JP3171004B2 - Dielectric barrier discharge lamp - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called dielectric barrier which forms excimer molecules by a dielectric barrier discharge used as an ultraviolet light source for a photochemical reaction and utilizes light emitted from the excimer molecules. It relates to improvement of a discharge lamp.

[0002]

2. Description of the Related Art As a technique related to the present invention, there is, for example, Japanese Patent Laid-Open Publication No. 2-7353, in which a discharge vessel is filled with a discharge gas for forming excimer molecules, and a dielectric material is filled. Excimer molecules are formed by barrier discharge (also known as ozonizer discharge or silent discharge; see the revised edition of “Discharge Handbook” published by the Institute of Electrical Engineers of Japan, reprinted on June 7, 2001, page 263), and light emitted from the excimer molecules is extracted. A radiator, a dielectric barrier discharge lamp, is described. It also describes that a mixed gas of krypton and chlorine is used as a discharge gas, and that light emitted from krypton chloride excimer molecules is used. The dielectric barrier discharge lamp as described above is useful because it has various features not found in conventional low-pressure mercury lamps and high-pressure arc discharge lamps. However, the above-mentioned dielectric barrier discharge lamps do not always have sufficient luminous efficiency, and the luminous efficiencies of the conventional dielectric barrier discharge krypton chloride excimer lamps are 4-7.
%, And the discharge is not always stable enough,
Further, there is a problem that the life is short.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a long-life dielectric barrier discharge lamp having high luminous efficiency and stable discharge, and in particular, a dielectric barrier discharge krypton chloride excimer lamp. .

[0004]

An object of the present invention is to provide an electrode for performing a dielectric barrier discharge, a discharge vessel filled with krypton gas and chlorine gas, and a krypton chloride excimer generated by the dielectric barrier discharge. In a dielectric barrier discharge lamp having a window member for extracting light emitted from molecules, a discharge sustaining voltage expressed in volts is V,
The problem is solved by defining the value of (V / d) / p in the range of 35 to 80, where d is the discharge gap length in cm and p is the pressure of the sealing gas in kilopascals. Further, the object of the present invention can be more effectively solved by defining the OH group content of the discharge vessel.

[0005]

We have an electrode for performing a dielectric barrier discharge, a discharge vessel filled with krypton gas and chlorine gas,
In a dielectric barrier discharge lamp having a window member for extracting light emitted from krypton chloride excimer molecules generated by the dielectric barrier discharge, the discharge gap length d (cm) and the pressure p (kilopascal) of the filling gas are variously changed. Then, the luminous efficiency and discharge stability were examined. The discharge gap length d in the present invention is the distance between the surfaces of the dielectric body sandwiching the discharge space when the discharge space structure is an electrode-dielectric-discharge space-dielectric-electrode. In the case of dielectric-discharge space-electrode, it is the distance between the inner surface of the dielectric and the inner surface of the electrode facing the discharge space. The pressure p of the sealing gas is a value at 25 ° C.

It is considered that the largest factor governing the luminous efficiency is the energy of electrons in the discharge plasma. Here, V / d is replaced with E, and E / p is called a converted electric field, but the energy of electrons strongly depends on the converted electric field E / p. Therefore, the luminous efficiency eventually depends on E / p. FIG. 2 shows the relationship between the converted electric field E / p and the luminous efficiency. Converted electric field E /
The discharge sustaining voltage V for obtaining p is the integrated value of the applied voltage and the current flowing through the lamp, described in page 112 of the “Ozonizer Handbook” published by Corona, edited by the Ozonizer Technical Committee of the Institute of Electrical Engineers of Japan, ie, The charge amount (symbol Q) was determined from measurement of a Lissajous figure. In FIG.
An example of a Lissajous diagram in which the horizontal axis indicates the applied voltage and the vertical axis indicates the charge amount is shown. Straight line AB and straight line CD are parallel, straight line BC
And a straight line AD is obtained in parallel, and a half of the voltage difference between the straight line AB and the straight line CD corresponds to the discharge sustaining voltage V. In some cases, the straight line AB and the straight line CD were slightly deviated from each other and became curved, but in this case, these curves were approximated by straight lines.

