JP2000001673A - Trivalent metal-activated fare earth metal aluminate fluophor and radiation image transformation panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject fluophor capable of manifesting accelerated luminescence in the ultraviolet region when irradiated with radiation or visible rays and useful in e.g. radiation image transformation panels by activating a rare earth metal aluminate with a specific trivalent metal. SOLUTION: This fluophor is a trivalent metal-activated rare earth metal aluminate accelerated fluophor and composed of a composition of the formula : LnAlO3:xA (Ln is a rare earth metal, i.e., Y, La or Gd; A is a trivalent metal, i.e., Ce, Gd or Bi; 0<(x)<=0.1). This fluophor is obtained, for example, by mixing under agitation a rare earth metal oxide, aluminum oxide and a trivalent metal halide with lithium fluoride or chloride as flux followed by baking the mixture at 1,100-1,300 deg.C for 1-7 h in an atmosphere such as the air or nitrogen gas, and, as necessary grinding and/or sieving the baked product.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel trivalent metal-activated rare earth aluminate stimulable phosphor and a radiation image conversion panel using the stimulable phosphor.

[0002]

2. Description of the Related Art A radiation image recording / reproducing method using a stimulable phosphor is known as an alternative to the conventional radiographic method. This method uses a radiation image conversion panel (a stimulable phosphor sheet) containing a stimulable phosphor, and transmits radiation transmitted through a subject or emitted from a subject to the stimulable phosphor of the panel. By absorbing the stimulable phosphor with electromagnetic waves (excitation light) such as visible light and infrared light in a time series manner, the radiation energy stored in the stimulable phosphor is absorbed by the body. The fluorescent light is emitted (stimulated emission light), the fluorescent light is read photoelectrically to obtain an electric signal, and a radiation image of a subject or a subject is reproduced as a visible image based on the obtained electric signal. . After the reading, the panel is prepared for the next photographing after the remaining image is erased. That is, the radiation image conversion panel can be used repeatedly.

According to the above-described radiographic image recording / reproducing method, a radiation having a much smaller amount of exposure and a richer amount of information than a conventional radiographic method using a combination of a radiographic film and an intensifying screen. There is an advantage that an image can be obtained. Furthermore, while the conventional radiographic method consumes radiographic film for each shot, the radiographic image recording / reproducing method uses a radiographic image conversion panel repeatedly, which leads to resource conservation and economic efficiency. Is also advantageous.

A stimulable phosphor is a phosphor that emits stimulable light when irradiated with radiation and then with excitation light. However, in practice, the stimulable phosphor has a wavelength of 400 to 900 nm due to the excitation light. Phosphors that exhibit stimulated emission in the 500 nm wavelength range are commonly used. Examples of stimulable phosphors conventionally used in radiation image conversion panels include europium or cerium activated alkaline earth metal halide phosphors and cerium activated rare earth oxyhalide phosphors. .

The radiation image conversion panel used in the radiation image recording / reproducing method has, as a basic structure, a support and a stimulable phosphor layer provided on the surface of the support. However, when the stimulable phosphor layer is self-supporting, a support is not necessarily required. The phosphor layer usually comprises a stimulable phosphor and a binder containing and supporting the stimulable phosphor in a dispersed state. However, there is also known a phosphor layer which does not include a binder formed by a vapor deposition method or a sintering method and is composed only of an aggregate of a stimulable phosphor. There is also known a radiation image conversion panel having a phosphor layer in which a polymer substance is impregnated in a gap between stimulable phosphor aggregates. In any of these phosphor layers, the stimulable phosphor has a property of exhibiting stimulable emission when irradiated with excitation light after absorbing radiation such as X-rays. Radiation emitted from the specimen is absorbed by the phosphor layer of the radiation image conversion panel in proportion to the radiation dose,
On the panel, a radiation image of a subject or a subject is formed as an accumulated image of radiation energy. This accumulated image,
By irradiating the excitation light, it can be emitted as stimulated emission light, and it is possible to image a stored image of radiation energy by photoelectrically reading the stimulated emission light and converting it into an electric signal. Become.

The surface of the stimulable phosphor layer (the surface not facing the support) is usually provided with a protective film such as a polymer film or an inorganic vapor-deposited film. Is protected from chemical alteration or physical impact.

