Patent Description:
Many UV light sources emit light at various wavelengths within at least one relatively broad band of wavelengths. Some of the wavelengths are desirable, such as to disinfect the air and/or surfaces within an enclosed space, while other emitted wavelengths are undesirable for interfering with the disinfection or for other reasons. To provide an effective method of disinfection that utilizes these UV light sources, the UV light should be filtered to absorb any undesirable wavelengths and to transmit the desirable wavelengths of light which are needed to kill bacteria and viruses. The desirable wavelengths may be in the deep UV region of the electromagnetic spectrum, which is referred to herein as the region from <NUM> nanometers (nm) to <NUM>. Most known filters are designed for wavelength regions above <NUM>, and so cannot function to selectively transmit the desirable wavelengths in the deep UV region for disinfection.

One filter designed for the deep UV region is referred to as an interference filter, and is based on a multilayer stack of dielectric materials and metals which create a periodic modulation of the refractive index, resulting in reflection and transmission for certain wavelength ranges in the deep UV. The interference type of filter has several drawbacks. For example, the construction of the interference filter is complex and difficult. The materials are deposited at high temperature and low pressure in precise amounts in order to achieve precise periodic modulation of the refractive index. The interference filter is also known to suffer from relatively low transmission in the bandpass region, which defines the wavelengths permitted to pass through the filter, as well as high dependence on the angle of incidence of light that impinges on the filter. The low transmission in the bandpass region and the high dependence on the angle of incidence are undesirable properties because these properties reduce the amount or rate of desirable UV light that gets emitted from the light source, limiting the disinfection efficacy of the UV light per unit time or energy.

<CIT> states, in accordance with its abstract, that an optical filter is provided which comprises: an organic, solar blind filter dye; and a UV-transparent, non-scattering and chemically stable substrate. The substrate may be a UV-transparent nanoporous silica glass solid having pores that are substantially filled with a UV-transparent solvent, which has been selected to dissolve said dye and also to match the refractive index of the nanoporous silica glass solid. Alternatively, the substrate may be a UV-transparent inorganic salt compressed to form a solid body. Described are also methods of making these embodiments and an optical device comprising such an optical filter. The filter provides an efficient solar blind filter that is chemically and dimensionally stable.

<CIT> states, in accordance with its abstract, that document relates to an optical filter material made of doped quartz glass, which at a low dopant concentration exhibits spectral transmission as high as possible of at least <NUM>% cm-<NUM> for operating radiation of <NUM>, transmission as low as possible in the wave range below approximately <NUM>, and an edge wavelength λc within the wave range of <NUM> to <NUM>. It was found that this aim is achieved by doping comprising a gallium compound, which in the wave range below <NUM> has a maximum of an absorption band and thus determines the edge wave range λc.

<NPL> states, in accordance with its abstract, that materials with high deep-ultraviolet (DUV: λ < <NUM>) transmissions are important for many industrial applications. Fluoride single crystals and various glasses, pure SiO2, fluoride, phosphate, multicomponent silicates, and organic materials (PMMA), were investigated. The role of intrinsic absorption (UV edge) due to electron transitions between the main components, and extrincis absorption due to trace impurities, effect of polyvalent ions, redox behavior, and radiation-induced transmission loss were considered. The optical basicity and optical properties were used to order the materials.

<NPL>states, in accordance with its abstract, that the transmission spectra of aqueous solutions of transition metal ions have been measured. The use of a combination of different ions makes it possible to obtain filters of adjustable transmission peak and band-width. A computer method has been developed for fast calculation of optimized filters. Use of these filters with high-intensity sources is discussed.

<NPL> states, in accordance with its abstract, that the problems involved in the developement of ultraviolet transmission filters are discussed and criteria of stability, efficiency, and ease of preparation are applied to the materials suggested by previous workers. By the selection of the most suitable previous filters and the introduction of several new filters, a set of band pass filters for the <NUM>-3800A region of the ultraviolet is developed. These have a half-width of 200A and a maximum transmission of <NUM> percent, on the average. Quantitative spectrophotometric data are given for all components and filter combinations used. Suggestions are made for the further developement of these tools.

<NPL> states that some liquid transmission filters suitable for use in the ultraviolet are described.

<CIT> states, in accordance with its abstract, that the purpose is to reproduce the spectrum distribution of the natural sunshine with high accuracy by providing a liquid filter which is filled with a metal ion containing solution between a xenon lamp and a tested material mount means and adjusting the spectrum with metal ion density. Unnecessary ultraviolet components are removed by a UV filter from the irradiation light from the xenon lamp first and near infrared components are removed by the liquid filter to obtain artificial sunshine. Then the metal ion density of the filter is varied to vary its spectral transmissivity. Consequently, a spectrum distribution which is extremely close to that of the natural sunshine is obtained.

