A PLASMA LIGHT SOURCE WITH LOW METAL HALIDE DOSE

Abstract

A low-dose, preferably unsaturated, fill of microwave excitable material (9), including at least two metal halides in a noble gas with an optional mercury buffer, is contained in a plasma crucible (2) to form a light emitting plasma therein.

Claims

1. A plasma light source comprising: a lucent envelope or a lucent crucible or fabrication having: a sealed void containing material excitable as a plasma, including at least two metal halides and an inert gas; the two metal halides together being provided in a concentration in use of less than 5.0×10.sup.−6 mol/cm of an inner wall-to-wall distance within the void with electrical energy being applied to excite the discharge with its electric field being in the direction of the wall-to-wall distance.

2. A plasma light source as claimed in claim 1, wherein the concentration of halides is such that the vapour within the void is unsaturated in use.

3. A plasma light source as claimed in claim 1, wherein there is no pool of excitable material in use.

4. A plasma light source as claimed in claim 1, wherein the lucent envelope is a lucent tube sealed at its ends to provide the sealed void, the length of the tube being in the direction of the wall-to-wall distance.

5. A plasma light source as claimed in claim 4, wherein the lucent envelope is provided within a central longitudinal bore in a separate lucent body.

6. A plasma light source as claimed in claim 5, wherein the lucent envelope is fixedly provided within the bore in the separate lucent body.

7. A plasma light source as claimed in claim 1, wherein the lucent crucible is a body of lucent material having a sealed, central longitudinal bore which provides the sealed void, the length of the bore being in the direction of the wall-to-wall distance.

8. A plasma light source as claimed in claim 5, wherein the crucibel or lucent body is enclosed by: an HF electromagnetic-wave-enclosing Faraday cage: surrounding the crucible on an outside and an end thereof and being at least partially light transmitting for light exit from the plasma crucible, the arrangement being such that light from a plasma in the void can pass through the plasma crucible and radiate from it via the cage.

9. A plasma light source as claimed in claim 1, wherein the inert gas is a noble gas or a mixture of noble gases, preferably chosen from: neon (Ne), argon (Ar), krypton (Kr), xenon (Xe).

10. A plasma light source as claimed in claim 1, wherein the fill sealed void further includes mercury as a buffer.

11. A plasma light source as claimed in claim 1, wherein the halides are chosen from chlorides, bromides and iodides and the lucent envelope or crucible is of quartz or ceramic.

12. A plasma light source as claimed in claim 1, wherein the halides are chosen from fluorides and the lucent envelope or crucible is ceramic material.

13. A plasma light source as claimed in claim 1, wherein the halides are chosen from the halides group consisting essentially of Al, As, Bi, Cd, Ga, Ge, In, Nb, Pb, Sb, Sn, Ti, Tl, V, and Zn.

14. A plasma light source as claimed in claim 1, wherein the total metal halide content of the plasma crucible is between 1.60×10.sup.−8 and 4.99×10.sup.−6 mol/cm of the inner wall-to-wall distance in the direction of the electric field of the electrical energy applied to excite the discharge.

15. A plasma light source as claimed in claim 14, wherein the total metal halide content is between 4.10×10.sup.−8 and 1.85×10.sup.−6 mol/cm.

16. A plasma light source as claimed in claim 1, wherein the inert gas content of the plasma crucible is between 1.00×10.sup.−8 and 3.25×10.sup.−6 mol/cm of the wall-to-wall distance in the direction of the electric field of the electrical energy applied to excite the discharge.

17. A plasma light source as claimed in claim 1, wherein the Hg buffer content of the plasma crucible is between 1.25×10.sup.−6 and 1.25×10.sup.−6 mol/cm of the wall-to-wall distance in the direction of the electric field of the electrical energy applied to excite the discharge.

18. A plasma light source as claimed in claim 17, wherein the Hg buffer content is between 1.2×10.sup.−5 and 7.5×10.sup.−5 mol/cm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] To help understanding of the invention, a specific embodiment thereof and variations will now be described by way of example and with reference to the accompanying drawing, in which:

[0043] FIG. 1 is a graph showing a broad spectrum of light produced by a bulb, such as used in U.S. Pat. No. 5,864,210;

[0044] FIG. 2 is a plot of solar radiation showing UV, visible and infra-red radiation both as it reaches the outer atmosphere and as it reaches sea level;

[0045] FIG. 3 is a perspective view of a lucent plasma crucible of the invention;

[0046] FIG. 4 is a cross-sectional view of a lucent envelope and body, such as used in WO 2014/045044, which can be used in a variant of the invention, the view is FIG. 5 of WO 2014/045044;

[0047] FIG. 5 is a similar cross-sectional view of another lucent envelope and body, such as used in WO 2015/189632, which can be used in another variant of the invention, the view is FIG. 1 of WO 2015/189632;

