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    • 专利摘要:
    The present invention generally relates to an extraction structure for a UV lighting element. The present invention also relates to a UV lamp comprising such an extraction structure.For publication: Fig. 1
    公开号:SE1551295A1
    申请号:SE1551295
    申请日:2015-10-08
    公开日:2017-04-09
    发明作者:Tirén Jonas；Volkan Demir Hilmi
    申请人:
    IPC主号:
    专利说明:

    EXTRACTION STRUCTURE FOR A UV LAl/IPTECHNICAL FIELDThe present invention generally relates to an extraction structure for a UVlighting element. The present invention also relates to a UV lamp comprising such anextraction structure.
    BACKGROUND OF THE INVENTIONUltraviolet (UV) emitting lamps are used in numerous applications. They arefor example used for curing of resins (glues), for tanning, for disinfection, for fluorescence(in itself a field with many applications) and many more. These applications are wide spread.ln practice, UV lamps covering a range from 180- 400nm generally uses UV light sourcesbased on mercury (Hg) vapor, so called low pressure (LP), medium pressure (MP) and highpressure (HP) lamps, but other types are available such as for example Excimer lightsources.Light sources based on Light Emitting Diode (LED) and Field Emission Lamp(FEL) technology are emerging as alternatives. The main advantages with these technologiesare that they are completely free of mercury, well known as being environmentallydangerous, and that they turn on instantly (within milliseconds) something for example LPHg light sources tend not to do.ln forming a UV lamp, at least one ofthe above mentioned light sources areenclosed by an enclosing structure, the enclosing structure typically comprising a materialthat is transparent to UV light emitted by the UV light source. Many times, the UV lamp isalso covered by an additional protective structure, again made of a material that istransparent to the desired wavelengths. A common material used, especially forwavelengths between 200 and 300nm (in principle the UVC + UVB regions), is quartz,although a few other materials can be used as well. This wavelength range is especiallyinteresting for germicidal (disinfecting) applications since bacteria and other organismsgenerally are affected in this region but not by higher wavelengths. Other applications arefor example disinfection of air, sterilization of medical tools and surgery theaters, curing ofresins, tanning etc.
    Energy effectiveness is important for environmental reasons, lamp cost andlamp life time. For germicidal applications, the UVC energy delivered to the medium thatshall be disinfected is in principle determining to what extent the living bacteria arereduced. Thus for a water purification application, the UVC wattage and the flow of themedium together, will determine to what extent the disinfections performed. ln the case ofa fixed volume being treated, the wattage and time will determine the same. Typical rangesin practice is to reduce the number of living organisms in the order of 1:10 000 to 1: 10 000000.
    Larger disinfection systems may use several kilowatts to operate the largevolume flows (usually of water). ln these systems it is obvious that saving energy, i.e.improving the efficiency, becomes important. For smaller systems, such improvements maypredominantly be used to lower the system cost (i.e. by using smaller lamps to reach thedesired effect).
    A problem facing currently available UV lamps is the light extractionefficiency of the enclosing glass structure(s) of the lamps. The light extraction efficiency ofthe UV lamp may be defined as the ratio between the energy ofthe light that has escapedoutside the lamp and the energy ofthe light generated inside the lamp (or LED). The lightextraction efficiency ofthe UV lamp is always less than unity (one), i.e., portions of the lightgenerated ”inside” the UV lamp never reaches the external environment.
    With an urge to improve the energy efficiency ofthe UV lamp, there is thus isa great need to supply a solution to enhance the effectiveness for UV lamps by providing aneffective light extracting technology that may be manufactured and implemented easily andcost effectively. Such a solution may help to improve performance and save energy formany UV applications.
    SUMMARY OF THE INVENTIONAccording to an aspect ofthe invention, the above is at least partly alleviatedby an extraction structure for a UV light source, comprising a substrate at least partlytransparent to UV light, the substrate having a first and a second side, the first side of thesubstrate arranged to face the UV light source and to receive UV light emitted by the UVlight source, and a plurality of nanostructures arranged on at least one ofthe first and thesecond side of the substrate, the plurality of nanostructures configured to reduce anamount of UV light reflected by the substrate.
    The present invention is as mentioned above, based on the understandingthat to make effective lamps it is important that as much as possible ofthe light generatedinside the light source is also coming out ofthe same, as the part that does not is wastedenergy. By means of the invention, the efficiency of e.g. a resulting UV lamp comprising theextraction structure can be improved, using inexpensive methods. The present invention isapplicable to different geometries and has been evaluated on flat quartz substrate.
