Compositions – Inorganic luminescent compositions – Compositions containing halogen; e.g. – halides and oxyhalides
Patent
1995-10-06
1998-01-13
Bonner, Melissa
Compositions
Inorganic luminescent compositions
Compositions containing halogen; e.g., halides and oxyhalides
501 12, 501 32, 501 39, 976DIG439, C03B 802, C09K 1102
Patent
active
057075484
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to materials and devices incorporating phosphors especially storage phosphors, which may be used in the detection of radiation by stimulated luminescence.
In the prior art a phosphor material is known in which the following electronic processes may be obtained: incident radiation; below, the conduction band of the or by photostimulation, e.g. applying incident optical radiation; releasing a photon as luminescence.
Such a phosphor may be used to detect ionizing radiation such as alpha, beta or gamma rays, X-rays and neutrons. The number of electrons excited and trapped is a measure of the intensity of the incident radiation and can itself be measured by detecting the number of photons released when the trapped electrons are photostimulated. The feature which distinguishes phosphors of the kind described from other known phosphors is the length of time the electrons can remain in their trapped sites. Such sites can be very stable and therefore reading by photostimulation of the number of electrons trapped can take place many hours after the original ionization. Furthermore, the total dose of radiation over a given period of time will be intended in terms of the number of electrons excited. The phosphors are therefore known as storage phosphors.
In the prior art, storage phosphors of the kind described have been incorporated as polycrystalline powder with an organic binder in a polymer film in a manner similar to a photographic film. Such films and their method of use are described for example in the article by Miyahara J., Takahashi K., Amemiya,, Kamiya N. and Satow Y. entitled "A new type of X-ray detector utilizing laser stimulated luminescence" in Nuclear Instruments and Methods in Physics Research, A246, p 572-578 (1986).
Although storage phosphor materials produced in the manner described have produced high sensitivity and dynamic range compared for example to conventional X-ray films, we have found that they are not ideal in all respects.
It is a purpose of the present invention in one aspect to provide an improved storage phosphor material.
According to the present invention in a first aspect there is provided a storage phosphor material comprising a storage phosphor of the kind in which electrons excited by incident ionizing radiation may be trapped in stable trap sites and subsequently released by stimulation such as photostimulation, wherein the phosphor is contained within a host matrix which comprises a sol-gel glass in which the storage phosphor is incorporated as a dopant.
Storage phosphor materials according to the present invention unexpectedly and beneficially have several advantages over those made using polymer films as in the prior art. The sol-gel glass forms an excellent highly transparent support material. Thus, the materials according to the present invention provide better optical coupling to the read-out systems, e.g. photostimulation and photoemission systems, and give better optical absorption of the photostimulation radiation and provide a host material with better mechanical rigidity and thermal and chemical stability. The materials can show the further benefits described below.
The storage phosphor in the material according to the present invention may, as in the prior art, comprise an alkaline earth fluorohalide doped with one or more rare earth, metals, e.g. a phosphor of the formula BaFHa:R.sup.2+ where Ha is either Br or Cl and R is selected from one or more of Eu, Ce, Sm, La, Y and Gd, especially Eu.
Sol-gel glasses are well known in the optical glass field. They comprise a matrix prepared from condensation reactions of a solution, e.g. Si(OH).sub.4, to form a three dimensional network, e.g. based upon --Si--O--Si-- chains. By drying, ageing and controlled sintering over temperatures in the range 100.degree. C. to 1000.degree. C. a porous glass is formed with a porosity dependent upon the processing temperature. During the sintering process porosity and refractive index increase.
The sol-gel glass may be pre-formed and subsequently doped with
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King Terence Alan
Roden Sven Glyn
Shuttleworth Stephen
Bonner Melissa
British Nuclear Fuels PLC
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