[0048] FIG. 6 is the output spectral power distribution between 300 nm to 550 nm for example A;

[0049] FIG. 7 is the output spectral power distribution between 300 nm to 1100 nm for example A;

[0050] FIG. 8 is the output spectral power distribution between 300 nm to 550 nm for example B;

[0051] FIG. 9 is the output spectral power distribution between 300 nm to 1100 nm for example B;

[0052] FIG. 10 is the output spectral power distribution between 300 nm to 550 nm for example C;

[0053] FIG. 11 is the output spectral power distribution between 300 nm to 1100 nm for example C;

[0054] FIG. 12 is the output spectral power distribution between 300 nm to 550 nm for example D;

[0055] FIG. 13 is the output spectral power distribution between 300 nm to 1100 nm for example D;

[0056] FIG. 14 is the output spectral power distribution between 300 nm to 550 nm for example E;

[0057] FIG. 15 is the output spectral power distribution between 300 nm to 1100 nm for example E;

[0058] FIG. 16 is the output spectral power distribution between 300 nm to 550 nm for example G;

[0059] FIG. 17 is the output spectral power distribution between 300 nm to 1100 nm for example G;

[0060] FIG. 18 is the output spectral power distribution between 300 nm to 550 nm for example H;

[0061] FIG. 19 is the output spectral power distribution between 300 nm to 1100 nm for example H.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0062] Referring to FIG. 3, a light source 1 to be powered by microwave energy is shown. It is similar to that described in our WO 2010/133822, whose abstract is quoted above. The source has a circularly cylindrical body 2 of quartz, forming a solid plasma envelope or crucible. Quartz is transparent to visible light and the outer surfaces of the quartz are polished. The crucible could be of translucent ceramic such as alumina. We use “lucent” to mean either transparent or translucent. The crucible has a length 1 and a diameter d. Aligned centrally is a void 3. It is short and of small diameter with respect to the dimensions of the crucible itself. The void is sealed by working of the material of the crucible or an additional piece of quartz. Methods of sealing are described in our International application WO 2010/094938.

[0063] A Faraday cage 4 surrounds the curved side surface 5 and one end surface 6 of the crucible. It can be of metallic mesh or reticular metallic sheet, such that the majority of light passing out of the crucible at these surfaces passes through the cage, whilst microwaves cannot. A band 7 of the cage extends around an end of a carrier 8 to which the cage is fastened, thereby carrying the crucible.

[0064] A fill of microwave excitable material 9, of metal halide with a mercury buffer in a noble gas, is contained to form a light emitting plasma therein An antenna 10 is arranged in a bore 11 extending within the plasma crucible for transmitting plasma-inducing microwave energy to the fill. The antenna has a connection 12 extending outside the plasma crucible for coupling to a source of microwave energy 14—the source being shown diagrammatically. Details of such a source and means for feeding microwave energy into the connection are described in International patent application WO 2010/128301.

[0065] More recently, as described in our WO 2014/045044 and WO 2015/189632, we have moved from a quartz crucible having an excitable material envelope secured within it to an envelope fixed or free within the crucible, which we have described as a lucent body as opposed to a crucible as such. The body has remained sized for microwave resonance.

[0066] FIG. 4 is a FIG. 5 of WO 2014/045044, whose abstract is as follows—albeit with altered reference numerals:

[0067] A crucible 101 for a LUWPL is formed from a wave guide body 102 having a central bore 103 through it. Received within the central bore is a drawn quartz tube 104, having its ends sealed, one 141 having been worked flat to be coplanar with one face 121 of body. The other end 142 has a vestigial tip 143. This is secured to the body at the orifice 122 of the bore in the other face 123 of the body. The securement is by means of ceramic adhesive compound 105.

[0068] FIG. 5 is a FIG. 1 of WO 2015/189632, whose abstract is as follows—albeit with altered reference numerals:

[0069] A light source 201 to be powered by microwave energy, having a dielectric body 203 or fabrication of material lucent for exit of light therefrom, a receptacle 222 within the dielectric body or fabrication, and a lucent microwave-enclosing Faraday cage 209 surrounding the dielectric body or fabrication. The dielectric body or fabrication within the Faraday cage forms at least part of a microwave resonant cavity. A sealed plasma enclosure 221 of lucent material within the receptacle 222 has a means—not visible—for locating the plasma enclosure within the receptacle with respect to the dielectric body or fabrication.

[0070] In the language of the present application, the “enclosure” and the “receptacle” of WO 2014/045044 are the present envelope and bore in the body.

[0071] For the avoidance of doubt, the lucent bodies and envelopes of WO 2014/045044 or WO 2015/189632 can be used with the fills of the present invention, as exemplified below.