    For light passing through a substrate with higher refractive index nl into amedium with lower refractive index n; the light is refracted follow Snell's law:nl sin 61 = nz sin 62|fthe angle of incidence 61 is larger than the critical angle Gctotal reflection will occur. Thecritical angle is given by._ 7126C=s1n 1-711Therefore, photons that incident on the surface with an angle larger than the critical angle,are all reflected and are either entering the lamp inwards again and may keep beingreflected and are trapped inside the lamp. Secondly they may enter the glass envelope ofthe lamp, but will be reflected when impacting the outer glass wall and may be trappedinside the glass until they have lost the energy by e.g. absorption to the glass material. Thismeans that in a three dimensional aspect there is a cone (commonly referred to as the lightcone) in which incident light will escape.
    Also for angles lower than the critical angle, portions of the incident light arestill reflected. The reflectivity and the transmissivity are described by the Fresnel equations.
    Without going into details, the Fresnel equations describe the reflective and transmissiveportions of S-polarized and P-polarized components of the electrical fields (denotingpolarization perpendicular and parallel to the plane ofthe incident light wave, respectively).
    Antireflective coatings for visible light have been known for many decades.These kinds of layers form a stepwise adoption of the refractive indices between thetransparent material and its surrounding materials (air, gas, water, etc.) and in principle willact by widening the effective critical angle and reduce the amount of light that is reflectedand trapped and thus increase the throughput.ln accordance to the invention, enhanced light output is achieved by using aplurality of nanostructure arranged on at least one ofthe first and the second side of thesubstrate to reduce the reflectance of light emitted by the UV light source. Thenanostructures according to the invention may in some instances be referred to as e.g.nanorods, nanowires, nanotubes, nanopenciles, nanospikes, nanoneedles and nanofibres.
    The nanostructures differ from the antireflective coatings in that they, in oneembodiment, may also consist of separated nanostructures (thus not a continuous layer orfilm) and in that the nanostructures are very small, for example in the range of 5 - 1000 nm.
    These nanostructure may rely on increased scattering (e.g., via creating electromagneticand plasmonic resonances). However, when going to such nanostructures the aboveclassical models may not be enough, analytical models are not available and advancedcomputer simulations are used to study the effects. Typically such advanced models forlight-extraction efficiency in the UV region use the finite-difference time-domain (FDTD)techniques to solve the I/laxwell equations in the devices.
    The choice of material is crucial when designing the nanostructures. ln anembodiment, the nanostructures are at least partly transparent to the UV light and areselected to comprise at least one of CaFZ, BaFZ and SrFZ nanostructures. ln a preferredembodiment, the plurality of nanostructures comprises IVIgFZ nanostructures. Otherpossibilities are the use of SiOZ nanoparticles.ln regards to the substrate, the substrate is preferably selected to be formedfrom at least one of borosilicate glass, soda lime glass, sapphire and quartz (e.g. including(crystalline SiOZ, silica, fused quartz). Other materials e.g. also the substrate being IVIgFZ arealso possible.
    The exact target geometry of the nanostructures is depending on thesubstrate material, the medium outside the lamp and the desired wavelength that shouldbe amplified to an optimum. The nanostructures can be placed with some variation in theirgeometrical properties (height, length, shape, distance). Typical dimension are 5 - 100 nmin width and 10 - 5000 nm in height.ln practice, it is desirable to be able to coat a glass sleeve, window or similaras well as lamp envelopes with the mentioned nanostructures in a way that is fast, reliableand inexpensive. ln an embodiment, the plurality of nanostructures are at least partlyseparated from each other on at least one of the first and the second side of the substrate,for example by at least 1 nm.
    However, ordered structures need a process that for example uses some kindof lithography. Lithographic methods are generally feasible but expensive and are difficult touse on curved surfaces. Thus, in an alternative embodiment the nanostructures are insteadrandomly arranged at least one of the first and the second side of the substrate, still givinggood performance enhancements. ln either case it may be desirable to arrange thenanostructures on not only one side ofthe substrate. Accordingly, in an embodiment theplurality of nanostructures are arranged on both sides of the substrate.ln a possible embodiment of the invention, nanostructures are formed usinghydrothermal techniques. Alternatively, the nanostructures may be formed at the substrateusing sputtering or any other suitable technology for the formation of the above mentionednanostructures.
