CA1302210C - Multi-layer faceted luminescent screens - Google Patents
Multi-layer faceted luminescent screensInfo
- Publication number
- CA1302210C CA1302210C CA000525128A CA525128A CA1302210C CA 1302210 C CA1302210 C CA 1302210C CA 000525128 A CA000525128 A CA 000525128A CA 525128 A CA525128 A CA 525128A CA 1302210 C CA1302210 C CA 1302210C
- Authority
- CA
- Canada
- Prior art keywords
- screen
- sublayer
- overlayer
- luminescent
- layer
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
- H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
- H01J29/10—Screens on or from which an image or pattern is formed, picked up, converted or stored
- H01J29/18—Luminescent screens
- H01J29/26—Luminescent screens with superimposed luminescent layers
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
- C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
- C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
- C09K11/7766—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals
- C09K11/7767—Chalcogenides
- C09K11/7769—Oxides
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
- C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
- C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
- C09K11/7766—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals
- C09K11/7774—Aluminates
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
- C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
- C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
- C09K11/7783—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals one of which being europium
- C09K11/7784—Chalcogenides
- C09K11/7787—Oxides
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
- H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
- H01J29/10—Screens on or from which an image or pattern is formed, picked up, converted or stored
- H01J29/18—Luminescent screens
- H01J29/24—Supports for luminescent material
Abstract
ABSTRACT OF THE DISCLOSURE
MULTI-LAYER FACETED LUMINESCENT SCREENS
A multi-layer luminescent screen includes a luminescent crystalline sublayer and a faceted over-layer. The faceted overlayer causes the emission from the screen of a greater fraction of the luminescence than would otherwise be the case. The screens, which are typically cathodoluminescent, find application in computer displays, lithography, and flying spot scanners.
MULTI-LAYER FACETED LUMINESCENT SCREENS
A multi-layer luminescent screen includes a luminescent crystalline sublayer and a faceted over-layer. The faceted overlayer causes the emission from the screen of a greater fraction of the luminescence than would otherwise be the case. The screens, which are typically cathodoluminescent, find application in computer displays, lithography, and flying spot scanners.
Description
~LV
82-2~40 DESÇRIPTION
MVLTI-LAYER ACETED LU~INESCENT SCREENS
BACKGROUND OF T~IE_INVENTION
l. Field of _hç_Invention This invention relates to luminescent screens of at least two crystalline layers; more particularly, screens in which a mismatch in lattice constant of a sublayer and overlayer provide enharlced luminescent output.
82-2~40 DESÇRIPTION
MVLTI-LAYER ACETED LU~INESCENT SCREENS
BACKGROUND OF T~IE_INVENTION
l. Field of _hç_Invention This invention relates to luminescent screens of at least two crystalline layers; more particularly, screens in which a mismatch in lattice constant of a sublayer and overlayer provide enharlced luminescent output.
2. _scriPtion of the Prior Art The use of rare-earth phosphor materials in cathodoluminescent screens or cathode ray tube applications is well known. One disadvantage of the conventional, powder phosphor layer in cathode ray tubes is its degradation due to heating effects from the enersy absorbed frorn the electron beam. A second disadvantage is that the screen resolution is limited by the size of the phosphor particles and the non-uniformity of the deposited phosphor layer.
Single crystal phosphor layers on suitable substrates solve both these problems. The intimate contact between an epitaxial phosphor layer and its substrate facilitates heat transEer out of the phosphor layer. Since the phosphor is a single crystal, there is no particle-size-limiting resolution.
Such epitaxial single crystal phosphor layers have been reviewed in J.M. Robertson et al., Thin Sol. Films l~, 79221 (1984). A disadvantage of sinc~le c,rystal phosphor layers is that much of the light that is cJenerated in the cathodolurnineE;cerlt phosphor is "piped" to the edges of the phosphor layer/sub.strate compos;ite. This wavecJuide action reduces the use~ul light output at angles close to normal viewinCJ :incldence.
One method ~or increasirlcJ the :intenF;ity o~ light at norrnal inciclene, disclosed in U.S. Patent No.
r.
~Qt22~
4,298,820, issued on November 3, 1981, to Bongers et al, is to etch grooves into the phosphor layer to allow the escape of light. A disadvantage of this technique is that the resolution of the phosphor layer is limited by 5 the dimensions of the grooves. Another disadvantage is the extra processing required to form the g~ooves; some cathodoluminescent materials, such as yttrium aluminum garnet (YAG), are highly resistant to chemical and mechanical milling.
