the emitted light, that is, the blue to green region, is absorbed, thereby reducing the amount of light reflected between the phosphor particles and attenuating the emitted light on the path to the film, thereby broadening the light emitting output. It is known to suppress images and improve sharpness.

However, in these methods, improvement in sharpness is achieved by reducing the absolute value of the emission intensity of the phosphor. There is a problem in that sensitivity is inevitably lowered compared to a phosphor without treatment.

Therefore, an object of the present invention is to maintain and increase the original color of the phosphor without attaching pigment to the surface of the phosphor or changing the color of the surface of the rare earth oxysulfide phosphor. To provide a phosphor for an X-ray intensifying screen that can be used in a photosensitive screen to improve the sensitivity of the intensifying screen as well as the sharpness and graininess of the image quality, and an X-ray intensifying screen using the same. be.

[Means for Solving the Problems] In order to improve the relationship between sharpness and sensitivity, which are generally contradictory, the present inventors attempted to match the spectral sensitivity curve of the latest X-ray film with the emission spectrum of a phosphor. Paying attention to
As a result of repeated various experiments, we have newly discovered that sensitivity can be improved without reducing sharpness, which was extremely difficult in the past.

That is, by incorporating a small amount of dysprosium (Dy) as a co-activator into a conventionally known terbium-activated rare earth oxysulfide phosphor, blue light (416 nm), which is the cause of light scattering and crossover light, is produced. ) and can increase the green main beam emission (545 nm) necessary to improve sensitivity.
We have newly discovered that it is possible to obtain an ideal phosphor with an emission spectrum that is well matched to the spectral sensitivity curve of a linear film.

The compositional formula of the terbium-activated rare earth oxysulfide phosphor of the present invention is (Lnl-x-yTbx Dy
y) 2 02 S (However, Ln is Y, Gd
, La and Lu, and the xlrri and y values are each 5 x 10
-5≦x≦2X10-2.0<y≦2X10-2). It is known that sufficient luminous intensity can be obtained when the activation amount of terbium, ie, xlti, is in the range of 5X10-5≦x≦2X10-2.

The content of dysprosium is generally in the range of more than O and 2.0 mol % or less, more preferably 0.1 to 1.0 mol %, per 1 mol of the terbium-activated rare earth oxysulfide phosphor.
It is 0 mol%.

This is illustrated in FIG. In Figure 1, (
G d O,9945T b O,0055) 2O2
Based on the emission intensity of 416 nm and 545 nm in the S phosphor as a reference (100%), the activation amount of Tb was set to 0.005.
The relative emission intensities at 416 nm and 545 nm are shown when the content of dibsylosium (Dy) is changed while being constant at 5 moles.

As is clear from FIG. 1, when dibsylosium is contained in the acidified gadolinium phosphor, the amount of blue light emitted, which has a peak at a wavelength of 416 nm, decreases.

When the content of dibsylosium is 0.4 mol % based on the acidified gadolinium phosphor, the amount of blue light emission is halved. The content of dibsylosium is 1. When it is 0 mol%, the amount of blue light emission is about 2
It becomes 0%.

Furthermore, as is clear from Figure 1, when dibsylosium is added to the acidified gadolinium phosphor, the amount of green light emitted with a peak wavelength of 545 nm increases, and the content of dibsyllosium is higher than that of the acidified gadolinium phosphor. Approximately 2.0
% by mole, the amount of green light emitted will be approximately the same as that of a conventional terbium-activated gadolinium oxysulfide phosphor that does not contain dibsilosium. The content of dibsylosium is 0.0% compared to the acidified gadolinium phosphor. When the amount is 1 to 1.0 mol %, the amount of green light emitted with a peak wavelength of 545 nm increases by 5% or more.

Although FIG. 1 shows the case where the rare earth element is gadolinium, the same tendency can be obtained even when the rare earth element is yttrium, lanthanum, or lutetium.

