RU2210140C2 - Method and device for producing optical radiation - Google Patents

Abstract

FIELD: optical radiation sources for microelectronics, medicine, lighting equipment production, and other industries. SUBSTANCE: electrons are produced due to their emission from cathode surface, and radiation is excited due to acceleration of electrons in gas gap by voltage between cathode and anode to energy higher than excitation energy of gas radiating levels but lower than self-maintained discharge firing voltage. Choosing voltage below gas ionization potential will make it possible to practically eliminate ionization so that essential part of inserted energy will be used for exciting radiating states of gas. Device implementing proposed method has chamber formed by radiating gas with at least two opposing electrodes, cathode and anode; at least electrode surface that carries electrodes or electrode surface and surface of electrodes proper are transparent for radiation. Novelty is that radiating gas pressure depends on electrode-to-electrode distance chosen in the order of electron track energy length. Cathode can be made in the form of thermionic cathode, photocathode, and autoemission cathode. EFFECT: enhanced brightness of optical radiation sources at low supply voltage. 10 cl, 1 dwg

Description

 Sources of optical radiation are widely used in industry. In particular, the vacuum ultraviolet radiation is used to etch the resist in microelectronics, to sterilize consumables, tools and equipment in medicine. Sources of visible radiation of various spectral composition are lighting devices and various kinds of information screens. One of the most common methods and sources of optical radiation created on their basis are gas-discharge sources. Visible fluorescent lamps, for example, realize gas discharge in a noble low-density gas with mercury additives, the ultraviolet radiation of which is converted by means of a phosphor into visible radiation, for example. The same principle applies to the manufacture of plasma displays, where the same type of discharge is used, but without mercury and at higher gas pressures. The breadth of applications makes it important to create an effective, compact source of optical radiation.

 Known methods for producing low-pressure optical radiation, used, for example, in fluorescent gas-discharge lamps [1], are most effective, but they have a number of disadvantages that cannot be overcome, in particular, mercury pollution arising from the destruction of the lamp.

 A known method of producing optical radiation and sources based on it, in which the electrons emitted by the cathode are accelerated in the vacuum gap under the action of a voltage applied to it and excite the optical radiation of the cathodoluminophore [2]. The main disadvantage of sources based on this method is the low cathodoluminescence efficiency, especially at low voltages.

 The known method, which consists in generating electrons and exciting radiation in the gas discharge gap, and a device for producing optical radiation, consisting of a chamber filled with a radiating gas, with at least two electrodes located opposite each other, a cathode and an anode, at least one of the electrode surfaces on which the electrode is located, or the electrode surface and the surface of the electrodes themselves are transparent to radiation [3]. Optical radiation arises as a result of gas excitation in a discharge. The disadvantage of this method and its implementing device is the low efficiency of the conversion of electrical energy into radiation.

 The aim of the invention is to increase the efficiency of conversion of electrical energy into optical radiation at low supply voltages.

 The proposed method for producing optical radiation consists in generating an electron flux due to their emission from the cathode surface and exciting the radiation by accelerating the electrons in the gas gap with a voltage applied between the cathode and anode to an energy higher than the excitation energy of the emitting gas levels, but lower than the self-discharge ignition voltage, and just below the voltage at which the ionization of the gas becomes significant and, therefore, there are limitations associated with the appearance of an ion in the gas gap in that when there are additional energy losses associated with the establishment of electrode layers, and reducing power resource because of the emerging cathode bombardment by energetic ions. In practice, ionization can be eliminated by choosing a voltage below the gas ionization potential.

 A device for producing optical radiation consists of a chamber filled with a radiating gas, for example, some noble gas, and at least two electrodes, a cathode and anode located opposite each other, at least one of the electrode surfaces on which the electrodes are located , or the electrode surface and the surface of the electrodes themselves are transparent to radiation. The gas pressure is determined by the choice of the distance between the electrodes of the order of the electron mean free path.

 The radiation obtained by the excitation of gas particles by electrons can be removed through transparent surfaces or converted into radiation of a different range due to the excitation of the emitting states of the photoluminophore. It is possible to place the photoluminophore on both the internal and external sides of the electrode surfaces, or electrode surfaces and the surfaces of the electrodes themselves.

 To obtain the high efficiency of this method, it is necessary to ensure the conditions under which a significant part of the energy input is used to excite the emitting states of the gas. This can be achieved by choosing the appropriate range of gas pressures and device dimensions.

 In order to create a radiation source with color parameters adjustable in each spatial point, the phosphor is applied in the form of RGB triads filling each individual point.

 In order to further control the current between the anode and cathode, at least one mesh electrode may be located.

 The necessary rate of electron emission by the cathode can be provided in various ways. In the case of a field emission cathode, the electric field at the cathode E must be sufficiently high for a significant field emission current to appear (E ~ 2-10 V / μm when using a cold emission film cathode).

