EP0324953B1 - High power radiation source - Google Patents

Description

TECHNICAL AREA

The invention is based on a high-power radiator with a discharge space filled under filling conditions forming excimers, defined by a first and a second wall, the first wall being formed by a dielectric which directly delimits the discharge space, the dielectric on its side facing away from the discharge space Surface is provided with a first electrode, and the second wall is formed either by a second electrode or by a further dielectric, which is provided with a second electrode on its surface facing away from the discharge space, with a to the said electrodes (6.2 ) connected AC power source.

TECHNOLOGICAL BACKGROUND AND PRIOR ART

The starting point for the present invention is a UV high-power radiator, as described, for example, in the lecture by U.Kogelschatz "New UV and VUV excimer radiators" at the 10th lecture conference of the Society of German Chemists, Photochemistry Group, from November 18-20 Was introduced in Würzburg in 1987. European UV application 87109674.9 dated July 6, 1987 with publication number 0 245 111, a document in accordance with Art 54 (3) EPC, describes the UV high-power lamp presented at the aforementioned conference in detail.

This high-performance radiator can be operated with high electrical power densities and high efficiency. Its geometry is widely adaptable to the process in which it is used. In addition to large, flat spotlights, cylindrical ones that radiate inwards or outwards are also possible. The discharges can be operated at high pressure (0.1 - 10 bar). With this design, electrical power densities of 1-50 KW / m can be realized. Since the electron energy in the discharge can be largely optimized, the efficiency of such emitters is very high, even if one excites resonance lines of suitable atoms. The wavelength of the radiation can be set by the type of fill gas, e.g. Mercury (185 nm, 254 nm), nitrogen (337-415 nm), selenium (196, 204.206 nm), arsenic (189, 193 nm), iodine (183 nm), xenon (119, 130, 147 nm), krypton (142 nm). As with other gas discharges, it is also advisable to mix different types of gas.

The advantage of these emitters is the areal radiation of large radiation outputs with high efficiency. Almost all of the radiation is concentrated in one or a few wavelength ranges. It is important in all cases that the radiation can escape through one of the electrodes. This problem can be solved with transparent, electrically conductive layers or else by using a fine-mesh wire mesh or applied conductor tracks as an electrode. which on the one hand ensure the current supply to the dielectric, but on the other hand are largely transparent to the radiation. A transparent electrolyte, e.g. H₂O, are used as a further electrode, which is particularly advantageous for the irradiation of water wastewater, since in this way the radiation generated passes directly into the liquid to be irradiated and this liquid also serves as a coolant.

SUMMARY OF THE INVENTION

The object of the present invention is to modify the generic high-power radiator in such a way that it preferably emits light in the wavelength range from 400 nm to 800 nm, i.e. in the range of visible light. emits.

This object is achieved by the features characterized in the independent claims 1 and 2.

The invention is based on the same discharge geometry as that of the UV high-power lamp described in the patent applications mentioned.

The UV photons generated by excimer radiation in the discharge space cause the layer to fluoresce or phosphoresce upon impact and thus generate visible radiation. With modern phosphors this conversion process into visible light can be very efficient (quantum yield up to 95%). The layer is advantageously applied to the inside of the dielectric, because this means that the dielectric itself can only consist of ordinary glass. All difficulties that arise in connection with a UV source with UV-transparent materials do not arise. The luminescent layer is protected against the attack of the discharge by a thin UV-transparent layer.

The desired UV wavelength can be selected with the gas filling. For example, excimers can be used as radiating molecules (noble gases, mixtures of noble gases and halogens, mercury, cadmium or zinc) or mixtures of metals with strong resonance lines (mercury, selenium etc.) in very small quantities and noble gases, the mercury-free filling gases being the Preference should be given since this does not create any disposal problems. In this way, for example, a mercury lamp can be built with properties similar to those on which the conventional fluorescent tube and the new gas discharge lamps are based.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1

ein Ausführungsbeispiel der Erfindung in Gestalt eines ebenen einseitig abstrahlenden Flächenstrahlers im Schnitt;

Fig. 2

ein Ausführungsbeispiel nach Fig. 1 mit innenliegender Lumineszenzschicht im Schnitt;

Fig. 3

ein Ausführungsbeispiel der Erfindung in Gestalt eines ebenen nach zwei Seiten abstrahlenden Flächenstrahlers im Schnitt;

Fig. 4

eine Abwandlung des Ausführungsbeispiels nach Fig. 3 mit innenliegenden Lumineszenzschichten im Schnitt;

Fig. 5

ein Ausführungsbeispiel eines zylindrischen nach aussen abstrahlenden Strahlers;

Fig. 6

eine Abwandlung des Ausführungsbeispiels nach Fig. 5 mit innenliegender Lumineszenzschicht.

