WO1999031546A1 - Liquid-crystal display using uv light source - Google Patents
Liquid-crystal display using uv light source Download PDFInfo
- Publication number
- WO1999031546A1 WO1999031546A1 PCT/GB1998/003688 GB9803688W WO9931546A1 WO 1999031546 A1 WO1999031546 A1 WO 1999031546A1 GB 9803688 W GB9803688 W GB 9803688W WO 9931546 A1 WO9931546 A1 WO 9931546A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- phosphor
- light
- liquid
- cas0
- narrow
- Prior art date
Links
- 239000004973 liquid crystal related substance Substances 0.000 title claims abstract description 15
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims abstract description 38
- 229910052925 anhydrite Inorganic materials 0.000 claims abstract description 16
- 239000000203 mixture Substances 0.000 claims abstract description 11
- 229910052921 ammonium sulfate Inorganic materials 0.000 claims abstract description 8
- 239000012298 atmosphere Substances 0.000 claims abstract description 7
- 238000010438 heat treatment Methods 0.000 claims abstract description 6
- 238000001816 cooling Methods 0.000 claims abstract description 4
- 239000003638 chemical reducing agent Substances 0.000 claims abstract description 3
- 239000002245 particle Substances 0.000 claims abstract description 3
- 239000011369 resultant mixture Substances 0.000 claims abstract description 3
- 238000000034 method Methods 0.000 claims description 5
- 239000000843 powder Substances 0.000 claims description 4
- OSGAYBCDTDRGGQ-UHFFFAOYSA-L calcium sulfate Chemical compound [Ca+2].[O-]S([O-])(=O)=O OSGAYBCDTDRGGQ-UHFFFAOYSA-L 0.000 abstract description 5
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonia chloride Chemical compound [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 abstract 1
- 235000019270 ammonium chloride Nutrition 0.000 abstract 1
- BFNBIHQBYMNNAN-UHFFFAOYSA-N ammonium sulfate Chemical compound N.N.OS(O)(=O)=O BFNBIHQBYMNNAN-UHFFFAOYSA-N 0.000 abstract 1
- 235000011130 ammonium sulphate Nutrition 0.000 abstract 1
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 5
- 229910052753 mercury Inorganic materials 0.000 description 5
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 4
- 230000003098 cholesteric effect Effects 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 239000012190 activator Substances 0.000 description 3
- 238000010304 firing Methods 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- -1 Eu2+ ions Chemical class 0.000 description 2
- 229910052693 Europium Inorganic materials 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 229910052786 argon Inorganic materials 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 239000001175 calcium sulphate Substances 0.000 description 2
- 235000011132 calcium sulphate Nutrition 0.000 description 2
- 210000004027 cell Anatomy 0.000 description 2
- 238000000295 emission spectrum Methods 0.000 description 2
- OGPBJKLSAFTDLK-UHFFFAOYSA-N europium atom Chemical compound [Eu] OGPBJKLSAFTDLK-UHFFFAOYSA-N 0.000 description 2
- RSEIMSPAXMNYFJ-UHFFFAOYSA-N europium(III) oxide Inorganic materials O=[Eu]O[Eu]=O RSEIMSPAXMNYFJ-UHFFFAOYSA-N 0.000 description 2
- 230000005284 excitation Effects 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 238000010926 purge Methods 0.000 description 2
- 229910052761 rare earth metal Inorganic materials 0.000 description 2
- 150000002910 rare earth metals Chemical class 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- 230000007704 transition Effects 0.000 description 2
- 229910052723 transition metal Inorganic materials 0.000 description 2
- 150000003624 transition metals Chemical class 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 239000005132 Calcium sulfide based phosphorescent agent Substances 0.000 description 1
- 241000288030 Coturnix coturnix Species 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 238000003491 array Methods 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000000903 blocking effect Effects 0.000 description 1
- ZCCIPPOKBCJFDN-UHFFFAOYSA-N calcium nitrate Inorganic materials [Ca+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O ZCCIPPOKBCJFDN-UHFFFAOYSA-N 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000003086 colorant Substances 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 210000002858 crystal cell Anatomy 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000000706 filtrate Substances 0.000 description 1
- 238000004020 luminiscence type Methods 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 241000894007 species Species 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
- 238000001429 visible spectrum Methods 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
- G02F1/1336—Illuminating devices
- G02F1/133617—Illumination with ultraviolet light; Luminescent elements or materials associated to the cell
Definitions
- the invention relates to liquid-crystal displays, particularly those having a source of narrow-band UVA light to activate phosphors.
- Photoluminescent liquid-crystal display (PLLCD) architectures as described, for example, in the patent applications GB 2154355 (Ricoh Ltd) , WO 95/27920 (Crossland et al) and GB 2291734 (Samsung) , utilise a combination of a light source, liquid-crystal cells and a phosphor material to produce an image. This combines the viewing-angle characteristics of a CRT with the compactness and cost of a passive LCD.
