Electric lamp and discharge devices: systems – Surge generator or inductance in the supply circuit
Reexamination Certificate
2001-05-25
2003-01-07
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Surge generator or inductance in the supply circuit
C315S291000, C313S485000
Reexamination Certificate
active
06504320
ABSTRACT:
The invention relates to a gas discharge lamp for dielectrically impeded discharges, which gas discharge lamp is provided with a discharge vessel filled with a gas filling, which discharge vessel comprises at least a wall of a dielectric material and at least a wall having a surface which is at least partly transparent to visible radiation and coated with a phosphor layer, and provided with an electrode structure for a dielectrically impeded discharge, and with means for igniting and maintaining the dielectrically impeded discharge.
Gas discharge lamps for dielectrically impeded discharges are used, particularly, in office automation devices, for example color copiers and color scanners, in signal devices, for example as brake lights and direction indicator lights in automobiles, in auxiliary illumination devices, for example, the courtesy lighting of automobiles, as well as, in particular, for the background lighting of displays and display screens, for example of liquid crystal displays.
Said applications require the luminance to be both uniform throughout the length of the lamp and high. To increase the luminance, it is necessary to increase the power that is coupled into the system. However, this also causes a higher load to be imposed on, inter alia, the phosphors in the phosphor layer. The phosphors degrade more rapidly and the luminous output decreases more rapidly during operation as the power coupled in increases.
A luminescent screen, in particular a plasma display screen comprising a phosphor preparation of an aluminate phosphor provided with a coating including one or more catenation polyphosphates of metals selected from of the group formed by the alkaline earth metals, zinc, cadmium or manganese, which protect the phosphor against degradation, are already disclosed in DE 197 27 607 A1.
It is an object of the invention to provide a gas discharge lamp for dielectrically impeded discharges, which discharge lamp can be reliably operated at a high power for a long period of time.
In accordance with the invention, this object is achieved by a gas discharge lamp for dielectrically impeded discharges, which gas discharge lamp is provided with a discharge vessel filled with a gas filling, which discharge vessel comprises at least a wall of a dielectric material and at least a wall having a surface which is at least partly transparent to visible radiation and coated with a phosphor layer, which phosphor layer comprises a phosphor preparation of a phosphor powder and a coating, which coating comprises a compound selected from the group formed by the fluorides and orthophosphates of the elements magnesium, calcium, barium, aluminum, scandium, yttrium and lanthanum, and provided with an electrode structure for a dielectrically impeded discharge, and with means for igniting and maintaining the dielectrically impeded discharge.
In such a gas discharge lamp for dielectrically impeded discharges, the degradation of the phosphor under the influence of VUV or UV-C radiation is reduced or completely suppressed.
The fluorides and orthophosphates mentioned hereinabove form a hard, water-insoluble coating on the phosphor particles, they do not react with the phosphors and even exposure to radiation does not lead to degradation of these fluorides and orthophosphates. As they are colorless, they do not influence the colors of the phosphors. They are hydrophilic, so that the coated phosphor particles can be readily dispersed.
It has also been found that the gas discharge couples very well to the wall coated with the phosphor layer.
Within the scope of the invention it is preferred that the coating is applied in a quantity in the range from 0.1 to 10% by weight with respect to the phosphor.
It is particularly preferred that the phosphor is BaMgAl
10
O
17
:Eu.
Particularly advantageous effects in comparison with the prior art are achieved when the phosphor is BaMgAl
10
O
17
:Eu and the coating comprises a compound selected from the group formed by the fluorides and orthophosphates of the elements magnesium, barium and aluminum. The coating completely and homogeneously covers the surface of the BaMgAl
10
O
17
:Eu powder and the adhesion of said coating is excellent.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.
A gas discharge lamp for dielectrically impeded discharges in accordance with the invention comprises a discharge vessel containing a gas filling, which discharge vessel comprises at least a wall of a dielectric material and at least a wall comprising a surface which is at least partly transparent to visible radiation and coated with a phosphor layer. Said phosphor layer comprises a phosphor composition of a phosphor powder provided with a coating, which coating includes a compound selected from the group formed by the fluorides and orthophosphates of the elements magnesium, calcium, barium, aluminum, scandium, yttrium and lanthanum. In addition, the gas discharge lamp is provided with an electrode structure for a dielectrically impeded discharge, and with means for igniting and maintaining said dielectrically impeded discharge.
A typical construction of the gas discharge lamp comprises a cylindrical, xenon-filled lamp bulb of glass whose outer wall is provided with a pair of stripe-shaped electrodes which are arranged so as to be electrically insulated from each other. The stripe-shaped electrodes extend throughout the length of the lamp bulb so as to face each other with their long sides, while leaving two gaps clear. The electrodes are connected to the poles of a high-voltage source, which is operated at an alternating voltage of the order of 20 kHz to 500 kHz in such a manner that an electric discharge develops only in the area of the inside surface of the lamp bulb.
If an alternating voltage is applied to the electrodes, a corona discharge can be ignited in the xenon-containing filling gas. This leads to the formation of excimers in the xenon, i.e. molecules which consist of an excited xenon atom and a xenon atom in the ground state.
Xe+X*=Xe
2*
The excitation energy is delivered as UV radiation with a wavelength &lgr;=170 to 190 nm. This conversion of electron energy to UV radiation takes place very efficiently. The generated UV photons are absorbed by the phosphors of the phosphor layer and the excitation energy is partly delivered again in the region of the spectrum having a longer wavelength.
In principle, a plurality of different structural shapes are possible for the discharge vessel, such as plates, simple tubes, coaxial tubes, straight, U-shaped, circularly bent or coiled cylindrical, or differently shaped, discharge tubes.
As the material for the discharge vessel use is made of quartz or glass types which are transparent to VUV and UV-C radiation.
The electrodes consist of a metal, for example aluminum or silver, a metal alloy or a transparent, conductive, inorganic compound, for example ITO. They can be embodied so as to be a coating, an adhesive foil, wire or wire netting.
To concentrate the light intensity in a specific direction, a part of the discharge vessel may be provided with a coating serving as a reflector for VUV and UV-C light.
The discharge vessel is filled with a gas mixture comprising an inert gas such as xenon, krypton, neon or helium. Gas fillings comprising predominantly oxygen-free xenon are preferred.
The inner wall of the gas discharge vessel is partly, or entirely, coated with a phosphor layer containing one or more phosphors or phosphor preparations. In addition, the phosphor layer may comprise organic or inorganic binders or a binder composition.
For the phosphor use is preferably made of a VUV phosphor which generally comprises a host lattice of an inorganic oxygen-containing material such as oxides, aluminates, phosphates, borates or silicates, doped with a few percent of an activator. The aluminate phosphors which, in accordance with the invention, are provided with a stabilizing coating are first and foremost phosphors on the basis o
Feldmann Claus
Juestel Thomas
Jungk Hans Otto
Merikhi Jacqueline
Ronda Cornelis Reinder
Bartlett Ernestine C.
Koninklijke Philips Electronics , N.V.
Vu Jimmy T.
Wong Don
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