JPH01251026A - Method of stimulating europium activated barium-strontium-magnesium fluorohalide phosphor - Google Patents

Abstract

PURPOSE: To maximize the luminance of phosphor by exposing the phosphor to high energy radiation to form the phosphor having storage energy and exposing the excited phosphor to radiation of a specific wavelength to allow the greater part of the storage energy to be released in the form of luminescence. CONSTITUTION: The phosphor is first exposed to the high energy radiation and the energy is stored in the phosphor. The phosphor having the storage energy is thereafter exposed to the radiation for stimulation, such as light source from a diode or laser. The wavelength of the radiation is about 565 to about 890nm, more preferably about 585 to 633nm. The stimulated radiation emits and releases substantially all of the energy stored in the phosphor in the form of luminescence. As a result, the luminance of the phosphor is maximized.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises a europium-activated barium-strontium-magnesium-fluorohalide (halide) phosphor by exposing the phosphor to high-energy radiation, storing the energy in the phosphor, and The invention then relates to a method of stimulating the phosphor by exposing it to radiation of a particular wavelength, thereby causing it to emit most of its stored energy in the form of light emission, or luminescence. In particular, the present invention seeks to maximize the brightness of the phosphor by controlling the wavelength of the stimulating radiation.

Luminescent materials of the following types have the ability to store energy when exposed to high energy radiation such as X-rays, gamma-rays, ultraviolet (UV) radiation, or cathode radiation. These materials release their stored energy in the form of light when stimulated by heat or stimulating radiation. Materials that release stored energy upon stimulation with IR/visible radiation are photostimulable.
ble) is called a phosphor. The utility of using such photostimulable phosphors in filmless radiography is well established. This radiographic technology application requires that the phosphor emit high photostimulated luminescence (brightness) with a short extinction time (decay time) of 2 to 10 μs in order to obtain high quality radiographs. The higher the luminance and the shorter the decay time of the emission, the better the signal/noise ratio in radiography.

In this filmless radiography,
The line passes through the object and reaches the fluorescent screen, and the corresponding energy is stored in the fluorescent screen. Such a fluorescent screen is then typically exposed to 633 nm He/Ne.
It is stimulated by suitable stimulating light (IR/visible light), which is a laser beam, so that the stored energy associated with the object image is released in the form of fluorescence. Such fluorescence is detected by a photomultiplier, converted to a digital signal, and the image is then detected in a CRT (cathode ray tube) terminal. It is desirable to use as low a dose of x-rays as possible for the patient in order to reduce health risks. One possible way to reduce the exposure is -
The first step is to use phosphors that emit stimulated luminescence of higher intensity.

At the same time, it is also important that all of the stored energy is released from the phosphor. This is accomplished by selecting an appropriate stimulating light sufficient to produce a stimulus effective to cause the phosphor to release all of its stored energy.

No. 4,261,854 teaches that barium fluorohalide phosphors receive light upon exposure to X-rays and are then stimulated by 632.8 nm He/Ne laser light. Alkaline earth metal sulfide phosphors are also known to be photostimulable phosphors. US Pat. No. 4,507,562 involves excitation of these phosphors using X-rays and subsequent stimulation with an 11064n pulsed neodymium yttrium aluminum garnet laser.

However, these conventional techniques have not yet achieved sufficient brightness for application, especially in filmless radiography. It is desired to develop a technology that can be used easily.

The inventors of the present invention have proposed the following: - The selection of a particular type of phosphor and its use in such a way that all of the stored energy is released from the phosphor while at the same time using a phosphor that emits stimulated luminescence of high intensity. We succeeded in maximizing the brightness of the phosphor by controlling the wavelength of the stimulating radiation.

In accordance with the present invention, a method of stimulating a europium-activated barium-strontium-magnesium-fluorohalide phosphor is disclosed, which comprises exposing the phosphor to high-energy radiation to produce stored energy in the phosphor. , and then the generated excited phosphor is about 565-89
It consists of producing a phosphor which, upon exposure to radiation at a wavelength of 0 nm, is able to emit most of its stored energy in the form of luminescence.