The luminous efficiency falls below 7% when the converted electric field E / p is smaller than 35, and the purpose of increasing the efficiency of the dielectric barrier discharge lamp cannot be obtained. When the converted electric field E / p exceeds 80, the luminous efficiency is considerably reduced,
Discharge became unstable and light output became unstable. That is,
By adjusting the discharge gap length d and the pressure p of the filling gas so that the converted electric field E / p is in the range of 35 to 80, the dielectric barrier discharge lamp whose luminous efficiency exceeds 7% and whose discharge is stable is obtained. can get. When E / p exceeded 70, the discharge / light output became somewhat unstable. That is,
Within the range of 35 to 70, the stability of discharge / light output is higher and the efficiency is good.

In a dielectric barrier discharge lamp, when an impurity gas, particularly a molecular gas such as hydrogen, oxygen, carbon monoxide, or water, is present, the rate of decrease in the ultraviolet output is reduced by the conventional arc discharge lamp or glow discharge lamp. It was found to be significantly larger than. Although this mechanism is not always clear, it is considered as follows. One of the features of the dielectric barrier discharge lamp is that it can generate ultraviolet light having a wavelength that cannot be obtained by a conventional arc discharge lamp with high efficiency. Generation of the characteristic ultraviolet rays is based on the following mechanism. That is, first, high-energy plasma that is not present in the conventional arc discharge lamp is generated by the dielectric barrier discharge. This plasma generates excimer molecules through various collision processes, and the excimer molecules emit characteristic ultraviolet rays. Therefore, impurity gases existing in the discharge space, particularly molecular gases such as hydrogen, oxygen, carbon monoxide, and water, not only directly destroy the excimer molecules, but also act on the various collision processes to produce the excimer molecules. And thus the UV output is reduced. That is, the dielectric barrier discharge lamp is more susceptible to the impurity gas than the conventional arc discharge lamp. In particular, in the case where chlorine is contained in the discharge gas, when oxygen, water, and the like are released, chlorine erosion of the quartz glass occurs, and the decrease in ultraviolet output becomes large. That is, in the dielectric barrier discharge lamp containing chlorine, the rate of decrease in the ultraviolet output due to the impure gas is remarkably large as compared with the conventional arc discharge lamp.

[0009] We have investigated the origin of the impure gases and have found that quartz glass used for the dielectric or extraction window member is the main emission source. In particular, when the OH group concentration in quartz is high, water is released more. It is considered that the ≡Si—OH bond (≡ represents a bond to oxygen) is broken by ultraviolet light and released as H 2 O. We investigated various quartz glasses and found that by using quartz having an OH group concentration of 10 ppm or less by weight, it was possible to prevent a decrease in the density of excimer molecules and thus a decrease in light output. . For example, a description will be given of a result of manufacturing a lamp using quartz glass having different OH group contents, setting a light output value 100 hours after lighting to 100, and measuring an excimer light attenuation rate from then to 1000 hours later. . Figure 1 shows the lamp used.
2 is a dielectric barrier discharge lamp shown in FIG. As a result, when the OH group concentration in the quartz exceeds 10 ppm, the optical attenuation
While it is as large as 0% to 60%, it is 3% at 10ppm or less.
It was found to be very small at 0% or less and extremely effective.
That is, when the value of E / P is in the range of 35 to 80,
When quartz glass having an OH group concentration of 10 ppm or less is used, a dielectric barrier discharge lamp with high efficiency and long life can be realized.

[0010] In order to perform a dielectric barrier discharge,
The life and the stability of discharge were examined by varying the concentration of chlorine gas charged in the discharge vessel. When the chlorine concentration was less than 0.1% by volume with respect to krypton , the chlorine was significantly consumed and the life was shortened. Further, when the chlorine concentration with respect to krypton exceeded 2% by volume, the discharge became extremely unstable. That is, when the concentration of chlorine to be charged is within the range of 0.1% to 2%,
A dielectric barrier discharge lamp having a long life and a very stable discharge is obtained. When the chlorine concentration is 0.2% to 1%, the above effect is remarkable, and a highly stable dielectric barrier discharge lamp can be obtained.

In addition, we investigated the stability of discharge by changing the filling pressure variously. As a result, it was found that when the sealing pressure exceeded 133 kilopascals, it was extremely difficult to turn on the light and the discharge became unstable. It has also been found that the discharge becomes unstable when the pressure is less than 13.3 kPa. Therefore, when the filling pressure is in the range of 13.3 kPa to 133 kPa, a dielectric barrier discharge lamp with stable discharge can be obtained. In particular, when the filling pressure is in the range of 20 to 70 kPa, the discharge is very stable, and a dielectric barrier discharge lamp with good lighting properties can be obtained.

