Process for producing a phosphor layer by reacting a doped subst

Details Process for producing a phosphor layer by reacting a doped subst Process for producing a phosphor layer by reacting a doped subst

1993-12-15

1995-03-21

Jones, W. Gary

Glass manufacturing

Processes of manufacturing fibers, filaments, or preforms

Process of manufacturing optical fibers, waveguides, or...

427157, 427399, 65 601, 65 608, 65 605, C03C 1700

Patent

active

053991850

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention is directed to a process for producing a phosphor layer on a substrate, suitable for producing a scintillator.
X-ray radiation can be converted into visible light with the aid of scintillators. This visible light can then be registered by photodetectors. Such scintillators are used, for example, for producing medical radiographs.
2. Description of the Prior Art
A phosphor layer which is disposed on a glass substrate is often used as a scintillator. In addition to a good light yield and a narrowly defined particle size and layer thickness of the phosphor layer, a good adhesion of the phosphor layer to the substrate is also important.
To measure the intensity distribution of a wide X-ray beam, for example for producing medical radiographs, a positional resolution is necessary in the plane of the intensity distribution to be measured. For this purpose, small scintillators which are disposed alongside one another are generally used. In the direction of the radiation propagation of the X-ray radiation, said scintillators have to be so thick that they protect the photodetectors against radiation damage by absorbing the X-ray radiation.
It is known to produce phosphor layers on a substrate by vapor deposition, screen printing or sedimentation of phosphors. The technical complexity and the susceptibility to defects of this process is generally high. A good adhesion of the phosphor layer to the substrate can only be achieved if the substrate is carefully cleaned. The phosphor is applied as powder. The powder already has the chemical composition necessary for the phosphor layer. This powder has to be produced beforehand in a process which is usually complex. In order to achieve a uniform layer thickness of the phosphor, the substrate must if possible have no profile (i.e., the substrate must be as smooth as possible).
It is known to produce scintillators in the form of layers composed of crystal needles disposed perpendicularly to the layer. The crystal needles comprise, for example, CsI:Na. In this case, the needles must have large enough dimensions in the direction of the incident X-ray radiation for the X-ray light to be largely absorbed. The positional resolution is determined by the diameter of the needles perpendicular to the direction of incidence of the X-ray radiation. In these scintillators, most of the X-ray light is converted into luminescent light in the first third of the scintillator crystal. In the rest of the crystal, the still unabsorbed radiation is attenuated to such an extent that the photodetectors are protected against radiation damage. The layers produced must therefore be disproportionately thick, compared with their light yield.


SUMMARY OF THE INVENTION

The invention is directed to the problem of providing a process for producing phosphor layers, with which process uniform phosphor layers can be produced even on uneven substrates or arbitrarily structured substrates. The process is intended to make it possible to produce phosphor layers either for large-area detectors or for scintillators having a high positional resolution.
According to the invention, the problem is solved in a process wherein a layer composed of a doped starting substance is applied to a SiO.sub.2 glass substrate, and wherein the phosphor layer is produced by reacting the starting substance with the SiO.sub.2 of the substrate to form a silicate of the starting substance in a heat-treatment process conducted at a reaction temperature in an oxygen-containing atmosphere, the SiO.sub.2 glass substrate having a softening point which is above the reaction temperature. The phosphor layer is produced by reaction of a starting substance, which is applied as a layer to a substrate composed of SiO.sub.2 glass, with the SiO.sub.2 from the substrate surface. It therefore has very good adhesion to the surface of the substrate. Furthermore, the phosphor layer is produced in a uniform thickness.
In the process according to the invention, for example, phosphor

REFERENCES:
patent: 2219895 (1940-10-01), Hanlein
patent: 2408475 (1948-10-01), Nichke
patent: 2689188 (1954-09-01), Hushley
patent: 3279903 (1966-10-01), Siegmund
patent: 3291706 (1966-12-01), Gebel
patent: 5302423 (1994-04-01), Tran
Reisman et al. "Process for Adhering CdSe Layers to Silica Substrates", Dec. 1961, IBM Technical disclosure Bull.
Mat. Research Bull. vol. 24, pp. 175-179, Feb. 1989, Morimo et al., Preparation of Zn.sub.2 SiO.sub.4 -Mn Phosphors.

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