    Other ways to improve light extraction such as micro-lenses in the glassmaterial, lapping etc. are widely known and may be combined with the use of random UV-light extracting nanostructures.
    The extraction structure according to the invention may form part of a UVlamp, further comprising a UV light source. ln a possible embodiment, the UV lamp furthercomprises an electronic drive unit configured to operate the UV light source.
    The UV light source may comprise at least one of a mercury (Hg) vapor basedlight source, a field emission based UV light source (FEL), a UVC Light Emitting Diode (LED),and an Excimer lamp.lt should be understood that the UV light source may comprise e.g. a pluralityof LEDs and/or a combination of light sources based on different technologies to suit theapplication. That is, emerging technologies, such as field emission light sources (FEL) andUVC Light Emitting Diodes (LEDs), offer turn on times that are in the order of milliseconds,mainly governed by the electronic drive unit. UVC-LEDs are currently being developed, butare at this time exhibiting reportedly very short life times and very low energy efficiencies.Significant efforts are being used in order to improve this and will surely and eventually besuccessful. Field emission light sources may have life times in the order of 1000 - 6000hours depending on the desired power density and have been measured to reachefficiencies around 10%, albeit 3-5% in the UVC region.
    Further features of, and advantages with, the present invention will becomeapparent when studying the appended claims and the following description. The skilledaddressee realize that different features of the present invention may be combined tocreate embodiments other than those described in the following, without departing fromthe scope ofthe present invention.
    BRIEF DESCRIPTION OF THE DRAWINGSThe various aspects of the invention, including its particular features andadvantages, will be readily understood from the following detailed description and theaccompanying drawings, in which:Fig. la disclose an exemplary extraction structure according to a currentlypreferred embodiment of the invention, and Fig. lb shows an example of two different lightpaths, with and without a light extracting nano structure , in cross section , as depicted e.g.in fig. la; Fig. 2 is a diagram illustrating light output in the UV region with and withoutthe inventive solution;Fig. 3 shows a first exemplary embodiment of the inventive UV lamp;Fig. 4 shows a second exemplary embodiment of the inventive UV lamp, andFig. 5 shows a third exemplary embodiment of the inventive UV lamp;DETAILED DESCRIPTIONThe present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which currently preferred embodiments of theinvention are shown. This invention may, however, be embodied in many different formsand should not be construed as limited to the embodiments set forth herein; rather, theseembodiments are provided for thoroughness and completeness, and fully convey the scopeof the invention to the skilled addressee. Like reference characters refer to like elementsthroughout.
    Referring now to the drawings and to Fig. 1a in particular, there is illustratedan extraction structure 100 comprises a flat substrate 101, which may be the envelope of alamp or a protective cover or sleeve. A large number of randomly placed nanostructures102 are applied to the opposite side of the omnidirectional light source 103, however theymay alternatively be adopted to either one or both sides to the substrate 101. When a lightbeam 104 incidents on the surface of the substrate 101 it may be transmitted 105, andreflected 106 as indicated.
    Using ordinary ray optics, Snell's and Fresnel's equations, is useful tounderstand the classical physics as part of the invention. Fig. 1b shows a cross section of theflat substrate 101 and one single randomly placed nanostructure 102. The shape of thenanostructure is drawn in an ideal manner to facsilitate the understanding., and also, asunderstood, Fig. 1b is not to scale. On the upper section light is incident on the glasssubstrate with refractive index n=1.5 from air with a refractive index of n=1. Using thementioned equations the transmission part at this particular angle of incidence (70°, chosenarbitrarily to demonstrate the effect) is 69% - thus 31% is lost.ln the lower section the same ray optics is used, but the light will exit throughthe nanostructure 102. The transmission in this case is calculated to 83%. ln all this is 20%higher than in the case without the nanostructure. ln order to get an overall improvementthis behavior must be analyzed by integration ofthe two cases over the angle 0-90°. ltshould be noted that interference, phase shifts and so forth is not taken into account here,this example is to demonstrate the usefulness. ln addition nanostructures on both sides willfurther improve the transmission, as may the above mentioned plasmonic andelectromagnetic resonance effects.ln Fig. 2 the measured difference in light output in the UV region, using aquartz substrate with IVIgFZ nanostructures as indicated by Fig. 1a is shown. Line 202indicates the case where no nanostructures are used, and line 204 where IVIgFZnanostructures have been applied to the substrate. As can be seen a significantimprovement of around 15% at the Hg emission peak at approximately 254 nm is made.