On the other hand, aluminate compounds such as (Ba, Eu) Mg ₂ Al ₁₆ O ₂₇ and (Ce, Tb) MgAl ₁₁ O ₁₉ exhibit instantaneous light emission in the visible region, so that they can be used as phosphors for lamps. Is known (JMPJVerste
gen, D. Radidielovic, and LEVrenken, J. Electrochem.
Soc., 121 (1974), 1627). Although these aluminate phosphors have drawbacks such as the need to be fired at a high temperature during production and are expensive, they are highly efficient as phosphors, and are being developed in the phosphor field, including phosphors for lamps. ing. However, it has not been reported that the aluminate phosphor exhibits stimulated emission.

[0008]

SUMMARY OF THE INVENTION The present invention provides a novel trivalent metal-activated rare earth aluminate stimulable phosphor and a radiation image conversion panel using the phosphor. That is, the present inventor has found that when activated with a trivalent metal such as Ce or Gd, the aluminate phosphor exhibits stimulated emission in the ultraviolet region, leading to the present invention.

[0009]

Means for Solving the Problems The present invention provides a composition represented by the following formula (I): LnAlO ₃ : xA (I) wherein Ln is at least one rare earth element selected from the group consisting of Y, La and Gd; A is at least one trivalent metal selected from the group consisting of Ce, Gd and Bi; and x is a numerical value in the range of 0 <x ≦ 0.1. ] The trivalent metal activated rare earth aluminate stimulable phosphor, and a radiation image conversion panel containing the same.

The above-mentioned coefficient x in the phosphor composition described in the present specification is a numerical value obtained by analyzing the obtained phosphor. Since the composition changes before and after the firing step in the manufacture of the phosphor, the ratio of each component of each raw material used in the manufacture of the phosphor and the ratio of each component of the completed phosphor may be slightly different.

In the above formula (I), Ln is preferably La and / or Gd, A is preferably Ce and / or Gd, and x is 0.0
It is preferably a numerical value in the range of 001 ≦ x ≦ 0.01.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The trivalent metal activated rare earth aluminate stimulable phosphor of the present invention can be produced, for example, as follows.

As a raw material for a phosphor, a rare earth oxide, aluminum oxide, and a trivalent metal halide are prepared, and further, lithium fluoride or lithium chloride is prepared as a flux. These phosphor raw materials are mixed in a solid phase while stirring using various known mixers.

Next, the phosphor material mixture is filled in a heat-resistant container such as an alumina crucible, a quartz boat, and the like, and placed in a furnace core of an electric furnace for firing. Firing temperature is 1100-1300
C. is appropriate, particularly preferably around 1200.degree. As the firing atmosphere, in addition to the air, a nitrogen gas atmosphere, a nitrogen gas atmosphere containing a small amount of oxygen gas, or the like is used. The firing time varies depending on the filling amount of the mixture, the firing temperature, the temperature at which the mixture is taken out of the furnace, and the like, but is generally appropriate for 1 to 7 hours, preferably 3 to 5 hours.

The phosphor thus obtained may be subjected to various general operations in the production of the phosphor, such as pulverization and sieving, if necessary. Thereby, the desired trivalent metal activated rare earth aluminate stimulable phosphor represented by the following composition formula (I) is obtained. LnAlO ₃ : xA (I) wherein Ln is at least one rare earth element selected from the group consisting of Y, La and Gd; A is at least one trivalent metal selected from the group consisting of Ce, Gd and Bi And x is a number in the range 0 <x ≦ 0.1. ]

In the radiation image storage panel of the present invention, the stimulable phosphor layer contains a trivalent metal-activated rare earth aluminate stimulable phosphor represented by the above composition formula. The stimulable phosphor layer usually comprises a stimulable phosphor and a binder which contains the stimulable phosphor in a dispersed state, and further contains another stimulable phosphor or a coloring agent in the phosphor layer. An agent may be included.

The method for producing the radiation image storage panel of the present invention will be described below, taking as an example the case where the stimulable phosphor layer comprises a stimulable phosphor and a binder containing and supporting the stimulable phosphor in a dispersed state. I do.

The stimulable phosphor layer can be formed on a support by the following known method. First, a stimulable phosphor and a binder are added to a solvent and mixed well to prepare a coating solution in which the phosphor is uniformly dispersed in a binder solution. The mixing ratio of the binder and the phosphor in the coating solution is
Generally, the mixing ratio of the binder to the phosphor is selected from the range of 1: 1 to 1: 100 (weight ratio), although it depends on the characteristics of the intended radiation image conversion panel, the kind of the phosphor, and the like. In particular, it is preferable to select from the range of 1: 8 to 1:40 (weight ratio). The coating solution containing the stimulable phosphor and the binder prepared as described above is then uniformly applied to the surface of the support to form a coating film. This coating operation can be performed by using ordinary coating means, for example, a doctor blade, a roll coater, a knife coater or the like.