[Function] The body color of the terbium and dysprosium co-activated rare earth phosphor of the present invention is white. Therefore, by maintaining the original color of the phosphor without changing the surface color of the rare earth oxysulfide phosphor, the phosphor of the present invention can be used in an intensifying screen. It is possible to improve not only the sensitivity but also the sharpness and graininess of the image quality.

[Example code] Examples of the present invention will be described below.

(Example 1) Gadolinium oxide 360. 5g of terbium Wti, 2.06g of dysprosium oxide, and 2.75g of dysprosium oxide were dissolved in 940ml of 10N hydrochloric acid, and 960ml of distilled water was added to this hydrochloric acid solution.
ml, stir well and heat to 80°C (Solution A)
. On the other hand, an aqueous oxalic acid solution prepared by dissolving 590 g of silicic acid in 31 parts of distilled water is heated to 80°C (solution B). solution B,
Add to solution A with stirring, and after addition, add 3 more
Continue stirring for 0 minutes. In this way, oxalates of gadolinium, terbium, and dysprosium are produced and coprecipitated in the mixed solution.

Next, the solution containing the precipitate is allowed to cool, and then washed three times with distilled water by decantation, and the precipitate is suction-filtered. This precipitate is filled into a quartz container and heated and decomposed in an electric furnace at 850° C. for 3 hours to convert oxalate into an oxide.

Sodium carbonate J1106 was added to 362.6 g of the obtained oxide.
．． 0g, 64.1g of sulfur, and 18.1g of diammonium hydrogen phosphate were mixed well, and filled into an alumina crucible.
Bake at 150°C for 7 hours.

After washing the obtained sintered body with water, it is pulverized in a ball mill, separated into solid and liquid, and then dried at 120°C.

The compositional formula of the phosphor thus obtained is (G d
O,9B? 2T b 0.0055D y 0.00
73) Represented by 2O2S.

The X-ray excitation emission spectrum of this phosphor is shown in FIG.

FIG. 2 shows (G d O,9B?2T b
0.0055D y 0.0073) The X-ray excitation emission spectrum of the 2O2S phosphor powder is shown.

For comparison, the broken line in Figure 2 shows a sample that does not contain dysprosium (Gd O, 9945T b O, 0055) 2
The X-ray excitation emission spectrum of the O2S fluorophore is shown. As is clear from Figure 2, the amount of green light emitted by the phosphor containing dysprosium with a peak at 545 nm is
It is about 10% stronger than a phosphor that does not contain dysprosium, while the amount of blue light emitted with a peak at 416 nm is about 6
5% is also low.

Next, an X-ray intensifying screen was produced using the obtained phosphor and a conventional phosphor containing no dysprosium and having the same amount of terbium activation for comparison. A method for producing an X-ray intensifying screen will be described below.

Methyl ethyl ketone was added to a mixture of phosphor particles and linear polyester resin, and nitrocellulose with a degree of nitrification of 11.5% was further added to prepare a phosphor dispersion. After adding diethyl phthalate, phthalic acid, and methyl ethyl ketone to this dispersion, they were sufficiently stirred and mixed using a homogenizer, so that the mixing ratio of the binder and the phosphor was 1:2O (weight ratio), and the viscosity was 30PS (at 25℃). ) coating solution was prepared.

This coating solution was uniformly applied using a doctor blade onto a polyester sheet support (thickness: 200 μm) arranged horizontally on a glass plate and into which a light-reflecting substance made of titanium dioxide was kneaded. After coating, the support with the coating film formed thereon is dried in a drying oven to give a film thickness of 1
A phosphor layer of 80 μm was formed. Then, a polyethylene transparent film was adhered onto this phosphor layer using a polyester adhesive to form a transparent protective film (thickness: 10 μm), thereby producing an X-ray intensifying screen.

Regarding the X-ray intensifying screen thus produced, the sensitivity and sharpness of the intensifying screen were measured using a high-sensitivity film.