[0012]

FIG. 1 is a schematic view of a coaxial cylindrical dielectric barrier discharge lamp according to a first embodiment of the present invention. Discharge vessel 1
Is made of quartz glass with a total length of about 150 mm and an outer diameter of 10.5 m
m, an inner tube 2 having a thickness of 1 mm and an outer tube 3 having an inner diameter of about 23.5 mm and a thickness of 1.5 mm are coaxially arranged to form a hollow cylinder. The inner tube 2 and the outer tube 3 also serve as dielectrics for dielectric barrier discharge, and are made of quartz glass having an OH group concentration of 5 ppm or less. In addition, electrodes 4 and 5 made of a metal net that transmits light are provided on the outer surfaces thereof. Therefore, the discharge gap length d in the discharge space 6 is 6.5 mm. 40 as discharge gas in the discharge space 6
Filled with a filling gas of kilopascal and lit with an input power of 0.2 Watt per square centimeter of surface area of the dielectric barrier discharge lamp using the high frequency power supply 7, the discharge sustaining voltage V becomes 1300V, that is, , The converted electric field E / p becomes 50 (V / (cm · kPa)), and the wavelength 22 radiated from the excimer molecule of krypton chloride.
From the wavelength of 205 nm having a maximum value at 2 nm to the wavelength of 230
Vacuum ultraviolet radiation in the nm range was emitted with a high efficiency of more than 7%. Even when the lamp was lit for a long time, almost no impurity gas was generated from the quartz glass, and a dielectric barrier discharge lamp having excellent life characteristics was obtained. Life time is 7
Assuming the time to maintain 0%, this lamp has been used for 1,
It maintains a high efficiency of about 5% even for 000 hours.

A coaxial cylindrical dielectric barrier discharge lamp according to a second embodiment of the present invention has a structure in which the electrode 4 in the first embodiment is changed to an aluminum film formed by vapor deposition. The aluminum film has a wavelength of 205 n having a maximum value at a wavelength of 222 nm emitted from krypton excimer molecules.
Ultraviolet light in the wavelength range from m to 230 nm is efficiently reflected, and a luminous efficiency of 5.5% or more can be obtained even after 1,000 hours of use, as in the lamp of the first embodiment.

FIG. 4 is a schematic diagram of a coaxial cylindrical dielectric barrier discharge lamp according to a third embodiment of the present invention. The discharge vessel 11 is made of quartz glass having a total length of about 150 mm, and has an outer diameter of 10 mm.
5 mm, inner tube 12 of 1 mm thickness, inner diameter of about 23.5 m
The outer tube 13 having a thickness of 1.5 mm and a thickness of 1.5 mm is coaxially arranged to form a hollow cylindrical discharge space 17. Inner tube 1
2. The outer tube 13 also serves as a dielectric for dielectric barrier discharge, and is made of quartz glass having an OH group concentration of 5 ppm or less. At one end of the outer tube 13, a light extraction window member 20 made of a quartz glass disk having an OH group concentration of 700 ppm or less,
It was provided by welding. At this time, since the light extraction window member 20 is not directly exposed to the discharge, the OH group concentration may be higher than that of the tube. A light reflecting plate 16 was provided at the other end of the inner tube 12 and the outer tube 13 for sealing. One end of the inner tube 12 which is close to the light extraction window member 20 is airtightly closed, and a closing portion 18 is provided.
Was formed. Further, the shortest distance X between the closed portion and the light extraction window member was set to 6.5 mm, which is the same as the discharge gap d of the hollow cylindrical discharge space. By depositing aluminum on the outer surface of the outer tube 13, the electrode 1 serving also as a light reflecting plate
5 were provided. The outer electrode 15 is provided so as to extend until it contacts the light extraction window member 20. Aluminum 14 was vapor-deposited on the outer surface of the inner tube 12 and the closed portion 18 on the side opposite to the discharge space to provide the electrode 14 also serving as a light reflection plate and the tip electrode 19 electrically connected to the electrode 14. . Although not shown, the aluminum electrode was covered with a protective film of boron nitride to mechanically and chemically protect the aluminum electrode. Discharge space 17 of discharge vessel
A krypton gas and a chlorine gas were sealed as discharge gases in the furnace.