Certain epitaxial growth conditions on garnet result in a type o~ defect known as faceting. The conditions for such facet growth in a type of magneto-optical garnet were disclosed by D. M. Gualtieri at the 30th annual Conference on Magnetism and Magnetic 15 Materials, San Diego, November 1984 (D. M. Gualtieri and P.F. Tumelty, to be published in J. Appl, Phys.). J. ~.
Robertson et al. (op. cit., p.227) reported such a facet defect in garnet phosphor layers and observed that facets scatter cathodoluminescence to forward 20 directions. They also disclosed that such a defect reduced the resolution, because of multiple internal reflections, and concluded that facets should be avoided in the preparation of such layers.
SUMMARY OF THE INVENTION
In accordance with the present invention, a luminescent screen is provided, having at least two layers. The screen comprises a luminescent crystalline sublayer that has a surface on which is a crystalline overlayer that has (a) the same~ crystal structure as the sublayer and (b) a lattice constant that suficient1y exceeds the lattice constant oE the sublayer that the overlayer is faceted.
The screen of the present invention provides a unique combination of high image cluality and high efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 depicts a prior art powder luminescent screen.
~31[~
Fig. 2 depicts a prior art crystalline layer luminescent screen.
Fig. 3 depicts a lumlnescent screen of the present invention.
Fig. 4 depicts an embodiment of a luminescent screen o~ the present invention that has a luminescent overlayer.
DETAILED DESCRIPTIO~ OF THE INVENTION
The luminescent screens of the present invention 10 are intended for use in cathode ray tubes, electron microscopes, x-ray image intensifiers, and other applications where light output is generated from particle beam or high-energy electromagnetic radiation input.
Prior art luminescent screens are generally of two types - "powder" and "crystalline layer." A powder screen comprises phosphor particles that are dispersed in a binder and coated onto a substrate. A crystalline layer screen has a crystalline phosphor layer in place 20 of the particles and binder. Both types oE screen were described by Robertson et al., and our Figs. 1 and 2 are based on their Figs. 2a and 2b.
Fig. 1 shows powder screen 10, which incLudes a substrate 11 supporting the powder layer 12, on which is 25 an optional reElective backing layer 13. An incident electron beam 1~ generates light in the phosphor particles. The :Light may he emitted through the transparent substrate, as depicted by rays 15, 16, and 17, or it may be totally internally re~lected (ray 18). Any light ray incident on phosphor particLes may be scattered. Dif~use scatterincJ by the phosphor particles, as depicted by rays 18a4..18e, creates an undesirable "halo" e~fect.
Better image ~uality, due to reduced scattering, is achieved by a crystalline layer screen oE the type shown in Fig. 2, where crystalline layer 22 replaces powder layer 12. A crystalline layer, preferably a single crystal, also has desirably higher thermal conductivity 2~
than does powder. Likewise, for the best image quality, layer 22 is a single crystal, with a minimal number of defects or dislocations, which can scatter the light.
However, multiple internal reflections, exemplified by ray 28, cause a reduction in light emitted Erom the front of the substrate, compared with the output from powder screens.
A goal of the present invention is to combine the high light output of the powder screen with the good image quality of the layer screen. A means for accomplishing the goal is a two-layer screen structure. Each of the layers ("sublayer" and "overlayer") is crystalline; the sublayer is luminescent and the overlayer may be luminescent as well. The distinctive features are that the two layers have the same crystal structure and that the lattice constant of the overlayer exceeds that of the sublayer sufficiently that the overlayer is "faceted." Some background information should help to explain faceting.
Crystals tend to assume certain gross shapes in bulk form. The crystals exhibit certain faces, or "facets," which are a consequence of atomic symmetry.
As an example, sodium chloride, common table salt, is Eound as crystalline cubes because of its cubic struc-ture. The sublayer and overlayer of the present invention are preferably garnets. Garnet is crystal-lographically cubic, but it has a more complex space group than sodium chloride, and its crystals have many more facets. F`or convenience we limit the discussion to garnets, but there should be no inference that the invention is limited to yarnets.
Although other growth processes may be suitable, the overlayers of this invention are generally grown by liquid phase epitaxy (LPE), described in ~lank et al., ~J. Cryst. Gro~th 17, 302 (1972). The optirnum situation of epitaxial c~rowth is "homoepitaxy," where the sub-strate and overgrowth are of the same material. The ~3a)~2~
present invention involves heteroepitaxy onto a sublayer of a different (garnet) overlayer. Such heteroepitaxy generally causes the overgrowth to be straineci, clue to lattice constant mismatch. When strained layers a~e 5 grown, the strain, increasing with layer thickness, can exceed the elastic limits of the material. In this case, dislocations are formed, and the material is in the "plastic" region of a stress-strain curve. The effect of epitaxial growth in the "plastic" region is 10 the generation of facets on a local scale, but, initially, not over the total dimension of the crystal. The dislocations that separate the facet regions give stress relief to the epitaxial over-growth. Ultimately, as thickness increases, facets 15 cover the entire area.