A need exists for a UV wavelength filter for deep UV light that offers selective filtering to enable a narrow range transmission (or bandpass) region, high transmission in the transmission region, has limited or no angular dependence of incident light, and is less complex and/or costly to manufacture than known filters, such as the interference filter described above. The UV wavelength filter should be selectively designed such that the narrow transmission region encompasses one or more desirable wavelengths and excludes undesirable wavelengths. The desirable wavelengths may be wavelengths associated with disinfection via killing or neutralizing bacteria and viruses.

With those needs in mind, a wavelength selective filter according to claim <NUM> is provided.

Further, a method for selectively filtering ultraviolet (UV) light according to claim <NUM> is provided.

In one or more embodiments, a light source is provided that includes a housing, an origin of light generation held by the housing, and a wavelength selective filter. The origin of light generation is configured to emit ultraviolet (UV) light. The wavelength selective filter is disposed in a light propagation path of the UV light emitted by the origin of light generation. The wavelength selective filter includes a filter material having a host matrix doped with metal ions. The filter material has a transmission region within a deep ultraviolet (UV) wavelength range. A portion of the UV light emitted by the origin of light generation having wavelengths within the transmission region is transmitted through the wavelength selective filter.

The foregoing summary, as well as the following detailed description of certain embodiments will be better understood when read in conjunction with the appended drawings. Further, references to "one embodiment" are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments "comprising" or "having" an element or a plurality of elements having a particular condition can include additional elements not having that condition.

Embodiments of the present disclosure provide a wavelength selective filter for UV light. The wavelength selective filter is designed to allow a selected narrow wavelength range of light in the deep UV region (e.g., about <NUM> to about <NUM>) of the electromagnetic spectrum to pass through the filter with high transmission, while absorbing other wavelengths with high optical density so that the other wavelengths cannot pass through the filter. In particular, the embodiments of the wavelength selective filter are useful for turning a broadband (deep) UV light source into a narrowband deep UV light source. Many deep UV light sources produce light at multiple wavelengths throughout the deep UV. For certain applications it is desirable to have the deep UV light source emit only within a narrow wavelength range. One such application is the use of UV light to sanitize and disinfect within an internal cabin of a vehicle, such as an aircraft, or a building, such as a hospital, theatre, commercial business, and the like. The wavelength selective filter can be designed to enable high transmission of wavelengths determined to have antibacterial and antiviral effects without harming human tissue.

The wavelength selective filter can be utilized as a bandpass filter (which absorbs (or blocks) light at wavelengths both above and below a transmission region, referred to as a bandpass region), a bandstop filter (which only absorbs light at wavelengths within the transmission region, referred to as a bandstop region), a shortpass filter (which only absorbs light at wavelengths above the transmission region), or a longpass filter (which only absorbs light at wavelengths below the transmission region). However, only the bandpass filter option falls within the scope of the appended claims. The term transmission region broadly refers to the range of wavelengths of light permitted to pass through the wavelength selective filter according to the embodiments described herein. Depending on the composition of the filter, the filter may be designed as a bandpass filter, a bandstop filter, a shortpass filter, or a longpass filter. References herein to terms such as bandpass region and/or passband region refer to the transmission region, and are intended to limit the application of the wavelength selective filter to use only as a bandpass filter, as defined by the independent claims.

The wavelength selective filter according to embodiments herein has a filter material that includes metal ion dopants dispersed within a transparent host matrix. The host matrix in some embodiments is solid, and in other embodiments is liquid. The metal ion dopants have distinguishable inherent absorption bands in the deep UV region, and define at least one transmission or bandpass region in which the metal ions do not absorb the light. The bandpass region is affected by the identities of the metal ion dopants present and the composition of the host matrix. For example, the bandpass region is tuned during the production of the wavelength selective filter by selecting different combinations of metal ions and optionally by selecting different compositions of the host matrix.

One or more technical effects of the wavelength selective filter described herein is that the filter is able to selectively transmit a narrow band of wavelengths in the deep UV region and block other wavelengths. As a result, the wavelength selective filter can be coupled to a broadband UV light source to cause the broadband UV light source to operate as a narrowband light source. Furthermore, the wavelength selective filter can be tuned such that the narrow band of wavelengths includes desirable wavelengths, such as wavelengths associated with sanitization and disinfection of air and surfaces without harming human tissue, and excludes undesirable wavelengths. The wavelength selective filter also desirably provides high transmission of the light in the bandpass region, which can improve disinfection efficiency relative to filters that permit less of the disinfecting wavelengths therethrough. The filter material may reduce or limit luminescence, and may have very limited, if any, sensitivity to the angle of incident light, such that the incident angle of light does not affect the intensity or amount of transmitted light through the filter. For these reasons, the wavelength selective filter described herein can outperform other known UV filtering devices. Another technical effect is that the production of the wavelength selective filter may be less complex and less costly than other known UV filtering devices. Furthermore, the optical density of the absorbing regions in the wavelength selective filter can be tuned during production by varying the concentration of metal ion dopants and/or changing the thickness of the filter material, without significant effect on transmission in the bandpass region. For comparison, in order to modify the optical density in an interference filter, additional layers must be added to the filter, which will inevitably reduce transmission in the bandpass region.