Exemplary embodiments of the invention are shown schematically in the drawing, namely:

Fig. 1

an embodiment of the invention in the form of a flat single-sided radiating surface radiator in section;

Fig. 2

an embodiment of Figure 1 with internal luminescent layer in section.

Fig. 3

an embodiment of the invention in the form of a planar radiating surface emitter on two sides in section;

Fig. 4

a modification of the embodiment of Figure 3 with internal luminescent layers in section.

Fig. 5

an embodiment of a cylindrical radiating emitter;

Fig. 6

a modification of the embodiment of FIG. 5 with an internal luminescent layer.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

1 consists essentially of a quartz or sapphire plate 1 and a metal plate 2, which are separated from one another by spacers 3 made of insulating material, and delimit a discharge space 4 with a typical gap width between 1 and 10 mm. The outer surface of the quartz plate 1 is covered with a luminescent layer 5, which is followed by a relatively wide-mesh wire network 6, of which only the warp or weft threads are visible. This wire mesh 6 and the metal plate 2 form the two electrodes of the radiator. The electrical feed is provided by an alternating current source 7 connected to these electrodes. As a current source, use can generally be made of those that have long been used in connection with ozone generators.

The discharge space 5 is closed on the side in the usual way, was evacuated before closing and filled with an inert gas or a substance which forms excimers under discharge conditions, e.g. Mercury, noble gas, noble gas-metal vapor mixture, noble gas-halogen mixture, filled, optionally using an additional further noble gas (Ar, He, Ne) as a buffer gas.

Depending on the desired spectral composition of the radiation and luminescent layer, a substance according to the following table can be used: FILLING GAS RADIATION helium 60-100 nm neon 80 - 90 nm argon 107 - 165 nm xenon 160-190 nm nitrogen 337 - 415 nm krypton 124 nm, 140-160 nm Krypton + fluorine 240 - 255 nm Mercury + argon 235 nm deuterium 150-250 nm Xenon + fluorine 400 - 550 nm Xenon + chlorine 300-320 nm Xenon + iodine 240-260 nm In addition to the above gases or gas mixtures, noble gas-metal mixtures are also possible, with metals with strong resonance lines being preferred: zinc 213 nm cadmium 228.8 nm mercury 185 nm, 254 nm

worin d die Spaltweite des Entladungsraums in Millimetern (typisch 1 - 10 mm), P_M den Metalldampfdruck bedeutet.For the resonance line emitters, the amount of metal in the gas mixture is very small in relation to the amount of noble gas, so that as little self-absorption as possible occurs. The following relationship can serve as a guideline for the upper limit $${\text{dx P}}_{\text{M}}\text{≤ 1333 Pa · mm (10 Torr · mm)}$$

where d is the gap width of the discharge space in millimeters (typically 1 - 10 mm), P _{M is} the metal vapor pressure.

The upper limit for the metal vapor is the excimer formation such as HgXe, HgAr, HgKr, for which already 133-2 666 Pa (1 - 20 Torr) Hg in e.g. 40 kPa (300 Torr) noble gas are sufficient. These excimers radiate at 140 - 220 nm and are also very efficient UV lamps. At higher mercury pressure, the Hg₂ excimer forms, which radiates at 235 nm.

The lower limit for the above relationship is about 1.33 Pa · mm (10⁻ Torr · mm).

In the silent discharge (dielectric barrier discharge) that forms, the electron energy distribution can be optimally adjusted by varying the gap width of the discharge space, pressure and / or temperature.

For very short-wave radiation, plate materials such as magnesium fluoride and calcium fluoride can also be used. Instead of a wire mesh, there can also be a transparent, electrically conductive layer, the layer of indium or tin oxide being used for visible light and a 5-10 nm (50-100 angstroms) thick gold layer for visible and UV light.

The luminescent layer 5 preferably consists of modern phosphors, i.e. phosphor doped with rare earths, which enable a quantum yield of up to 95% (cf. E. Kauer and E. Schnedler "Possibilities and Limits of Light Generation" in "Phys. Bl. 42 (1986), No. 5, p. 128 - 133, especially p. 132).

In order to practically double the usable radiation, the metal electrode 2 itself can be made of UV-reflecting material, e.g. Aluminum or be provided with a UV-reflective layer 8.

The embodiment according to FIG. 2 differs from that according to FIG. 1 only in the sequence of the layers. The luminescent layer 5 is on the surface of the plate 1 facing the discharge space 4 and is preferably protected against the discharge attack by a protective layer 9. It must be UV-transparent and e.g. made of magnesium fluoride (MgF₂) or Al₂O₃. Such layers are applied in a known manner by "sputtering" (ion sputtering).