- the specific components of such a system can include cholesteric polarisers and compensating retarders as well as the liquid crystal cells. These components tend to be optimised for a specific wavelength and to work less well at other wavelengths. As a consequence, if the bandwidth of the excitation light is large, the performance of the components generally deteriorates. Superior display performance can be obtained by directing the excitation light as closely as possible to the optimum direction and in a narrow spectral range . It has been found advisable when constructing such displays to use UVA light (a wavelength of about 350 - 400 nm) rather than shorter wavelengths. Such light is transmitted through conventional glasses and polymers better than shorter-wavelength UV light, and yet still has enough energy to excite red, green and blue phosphors. Also, such longer UV wavelengths cause less degradation of the liquid-crystal materials themselves. It is therefore desirable to find a suitable source of light for PLLCDs .
- a liquid-crystal-type display comprising an ultra-violet light source, a first phosphor that emits UVA light when struck by light from this source, a liquid-crystal device for modulating the light emitted by the first phosphor and a second phosphor acting as a display surface and emitting visible light when excited by the modulated narrow-band UVA light;
- the first phosphor is preferably Eu 2+ -doped CaS0 4 .
- This phosphor produces narrow-band light in the UVA band from 350-400 nm with a full width at half maximum bandwidth of about 15 nm or less. Its spectrum is shown in Fig. 1.
- the narrow emission characteristics of phosphors used in the present invention also largely eliminate another disadvantage of the prior art.
- a significant amount of visible light is emitted and this must be filtered out, to prevent it adding to the visible emissions of the phosphors in the PLLCD architecture and desaturating the observed colours.
- the considerable amount of blue light emitted by conventional long-wave UV phosphors needs a very sharp transmission cut-off filter to avoid significant loss of the useful UVA light whilst blocking visible light.
- the phosphor of the present invention emits much less in the visible spectrum.
- UVA emissions are the lines of, for example, low-pressure mercury cold- cathode fluorescent lamps (CCFL) .
- CCFL low-pressure mercury cold- cathode fluorescent lamps
- Such lines are typically no wider than about 2 nm, but those in the desired near-visible region are unsuitable because of their low relative intensity.
- the primary emission from low-pressure mercury CCFLs is at 254 nm and this is used to excite phosphor powders coated onto the inside of the fluorescent tubes.
- phosphor emission bandwidths are generally rather large and in most cases the spectra extend over several tens of nanometres.
- Commercially available UVA-emitting phosphors typically have full width at half-maximum (FWHM) bandwidths of 18 nm or more.
- the phosphor of the invention ideally comprises a transition metal or rare earth activator incorporated into a host lattice. Transitions involving transition metal or rare earth species as an activator generally have lower bandwidths than ' defect' -type phosphors. It is of course also essential that the activator fits properly into the host lattice, since otherwise increased disorder would be created that would lead to a broader emission spectrum. The design of the phosphors is thus also important . In the phosphor the europium should be incorporated into the calcium sulphate lattice in the form of doubly charged Eu 2+ ions .
- CaS0 4 :Eu 2+ phophor is prepared by heating a mixture of CaS0 4 , (NH 4 ) 2 S0 4 and Eu 2 0 3 in an inert atmosphere, cooling the resultant mixture, adding a reducing agent, in particular NH 4 C1 , heating again in an inert atmosphere and grinding or otherwise processing to the required particle size.
- the powder can then be applied to the inside or outside of a cold-cathode mercury-vapour tube, or it can be supported on a separate substrate.
- FIG. 2 is a highly schematic diagram of a liquid-crystal display in accordance with the invention.
- a low-pressure mercury cold-cathode discharge tube 1 has electrodes, not shown, and a phosphor 3 coated on the inside of the tube 1.
- the phosphor is made from a calcium sulphate host lattice incorporating europium.
- the low-pressure mercury emits light mostly at a wavelength around 254 nm; this light is incident on the phosphor which in turn emits narrowband UV radiation 5 centred at 388 nm and having a bandwidth of 13nm FWHM.
- the quantum efficiency was measured to be 85% which is comparable to conventional phosphors.
- the light 5 emitted by the phosphor is then passed through a collimator 7 and a modulator, here a liquid- crystal modulator 9, and is then incident on a display phosphor 11 upon which images can be displayed.
- the liquid crystal is of a type suited to the 388 nm wavelength, and is equipped with orthogonal arrays of ITO electrodes, alignment layers and polarisers in the usual way.
- the output phosphor 11 can be pixellated to correspond with the modulator pixels, or it can be a uniform layer.
- the polarisers can be cholesteric, since such polarisers are well adapted to work with a narrow range of wavelengths.
- the liquid crystal can then either modulate circularly polarised light or have the light converted to linearly polarised light by a quarter-wave plate.
- the input-light phosphor 3 following the invention is a narrow-band phosphor means that the cholesteric polariser can operate at a narrower band of wavelengths for a given collimation and contrast ratio, and the compensation films can be simpler or even omitted for a given collimation and contrast ratio. Also the fact that the input light is only just sub- visible means that the transmission and lifetime of components are improved.