<FIG> illustrates a UV light source <NUM> or lamp according to an embodiment. the UV light source <NUM> includes an origin of light generation <NUM>, a housing <NUM>, and a wavelength selective filter <NUM>. The origin <NUM> is disposed within a cavity <NUM> that is defined by the housing <NUM> and may also be partially defined by the filter <NUM>. The cavity <NUM> may be filled with gas. The housing <NUM> may be reflective along an interior surface <NUM> thereof. The origin <NUM> may be a bulb, LED, or the like, that generates and emits UV light. The filter <NUM> is placed in a light propagation path from the origin <NUM> such that the UV light from the origin <NUM> directly or indirectly (via reflection) impinges upon an inside surface <NUM> of the filter <NUM>. The wavelength selective filter <NUM> allows some of the light rays <NUM> within a narrow wavelength transmission range (e.g., bandpass region) to transmit through the filter <NUM> and exit an outside surface <NUM> of the filter <NUM> into the surrounding environment. In an embodiment, the filter <NUM> is a bandpass filter that absorbs light rays <NUM> that have wavelengths outside of the narrow wavelength transmission region, such that those light rays <NUM> do not pass through the outside surface <NUM> into the surrounding environment. The wavelength selective filter <NUM> is designed to allow a selected narrow wavelength range of light in the deep UV region (e.g., rays <NUM>) to pass through the filter <NUM> with high transmission, while absorbing other wavelengths of light (e.g., rays <NUM>) with high optical density so that the absorbed light cannot pass through the filter <NUM>. The filter <NUM> is configured to be transparent to light in the selected wavelength range (e.g., bandpass region). The term transparent as used herein means that at least <NUM>% of the light rays or beams averaged over the selected wavelength transmission region are transmitted through the filter <NUM>. For example, the transmission of light having wavelengths within the transmission region may be less than <NUM>% but greater than <NUM>%, such as around <NUM>%, <NUM>%, or <NUM>%.

A specific application of the wavelength selective filter <NUM> is the conversion of a deep UV broadband light source into a narrowband light source. For example, the light source <NUM> may be a broadband deep UV light source, which has its output power centered at one wavelength with a broad distribution of output light around that center wavelength. The broadness of a peak is typically described by its full-width at half-maximum (FWHM). The FWHM of a broadband source in this example is greater than or equal to <NUM>. The light source <NUM> can represent or include an Excimer lamp such as KrCI or KrBr, a mercury vapor lamp, a deuterium lamp, a xenon lamp, a mercury xenon lamp, a UV LED or UV laser (which uses a phosphor in order to downshift the emission and output light in the deep UV region), an LED with an emission FWHM of <NUM> or more, or the like. Installing the wavelength selective filter <NUM> on the light source <NUM> in the propagation path of the emitted broadband light converts the light source <NUM> to a narrowband light source. The light that exits the filter <NUM> becomes narrowband in nature.

The effect of our filter on a source of this kind is demonstrated in <FIG>, which is a diagram showing how the wavelength selective filter can modify the output of a first broadband light source. <FIG> shows a first graph <NUM> depicting an unfiltered emission spectrum <NUM> of a broadband deep UV light source, a second graph <NUM> depicting a transmission spectrum <NUM> provided by a wavelength selective filter <NUM> according to an embodiment, and a third graph <NUM> depicting the resultant output spectrum <NUM> when the filter <NUM> is applied in the propagation path of the broadband deep UV light source. The resultant output spectrum <NUM> shows a relatively narrow bandpass region <NUM> that extends from about <NUM> to about <NUM>, which represents narrowband deep UV light transmission. The light source <NUM> shown in <FIG> with the filter <NUM> installed may emit UV light in the spectrum <NUM> shown in the third graph <NUM>.

In another example, the light source <NUM> can represent another type of broadband light source in which the unfiltered output light is distributed in multiple peaks centered at different wavelengths. <FIG> is a diagram showing how the wavelength selective filter can modify the output of a second broadband light source. <FIG> shows how the wavelength selective filter <NUM> can be placed in the propagation path of such a broadband light source to convert output light to narrowband. For example, <FIG> shows a first graph <NUM> depicting an unfiltered emission spectrum <NUM> of a broadband deep UV light source, the second graph <NUM> shown in <FIG> depicting the transmission spectrum <NUM> provided by the wavelength selective filter <NUM>, and a third graph <NUM> depicting the resultant output spectrum <NUM> when the filter <NUM> is applied in the propagation path of the broadband deep UV light source. The output spectrum <NUM> has a narrow bandpass region <NUM> that extends from about <NUM> to about <NUM>, which represents narrowband deep UV light transmission.