    There are several ways to implement the nanostructures. A tubular lampenvelope is used here as an example as those are commonly used but other forms areequally relevant. For example flat structures (e.g. as used in swimming pools) would beequally relevant.ln a preferred embodiment, the nanostructures are placed on the surface ofthe inside of a tubular lamp envelope, the envelope confining a mercury (Hg) vapor actingas the light emitting medium. Alternatively the nanostructures may be placed on theoutside surface ofthe envelope or on both sides. This implementation is shown in Fig. 3.The first embodiment of the inventive UV lamp 300 comprises a UV transmissive envelope301 and is filled with Hg plasma 302. Nanostructures as discussed above, e.g. IVIgFZnanostructures 303, 304 (the latter indicated but not shown) may be attached randomly onthe inner surface or the outer surface ofthe envelope 301, or both. The transmission of theUV light 305 generated by the plasma 302 will thus be significantly increased.
    Yet another embodiment of the inventive UV lamp 400 is shown in Fig. 4,comprising a mercury based UV light source 401 (which may or may not containnanostructures as described in the second preferred embodiment above) is protected by asleeve 402, typically by quartz, which protects the surrounding media (water, air, etc.)should the lamp break, e.g. to prevent Hg to enter the surrounding media. ln this case it ispossible to place light extracting features, nanostructures 403, on the inside surface or theoutside surface ofthe protective sleeve, or both surfaces, depending on what theapplication requires.ln yet another implementation, as is shown in Fig. 5, the light is generated ina light powder, either by electron bombardment such as used in Field Emission Lamps or bya lower wavelength mercury plasma or in other ways (e.g. Excimer lamps. The lamp 500consists of an envelope 501 which is covered on the inside of a light generating material 502usually referred to as a ”phosphor” or a ”light powder”. Since this light generating material502 in general has a higher refractive index as compared to the light extracting materialsmentioned above, it is not advantageous to place the nanostructures between the lightgenerating layer 502 and the lamp envelope 501. ln this case the nanostructures 503 areadvantageously placed on the outside of the lamp envelope as previously discussed.Obviously the nanostructures 503 may be adapted to the surfaces of any transparent coverto UV lamps in order to increase the UV output of such an arrangement.ln case of using a FEL light source, the FEL light source will comprise a(centrally arranged, not shown) field emission cathode and an electrically conductive anodestructure, where the anode structure for example may be arranged adjacently to the lightgenerating material 502. During operation, a power supply will be configured to apply a highvoltage between the cathode and the anode such that electrons will be emitted from thecathode towards the anode. Once the electrons are received by the adjacently arrangedlight generating material 502, the light generating material 502 will emit photos, i.e. UVlight.
    The nanostructures may be deposited in several ways. Hydrothermaltechniques have been tested followed by a heat treatment. The shape of the nanostructuresmay be rectangular pillars, slanted pillars, spherical segments etc. Several of the possiblemethods to deposit such layers are by nature random, and all the resulting nanostructureswill not have the exact same dimensions but will be characterized by distribution. Theiraverage width is typical ranging from 5 - 500 nm and their average heights from 5 - 1500nm. The exact desired shape and dimension is e.g. determined by the exact wavelengthdistribution to be transmitted, the exact refractive indices of other materials involved aswell as the refractive index ofthe media surround the light source. The nanostructuresshould in general be separated from each other but may also form a continuous layerclosest to the surface ofthe substrate or envelope surface. The average separation ofthenanostructures should be in the range of 0.1 - 1000 nm. lt should be noted that, since thenanostructures are randomly placed, it is inevitable that some nanostructures will beattached to each other (i.e. not separated). Furthermore, the nanostructures maythemselves be composed by even smaller substructures.
    Sputtering may be an alternative approach as well as mechanical (spray,slurry, sedimentation, sol-gel) techniques, followed by heat treatment schemes to ensureadhesion and an optical interface. Other methods are equally possible and within scope ofthe inventionln summary, the present invention relates to an extraction structure for a UVlight source, comprising a substrate at least partly transparent to UV light, the substratehaving a first and a second side, the first side of the substrate arranged to face the UV lightsource and to receive UV light emitted by the UV light source, and a plurality ofnanostructures arranged on at least one ofthe first and the second side of the substrate,the plurality of nanostructures configured to reduce an amount of UV light reflected by thesubstrate.