When the dielectric barrier discharge lamp was turned on using a high-frequency, high-voltage power supply 21, first of all, E
/ P is optimum, and secondly, creeping discharge occurs on the inner surface and the outer surface of the light extraction window member 20 despite the fact that the electrode 15 is extended to contact the light extraction window member 20. And the light output is stable. Thirdly, since the light extraction window member 20 has a disk shape, it is possible to efficiently extract radiated light from the plasma generated near the inner surface 121 of the inner tube 12. done. As a result, a wavelength of 205 nm having a maximum value at a wavelength of 222 nm
, A UV light having a wavelength in the range of 230 nm can be radiated with high efficiency, and a dielectric barrier discharge lamp having high radiance, stable light output, and high safety can be obtained.

A fourth embodiment of the present invention is the same as the lamp of the first embodiment, except that the inner surface 211 of the inner tube 2 on the discharge space side has M
gF ₂ and LaF ₃ are alternately laminated in 25 layers, and the wavelength 222
In this example, a multilayer dielectric reflection film is formed to reflect light of nm and its vicinity. The wavelength of 222 nm is reflected by the multilayer dielectric reflection film and radiated outward from the outer tube 3. In this embodiment, the inner surface where the temperature rises is MgF ₂ -LaF ₃
Since the quartz glass is covered with the multilayer film and is not exposed to UV irradiation, the emission of OH from the inner tube is small, so that a long-life lamp is obtained.

Although all of the above examples are so-called dielectric barrier discharge ultraviolet light emitting lamps having no fluorescent material, it is also applicable to so-called dielectric barrier discharge fluorescent lamps having a fluorescent material provided in a discharge vessel. It is obvious.

[0018]

As described above, according to the present invention, a long-life dielectric barrier discharge lamp having high luminous efficiency and stable light output can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an embodiment of a dielectric barrier discharge lamp of the present invention.

FIG. 2 is an explanatory diagram of luminous efficiency.

FIG. 3 is an explanatory diagram of a Lissajous figure.

FIG. 4 is an explanatory view of another embodiment of the dielectric barrier discharge lamp of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Discharge container 2 Inner tube 3 Outer tube 4,5 Transparent electrode 6 Discharge space 7 Power supply 11 Discharge container 12 Inner tube 13 Outer tube 14,15 Electrode 16 Light reflector 17 Discharge space 18 Closed part 19 Tip electrode 20 Light extraction window member 21 Power supply

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasuo Onishi 1194, Sado, Bessho-cho, Himeji-shi, Hyogo Ushio Electric Co., Ltd. Inside Electric Co., Ltd. (72) Inventor Kunio Kasagi 1194 Sado, Bessho-cho, Himeji-shi, Hyogo Ushio Electric Co., Ltd.Examiner, Katsumi Enari (56) References JP-A-2-7353 (JP, A) JP JP-A-3-201358 (JP, A) JP-A-5-144413 (JP, A) JP-A-5-190152 (JP, A) JP-A-3-247522 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) H01J 65/04

Claims (5)

(57) [Claims] An electrode for performing a dielectric barrier discharge;
In a discharge vessel filled with krypton gas and chlorine gas, and a dielectric barrier discharge lamp having a window member for taking out light emitted from krypton chloride excimer molecules generated by the dielectric barrier discharge, a discharge sustaining voltage expressed in volts is obtained. When the discharge gap length in V and cm is d and the pressure of the sealing gas in kilopascal is p, (V
A dielectric barrier discharge lamp characterized in that the value of / d) / p is specified in the range of 35 to 80. 2. The discharge vessel has an OH group concentration of 10 ppm by weight.
2. The following quartz glass is used.
4. The dielectric barrier discharge lamp according to claim 1. 3. The dielectric barrier discharge lamp according to claim 1, wherein the chlorine concentration is 0.1% by volume or more and 2% by volume or less with respect to krypton . 4. The dielectric barrier discharge lamp according to claim 1, wherein the pressure of the filled gas is not less than 13.3 kPa and not more than 133 kPa. 5. The discharge vessel according to claim 1, wherein a film of a metal boride reflecting ultraviolet light is formed on an inner surface of the discharge vessel.
5. The dielectric barrier discharge lamp according to any one of items 1 to 4.