Referring back to <FIG>, the wavelength selective filter <NUM> includes a filter material <NUM>. The filter material <NUM> is disposed between the inside and outside surfaces <NUM>, <NUM> of the wavelength selective filter <NUM> and is the material that selectively filters the impinging light. <FIG> illustrates the filter material <NUM> according to an embodiment. The filter material <NUM> includes a host matrix <NUM> doped with metal ions <NUM>, specifically metal cations. The host matrix <NUM> is transparent. The metal ions <NUM> (also referred to as metal ion dopants) are dispersed throughout the host matrix <NUM>.

The metal ions <NUM> may function as the primary filtering agent. The metal ions <NUM> may have a valence electron configuration (n-<NUM>)d<NUM> ns<NUM>, where n represents the principal quantum number of the ion's valence shell, (n-<NUM>)d<NUM> indicates <NUM> electrons occupying the d orbitals having principal quantum number n-<NUM>, and ns<NUM> indicates that there are two electrons occupying the s orbital with quantum number n. The metal ions <NUM> absorb light within specific, inherent absorption ranges based on the elemental compositions. The specific metal ions <NUM> present in the filter material <NUM> may be selected based on the absorption ranges in order to control the absorption and bandpass regions of the filter <NUM>. Non-limiting examples of the metal ions <NUM> can include indium (In+), thallium (Tl+), tin (Sn<NUM>+), lead (Pb<NUM>+), and/or bismuth (Bi<NUM>+). The filter material <NUM> may include only a single element (e.g. In+) or a combination of multiple different elements (e.g. In+ and Sn<NUM>+) for the primary filtering agent. These ions are able to absorb light in certain regions of the deep UV, while being transparent (non-absorbing) in other regions.

<FIG> is a diagram showing that two metal ions with different respective absorbance spectrums are combined within the filter material to achieve regions of high and low absorbance, as defined by the independent claims. A first graph <NUM> depicts the absorbance spectrum <NUM> of a first metal ion (e.g., metal ion "A"), a second graph <NUM> depicts the absorbance spectrum <NUM> of a second metal ion (e.g., metal ion "B"), and a third graph <NUM> depicts the combined absorbance spectrum <NUM>. The combined absorbance spectrum <NUM> defines a passband region <NUM> that is shaped by the absorption ranges of the two metal ions.

In one embodiment, the two metal ions shown in <FIG> are combined within the same host matrix <NUM> (shown in <FIG>). In an alternative embodiment, the wavelength selective filter <NUM> may be defined by multiple layers of different filter materials in a stack such that the light propagation path travels through the stack. A first layer may include the first metal ion characterized in the first graph <NUM> dispersed within a host matrix (but not the second metal ion characterized in the second graph <NUM>). The second layer may include the second metal ion characterized in the second graph <NUM> dispersed within a host matrix (but not the first metal ion). As described herein, the host materials also affect the absorbance and transmission of the filter <NUM>. Thus, a single type of metal ion and combinations of multiple types will result in regions of high transparency and regions of low transparency within the deep UV, enabling the formation and tuning of the wavelength selective filter <NUM>. Absorbance (A) and transmission (T) are related through the equation A=<NUM>-log(T), which is the operating principle of the wavelength selective filter <NUM>. For example, layer 'A' might consist of a KBr host matrix and In+ metal ion. Layer 'B' might consist of a CaCl<NUM> host matrix with Sn<NUM>+ and Tl+ metal ions. The host matrices of the various layers may be the same or different. Stacking layer A and layer B either directly together, or perhaps with some deep UV transparent material in between, could produce desirable filtering properties. The number of layers could be two, three, four, or the like.

The host matrix <NUM> is solid in one or more embodiments and liquid in other embodiments. The host matrix <NUM> is transparent in the portion of the deep UV region where the filter <NUM> is designed to operate, i.e. it must at least be transparent in the bandpass region(s) of the filter <NUM>. In the embodiments in which the host matrix <NUM> is solid, the host matrix <NUM> can include various materials.

In a first solid host embodiment, the host matrix <NUM> includes an ionic salt containing a halogen anion and an alkali metal or alkaline earth metal cation. The halogen anion may be fluorine, chlorine, bromine, and/or iodine. The alkali metal may be lithium, sodium, potassium, rubidium, and/or cesium. The alkaline earth metal may be beryllium, magnesium, calcium, strontium, and/or barium. The filter material <NUM> according to a first non-limiting example, is an NaCl host matrix doped with indium (In+) metal ions. The filter material <NUM> according to a second non-limiting example, includes a first layer having an Nal host matrix doped with thallium metal ions and a second layer having a KBr host matrix doped with tin (Sn) metal ions.