 In the case of a thermionic cathode, the gas pressure and voltage at the discharge are limited by the condition not only of the absence of significant ionization of the gas, but also of the permissible amount of energy loss for heating the cathode and the inadmissibility of the phosphor overheating. To minimize these losses, it is necessary to use a low-temperature thermionic cathode located inside the chamber, as well as a gas with low thermal conductivity, such as xenon.

где γ_ph - коэффициент фотоэмиссии с катода, γ_ph≈0,1 в лучших фотокатодах;

- средняя энергия в электрон-вольтах, необходимая для образования одного фотона, η - кпд преобразования поступающей в устройство энергии в энергию оптического излучения, β - геометрический фактор. Например, в ксеноне при оптимальной величине приведенного электрического поля и β=2 получим η≈0.9,

и U>130 В.In the case of the photocathode, a limitation appears on the value of the minimum discharge voltage U. It must be chosen in such a way as to ensure sufficient photoemission of electrons from the cathode, provided that there is no ionization in the interelectrode gap:

where γ _ph is the coefficient of photoemission from the cathode, γ _ph ≈ 0.1 in the best photocathodes;

is the average energy in electron volts required for the formation of one photon, η is the efficiency of conversion of the energy supplied to the device into the energy of optical radiation, β is the geometric factor. For example, in xenon with an optimal magnitude of the reduced electric field and β = 2, we obtain η≈0.9,

and U> 130 V.

 The invention is illustrated by the drawing, which schematically shows a device for producing optical visible radiation, consisting of a power source 1, a gas filled chamber 2, a cathode 3, anode 4 and a phosphor 5. The cathode 3 should be made of a material that provides the highest electron emission efficiency .

 By selecting the operating parameters of the cathode, the electron current is maintained at a given level. These electrons drift under the action of a voltage applied between the cathode 3 and the anode 4, and cause excitation and ultraviolet radiation of the gas filling the chamber 2, followed by excitation of the phosphor 5.

 A constant or pulsed electrical voltage is applied from the power source 1. The operating voltage range can be from several to tens of volts. The minimum voltage is determined by the excitation threshold of the lower radiating state, in xenon it is 8.5 eV, and the maximum is determined by the condition for the appearance of an independent discharge.

 The brightness of the source increases with increasing voltage between the electrodes, and at a fixed voltage, with increasing electric field in the gap. In the case of a pulse voltage, the brightness can also be controlled by the pulse repetition rate and the change in pulse duration.

 An optical radiation device based on the proposed method will have a wide range of applications: from medicine to high technology, where light sources of different spectral ranges with controlled brightness are needed. It is possible to use the proposed optical radiation device in projectors, backlight lamps, LCD displays, displays, elements of light displays where high brightness is required, in compact and autonomous light sources where it is possible to use only low voltage. It can also be used in any application where it is important to have a large aperture radiation source.

Sources of information
1. Rokhlin G. N. Discharge light sources. Energoatomizdat, 1991, p. 392.

 2. Dobretsov L. N., Gamayunova M.V. Emission electronics. M .: Nauka, 1966, p. 245.

 3. Displays. Edited by Jacques Pankov. M.: Mir, 1982, pp. 123-126.

Claims (10)

 1. The method of obtaining optical radiation, which consists in the generation of electrons and subsequent excitation of radiation in a gas, characterized in that the generation of electrons is carried out by their emission from the surface of the cathode, and the excitation of radiation is carried out by accelerating electrons in the gas gap by the voltage between the cathode and the anode to energy higher than the excitation energy of the emitting gas levels, but lower than the ignition voltage of the self-discharge.  2. The method according to p. 1, characterized in that the generation of electrons and their subsequent acceleration in the gas gap is carried out by a voltage whose value is less than I / e, where I is the ionization potential of atoms or molecules of the gas, and e is the electron charge.  3. A device for producing optical radiation, consisting of a chamber filled with a radiating gas, with at least two electrodes located opposite each other, a cathode and an anode, with at least one of the electrode surfaces on which the electrodes are located, or the electrode surface and the surface of the electrodes themselves are transparent to radiation, characterized in that the pressure of the radiating gas is determined from the condition of choosing the distance between the electrodes of the order of the electron mean free path.  4. The device according to p. 3, characterized in that the cathode is made in the form of field emission cathode.  5. The device according to claim 4, characterized in that the field emission cathode is made in the form of a cold emission film cathode containing a substrate with a nanocrystalline diamond-carbon film emitter of electrons deposited on it.  6. The device according to p. 3, characterized in that the cathode is made in the form of a photocathode.  7. The device according to p. 3, characterized in that the cathode is made in the form of a thermal cathode.  8. The device according to p. 3, characterized in that at least one of the electrode surfaces on which the electrode is located, or the electrode surface and the surface of the electrodes themselves are coated with a phosphor layer from the outside or from the inside.  9. The device according to claim 3, characterized in that at least one of the electrode surfaces on which the electrodes are located, or the electrode surface and the surface of the electrodes themselves are coated on the outer or inner side with phosphor triads filling each individual point on the surface.  10. The device according to p. 3, characterized in that between the cathode and the anode is located at least one grid electrode.