The results are shown in the table. As is clear from the table,
The intensifying screen using the phosphor of this example had better sensitivity and sharpness than the conventional intensifying screen using the conventional phosphor not containing dibsyllium.

(Example 2) Yttrium oxide 225.4g, terbium oxide 0.7g
5g, dysprosium oxide 1. 00g, sodium carbonate 106. Weighed Og, 64.1 g of sulfur, and 64.1 g of potassium hydrogen phosphate, and prepared in the same manner as in Example 1 (Y
O,9953T b 0.002D yo, 0027)
A phosphor having a compositional formula of 2O2S was obtained. In addition, an X-ray intensifying screen was obtained using this phosphor in the same manner as in Example 1, and a comparison using a high-sensitivity film revealed that, as shown in the table,
It was confirmed that the sensitivity and sharpness of the intensifying screen of this example were improved.

(Example 3) 324.8 g of gadolinium oxide, 22 g of yttrium oxide
．． 6g, terbium oxide 1. 50g, dysprosium oxide2. Weighed OOg, Mm sodium 106, Og, sulfur 64.1g, and diammonium hydrogen phosphate 18.0g, and prepared in the same manner as in Example 1 (G d O, 891
2Y O,0995T b 0.00/l D yO,
0053) A phosphor having a compositional formula of 2O2S was obtained. Also,
Using this phosphor, an X-ray intensifying screen was obtained in the same manner as in Example 1, and a comparison using a high-speed film revealed that the sensitivity and sharpness of the intensifying screen of this example were as shown in the table. An improvement in the degree of improvement was confirmed.

(Example 4) Lanthanum oxide 324.8g, terbium oxide 1°12
Weighed 49 g of dysprosium l-gfrl, 106.0 g of sodium carbonate, 64.1 g of sulfur, and 23.9 g of potassium hydrogen phosphate, and prepared in the same manner as in Example 1 (La
O,993T b 0.003D y 0.004)
A phosphor having a compositional formula of 2O2S was obtained. In addition, an X-ray intensifying screen was obtained using this phosphor in the same manner as in Example 1, and a comparison using a high-sensitivity film revealed that the sensitivity of the intensifying screen of this example was as shown in the table. and improvement in sharpness was confirmed.

Ta.

[Effect of the invention] When the present phosphor is applied to an X-ray intensifying screen, the conventional X-ray intensifying screen
! According to the present invention, it is possible to produce an X-ray intensifying screen that is superior to paper in sensitivity, sharpness of image quality, and graininess characteristics. When used as a rare earth oxysulfide phosphor, it is possible to provide a rare earth oxysulfide-based phosphor useful for an X-ray intensifying screen.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the dysprosium content and the relative luminescence amount in the terbium-activated gadolinium oxysulfide phosphor of the present invention, and FIG. FIG. 3 is a diagram showing an X-ray excitation emission spectrum. Patent applicant: Nichia Chemical Industries, Ltd.

Claims (4)

[Claims] (1) The compositional formula is (Ln_1_−_x_−_yTb_x
Dy_y)_2O_2S (However, Ln is Y, Gd, La
and Lu, and x and y are each 5×10^-^5≦x≦2
x10^-^2, 0<y≦2x10^-^2). (2) The value of y in the above composition formula is 1×10^-^3
The phosphor according to claim 1, characterized in that the range satisfies ≦y≦1×10^-^2. (3) The compositional formula is (Ln_1_−_x_−_yTb_x
Dy_y)_2O_2S (However, Ln is Y, Gd, La
and Lu, and x and y are each 5×10^-^5≦x≦2
x10^-^2, 0<y≦2x10^-^2). (4) In the compositional formula of the phosphor above, the value of y is 1×1
The X-ray intensifying screen according to claim 3, characterized in that the range satisfies 0^-^3≦y≦1x10^-^2.