The phosphor of the present invention is a europium-activated barium-strontium-magnesium-fluorohalide phosphor, and most preferably has the general formula % (where X and y are greater than 0 and 0). a value less than .15;
The X to y ratio ranges from about 2:3 to about 3:2;
And Z is in the range of about 0.0004 to O,OO4.

) is a europium-activated barium-strontium-magnesium-fluorobromide phosphor.

Preferably, X is in the range of about 0.02-0.04;
y is in the range of about 0.01 to 0.03, and Z is about 0.
．． It is in the range of 001 to O, OO3.

The chemical formula of the phosphor particularly applicable to the present invention is Baa,
e++sro, oxzzMgo, ozsEtlo,
oo+aFBr.

The phosphor is first exposed to high energy radiation causing the phosphor to store the energy. Preferred types of post-energy radiation used for this purpose are X-rays, cathode rays, gamma rays and ultraviolet radiation.

This stored energy phosphor is then exposed to stimulating radiation such as a light source from a diode or a laser (LED), the wavelength of this radiation being between about 565 nm and about 890 nm, preferably between about 585 and 633 nm. It is. This stimulating radiation causes the phosphor to emit a large portion, and more typically substantially all, of its stored energy in the form of luminescence. This luminescence is called photostimulated luminescence (PSL emission). The luminance of the PSL source depends on the wavelength of the stimulation radiation, and within the above range, the shorter the wavelength, the higher the luminance.

The higher the brightness, the better the radiographs obtained when used in filmless radiography. When the stimulated luminescence emission of each sample stimulated by stimulating radiation of different wavelengths is compared to the stimulated luminescence emission intensity of a sample of the same type stimulated by a 633 nm He/Ne laser, the PSL intensity (brightness) is 5
It was found to be maximum when 85 nm stimulating radiation is used. A possible explanation for this could be that the stimulating radiant energy is not sufficient above 633 nm to provide effective stimulation of the phosphor to release all of its stored energy in the form of light. PSL brightness values at 565 nm are not expected to differ significantly from values obtained using 585 nm stimulating radiation.

Two samples of europium-activated barium-strontium-magnesium-fluorobromide phosphor were exposed to approximately 90 KV, 100 MA X-rays for approximately 2 seconds. These samples in the form of powder black were then subjected to 633 nm
It was activated by stimulating radiation and the stimulated light output was measured. The measurements were repeated several times in order to use these as standard PSL brightness values for the phosphor samples. Other samples of these types of phosphors were exposed to X-11t as the standard and exposed to varying wavelengths of stimulating light (pulsed radiation).

PSL brightness was measured as follows. The stimulated luminescence was passed through an optical filter and detected by a photomultiplier tube. This signal was amplified and recorded on a strip chart recorder. The results are shown in the table below, and the data is also plotted in FIG.

These results show that the brightness varies with the wavelength of the stimulating radiation and is at a maximum when the wavelength is 585 nm. This indicates that the wavelength of the stimulating radiation can be optimized to have maximum PSL light output from the phosphor, improving the signal/noise ratio in radiographic applications.

Although specific examples of the invention have been shown, it should be noted that various modifications may be made within the scope of the invention.

The present invention has succeeded in maximizing the brightness of the phosphor by selecting a specific type of photostimulable phosphor and controlling the wavelength of the stimulating radiation.

The present invention is particularly advantageous in filmless radiography, in which a lower dose of X-rays can be used to reduce the health risks to the patient.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between wavelength of stimulating radiation and brightness. PSL Rumikit〉S

Claims (1)

Claims: 1) A method of stimulating a europium-activated barium-strontium-magnesium-fluorohalide phosphor, comprising: (a) exposing the phosphor to high-energy radiation to stimulate the activated phosphor with stored energy; and (b) exposing the activated phosphor to radiation at a wavelength of about 565-890 nm to produce a phosphor capable of emitting a majority of its stored energy in the form of luminescence. A phosphor stimulation method consisting of: 2) The method according to claim 1, wherein the phosphor is a europium-activated barium-strontium-magnesium-fluorobromide phosphor. 3) The method of claim 1, wherein the high energy radiation source is selected from the group consisting of X-rays, cathode radiation, ultraviolet radiation and gamma radiation. 4. The method of claim 1, wherein 4) has a length in the range of about 585-633 nm.