In the converltional view, "the most important requirement for successful garnet epitaxy has been the need for lattice parameter match. This has been the best single predictor for success." (L. Varnerin, IEEE
20 Trans. on ~agn. MAG-7, 404 (1971)) Faceting of an LPE
layer has been considered a defect, and identification of parameters to suppress faceting "a major achievement," (ibid.) A Icey element of facet suppression is good lattice match (to within 1 to 2 25 ppm)-The present invention departs from the conventional view. Under controlled conditions, the crystal morphology oE a LPE yarnet film changes (as growth parameters change) from a continuous, low-deEect film (Eor small lattice mismatch) to a highly defective Eacet structure (for large mismatch). However, if lattice mismatch is too yreat, epitaxial yrowth is preventecJ.
Thus, the LPF' overlayer lattice constant preferably exceeds that oE the sublayer by less than about 2%.
Fig. 3 depicts an embodiment of the present inven-tion. The screen depicted there includes a faceted overlayer 30, in addition to optional substrate 31, which supports the luminescent sublayer 32. Also shown is optional reflective backing layer 33. Rays lilce 3~
and 39, which would be totally internally reflected if they were generated in the prior art "layer" screen depicted in Fig. 2, are emitted from the front of 5substrate 31. At the same time, the sublayer, which is preferably a single crystal, provides minimal image-degrading scattering sites. Lu~inescent materials suitable for sublayer 32 are known in the art and generally comprise a doped crystal. Preferred host crystals are garnets, such as YAG or gadolinium gallium garnet (GGG), and preferred dopants are luminescent ions of one or more rare earths or transition metals. More-preferred dopants are ions of Ce, Tb, or Eu, with Ce most preferred. Dopant levels for luminescent layers of 15 this invention are generally limited by the compatibil-ity of dopant and host and/or by quenching. High dopant level is desirable, because it provides high saturation intensities. Typical dopant levels are in the range be-tween about 0.1 and 5 atomic ~.
When the sublayer is YAG or GGG, the surface onto which the overlayer is deposited is preferab:Ly the (lll) face. Sublayer thickness is not critical. For effi-clent operation, the sublayer should be thick enough to absorb a substantial fraction of the incident beam 3~, 25 but not so thick that it absorbs too much of the light that must pass through it. Depending on the nature oE
the incident beam and the sublayer material, thicknesses between one micrometer and one miLLimeter are suit-able. The thinner sublayers generally require a support 30 substrate, while the thicker ones ma~y be selE-supporting.
When a support is re~luired or desirecl, its material should be transparent to the light emitted and be suit-able Eor the sublayer to be deposited onto it. It 35 should also have good thermal conductivity to minimize the temperature at which the screen operates. High temperatures can damage the screen. If the sublayer is a host crystal that includes a l,uminescent ion, the 2~
undoped host crystal may be a suitable support material.
The overlayer material must have the same crystal structure as the sublayer but a laryer lattice constant.
The lattice constant mismatch required for facets to 5 develop depends on the elastic modulus ancl shear modulus of the overlayer~ For YAG, GGG and similar garnets, Eacets develop if the overlayer lattice constant exceeds that of the sublayer by at least about 0.5%. If the sublayer is YAG, a suitable overlayer is 10 Y3A15_a(Sc,In)aO12 (YSAG), where a is between O and about 2. If the sublayer is GGG, a suitable overlayer is Gd3Ga5_b(Sc,In)bO12 (GSAG), where b is between 0 and about 2. In the embodiment shown in Fig. 3, the overlayer thickness should be large enough to scatter 15 light out of the sublayer (with Eacets coveriny the entire area), but small enough to be substantially transparent to the incident beam 34. Preferably, overlayer thickness is less than about one micrometer if it is not luminescent.
Reflective backing layer 33, if present, serves two purposes. It re~lects out of the screen light that might otherwise escape. In addition, it facilitates making an electrical connection to the screen.
Typically, the screen is an anode in a cathode ray 25 imaging system and the metal backing is grounded throuyh the cathode. High reflectivity and low resistance are desirable and readily provlded by conventional coatings oE aluminum or silver.
Fig ~ depicts an embodiment in whlch the overlayer 40 is aLso luminescent. An advantage of that embodiment is that the screen can then be used with both low-energy electrons, which are absorbed in a thin layer, and high-energy electrons, which penetrate into the sublayer.