In a second solid host embodiment, the host matrix <NUM> includes a metal oxide. The metal could be silicon, providing a silicon dioxide host material. For example, the silicon dioxide material could be fused silica, quartz, or fused quartz. In other examples, the metal could be aluminum, hafnium, and/or zirconium.

In a third solid host embodiment, the host matrix <NUM> includes a nonmetal oxide salt. The nonmetal element may be boron, and the host matrix <NUM> may be a glass formed from borax, i.e. Na<NUM>[B<NUM>O<NUM>(OH)<NUM>]·<NUM><NUM>O. In another example, the nonmetal element may be phosphorus, and the host matrix <NUM> may be a glass formed from NaH<NUM>PO<NUM>.

In a fourth solid host embodiment, the host matrix <NUM> includes a metal fluoride, with the metal being aluminum, lanthanum, or yttrium. In yet another embodiment, the host matrix <NUM> includes a metal nitride, such as aluminum nitride or AlGaN.

The metal ions <NUM> can be incorporated in the solid host matrix <NUM> during the production of the wavelength specific filter <NUM> in various ways. In multiple embodiments, the metal ions are initially prepared as a salt with a halogen anion. The salt is referred to as a halide salt of the filtering agent. The halogen anion could be fluorine, chlorine, bromine, or iodine. In a first halide salt embodiment, the solid host matrix is heated above the melting temperature of the host matrix material and the metal ions are incorporated within the melted host matrix. For example, the halide salt of the filtering agent is added in powder form into a container holding the host matrix material, either in bulk form or in powdered form. The container is heated up to or beyond the melting temperature of the host matrix material, allowing the metal ion(s) which are the filtering agent to disperse throughout the host matrix. The mixture is allowed to cool, resulting in the formation of a glassy or crystalline solid comprised mainly of the host matrix material but which also contains the metal ion(s) which are the filtering agent dispersed throughout the matrix. The size and shape of the container, along with the amount of material present in it, will determine the dimensions of the filter material that is produced.

In a second halide salt embodiment, the solid host matrix is not heated above the melting temperature. Instead, the metal ion(s) which are the primary filtering agent can diffuse into the host matrix while the host matrix is below its melting temperature. The halide salt of the filtering agent is added in powder form into a container holding the host matrix material, either in bulk form or in powdered form. The mixture is heated for an extended period of time at a temperature below the melting point of the host matrix material, allowing the metal ion(s) which are the primary filtering agent to diffuse into the host matrix. If the host matrix is in bulk form, then the final shape of the material does not change substantially after this process. If the host matrix is in powdered form, then the material will remain in powdered form after this process. The powdered form can then be mechanically pressed into the desired shape and size.

In a third halide salt embodiment, the halide salt of the filtering agent is co-deposited with the host matrix material during a chemical or physical vapor deposition process.

Other embodiments may forego the preparation of a halide salt of the filtering agent. In one such embodiment, the metal ions of the primary filtering agent are initially prepared in their elemental form and then co-deposited with the host matrix material during a chemical or physical vapor deposition process.

Optionally, a cover material can be applied on at least a portion of the filter material. The cover material may be UV-grade silica or another stable material that is transparent in the deep UV region. The cover material may be applied on the filter material to fully encapsulate the filter material, such as if the filter material is hygroscopic or degrades under ambient environmental conditions (such as alkali halide host matrix), or is a liquid. Another example of a possible cover material is a water-stable metal fluoride, such as MgF<NUM>.

In various other embodiments, the host matrix <NUM> can be a liquid solution. Suitable liquid host matrices for the wavelength selective filter <NUM> include water, acetonitrile, cyclohexane, diethyl ether, <NUM>,<NUM>-dioxane, ethanol, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, glycerol, heptane, hexadecane, hexane, methanol, methylcyclohexane, pentane, pentyl acetate, <NUM>-propanol, <NUM>-propanol, tetrahydrofuran, and <NUM>,<NUM>,<NUM>-trimethylpentane. The liquid must be contained by a non-permeable solid material (e.g., container) which is also transparent in the deep UV, to retain the liquid host matrix in place. The solid may be one of the materials described above, such as the cover material or one of the potential solid host matrix materials. In one embodiment, the liquid host matrix may be contained within a container formed by one of the solid host matrices mentioned above that also has metal ion(s) present in it, providing an additional layer of filtering. For example, the metal ions may be present in both the liquid host matrix and the transparent container of the liquid host matrix. Optionally, as described above, a first subset of one or more types of metal ions may be present in the liquid host matrix and a second subset of one or more different types of metal ions may be present in the solid host container.