[0072] Further for the avoidance of doubt, the wall-to-wall distance in the direction of the applied electric field is the internal distance in the length l in FIG. 1 and the equivalent directions and distance in the lucent bodies and envelopes of WO 2014/045044 or WO 2015/189632.

[0073] In the latter case, the envelope can be provided with means location means such as in that application, i.e. fused on lugs locating in recesses in the body from the bore. Alternatively the bore can be and the envelope can be plain with other location means provided.

[0074] In the following examples of lucent crucibles in which we have lit plasmas, we use quartz, which has a dielectric constant of 3.78, as the material of the lucent crucible and we operate at a frequency of 2,450 MHz.

[0075] At an input power of approximately 265 W, we have tested the performance of plasma crucibles containing mixtures of:

TABLE-US-00001 Example A mol/cm SbI.sub.3 1.99 × 10.sup.−7 GaBr.sub.3 3.20 × 10.sup.−7 AlI.sub.3 2.45 × 10.sup.−7 Total metal halides 7.55 × 10.sup.−7 Hg 3.69 × 10.sup.−5 Xe 1.87 × 10.sup.−8

TABLE-US-00002 Example B mol/cm SbI.sub.3 1.99 × 10.sup.−7 GaBr.sub.3 3.20 × 10.sup.−7 AlBr.sub.3 3.75 × 10.sup.−7 Total metal halides 8.94 × 10.sup.−7 Hg 3.69 × 10.sup.−5 Xe 1.87 × 10.sup.−8

TABLE-US-00003 Example C mol/cm SbI.sub.3 1.99 × 10.sup.−7 GaBr.sub.3 3.20 × 10.sup.−7 TlI 1.60 × 10.sup.−7 Total metal halides 6.69 × 10.sup.−7 Hg 3.69 × 10.sup.−5 Xe 1.87 × 10.sup.−8

TABLE-US-00004 Example D mol/cm SbI.sub.3 1.99 × 10.sup.−7 GaBr.sub.3 3.23 × 10.sup.−7 SnI.sub.2 1.34 × 10.sup.−7 Total metal halides 6.47 × 10.sup.−7 Hg 3.69 × 10.sup.−5 Xe 1.87 × 10.sup.−8

TABLE-US-00005 Example E mol/cm GaCl.sub.3 2.84 × 10.sup.−7 ZnCl.sub.2 4.40 × 10.sup.−7 Total metal halides 7.24 × 10.sup.−7 Hg 3.69 × 10.sup.−5 Xe 1.87 × 10.sup.−8

TABLE-US-00006 Example G mol/cm GaCl.sub.3 2.84 × 10.sup.−7 InCl 3.33 × 10.sup.−7 Total metal halides 6.17 × 10.sup.−7 Hg 3.69 × 10.sup.−5 Xe 1.87 × 10.sup.−8

TABLE-US-00007 Example H mol/cm GaBr.sub.3 8.10 × 10.sup.−7 SbI.sub.3 4.78 × 10.sup.−7 Total metal halides 1.29 × 10.sup.−6 Hg 3.69 × 10.sup.−5 Xe 1.87 × 10.sup.−8

[0076] Summary of output 300 to 550 nm and 300 to 1100 nm at capsule input power of 265 W

TABLE-US-00008 Output/W Output/W Example 300 to 550 nm 300 to 1100 nm Example A 57.9 77.3 Example B 57.5 72.9 Example C 61.9 84.2 Example D 60.3 81.5 Example E 61.6 79.6 Example G 63.4 76.7 Example H 62.0 81.8

TABLE-US-00009 Example Capsule Ratio Blue UV-A UV-B Blue + UV Rank by Example_G Example_H 81.81 0.76 Example_C 84.17 0.74 Example_E 79.64 0.77 Example_D 81.47 Example_A Example_B Rank by “Blue” Example_H 81.81 0.76 Example_G Example_D 81.47 0.74 Example_A Example_B 0.79 Example_E 0.77 Example_C 84.17 Rank by “UV-A” Example_G 76.70 Example_C 0.74 Example_D 81.47 0.74 Example_A 77.27 0.75 Example_B 72.89 0.79 Example_H 81.81 Example_E 0.77 Rank by “UV-B” Example_G 76.70 Example_E Example_B Example_A 77.27 Example_H 81.81 Example_D 81.47 Example_C Rank by “Blue + UV” Example_G 76.70 Example_H Example_D 81.47 Example_B Example_A 77.27 0.75 Example_E 0.77 Example_C 0.74 indicates data missing or illegible when filed

[0077] The resulting spectra are show in FIGS. 6 & 7 (Example A), FIGS. 8 & 9 (Example B), FIGS. 10 & 11 (Example C), FIGS. 12 & 13 (Example D), FIGS. 14 & 15 (Example E), FIGS. 16 & 17 (Example G), FIGS. 18 & 19 (Example H). (NB there is no example F).