    By means of the invention, the efficiency of e.g. a resulting UV lampcomprising the extraction structure can be improved, using inexpensive methods.
    Although the figures may show a specific order of method steps, the order ofthe steps may differ from what is depicted. Also two or more steps may be performedconcurrently or with partial concurrence. Additionally, even though the invention has beendescribed with reference to specific exemplifying embodiments thereof, many differentalterations, modifications and the like will become apparent for those skilled in the art. Forexample, it should be mentioned that light extraction in the visible region (400-800nm) isalso improved.
    Variations to the disclosed embodiments can be understood and effected bythe skilled addressee in practicing the claimed invention, from a study of the drawings, thedisclosure, and the appended claims. Furthermore, in the claims, the word "comprising"does not exclude other elements or steps, and the indefinite article "a" or "an" does notexclude a plurality.
    权利要求:
    Claims (17)
    [1] 1. An extraction structure for a UV light source, comprising: - a substrate at least partly transparent to UV light, the substrate having afirst and a second side, the first side ofthe substrate arranged to face the UV light sourceand to receive UV light emitted by the UV light source; and - a plurality of nanostructures arranged on at least one ofthe first and thesecond side of the substrate, the plurality of nanostructures configured to reduce an amount of UV light reflected by the substrate.
    [2] 2. The extraction structure according to claim 1, wherein the plurality of nanostructures are at least partly transparent to the UV light.
    [3] 3. The extraction structure according to any one of claims 1 and 2, wherein the plurality of nanostructures comprises at least one of CaFZ, BaFZ and SrFZ nanostructures.
    [4] 4. The extraction structure according to any one of claims 1 and 2, wherein the plurality of nanostructures comprises IVIgFZ nanostructures.
    [5] 5. The extraction structure according to claim any one ofthe preceding claims,wherein the plurality of nanostructures at least partly separated from each other on at least one of the first and the second side of the substrate.
    [6] 6. The extraction structure according to claim 6, wherein the plurality of nanostructures are separated from each other by at least 0.1 nm.
    [7] 7. The extraction structure according to claim any one ofthe preceding claims,wherein the plurality of nanostructures are randomly arranged at least one of the first and the second side ofthe substrate. 12
    [8] 8. The extraction structure according to claim any one of the preceding claims, wherein the plurality of nanostructures are arranged on both sides of the substrate.
    [9] 9. The extraction structure according to any one ofthe preceding claims,wherein the substrate comprises at least one of borosilicate glass, soda lime glass, sapphire IVIgFZ, and quartz.
    [10] 10. The extraction structure according to any one of the preceding claims,wherein the width ofthe plurality of nanostructures is between 5 - 500 nm and the length of the nanostructures is between 5 - 1500 nm.
    [11] 11. The extraction structure according to any one of the preceding claims, wherein the plurality of nanostructures are applied using hydrothermal techniques.
    [12] 12. A UV lamp, comprising:- a UV light source, and - an extraction structure according to any one ofthe preceding claims.
    [13] 13. The UV lamp according to claim 12, wherein the extraction structure is arranged as an envelope of the UV light source
    [14] 14. The UV lamp according to any one of claims 12 - 13, further comprising an electronic drive unit configured to operate the UV light source.
    [15] 15. The UV lamp according to any one of claims 12 - 14, wherein UV light sourcecomprises at least one of a mercury (Hg) vapor based light source, a field emission based UV light source (FEL), a UVC Light Emitting Diode (LED), and an Excimer lamp.
    [16] 16. The UV lamp according to any one of claims 12 - 15, wherein the first side ofthe substrate is provided with a light generating material and the second side of the substrate is provided with the plurality of nanostructures. 13
    [17] 17. The UV lamp according to claim 16, wherein the UV light source comprises ata field emission based UV light source (FEL) and the light generating material is at least oneof a phosphor material and a light powder, the light generating material configured to receive electrons and to emit UV light.
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    同族专利:
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    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
    SE1551295A|SE540064C2|2015-10-08|2015-10-08|Extraction structure for a uv lamp comprising individually applied nanostructures|SE1551295A| SE540064C2|2015-10-08|2015-10-08|Extraction structure for a uv lamp comprising individually applied nanostructures|
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    PCT/SE2016/050874| WO2017052450A1|2015-09-22|2016-09-19|Extraction structure for a uv lamp|
    US15/759,727| US10840051B2|2015-09-22|2016-09-19|Extraction structure for a UV lamp|
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