In multiple embodiments, the liquid host matrix is water. The metal ions may be incorporated by dissolving the metal ions in the form of a salt into the water. The metal ion represents the cation, and the anion could be a halide, perchlorate, or some other compound. Optionally, the oxidation state of the metal ions can be stabilized by an acid or base additive that is added into the solution. In addition, or as an alternative, an electrical potential could be applied to the solution for stabilizing the oxidation state of the metal ions. The absorption regions of the metal ion(s) can be shifted by incorporating another anion in the form of a salt into the solution. It is also possible that a neutral compound, such as <NUM>-crown-<NUM> or ammonia, can act as a ligand to the metal ion, and thus shift the wavelength of absorption. The nature of the additive anion shifts of the absorption region of the metal ions to shorter or longer wavelengths. This enables tunability for the wavelength selective filter <NUM> in the liquid host embodiments.

Optionally, the liquid filter material <NUM> (e.g., solvent plus metal ions solution) can be used as a medium for cooling the light source <NUM>. For example, the bulb or other light generation origin <NUM> may be thermally connected to the liquid filter solution, which enables the solution to absorb heat emitted from the bulb <NUM>. The solvent of the liquid filter solution (such as, but not limited to, water) can serve as a cooling fluid that absorbs and dissipates heat, regulating the temperature of the light source <NUM> and improving energy efficiency. In a non-limiting embodiment, the liquid filter material <NUM> can be in direct physical contact with the light generation origin <NUM> (e.g., bulb) within the cavity <NUM> in <FIG>.

In other embodiments, the liquid host matrix is not water. For example, the halide salt of the metal ions may not be soluble in the non-aqueous liquid host. The metal ion may be prepared with an alternative anion which enhances its solubility in the non-aqueous liquid solvent. A surfactant may be added to facilitate dissolution of the metal ions. A supporting electrolyte with suitable solubility may be added to stabilize the metal ions. In addition, or as an alternative, an electrical potential could be applied to the solution for stabilizing the oxidation state of the metal ions. The filter <NUM> can be tuned by modifying or changing the anion of the metal ion salt to shift the region of absorption and the bandpass region of no absorption.

The composition of the host matrix, whether solid or liquid, can affect the regions of absorption of the metal ions which act as the primary filtering agent. For example, changing the host matrix material can result in shifting the absorption regions to longer or shorter wavelengths. <FIG> depicts a graph <NUM> showing an absorbance spectrum <NUM> of a first filter material. <FIG> depicts a graph <NUM> showing an absorbance spectrum <NUM> of a second filter material. The two graphs <NUM>, <NUM> show the same wavelength range. The two filter materials have the same types of metal ions. The only difference is that the first filter material has a different host matrix ("Matrix X") than the second filter material ("Matrix Y"). As shown in <FIG>, changing the host matrix from "X" to "Y" shifts the bandpass region <NUM> from between about <NUM> and about <NUM> to between about <NUM> and about <NUM>. The wavelength selective filter <NUM> described herein utilizes this operating principle or phenomenon to tune or adjust the bandpass (transparent) and bandstop (absorbing) regions of the filter <NUM>. For example, the identity of the metal ions present and the composition of the host matrix are selected to provide a filter material that has a desired narrowband bandpass region. Thus, if a desirable wavelength of UV light is <NUM>, the host matrix Y in <FIG> should be used to permit that designated wavelength through the filter <NUM>. On the other hand, if a desired wavelength is <NUM>, the host matrix X in <FIG> should be used.

The desired narrowband bandpass region may represent a narrow range of wavelengths that encompass one or more wavelengths associated with desirable properties, such as effective neutralization of bacteria and viruses without harming human tissue, even during prolonged exposure to the filtered UV light. For example, the filter <NUM> is tuned such that the emitted UV light exhibits a designated wavelength or narrow wavelength range that is safe (e.g., harmless) for human tissue. For example, the designated wavelength may be <NUM>. Thus, even if the UV light <NUM> in <FIG> persistently emits UV light onto passengers of a vehicle during a trip of the vehicle, such as during a flight of an aircraft, the passengers would be unharmed. The filter <NUM> absorbs or dissipates wavelengths outside of the designated wavelength or the narrow band such that emitted UV light in the field of illumination only consists of the designated narrowband range of wavelengths.

In a non-limiting example, the designated wavelength is <NUM>. It has been found that sanitizing UV light having a wavelength of <NUM> kills pathogens (such as viruses and bacteria), instead of inactivating pathogens. In contrast, UVC light at a wavelength of <NUM> may inactivate pathogens by interfering with their DNA, resulting in temporary inactivation, but may not kill the pathogens. Instead, the pathogen may be reactivated by exposure to ordinary white light at a reactivation rate of about <NUM>% per hour. As such, UVC light at a wavelength of <NUM> may be ineffective in illuminated areas, such as within an internal cabin of a vehicle. Moreover, UVC light at <NUM> is not recommended for human exposure because it may be able to penetrate human cells. In contrast, sanitizing UV light having a wavelength of <NUM> is safe for human exposure and kills pathogens. Further, the sanitizing UV light having a wavelength of <NUM> may be emitted at full power within one millisecond or less of the UV lamps <NUM> being activated (in contrast the UVC light having a wavelength of <NUM>, which may take seconds or even minutes to reach full power). In a non-limiting embodiment, the selective wavelength filter <NUM> is designed to have a narrow bandpass region that encompasses the desired wavelength <NUM>, and has a light blocking (e.g., absorbing) bandstop region that extends from about <NUM> to about <NUM>. Thus, the <NUM> UV light is transmitted through the filter <NUM> at a high transmittance while <NUM> UV light and other wavelengths in the bandstop region are absorbed and blocked.