The support can be arbitrarily selected from materials known as supports for conventional radiation image conversion panels. In a known radiation image conversion panel, sensitivity or image quality (sharpness, granularity) for strengthening the bond between the support and the stimulable phosphor layer or as a radiation image conversion panel
In order to improve the adhesion, a polymer substance such as gelatin is applied to the surface of the support on which the phosphor layer is provided to form an adhesion-imparting layer, or light reflection such as gadolinium fluoride, barium fluoride, gadolinium oxide, etc. It is known to provide a light reflecting layer made of a conductive material or a light absorbing layer made of a light absorbing material such as carbon black. The support used in the present invention can also be provided with these various layers, and the configuration thereof can be arbitrarily selected depending on the desired purpose and application of the radiation image storage panel. Further, as described in JP-A-58-200200, in order to improve the sharpness of the obtained image, the surface of the support on the side of the phosphor layer (the surface of the support on the side of the phosphor layer is adhered to). In the case where a property imparting layer, a light reflecting layer, a light absorbing layer, or the like is provided, the surface thereof may be formed with fine irregularities.

After forming the coating on the support as described above, the coating is dried to complete the formation of the stimulable phosphor layer on the support. The thickness of the phosphor layer varies depending on the characteristics of the intended radiation image conversion panel, the kind of the phosphor, the mixing ratio of the binder to the phosphor, and the like.
mm. However, this layer thickness is preferably 50 to 500 μm. Note that the phosphor layer does not necessarily need to be formed by directly applying a coating solution on the support as described above. For example, the coating solution may be separately applied to a sheet such as a glass plate, a metal plate, or a plastic sheet. After the phosphor layer is formed by drying, the phosphor layer may be bonded to the support by pressing the phosphor layer on a support or using an adhesive.

As described above, a protective film is usually provided on the stimulable phosphor layer. As the protective film, a solution prepared by dissolving a material having high transparency and low absorption of ultraviolet rays, for example, an organic polymer substance such as polyamide, acrylic resin, or fluororesin in a suitable solvent is used as the phosphor layer. A protective film-forming sheet such as a film formed of an organic polymer such as polyamide, acrylic resin, or fluororesin, or a transparent glass plate is separately formed on the surface of the phosphor layer. Various types are used, such as those provided using an appropriate adhesive or those formed by depositing an inorganic compound having low ultraviolet absorption on the phosphor layer by a method such as vapor deposition. The surface of the protective film may be embossed, or the protective film may contain a light-scattering substance such as gadolinium fluoride, barium fluoride, or gadolinium oxide that absorbs less ultraviolet light.

For the purpose of improving the sharpness of the obtained image, at least one of the layers constituting the radiation image conversion panel of the present invention absorbs excitation light,
The stimulated emission light may be colored with a coloring agent that does not absorb the light, or an independent colored intermediate layer may be provided (see Japanese Patent Publication No. 54-23400).

According to the above-mentioned method, the trivalent metal-activated rare earth aluminate stimulable phosphor represented by the composition formula (I) and the binder containing and supporting the trivalent metal aluminate stimulable phosphor represented by the composition formula (I) are dispersed on the support. The radiation image storage panel of the present invention provided with a stimulable phosphor layer can be manufactured.

[0024]

[Example 1] Production of GdAlO ₃ : 0.005 Gd phosphor 5.00 g (0.0138 mol) of gadolinium oxide and 1.41 g (0.0138 mol) of aluminum oxide, and 1.00 g of lithium chloride as a flux (0.0
(236 mol) was stirred and mixed with the solid phase for 15 minutes. After filling the obtained mixture into an alumina crucible and placing the crucible in a vertical electric furnace, the temperature in the furnace was raised to 1200 ° C. over 1 hour, and kept at this temperature in the atmosphere for 4 hours, The temperature was lowered to room temperature over 1 hour. The fired product was taken out and pulverized in a mortar to obtain gadolinium-activated gadolinium aluminate phosphor particles represented by the composition formula shown in the title.

Example 2 Production of LaAlO ₃ : 0.005 Ce Phosphor In Example 1, lanthanum oxide (4.49 g, 0.01%) was prepared.
38 mol), 1.41 g (0.013 g) of aluminum oxide
8 mol) and 0.0340 g of cerium chloride (1.38 ×
10 ^-4 mol) and lithium chloride as a flux.
Cerium-activated lanthanum aluminate phosphor particles represented by the title composition formula were obtained in the same manner as in Example 1 except that 00g (0.0236 mol) was mixed.