When the overlayer composition is luminescent, it includes a suitable dopant in the overlayer crystal.
Generally, if the overlayer is GSAG or YSAG, the dopant is a transition metal or rare earth ion, preferably, Ce, Tb, or Eu, with Ce most preferred. It may be convenient 2~L~
~8--to use the same dopant in sublayer and overlayer, but it is not necessary. When the ov0rlayer is luminescent, it should be thick enough to absorb a substantial fraction of incident beam 34.
Note that Figs 3 and 4 depict the electron beam incident on one surface of the screen and the light emitted from the opposite surface. In practice, the beam may be incident on the same surface that the light is emitted from; the criteria are that the incident 10 electron beam penetrate to the luminescent layer and the output light not be appreciably absorbed before it emerges from the screen.
Single crystal phosphor layers on suitable substrates solve both these problems. The intimate contact between an epitaxial phosphor layer and its substrate facilitates heat transEer out of the phosphor layer. Since the phosphor is a single crystal, there is no particle-size-limiting resolution.
Such epitaxial single crystal phosphor layers have been reviewed in J.M. Robertson et al., Thin Sol. Films l~, 79221 (1984). A disadvantage of sinc~le c,rystal phosphor layers is that much of the light that is cJenerated in the cathodolurnineE;cerlt phosphor is "piped" to the edges of the phosphor layer/sub.strate compos;ite. This wavecJuide action reduces the use~ul light output at angles close to normal viewinCJ :incldence.
One method ~or increasirlcJ the :intenF;ity o~ light at norrnal inciclene, disclosed in U.S. Patent No.
r.
~Qt22~
4,298,820, issued on November 3, 1981, to Bongers et al, is to etch grooves into the phosphor layer to allow the escape of light. A disadvantage of this technique is that the resolution of the phosphor layer is limited by 5 the dimensions of the grooves. Another disadvantage is the extra processing required to form the g~ooves; some cathodoluminescent materials, such as yttrium aluminum garnet (YAG), are highly resistant to chemical and mechanical milling.
Certain epitaxial growth conditions on garnet result in a type o~ defect known as faceting. The conditions for such facet growth in a type of magneto-optical garnet were disclosed by D. M. Gualtieri at the 30th annual Conference on Magnetism and Magnetic 15 Materials, San Diego, November 1984 (D. M. Gualtieri and P.F. Tumelty, to be published in J. Appl, Phys.). J. ~.
Robertson et al. (op. cit., p.227) reported such a facet defect in garnet phosphor layers and observed that facets scatter cathodoluminescence to forward 20 directions. They also disclosed that such a defect reduced the resolution, because of multiple internal reflections, and concluded that facets should be avoided in the preparation of such layers.
SUMMARY OF THE INVENTION
In accordance with the present invention, a luminescent screen is provided, having at least two layers. The screen comprises a luminescent crystalline sublayer that has a surface on which is a crystalline overlayer that has (a) the same~ crystal structure as the sublayer and (b) a lattice constant that suficient1y exceeds the lattice constant oE the sublayer that the overlayer is faceted.
The screen of the present invention provides a unique combination of high image cluality and high efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 depicts a prior art powder luminescent screen.
~31[~
Fig. 2 depicts a prior art crystalline layer luminescent screen.
Fig. 3 depicts a lumlnescent screen of the present invention.
Fig. 4 depicts an embodiment of a luminescent screen o~ the present invention that has a luminescent overlayer.
DETAILED DESCRIPTIO~ OF THE INVENTION
The luminescent screens of the present invention 10 are intended for use in cathode ray tubes, electron microscopes, x-ray image intensifiers, and other applications where light output is generated from particle beam or high-energy electromagnetic radiation input.
Prior art luminescent screens are generally of two types - "powder" and "crystalline layer." A powder screen comprises phosphor particles that are dispersed in a binder and coated onto a substrate. A crystalline layer screen has a crystalline phosphor layer in place 20 of the particles and binder. Both types oE screen were described by Robertson et al., and our Figs. 1 and 2 are based on their Figs. 2a and 2b.
Fig. 1 shows powder screen 10, which incLudes a substrate 11 supporting the powder layer 12, on which is 25 an optional reElective backing layer 13. An incident electron beam 1~ generates light in the phosphor particles. The :Light may he emitted through the transparent substrate, as depicted by rays 15, 16, and 17, or it may be totally internally re~lected (ray 18). Any light ray incident on phosphor particLes may be scattered. Dif~use scatterincJ by the phosphor particles, as depicted by rays 18a4..18e, creates an undesirable "halo" e~fect.