The selective wavelength filter <NUM> may exhibit luminescence upon deep UV radiation, which could be undesirable in certain applications. This luminescence may emit light in the UV-B, UV-A, or visible spectral regions. Various modifications may be made to the selective wavelength filter <NUM> to reduce or quench luminescence, if desired. For example, luminescence can be downshifted so that the filter luminesces primarily in the visible spectrum (above <NUM>). To accomplish the downshifting, a transition metal ion, or some combination of them, is added to the host matrix, in addition to the metal ions which are the primary filtering agent. Upon UV radiation, the metal ions which serve as the primary filtering agent will absorb some of the incident light, and then transfer that excitation energy to the transition metal ions, which then release the excitation energy in the form of a visible photon. The metal ions could transfer the energy directly (e.g., short range interaction). Or, the UV filters could fluoresce and emit light, and the transition metal ions can reabsorb this light and re-emit downshifted light (e.g., long range interaction). The transition metal ion could be Mn<NUM>+, which emits around <NUM>. Alternatively, a transition metal with low radiative quantum yield could be chosen in order to reduce the overall amount of luminescence intensity. The emission of visible light could be used as an indicator to the operator of the invention that the filter <NUM> is under UV illumination. UV illumination is not visible to the human eye and it may not be obvious if a UV light source is On or Off. If the filter <NUM> is used on a UV light source, it will emit some visible radiation and then user of the UV light source will know that the UV light source is On.

In another embodiment, the luminescence may be quenched by operating the filter <NUM> at high temperatures. At high temperatures, the absorption and emission bands in the metal ions overlap and cause quenching of the optical emission. In addition, high temperatures promote the occupation of vibrationally excited modes, which tends to increase the rate of non-radiative decay. The heating element that provides the high temperature may be the UV light source itself. Alternatively, a discrete heating element may be intentionally installed on the sides of the filter <NUM> in order to heat the filter <NUM> without obstructing the path of light going from the UV source and out of the filter <NUM>.

<FIG> is a flow chart <NUM> of a method for selective filtering of UV light according to an embodiment. The method in various embodiments utilizes and/or provides one or more aspects discussed above in connection with the example wavelength selective filter <NUM> discussed herein. It may be noted that steps may be added or omitted in various embodiments, and/or various steps may be performed in a different order than shown in <FIG>.

At <NUM>, a host matrix is doped with metal ions to form a filter material that has a bandpass region within a deep UV range. The deep UV range may be between about <NUM> and about <NUM>, inclusive of the end values. The metal ions are dispersed within the host matrix as a result of the doping.

Optionally, doping the host matrix with the metal ions may include adding a salt that includes the metal ions into the host matrix while heating the host matrix.

Optionally, the host matrix is a liquid. For example, the doping at <NUM> may include dissolving a salt that includes the metal ions in a water-based solution that represents the host matrix. When the host matrix is a liquid, the method includes, at <NUM>, pouring the host matrix (pre-doping) and/or filter material (post-doping) into a container that is transparent to light in the deep UV range. In embodiments in which the host matrix is not liquid, the step <NUM> can be omitted.

At <NUM>, the filter material is mounted on a light source in a light propagation path of light emitted by a bulb of the light source. Once in place, at <NUM>, the filter material filters the light in the light propagation path. The filter material may allow transmission of a first portion of the light, having wavelengths within the bandpass region, through the filter material, while blocking transmission of a second portion of the light, having wavelengths outside of the bandpass region, through the filter material. Thus, the filter material enables emission of the first portion of the light through the filter material along the light propagation path, while absorbing or otherwise blocking the emission of the second portion of the light.

The following strategies apply to quench the luminescence in embodiments that utilize a solid host matrix. Non-radiative impurities are (intentionally) introduced into the host matrix to quench the luminescence of the metal ion(s) which serve as the primary filtering agent. The impurity may have the same charge as one of the components in the host matrix, but is a different size. If the host matrix is an alkali halide, the impurity is an alkali metal other than that which constitutes part of the host matrix, or the impurity is a halogen other than that which constitutes part of the host matrix. If the host matrix is an alkaline earth metal halide, the impurity is an alkaline earth metal other than that which constitutes part of the host matrix, or the impurity is a halogen other than that which constitutes part of the host matrix.

Alternatively, the impurity may have a different charge and size from the individual components of the host matrix. If the host matrix is an alkali halide, the impurity may be an alkaline earth metal. If the host matrix is an alkaline earth metal halide, the impurity may be an alkali metal.