- a further advantage of the narrow-band source light is that it is easier to collimate the light, in particular by adding a collimating dielectric stack as the collimator 7, as described in PCT/GB 98/01203.
- the CaS0 4 : Eu 2+ phosphor can be produced from a range of synthesis routes and has previously been reported in Dhopte et al, Journal of Luminescence 50
- CaS0 4 • Dissolve 500g Ca(N0 3 ) 2 in 31 water;
- Phosphor • Mix 120g CaS0 4 with 1. lg Eu 2 0 3 .
- the powder thus prepared can be coated on to the inside of a glass tube in any known way, and electrodes and a gas filling introduced to produce a lamp.
- Several linear tubes, or a single serpentine tube, can be used as a backlight for the display, or a TIR lightguide with tubes along its sides can be constructed as a diffuse light source.
- a display comprising an ultra-violet light source, a phosphor (3) that emits UVA light (5) when struck by light from this source, a device (9) for modulating the light emitted by the phosphor and a display output material (11) acting as a display surface and emitting visible light when excited by the UVA light; in which the phosphor has a narrow-band emission spectrum with a FWHM of less than about 14 nm.
- a display as claimed in claim 2 in which the phosphor is Eu 2+ -doped CaS0 4 and emits wavelengths around 388 nm.
- a display as claimed in any preceding claim in which the display output material is itself a phosphor or a mixture of phosphors.
- a display according to any preceding claim in which the UV light source is a gas discharge in a vessel (1) lined by the first phosphor.
- the modulator (9) includes cholesteric polarisers optimised to work over the narrow emission
Landscapes
- Physics & Mathematics (AREA)
- Nonlinear Science (AREA)
- Mathematical Physics (AREA)
- Chemical & Material Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Devices For Indicating Variable Information By Combining Individual Elements (AREA)
- Liquid Crystal (AREA)
- Vessels And Coating Films For Discharge Lamps (AREA)
Abstract
Description
Claims
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP98960001A EP1040382A1 (en) | 1997-12-16 | 1998-12-16 | Liquid-crystal display using uv light source |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GBGB9726570.6A GB9726570D0 (en) | 1997-12-16 | 1997-12-16 | Liquid-crystal display using UV light source |
GB9726570.6 | 1997-12-16 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1999031546A1 true WO1999031546A1 (en) | 1999-06-24 |
Family
ID=10823696
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/GB1998/003688 WO1999031546A1 (en) | 1997-12-16 | 1998-12-16 | Liquid-crystal display using uv light source |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP1040382A1 (en) |
GB (1) | GB9726570D0 (en) |
WO (1) | WO1999031546A1 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US8226263B2 (en) | 2007-04-17 | 2012-07-24 | Koninklijke Philips Electronics N.V. | Illumination system |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3669897A (en) * | 1969-11-14 | 1972-06-13 | Westinghouse Electric Corp | Divalent europium activated alkaline earth metal sulfates and method of preparation |
GB2154355A (en) * | 1984-01-13 | 1985-09-04 | Ricoh Kk | Liquid crystal color display device |
GB2291734A (en) * | 1994-07-26 | 1996-01-31 | Samsung Display Devices Co Ltd | Backlight for display |
US5666174A (en) * | 1995-08-11 | 1997-09-09 | Cupolo, Iii; Anthony M. | Emissive liquid crystal display with liquid crystal between radiation source and phosphor layer |
WO1997040417A1 (en) * | 1996-04-19 | 1997-10-30 | The Secretary Of State For Defence | Liquid crystal display |
-
1997
- 1997-12-16 GB GBGB9726570.6A patent/GB9726570D0/en not_active Ceased
-
1998
- 1998-12-16 WO PCT/GB1998/003688 patent/WO1999031546A1/en not_active Application Discontinuation
- 1998-12-16 EP EP98960001A patent/EP1040382A1/en not_active Withdrawn
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3669897A (en) * | 1969-11-14 | 1972-06-13 | Westinghouse Electric Corp | Divalent europium activated alkaline earth metal sulfates and method of preparation |
GB2154355A (en) * | 1984-01-13 | 1985-09-04 | Ricoh Kk | Liquid crystal color display device |
GB2291734A (en) * | 1994-07-26 | 1996-01-31 | Samsung Display Devices Co Ltd | Backlight for display |
US5666174A (en) * | 1995-08-11 | 1997-09-09 | Cupolo, Iii; Anthony M. | Emissive liquid crystal display with liquid crystal between radiation source and phosphor layer |
WO1997040417A1 (en) * | 1996-04-19 | 1997-10-30 | The Secretary Of State For Defence | Liquid crystal display |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US8226263B2 (en) | 2007-04-17 | 2012-07-24 | Koninklijke Philips Electronics N.V. | Illumination system |
US8491154B2 (en) | 2007-04-17 | 2013-07-23 | Koninklijke Philips N.V. | Illumination system |
Also Published As
Publication number | Publication date |
---|---|
EP1040382A1 (en) | 2000-10-04 |
GB9726570D0 (en) | 1998-02-11 |
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