Because in this embodiment the UV-visible light is converted before it passes through the dielectric (plate 1), it can be made of a "normal" translucent material, e.g. GlaS, exist.

3 emits visible light on both sides. The discharge space 4 is delimited on both sides by plates 4, 10 made of UV-transparent material, for example quartz or sapphire glass. Both outer surfaces are covered with a luminescent layer 5 or 11. The electrodes are formed by wire networks 6 and 12, each of which is connected to the alternating current source 7. Analogous to the embodiments according to FIGS. 1 and 2, the wire networks 6, 12 can also be formed by transparent electrically conductive layers, for example made of indium or tin oxide, for visible light and UV a 5-10 nm (50 - 100 angstroms) thick gold layer can be replaced.

Analogously to Fig. 2, there is also the possibility to attach the luminescent layers 5 and 11 on the discharge space 4 facing surfaces of the dielectric plates 1, 10 and to protect them with a protective layer 9 or 13 made of MgF₂ or Al₂0₃ against the discharge attack. As with Fig. 2, the dielectric, i.e. the plates 1, 10 are made of glass.

In Fig. 5 cylindrical high power radiator is shown schematically in cross section. A metal tube 14 (inner electrode) is surrounded at a distance (1-10 mm) concentrically by a dielectric tube 15; the outer surface of the tube 15 is provided with a luminescent layer 16. This is followed by an outer electrode in the form of a wire mesh 17. The AC power source 7 is connected to both electrodes 14, 17. The metal tube 14 is made of aluminum or is provided with an aluminum layer 18 which reflects UV light.

6, the luminescent layer 16 is provided on the inner wall of the tube 15 and covered against the discharge space 4 with a protective layer 19 made of MgF₂ or Al₂O₃.

If necessary, a cooling medium can be passed through the interior of the tube 14. The type and composition of filling gas and luminescent layer correspond to those of the previous exemplary embodiments.

The invention is particularly suitable for generating visible light. Depending on the composition of the filling gas and / or the luminescent layer, however, it is also possible to convert UV radiation of one wavelength into UV radiation of another wavelength.

Claims (7)

1. A high power radiator with a discharge chamber (4) filled with filling gas forming excimers under discharge conditions, defined by a first and a second wall, in which at least the first wall is formed by a first dielectric (1) which directly delimits the discharge chamber (4), which first dielectric (1) is provided on its surface, facing away from the discharge chamber(4), with a first electrode (6), and the second wall, delimiting the discharge chamber (4), is formed by a second electrode (2) or a second dielectric (10), which is provided with a further electrode (12) on its surface facing away from the discharge chamber (4), in which at least the first wall and the first electrode (5) belonging thereto are penetrable by radiation, and in which to operate the high power radiator an alternating current source is able to be connected to the said electrodes (6,2), characterised in that at least the first dielectric (1) is provided on its surface facing the discharge chamber (4) with a luminescent layer (5), which layer (5) is protected from the discharge attack by a UV-transparent protective layer (9,13).
2. A high power radiator with a discharge chamber (4), filled with filling gas forming excimers under discharge conditions, defined by a first and a second wall, in which at least the first wall is formed by a first dielectric (1) which directly delimits the discharge chamber (4), which first dielectric (1) is provided on its surface facing away from the discharge chamber (4) with a first electrode (6), and the second wall, delimiting the discharge chamber (4), is formed by a second electrode (2) or a second dielectric (10), which is provided with a further electrode (12) on its surface facing away form the discharge chamber (4), in which at least the first wall and the first electrode (5) belonging thereto are penetrable by radiation, and in which to operate the high power radiator, an alternating current source is able to be connected to the said electrodes (6,2), characterised in that at least the first dielectric (1) is provided with a luminescent layer (5) on its surface facing away from the discharge chamber (4).
3. A high power radiator according to one of Claims 1 or 2, characterised in that the electrode(s) are of wire networks (6) or are electrically conducting layers penetrable by radiation.
4. A high power radiator according to one of Claims 1 to 3, characterised in that the filling medium is mercury, nitrogen, selenium, deuterium or a mixture of these substances alone or with a noble gas.
5. A high power radiator according to Claim 4, characterised in that the filling gas contains mixtures of sulphur, zinc, arsenic, selenium, cadmium, iodine or mercury.
6. A high power radiator according to Claim 1 or 2, characterised in that the metal electrode (2) and the dielectric (1) are constructed in a plate shape and the metallic electrode (2) is arranged at a distance from the dielectric plate (1) by means of spacer pieces (3).
7. A high power radiator according to Claim 1 or 2, characterised in that the metal electrode (14) and the dielectric (15) are constructed in a tubular shape and form Detween them the discharge chamber (4).

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