In another embodiment, the impurity is an oxygen ion, oxygen gas, or a sulfide ion. The oxide or sulfide compound of the metal ion which serves as the primary filtering agent can be introduced into the host matrix in addition to the halide form of the metal ion, thereby introducing oxide or sulfide ions as impurities to the host matrix.

In another embodiment, the impurity is a metal oxide, or combination of metal oxides, such that the metal(s) would otherwise not be present in the host matrix.

The impurity is water, or some other molecule which is a liquid at room temperature in another embodiment. The impurity could be a derivative of water, e.g. the hydroxide ion (OH-).

The luminescence can be quenched by producing a phenomenon known as 'concentration quenching', which involves packing the metal ion(s) which serve as the primary filtering agent close together in the solid matrix. The metal ion(s) are used in sufficiently high concentration such that upon absorption of a UV photon, the metal ion is able to transfer its excitation energy to a nearby metal ion. With each successive energy transfer, the probability of encountering a defect in the host matrix increases. Upon encountering a defect, the excitation energy is dissipated without the emission of a photon. Optionally, the metal ion(s) may be intentionally forced to aggregate in the host matrix and form clusters with a high local density of metal ion. This creates the formation of defects in the host matrix, which facilitate quenching of the metal ion(s). Clustering may be induced by using a high concentration of metal ions and/or via the preparation method. The preparation method may include heating the host matrix, applying the metal ions to the host matrix, and then allowing the host matrix to cool slowly, allowing the metal ion(s) to diffuse toward each other as the matrix solidifies.

The following strategies apply for luminescence quenching when the metal ions are dissolved in a liquid matrix. In a first strategy, oxygen gas is intentionally dissolved in the liquid in order to quench the luminescence of the metal ions. The oxygen gas may be introduced into the liquid by using pure oxygen or by using a gaseous mixture which contains some oxygen gas, for example, ambient air. Or, oxygen may be allowed to diffuse into the liquid with a gas permeable separator in the enclosure around the liquid.

In a second strategy with a liquid host matrix, a liquid other than that which comprises the host matrix is mixed into the host matrix in order to quench the luminescence of the metal ions. A third strategy involves adding a surfactant to the host matrix in order to induce aggregation of the metal ions, resulting in concentration quenching.

As described herein, embodiments of the present disclosure provide a filter for selective filtering of deep UV light. The filter can be designed to transmit a narrow range of wavelengths encompassing one or more desired wavelengths, while blocking wavelengths in ranges adjacent to the narrow range. One or more of the desired wavelengths may be utilized to sanitize and disinfect surfaces, air, and people within an internal cabin of a vehicle without harming the people exposed to the UV light.

Further, the disclosure comprises the following embodiments related to a method for selectively filtering ultraviolet (UV) light:.

The method may also comprise the following feature:.

Further, the disclosure comprises the following embodiments related to a light source:.

The light source may comprise the following feature:.

While various spatial and directional terms, such as top, bottom, lower, mid, lateral, horizontal, vertical, front and the like can be used to describe embodiments of the present disclosure, it is understood that such terms are merely used with respect to the orientations shown in the drawings.

As used herein, value modifiers such as "about," "substantially," and "approximately" inserted before a numerical value indicate that the value can represent other values within a designated threshold range above and/or below the specified value, such as values within <NUM>%, <NUM>%, or <NUM>% of the specified value.

It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) can be used in combination with each other. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the various embodiments of the disclosure without departing from their scope. While the dimensions and types of materials described herein are intended to define the parameters of the various embodiments of the disclosure, the embodiments are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the various embodiments of the disclosure should, therefore, be determined with reference to the appended claims.

In the appended claims and the detailed description herein, the terms "including" and "in which" are used as the plain-English equivalents of the respective terms "comprising" and "wherein. " Moreover, the terms "first," "second," and "third," etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.

Claim 1:
A wavelength selective filter (<NUM>) comprising:
a filter material (<NUM>) including a host matrix (<NUM>) doped with metal ions (<NUM>), the filter material (<NUM>) having a transmission region (<NUM>, <NUM>) within a deep ultraviolet (UV) range such that UV light at wavelengths within the transmission region (<NUM>, <NUM>) is transmitted through the filter material (<NUM>) and UV light at wavelengths above and below the transmission region (<NUM>, <NUM>) are blocked within the deep UV range,
wherein the metal ions (<NUM>) comprise first metal ions having a first absorbance spectrum (<NUM>), and second metal ions having a second absorbance spectrum (<NUM>),
wherein a combined absorbance spectrum (<NUM>) defined by absorption ranges of the first metal ions and the second metal ions defines the transmission region (<NUM>, <NUM>),
wherein the deep UV range is between <NUM> and <NUM>, and
wherein the transmission region (<NUM>, <NUM>) has a width no greater than <NUM>.