Better image ~uality, due to reduced scattering, is achieved by a crystalline layer screen oE the type shown in Fig. 2, where crystalline layer 22 replaces powder layer 12. A crystalline layer, preferably a single crystal, also has desirably higher thermal conductivity 2~
than does powder. Likewise, for the best image quality, layer 22 is a single crystal, with a minimal number of defects or dislocations, which can scatter the light.
However, multiple internal reflections, exemplified by ray 28, cause a reduction in light emitted Erom the front of the substrate, compared with the output from powder screens.
A goal of the present invention is to combine the high light output of the powder screen with the good image quality of the layer screen. A means for accomplishing the goal is a two-layer screen structure. Each of the layers ("sublayer" and "overlayer") is crystalline; the sublayer is luminescent and the overlayer may be luminescent as well. The distinctive features are that the two layers have the same crystal structure and that the lattice constant of the overlayer exceeds that of the sublayer sufficiently that the overlayer is "faceted." Some background information should help to explain faceting.
Crystals tend to assume certain gross shapes in bulk form. The crystals exhibit certain faces, or "facets," which are a consequence of atomic symmetry.
As an example, sodium chloride, common table salt, is Eound as crystalline cubes because of its cubic struc-ture. The sublayer and overlayer of the present invention are preferably garnets. Garnet is crystal-lographically cubic, but it has a more complex space group than sodium chloride, and its crystals have many more facets. F`or convenience we limit the discussion to garnets, but there should be no inference that the invention is limited to yarnets.
Although other growth processes may be suitable, the overlayers of this invention are generally grown by liquid phase epitaxy (LPE), described in ~lank et al., ~J. Cryst. Gro~th 17, 302 (1972). The optirnum situation of epitaxial c~rowth is "homoepitaxy," where the sub-strate and overgrowth are of the same material. The ~3a)~2~
present invention involves heteroepitaxy onto a sublayer of a different (garnet) overlayer. Such heteroepitaxy generally causes the overgrowth to be straineci, clue to lattice constant mismatch. When strained layers a~e 5 grown, the strain, increasing with layer thickness, can exceed the elastic limits of the material. In this case, dislocations are formed, and the material is in the "plastic" region of a stress-strain curve. The effect of epitaxial growth in the "plastic" region is 10 the generation of facets on a local scale, but, initially, not over the total dimension of the crystal. The dislocations that separate the facet regions give stress relief to the epitaxial over-growth. Ultimately, as thickness increases, facets 15 cover the entire area.
In the converltional view, "the most important requirement for successful garnet epitaxy has been the need for lattice parameter match. This has been the best single predictor for success." (L. Varnerin, IEEE
20 Trans. on ~agn. MAG-7, 404 (1971)) Faceting of an LPE
layer has been considered a defect, and identification of parameters to suppress faceting "a major achievement," (ibid.) A Icey element of facet suppression is good lattice match (to within 1 to 2 25 ppm)-The present invention departs from the conventional view. Under controlled conditions, the crystal morphology oE a LPE yarnet film changes (as growth parameters change) from a continuous, low-deEect film (Eor small lattice mismatch) to a highly defective Eacet structure (for large mismatch). However, if lattice mismatch is too yreat, epitaxial yrowth is preventecJ.
Thus, the LPF' overlayer lattice constant preferably exceeds that oE the sublayer by less than about 2%.
Fig. 3 depicts an embodiment of the present inven-tion. The screen depicted there includes a faceted overlayer 30, in addition to optional substrate 31, which supports the luminescent sublayer 32. Also shown is optional reflective backing layer 33. Rays lilce 3~
and 39, which would be totally internally reflected if they were generated in the prior art "layer" screen depicted in Fig. 2, are emitted from the front of 5substrate 31. At the same time, the sublayer, which is preferably a single crystal, provides minimal image-degrading scattering sites. Lu~inescent materials suitable for sublayer 32 are known in the art and generally comprise a doped crystal. Preferred host crystals are garnets, such as YAG or gadolinium gallium garnet (GGG), and preferred dopants are luminescent ions of one or more rare earths or transition metals. More-preferred dopants are ions of Ce, Tb, or Eu, with Ce most preferred. Dopant levels for luminescent layers of 15 this invention are generally limited by the compatibil-ity of dopant and host and/or by quenching. High dopant level is desirable, because it provides high saturation intensities. Typical dopant levels are in the range be-tween about 0.1 and 5 atomic ~.
When the sublayer is YAG or GGG, the surface onto which the overlayer is deposited is preferab:Ly the (lll) face. Sublayer thickness is not critical. For effi-clent operation, the sublayer should be thick enough to absorb a substantial fraction of the incident beam 3~, 25 but not so thick that it absorbs too much of the light that must pass through it. Depending on the nature oE
the incident beam and the sublayer material, thicknesses between one micrometer and one miLLimeter are suit-able. The thinner sublayers generally require a support 30 substrate, while the thicker ones ma~y be selE-supporting.
When a support is re~luired or desirecl, its material should be transparent to the light emitted and be suit-able Eor the sublayer to be deposited onto it. It 35 should also have good thermal conductivity to minimize the temperature at which the screen operates. High temperatures can damage the screen. If the sublayer is a host crystal that includes a l,uminescent ion, the 2~
undoped host crystal may be a suitable support material.
The overlayer material must have the same crystal structure as the sublayer but a laryer lattice constant.
The lattice constant mismatch required for facets to 5 develop depends on the elastic modulus ancl shear modulus of the overlayer~ For YAG, GGG and similar garnets, Eacets develop if the overlayer lattice constant exceeds that of the sublayer by at least about 0.5%. If the sublayer is YAG, a suitable overlayer is 10 Y3A15_a(Sc,In)aO12 (YSAG), where a is between O and about 2. If the sublayer is GGG, a suitable overlayer is Gd3Ga5_b(Sc,In)bO12 (GSAG), where b is between 0 and about 2. In the embodiment shown in Fig. 3, the overlayer thickness should be large enough to scatter 15 light out of the sublayer (with Eacets coveriny the entire area), but small enough to be substantially transparent to the incident beam 34. Preferably, overlayer thickness is less than about one micrometer if it is not luminescent.
Reflective backing layer 33, if present, serves two purposes. It re~lects out of the screen light that might otherwise escape. In addition, it facilitates making an electrical connection to the screen.
Typically, the screen is an anode in a cathode ray 25 imaging system and the metal backing is grounded throuyh the cathode. High reflectivity and low resistance are desirable and readily provlded by conventional coatings oE aluminum or silver.
Fig ~ depicts an embodiment in whlch the overlayer 40 is aLso luminescent. An advantage of that embodiment is that the screen can then be used with both low-energy electrons, which are absorbed in a thin layer, and high-energy electrons, which penetrate into the sublayer.
When the overlayer composition is luminescent, it includes a suitable dopant in the overlayer crystal.
Generally, if the overlayer is GSAG or YSAG, the dopant is a transition metal or rare earth ion, preferably, Ce, Tb, or Eu, with Ce most preferred. It may be convenient 2~L~
~8--to use the same dopant in sublayer and overlayer, but it is not necessary. When the ov0rlayer is luminescent, it should be thick enough to absorb a substantial fraction of incident beam 34.
Note that Figs 3 and 4 depict the electron beam incident on one surface of the screen and the light emitted from the opposite surface. In practice, the beam may be incident on the same surface that the light is emitted from; the criteria are that the incident 10 electron beam penetrate to the luminescent layer and the output light not be appreciably absorbed before it emerges from the screen.
Claims (18)
1. A luminescent screen having at least two layers and comprising a luminescent crystalline sublayer that has a surface on which is a crystalline overlayer that has (a) the same crystal structure as the sublayer and (b) a lattice constant that exceeds the lattice constant of the sublayer by an amount such that the overl-ayer is faceted.
2. The screen of Claim 1 in which the sublayer is a single crystal.
3. The screen of Claim 2 in which the sublayer comprises Y3Al5O12:M or Gd3Ga5O12:M, where M is at least one luminescent ion.
4. The screen of Claim 3 in which M is one or more ion of an element selected from the group consisting of Ce, Tb, and Eu.
5. The screen of Claim 4 in which M includes Ce ion.
6. The screen of Claim 3 in which the orientation of the sublayer surface is (111).
7. The screen of claim 3 in which the sublayer comprises Y3Al5O12:M and the overlayer comprises Y3Al5-a-(Sc,In)aO12 where a is in the range between 0 and about 2.
8. The screen of claim 3 in which the sublayer comprises Gd3Ga5O12:M and the overlayer comprises Gd3Ga 5-b(Sc,In)bO12 where b is in the range between 0 and about 2.
9. The screen of Claim 1 in which the lattice con-stant of the overlayer exceeds that of the sublayer by less than about 2%.
10. The screen of Claim 1 in which the overlayer is less than one micrometer thick.
11. The screen of Claim 1 in which the overlayer is luminescent.
12. The screen of Claim 3 in which the sublayer comprises Y3Al5O12:M and the overlayer comprises Y3Al5-a(Sc,In)a O12:M' where M' is at least one luminescent ion and a is in the range between 0 and about 2.
13. The screen of Claim 1 in which M' is one or more ion of an element selected from the group consisting of Ce, Tb, and Eu.
14. The screen of Claim 13 in which M' includes Ce.
15. The screen of Claim 3 in which the sublayer comprises Gd3Ga5O12:M and the overlayer comprises Gd3Ga5-b (Sc,In)b O12:M" in which M" is at least one luminescent ion and b is in the range between 0 and about 2.
16. The screen of Claim 1 further comprising a support for the sublayer.
17. The screen of Claim 16 in which the support comprises an undoped crystal and the sublayer comprises the same crystal and a dopant.
18. The screen of Claim 1 further comprising a reflective coating on the faceted layer.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/811,184 US4713577A (en) | 1985-12-20 | 1985-12-20 | Multi-layer faceted luminescent screens |
| US811,184 | 1985-12-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1302210C true CA1302210C (en) | 1992-06-02 |
Family
ID=25205807
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000525128A Expired - Fee Related CA1302210C (en) | 1985-12-20 | 1986-12-12 | Multi-layer faceted luminescent screens |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US4713577A (en) |
| EP (1) | EP0226824B1 (en) |
| JP (1) | JPS62157646A (en) |
| CA (1) | CA1302210C (en) |
| DE (1) | DE3680080D1 (en) |
Families Citing this family (36)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0232586A3 (en) * | 1986-02-10 | 1988-10-05 | AT&T Corp. | Cathode ray tube with single crystal targets |
| US4835437A (en) * | 1986-02-10 | 1989-05-30 | American Telephone And Telegraph Company, At&T Bell Laboratories | Cathode ray tube with single crystal target |
| FR2647261B1 (en) * | 1989-05-19 | 1991-07-05 | Thomson Tubes Electroniques | |
| US5237448A (en) * | 1991-02-05 | 1993-08-17 | American Ingenuity, Inc. | Visibility enhancing material |
| US5243457A (en) * | 1991-02-05 | 1993-09-07 | American Ingenuity, Inc. | Material with enhanced visibility characteristics |
| US5300783A (en) * | 1992-05-26 | 1994-04-05 | American Ingenuity, Inc. | Layered reflecting and luminous material |
| US5315491A (en) * | 1992-09-30 | 1994-05-24 | American Ingenuity, Inc. | Reflecting and luminous layered material |
| JP2509427B2 (en) * | 1992-12-04 | 1996-06-19 | 浜松ホトニクス株式会社 | Image tube |
| KR100265859B1 (en) * | 1996-12-21 | 2000-09-15 | 정선종 | Luminous particle for field emission display |
| US6529322B1 (en) * | 1999-01-27 | 2003-03-04 | University Of Georgia Research Foundation, Inc. | High contrast front and rear viewing surfaces for projection displays |
| US7090355B2 (en) * | 2003-05-19 | 2006-08-15 | Superimaging, Inc. | System and method for a transparent color image display utilizing fluorescence conversion of nano particles and molecules |
| US7452082B2 (en) * | 2004-04-19 | 2008-11-18 | Superimaging, Inc. | Excitation light emission apparatus |
| US20040227694A1 (en) * | 2003-05-14 | 2004-11-18 | Xiao-Dong Sun | System and method for a three-dimensional color image display utilizing laser induced fluorescence of nanopartcles and organometallic molecules in a transparent medium |
| US7976169B2 (en) * | 2003-05-14 | 2011-07-12 | Sun Innovations, Inc. | Waveguide display |
| US7040764B2 (en) * | 2003-10-23 | 2006-05-09 | Hewlett-Packard Development Company, L.P. | Projection system using ambient light |
| US6987610B2 (en) * | 2003-10-23 | 2006-01-17 | Hewlett-Packard Development Company, L.P. | Projection screen |
| US7293879B2 (en) | 2003-10-23 | 2007-11-13 | Hewlett-Packard Development Company, L.P. | Projection screen |
| CA2542793A1 (en) * | 2003-11-03 | 2005-05-12 | Super-Imaging, Inc. | Light emitting material integrated into a substantially transparent substrate |
| US7213923B2 (en) * | 2004-04-19 | 2007-05-08 | Superimaging, Inc. | Emission of visible light in response to absorption of excitation light |
| WO2006094262A2 (en) * | 2005-03-03 | 2006-09-08 | Superimaging, Inc. | Display |