[Evaluation of stimulable phosphor] The stimulable phosphor was evaluated for stimulable luminescence properties by the following method. After irradiating the stimulable phosphor with tungsten X-rays of 40 kVp and 30 mA, the halogen lamp light was excited by light (wavelength: 420 nm) spectrally separated by a monochromator, and the stimulable emission spectrum was measured. In addition, the peak wavelength of stimulated emission (about 3
The photostimulated excitation spectra at 13 nm and about 285 nm) were measured. Furthermore, the instantaneous emission spectrum by X-ray excitation was also measured. The obtained results are shown in FIGS. 1 and 2.

FIG. 1 is a graph showing a stimulated emission spectrum (solid line), a stimulated excitation spectrum (dashed-dotted line), and an X-ray emission spectrum (dotted line) of a GdAlO ₃ : 0.005 Gd phosphor. FIG. 2 is a graph showing a stimulated emission spectrum (solid line), a stimulated excitation spectrum (dashed-dotted line), and an X-ray emission spectrum (dotted line) of the LaAlO ₃ : 0.005 Ce phosphor. From the graphs shown in FIGS. 1 and 2, GdA
10 ₃ : 0.005 Gd phosphor and LaAlO ₃ : 0.005 Ce
Each of the phosphors was exposed to about 380 to 500 after X-ray irradiation.
It is clear that when excited by light in the wavelength range of nm, the photoluminescent material emits light in the ultraviolet region (peak wavelength: about 313 nm, about 285 nm).

Example 3 Production of Radiation Image Conversion Panel As the stimulable phosphor layer forming material, the above-mentioned GdAlO ₃ :
358 g of 0.005 Gd phosphor or LaAlO ₃ : 0.005 Ce phosphor and 57.3 g of Chris Coat (P1018GS, manufactured by Dainippon Ink and Chemicals, Inc.) were added to 90 g of methyl ethyl ketone, and dispersed with a propeller mixer to give a viscosity of 25 to 50 g. A coating solution of 30 PS was prepared. This coating solution was applied on an undercoated polyethylene terephthalate film using a doctor blade, and then dried at 100 ° C. for 15 minutes to form a 200 μm thick stimulable phosphor layer on a support. To obtain a radiation image conversion panel.

[0029]

According to the present invention, a rare earth aluminate activated with a trivalent metal is a novel stimulable phosphor which emits stimulable light in the ultraviolet region upon irradiation with radiation and visible light. It can be used for an image recording / reproducing method. The radiation image conversion panel of the present invention containing the stimulable phosphor can also be advantageously used in the radiation image recording / reproducing method.

[Brief description of the drawings]

FIG. 1 is a graph showing a stimulated emission spectrum (solid line), a stimulated excitation spectrum (dashed-dotted line), and an X-ray emission spectrum (dotted line) of the GdAlO ₃ : 0.005Gd phosphor of the present invention.

FIG. 2 is a graph showing a stimulated emission spectrum (solid line), a stimulated excitation spectrum (dot-dash line), and an X-ray emission spectrum (dotted line) of the LaAlO ₃ : 0.005 Ce phosphor of the present invention.

Claims (6)

[Claims] 1. Composition formula (I): LnAlO ₃ : xA (I) wherein Ln is at least one rare earth element selected from the group consisting of Y, La and Gd; A is from Ce, Gd and Bi At least one trivalent metal selected from the group consisting of: and x is a numerical value in the range of 0 <x ≦ 0.1. ] A trivalent metal activated rare earth aluminate stimulable phosphor represented by the formula: 2. The trivalent metal-activated rare earth aluminate stimulable phosphor according to claim 1, wherein Ln in the composition formula (I) is La and / or Gd. 3. In the composition formula (I), A is Ce and / or
Or the trivalent metal activated rare earth aluminate stimulable phosphor according to claim 1 or Gd. 4. x in the composition formula (I) is 0.0001.
The trivalent metal-activated rare earth aluminate stimulable phosphor according to any one of claims 1 to 3, which is a numerical value in a range of ≤x≤0.01. 5. After irradiation, 380 to 500 nm
2. A photostimulated luminescence when excited with light in the wavelength range of
5. The trivalent metal activated rare earth aluminate stimulable phosphor according to any one of items 4 to 4. 6. A radiation image conversion panel comprising the trivalent metal activated rare earth aluminate stimulable phosphor according to claim 1. Description: