Cathode Ray Tube Ultraviolet Light Source

Abstract

1. A cathode ray tube ultraviolet light source comprising: a metal housing with a light-transmitting window; a heat sink disposed within the metal housing; a phosphor having a first surface and a second surface opposite the first surface, the second surface of the phosphor being in thermal contact with the heat sink; and an electron gun capable of generating an electron beam that impinges on the first surface of the phosphor, wherein light emitted from the second surface of the phosphor is directed through the light-transmitting window.

Description

[Background technology]

[0001] Ultraviolet (UV) light is electromagnetic radiation with wavelengths ranging from approximately 10 nanometers (nm) to 400 nm. The wavelength of UV light is shorter than that of visible light but longer than that of X-rays. Short wavelength UV light damages DNA and sterilizes surfaces it comes into contact with. For humans, suntan and sunburn are common effects of skin exposure to UV light, as well as an increased risk of skin cancer.

[0002] Due to atmospheric absorption, there are no natural sources of ultraviolet light below about 280 nm. Such natural sources include the UVC spectrum from 190 nm to 280 nm, which can be used for sterilization. UVC light is strongly absorbed by nucleic acids and can damage DNA and RNA. However, because mammalian DNA is confined to the cell nucleus, proteins in the cytoplasm effectively shield mammalian nuclear DNA from ultraviolet light below 230 nm. Therefore, a UVC source with a wavelength of 190 to 230 nm is effective in sterilizing surfaces without posing a risk to the surrounding human body. UV light below 190 nm will generate large amounts of ozone, which is known to have harmful effects on the human body.

[0003] This portion of the spectrum is also called the solar blind band because light below about 280 nm is absorbed by the atmosphere. UV light with wavelengths below 280 nm has limited penetration due to absorption by the atmosphere and is efficiently scattered by aerosols and molecules into the atmosphere. Due to these factors, light with wavelengths of 280 nm is also sometimes used for non-line-of-sight (NLOS) covert communication systems.

[0004] Low pressure mercury vapor lamps have been used to generate UVC light for germicidal purposes. Although such lamps are energy efficient and cost effective, they have problems with the use of mercury, which is an environmentally harmful substance and can be toxic to humans. In recent years, there has been a movement away from the use of low pressure mercury vapor lamps due to environmental and health concerns.

[0005] Light emitting diodes have also been used to generate UVC light. They do not contain mercury or other heavy metals, but are less efficient and have a relatively low capacity compared to other UVC light technologies.

[0006] Pulsed xenon lamps produce a broad spectrum of ultraviolet light, but are relatively expensive compared to other technologies. Because the ultraviolet light spectrum is so broad, the output of these lamps requires filters to attenuate wavelengths outside the 190-230 nm range.

[0007] These and other limitations in the prior art will become apparent to one of ordinary skill in the art upon reading the following description and reviewing the several figures in the drawings. Summary of the Invention

[0008] The cathode ray tube ultraviolet light source includes a metal housing with a light-transmitting window, a heat sink disposed within the metal housing, a phosphor having a first surface and a second surface opposite the first surface, the second surface of the phosphor being in thermal contact with the heat sink, and an electron gun capable of generating an electron beam that impinges on the first surface of the phosphor, the light emitted from the first surface of the phosphor being directed through the light-transmitting window. In a particular embodiment, a reflector is disposed within the metal housing, the reflector directing the light emitted from the second surface of the phosphor through the light-transmitting window.

[0009] A method of operating a cathode ray tube ultraviolet light source includes directing an electron beam onto a first surface of a phosphor, the phosphor having a second surface in thermal contact with a heat sink, and reflecting light emitted from the second surface of the phosphor through a light-transmitting window. In certain embodiments, the focal point of the electron beam and / or scanning of the electron beam over the first surface of the phosphor is used to vary the angular emission characteristics of the light emitted by the light source. In another embodiment, multiple phosphors are also used to vary the spectral characteristics of the emitted light.

[0010] An advantage of the various embodiments is that UVC light can be produced efficiently and cost-effectively without the use of hazardous and environmentally unfriendly heavy metals such as mercury.

[0011] These and other embodiments, features and advantages will become apparent to those skilled in the art upon reading the following description and reviewing the several figures in the drawings. [Brief description of the drawings]

[0012] Certain exemplary embodiments will now be described with reference to the drawings, in which like elements are designated with like reference numerals, and in which these exemplary embodiments are intended to illustrate, but not to limit, the present invention. The drawings include the following figures:

[0013] [Figure 1] FIG. 1 is a first exemplary embodiment of a cathode ray tube ultraviolet light source.

[0014] [Figure 1A] FIG. 1A is a perspective view of an example heat sink with a radiation shield.

[0015] [Diagram 2] FIG. 2 is a second exemplary embodiment of a cathode ray tube ultraviolet light source.

[0016] [Diagram 3] FIG. 3 is a third exemplary embodiment of a cathode ray tube ultraviolet light source.

[0017] [Figure 4] FIG. 4 is a fourth exemplary embodiment of a cathode ray tube ultraviolet light source.

[0018] [Diagram 5] FIG. 5 is a fifth exemplary embodiment of a cathode ray tube ultraviolet light source.

[0019] [Figure 6] FIG. 6 shows a first method of spectral tuning of a cathode ray tube ultraviolet light source using multiple phosphors. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] 1 is a first exemplary embodiment of a cathode ray tube ultraviolet light source 10, including a metal housing 12 with a light-transmitting window (e.g., a transparent window) 14, a heat sink 16, a phosphor 18 having a first surface 20 and a second surface 22 opposite the first surface 20, the phosphor 18 being in thermal contact with the heat sink 16, and an electron source or electron "gun" 24 capable of generating an electron beam 26 that impinges on the first surface 20 of the phosphor 18. Light 28 emitted from the phosphor first surface 20 is directed as emitted light 29 through the light-transmitting window 14 by a reflector 30 that includes a first surface 32, a second surface 34, and an opening 36 through which the electron beam 26 can pass. The light source is placed under a vacuum to extend the life of the light source components without impeding the electron beam 26.

[0021] In this first exemplary embodiment, the reflector 30 is parabolic and has a reflective aluminum film on a first surface 32. A getter material 38 is applied as a film on a second surface 34 of the reflector 30 and on the interior of the metal housing 12. By designing the mirrors so that the phosphor 18 is at the focal point of the reflector 30, the emitted ultraviolet light 29 is collimated as shown.

[0022] The metal housing 12 replaces the glass envelope of a typical cathode ray tube (CRT). It is advantageous in that it provides shielding against x-rays, for example, generated by the electron beam 26 striking the phosphor 18, and can be much thinner and more durable than a glass envelope. It is therefore safer in that it reduces the chance of the envelope imploding. The metal housing 12 is preferably at least partially coated with a non-conductive material, thereby reducing the chance of ground faults and providing a non-conductive surface for mounting additional circuitry and devices. For example, the metal housing 12 may include porcelain coated steel or polymer coated steel. Other metals and metal alloys are also suitable for use in the metal housing.

[0023] The optically transmissive window 14 can be conveniently made from vitreous quartz, which is readily available and reasonably priced. Other suitable materials include magnesium fluoride glass and calcium fluoride glass. For high-end applications, flat sapphire is also suitable. Preferably, the optically transmissive window has high transparency for wavelengths between 190 and 230 nm.

[0024] In this exemplary embodiment, the heat sink 16 is formed as a flange or frame for connecting the light transmissive window 14 to the remainder of the metal housing 12. Thus, a portion of the heat sink 16 extends outside the metal envelope 12 and a portion extends across the inside of the metal housing 12 in the form of a web of material, thereby providing support for the phosphor 18. Thus, heat generated by the electron beam 26 impinging on the phosphor 18 is transferred to the heat sink 16 and thermally conducted to the exterior of the metal housing 12 for dissipation by convection and radiation into the surrounding environment. The metal housing 12 also functions as a heat sink to remove excess heat from the light source 10.

[0025] FIG. 1A shows an example of a heat sink 16' and a secondary radiation shield 15'. The exemplary heat sink 16' is wheel-shaped and includes a central hub 17', three radial spokes 19', and a circular rim 21' with a number of heat fins 23'. The heat sink 16' is designed to be sandwiched between, for example, the metal housing 12 and the light-transmitting window 14 of FIG. 1, forming a high-pressure seal with an appropriate gasket (not shown). The radiation shield 15' fits into a recess 25' in the hub 17' and is preferably held in place by a thermally conductive adhesive and / or mechanically. Heat generated by the electron beam impinging on the phosphor (not shown in this figure) can be thermally conducted from the hub 17' through the radial arms 19' to the heat fins 23' of the rim 21. The radiation shield 15' is preferably made of a high-density metal such as molybdenum to enhance radiation shielding against high-energy emissions of the phosphor, such as X-rays.

[0026] 1, as previously described, a getter material 38 is preferably provided within the UV light source 10, for example, on a portion of the reflector 30 and at least a portion of the interior surface of the metal housing 12. The getter may be, for example, barium or a barium alloy, and is provided to remove gaseous contaminants from within the metal housing. Typically, the getter is applied by evaporatively heating a disk or ring of barium 40 by a resistive heater 42, or the like, after the light source 10 is placed under vacuum. Wires 44 for the resistive heater 42 may extend as pins through an end plug 46, made, for example, of glass. Other pins through the end plug 46 may be used to power and control the electron source 24 and / or other internal components of the UV light source 10.

[0027] Figure 2 is a second example embodiment of a cathode ray tube ultraviolet light source 10' similar to the first example light source 10, with like reference numerals indicating like components or elements. The primary difference between the embodiment of Figure 1 and the embodiment of Figure 2 is that the heat sink 16' includes a primary reflector portion 48 that focuses the emitted light 28 onto a secondary reflector 30' before passing through the window 14 as emitted light 29. This allows the diameter of the secondary reflector 30' to be smaller than that of the reflector 30.

[0028] FIG. 3 is a third exemplary embodiment of a cathode ray tube ultraviolet light source 10″ having off-axis emission of UV light 29, in which like reference numerals as used with respect to FIGS. 1 and 2 denote like components or elements. In this embodiment, the electron beam 26 of the electron gun 24 passes through an aperture 36″ of a reflective optic 30″ to impinge on the phosphor 18 of a heat sink 16″ forming part of a substantially metallic housing 12″. The heat sink 16″ has an area 50 that functions as a reflective optic to direct the ultraviolet light 28 emitted by the phosphor towards the reflective optic 30″ and from there out of a window 14″. It should be noted that the window 14″ may also function as a refractive optic to help collimate or shape the emitted light 29, which in this example is approximately perpendicular to the electron beam 26.

[0029] FIG. 4 is a fourth exemplary embodiment of a cathode ray tube ultraviolet light source 10''' with notable modifications to the electron gun 24'''' and curved path 26''' for the electron beam, with like reference numerals indicating like components in the previous embodiments. This fourth exemplary embodiment provides a compact electron source with a curved beam path, thereby reducing the overall size of the metal housing 12'''. In this embodiment, a series of focusing and deflecting devices bend the electron beam 26''' so that it passes through an aperture 36'''' in a reflector 30'''' at an angle that strikes the phosphor 18. The UV light emitted by the phosphor 18 is reflected by the reflector 30'''' through a transparent window 14'''' supported by a heat sink 16''' as emitted light 29.

[0030] FIG. 5 is a fifth exemplary embodiment of a cathode ray tube ultraviolet light source 10'''' having a metal housing 12'''' with a heat sink area 16''''. In this embodiment, an electron gun 24 generates an electron beam 26 that strikes the phosphor 18'''' at an angle such that light 28'''' is emitted through a window 14''''. Note that this is the first embodiment that does not use a reflector to redirect or collimate the light 28'''' emitted by the phosphor 18''''. However, this exemplary embodiment is simpler in design and may be less expensive to manufacture than certain of the other exemplary embodiments.

[0031] The emission wavelength of the light source 10 is determined by the phosphor material being irradiated. For example, AlN is a material that can emit UVC light at 210 nm. As another example, AlGaN can emit at a different (longer) wavelength. For AlGaN, the amount of gallium will determine the emission wavelength, which will increase with the amount of gallium added to the alloy. Furthermore, the emission wavelength can be changed by adding dopants to AlN or AlGaN. As yet another example, hexagonal boron nitride emits UVC light in the range of 210-220 nm.

[0032] Other phosphor materials that emit UV light between 190 and 280 nm include: >LuF3:Nd > Sr(Al,Mg) 12 O9:Pr >CaAl2Si2O7:Pr >YSiO5:Pr >Lu2SiO5:Pr >Ca2P2O7:Pr >LaPO4:Pr >(Lu,Y,Sc)3(Al,Ga)5O 12 >(Lu,Y,Sc)(Al,Ga)O3:Pr >(Y,Lu)3(Al,Ga)5O 12 :La >YBO3:Pr >Sr3Y2Si6O 18 :Pr

[0033] The preferred electron beam energy is 6,000 to 34,000 V. The beam current can be 1 μA to 5 mA. For many applications, a spot size of 0.1 to 1.0 mm diameter is suitable. For other applications, a spot size of 5 mm diameter or less may be suitable.

[0034] Because the human visual system cannot detect light with wavelengths less than about 360 nm, in some embodiments, phosphor material emitting in the wavelength range of about 450 nm to about 650 nm may be incorporated along with phosphor material emitting in the wavelength range of about 190 nm to about 280 nm to provide a visual indication that the device is operating.

[0035] 6 is a diagram illustrating a first method of spectral tuning of a cathode ray tube ultraviolet light source using multiple phosphors. In this example, four different phosphors are arranged in a 2x2 grid 70 and include material A, material B, material C, and material D. As seen in 70A, a "spirograph" type electron beam ("e-beam") pattern 72A on material A produces an emission spectrum 74A. As seen in 70B, a spirograph type e-beam pattern 72B on materials C and D produces a different emission spectrum 74B.

[0036] While various embodiments have been described using specific terms and devices, such description is for illustrative purposes only. The words used are words of description rather than of limitation. It is to be understood that changes and modifications may be made by those skilled in the art without departing from the spirit or scope of the various inventions as supported by the written disclosure and drawings. In addition, it is to be understood that aspects of the various other embodiments may be interchanged in whole or in part. It is therefore intended that the claims be construed in accordance with the true spirit and scope of the invention, without limitation or estoppel.

Claims

1. an evacuated metal housing provided with a light-transmitting window; a heat sink disposed within the metal housing; a getter material disposed within the metal housing; a phosphor having a first surface and a second surface opposite the first surface, the second surface of the phosphor being in thermal contact with the heat sink; an electron gun capable of generating an electron beam that impinges on the first surface of the phosphor; light emitted from the first surface of the phosphor is guided through the light-transmitting window; A cathode ray tube ultraviolet light source, wherein the emitted light has a wavelength in the range of 190 to 230 nm.

2. 2. The cathode ray tube ultraviolet light source of claim 1, further comprising a reflector disposed within the metal housing for directing light emitted from the first surface of the phosphor through the light-transmitting window.

3. 3. The cathode ray tube ultraviolet light source of claim 2, wherein the reflector collimates light directed through the light-transmitting window.

4. 4. The cathode ray tube ultraviolet light source according to claim 3, wherein the reflector is parabolic with a focal point on the phosphor.

5. 5. A cathode ray tube ultraviolet light source according to claim 4, wherein said reflector is provided with an opening for allowing said electron beam to pass therethrough.

6. 10. The cathode ray tube ultraviolet light source of claim 1, wherein the metal housing comprises a metal at least partially coated with a non-conductive material.

7. A vacuum metal housing provided with a light-transmitting window, the metal housing comprising a metal at least partially coated with a non-conductive material, forming a porcelain-coated steel; a heat sink disposed within the metal housing; a getter material disposed within the metal housing; a phosphor having a first surface and a second surface opposite the first surface, the second surface of the phosphor being in thermal contact with the heat sink; an electron gun capable of generating an electron beam that impinges on the first surface of the phosphor; The light emitted from the first surface of the phosphor is directed through the light-transmitting window.

8. 7. The cathode ray tube ultraviolet light source of claim 6, wherein the metal housing comprises steel coated with a polymer.

9. A vacuum metal housing having a light-transmitting window, the light-transmitting window comprising at least one of quartz, magnesium fluoride, calcium fluoride, and sapphire; a heat sink disposed within the metal housing; a getter material disposed within the metal housing; a phosphor having a first surface and a second surface opposite the first surface, the second surface of the phosphor being in thermal contact with the heat sink; an electron gun capable of generating an electron beam that impinges on the first surface of the phosphor; The light emitted from the first surface of the phosphor is directed through the light-transmitting window.

10. 2. The cathode ray tube ultraviolet light source of claim 1, wherein the heat sink comprises a portion of the metal housing adjacent the light-transmitting window.

11. A cathode ray tube ultraviolet light source as described in claim 2, wherein the getter material is provided on a portion of the reflector.

12. 2. The cathode ray tube ultraviolet light source of claim 1, wherein a portion of the heat sink adjacent to the phosphor is configured as a reflector.

13. 2. The cathode ray tube ultraviolet light source of claim 1, further comprising a focusing mechanism for said electron beam disposed within said metal housing.

14. An evacuated metal housing provided with a light-transmitting window; a heat sink disposed within the metal housing; a getter material disposed within the metal housing; a phosphor having a first surface and a second surface opposite the first surface, the second surface of the phosphor being in thermal contact with the heat sink; an electron gun capable of generating an electron beam that impinges on the first surface of the phosphor; a deflection mechanism for the electron beam disposed within the metal housing; The light emitted from the first surface of the phosphor is directed through the light-transmitting window.

15. 10. The cathode ray tube ultraviolet light source of claim 1, further comprising a resistive heater for evaporating a getter material disposed within said metal housing.

16. 2. The cathode ray tube ultraviolet light source of claim 1, wherein the phosphor is one of a plurality of phosphors in thermal contact with the heat sink.

17. 2. The cathode ray tube ultraviolet light source of claim 1, further comprising a non-conductive base having a plurality of conductive pins extending into said metal housing.

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