| US7474286B2 (en) | 2005-04-01 | 2009-01-06 | Spudnik, Inc. | Laser displays using UV-excitable phosphors emitting visible colored light |
| US8089425B2 (en) | 2006-03-03 | 2012-01-03 | Prysm, Inc. | Optical designs for scanning beam display systems using fluorescent screens |
| US8000005B2 (en) | 2006-03-31 | 2011-08-16 | Prysm, Inc. | Multilayered fluorescent screens for scanning beam display systems |
| US8451195B2 (en) | 2006-02-15 | 2013-05-28 | Prysm, Inc. | Servo-assisted scanning beam display systems using fluorescent screens |
| US7846391B2 (en) | 2006-05-22 | 2010-12-07 | Lumencor, Inc. | Bioanalytical instrumentation using a light source subsystem |
| RU2442197C2 (en) * | 2007-05-17 | 2012-02-10 | Призм, Инк. | The multilayer screens with light emitting strips for the display system with a scan-off beam |
| US8556430B2 (en) | 2007-06-27 | 2013-10-15 | Prysm, Inc. | Servo feedback control based on designated scanning servo beam in scanning beam display systems with light-emitting screens |
| US7709811B2 (en) | 2007-07-03 | 2010-05-04 | Conner Arlie R | Light emitting diode illumination system |
| US8098375B2 (en) | 2007-08-06 | 2012-01-17 | Lumencor, Inc. | Light emitting diode illumination system |
| US8242462B2 (en) | 2009-01-23 | 2012-08-14 | Lumencor, Inc. | Lighting design of high quality biomedical devices |
| US20130209794A1 (en) * | 2010-12-20 | 2013-08-15 | Ocean's King Lighting Science & Technology Co., Ltd. | Light emission apparatus and manufacturing method thereof |
| US8389957B2 (en) | 2011-01-14 | 2013-03-05 | Lumencor, Inc. | System and method for metered dosage illumination in a bioanalysis or other system |
| US8466436B2 (en) | 2011-01-14 | 2013-06-18 | Lumencor, Inc. | System and method for metered dosage illumination in a bioanalysis or other system |
| CN103031127B (en) * | 2011-09-30 | 2014-10-29 | 有研稀土新材料股份有限公司 | Orange fluorescent powder and preparation method thereof, and electric light source made of fluorescent powder |
| US9642515B2 (en) | 2012-01-20 | 2017-05-09 | Lumencor, Inc. | Solid state continuous white light source |
| US9217561B2 (en) | 2012-06-15 | 2015-12-22 | Lumencor, Inc. | Solid state light source for photocuring |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL7707008A (en) * | 1977-06-24 | 1978-12-28 | Philips Nv | LUMINESCENCE SCREEN. |
| NL7800405A (en) * | 1978-01-13 | 1979-07-17 | Philips Nv | PROCEDURE FOR MANUFACTURE OF LUMINESCENT SCREENS, LUMINESCENT SCREENS ACCORDING TO THIS PROCEDURE, AND CATHODRAY TUBES FITTED WITH SUCH LUMINESCENT SCREEN. |
| NL7806828A (en) * | 1978-06-26 | 1979-12-28 | Philips Nv | LUMINESCENCE SCREEN. |
| US4550256A (en) * | 1983-10-17 | 1985-10-29 | At&T Bell Laboratories | Visual display system utilizing high luminosity single crystal garnet material |
| EP0166924A3 (en) * | 1984-07-02 | 1987-02-04 | Allied Corporation | Faceted magneto-optical garnet layer |
| WO1986000633A1 (en) * | 1984-07-09 | 1986-01-30 | American Telephone & Telegraph Company | Luminescent display device |
| US4757232A (en) * | 1985-01-16 | 1988-07-12 | American Telephone And Telegraph Company, At&T Bell Laboratories | Visual display system comprising epitaxial terbium-activated garnet material |
-
1985
- 1985-12-20 US US06/811,184 patent/US4713577A/en not_active Expired - Fee Related
-
1986
- 1986-11-20 EP EP86116052A patent/EP0226824B1/en not_active Expired
- 1986-11-20 DE DE8686116052T patent/DE3680080D1/en not_active Expired - Lifetime
- 1986-12-12 CA CA000525128A patent/CA1302210C/en not_active Expired - Fee Related
- 1986-12-19 JP JP61303577A patent/JPS62157646A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| EP0226824A3 (en) | 1988-02-17 |
| DE3680080D1 (en) | 1991-08-08 |
| JPS62157646A (en) | 1987-07-13 |
| EP0226824A2 (en) | 1987-07-01 |
| US4713577A (en) | 1987-12-15 |
| EP0226824B1 (en) | 1991-07-03 |
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