Abstract:
A protective composition for use in an optoelectronic device, said protective composition comprises an organometallic getter capable of reacting with sulfur and/or selenium to form crystals containing a metal and sulfur and/or selenium. The protective composition may form a layer or an optical component. Advantageously, the protective composition effectively removes sulfide gas and results in the formation of stable crystals, and does not merely reduce the permeation rate of the gas. The resulting crystals typically have high transparency and low light absorption.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to materials and components for use in optoelectronic devices for protection against detrimental substances, and to light emitting arrangements comprising such materials and components. 
       BACKGROUND OF THE INVENTION 
       [0002]    The presence or formation of corrosive gas, such as H 2 S, is a problem in many instances. For example, in lighting arrangements using silver reflectors, the reaction of silver with sulfide gas present in the surrounding atmosphere leads to darkening of the silver and hence impaired function of the reflector. 
         [0003]    In some light emitting arrangements based on phosphor-converted light sources, sulfide gas may be released from sulfur-containing phosphor materials, typically phosphors based on sulfide materials, such as calcium sulfide (CaS), strontium sulfide (SrS), zinc sulfide (ZnS) or combinations thereof such as (Ca,Sr)S. Sulfide based phosphor are particularly sensitive to water and may react to form calcium or strontium hydroxide and sulfide gas. In addition to the darkening of silver reflectors, the release of H 2 S is also a problem because it is a toxic, flammable and foul-smelling gas. Furthermore, phosphors based on Ca or Sr selenide or sulfide may upon reaction with water also release small amounts of selenide gas, which is highly toxic. 
         [0004]    It would be desirable not only to prevent corrosive and/or toxic gas from reaching a silver layer, but also from escaping from a device. 
         [0005]    In order to prevent silver reflectors from darkening, protective layers have been proposed. However, such protective layers usually have poor scratch resistance, and the application of an insulating protective layer directly on a silver layer may also be undesirable since silver is often used as an electrical conductor and must be wired. Furthermore, making such layers without pinholes, through which gas may leak, is almost impossible. 
         [0006]    US 2009/0121180 suggests a protective composition comprising a silica-loaded silicone composition which can be used for encapsulating an optoelectronic device. The composition comprises siloxane-grafted silica particles and yields a cured silicone composition that is highly transparent and has low permeability to corrosive gases. However, low permeability does not solve the problem but only delays it. 
         [0007]    Hence, there is a need in the art for improvements regarding the prevention or reduction of detrimental effects of toxic and/or corrosive gases in lighting arrangements. 
       SUMMARY OF THE INVENTION 
       [0008]    It is an object of the present invention to overcome this problem, and to provide means to capture sulfur, suitable for use in an optoelectronic device. 
         [0009]    According to a first aspect of the invention, this and other objects are achieved by a protective composition for use in an optoelectronic device, which protective composition comprises an organometallic getter capable of reacting with sulfur and/or selenium to form crystals, typically nanocrystals, containing a metal and sulfur and/or selenium. 
         [0010]    Generally, the term “getter” denotes a reactive substance that interacts with a target substance to immobilize said target substance, by adsorption and/or chemical binding. The getter used in the present invention primarily acts by chemically binding the target substance. In the present invention, the target substance is typically sulfur/sulfide or selenium/selenide. The chemical interaction between the getter and the target substance may be, typically, ionic binding. 
         [0011]    The removal of sulfide gas by reaction with a getter is advantageous because the reaction results in the formation of stable crystals, and does not merely reduce the permeation rate of the gas. The resulting crystals typically have high transparency and low light absorption. In embodiments of the invention, the composition comprising the getter (before reaction with sulfide gas) may also have low light absorption, which makes the composition including the getter particularly suitable for use in optoelectronic devices. In addition, the composition is easy to produce using conventional technology. 
         [0012]    In embodiments of the invention the organometallic getter may comprise a metal selected from the group consisting of copper, iron, cadmium, lead, and zinc. These metals are capable of forming suitable crystal complexes with sulfur and/or selenium. In particular, the organometallic getter may comprise zinc. Zinc sulfide or zinc sulfide crystals have high transparency. Advantageously, zinc is a nontoxic material. 
         [0013]    In embodiments of the invention the organometallic getter may comprise an organic anion. The organic anion is typically complexed to the metal, typically a metal ion (e.g. zinc ion). 
         [0014]    In embodiments of the invention, the protective composition further comprises a matrix comprising a polymer. The matrix acts as a carrier for the organometallic getter. The organometallic getter may be chemically attached to the polymer, for example by means of the organic moiety (organic anion) which may be attached to the polymer as a side chain. For example, the polymer may comprise silicone or a silicone derivative, or an acrylate based polymer. 
         [0015]    In embodiments of the invention, the protective composition may further comprise a wavelength converting material. Hence, the composition may combine protection against sulfide or selenide gas with wavelength converting properties. Such embodiments may be particularly useful when the wavelength converting material itself comprises sulfur or selenium. 
         [0016]    In embodiments of the invention, the protective composition may be in the form of a layer. 
         [0017]    Hence, in another aspect, the invention provides a protective layer comprising the protective composition described herein. 
         [0018]    In a further aspect, the invention provides a layer assembly comprising a protective composition or a protective layer as described herein and a wavelength converting layer comprising a wavelength converting material. The wavelength converting material, provided as a separate layer or contained within the protective composition or the protective layer, may comprise sulfur and/or selenium. 
         [0019]    In another aspect, the invention provides an optical component comprising a protective composition as described herein. The optical component may thus combine optical functionality with protection against sulfide or selenide gas. 
         [0020]    In yet another aspect, the invention provides a light emitting arrangement comprising at least one solid state light source and a protective composition, a protective layer, or a layer assembly as described herein. By including the protective composition in a light emitting arrangement, sulfide gas can effectively be prevented both from damaging sensitive structures within the arrangement, as well as from leaking out to the exterior. 
         [0021]    In embodiments of the invention, the light emitting arrangement further comprises a silver layer at least partly covered by the protective composition or protective layer. The silver layer may be a silver reflector. Furthermore, in embodiments of the invention, a wavelength converting material may be arranged to receive light emitted by said solid state light source, wherein said wavelength converting material is at least partly covered by said protective layer. In some embodiments, the protective composition may be arranged between a silver layer and a wavelength converting layer. 
         [0022]    Lastly, the invention provides the use of an organometallic getter for capturing corrosive or toxic gas, in particular sulfide or selenide gas, released from a wavelength converting material. 
         [0023]    It is noted that the invention relates to all possible combinations of features recited in the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention. 
           [0025]      FIG. 1  illustrates the reaction scheme between H 2 S gas and an organometallic getter bound to a polymer matrix. 
           [0026]      FIG. 2  is a cross-sectional side view of a light emitting arrangement according to embodiments of the invention, comprising a thin layer of a protective composition. 
           [0027]      FIG. 3  is a cross-sectional side view of a light emitting arrangement according to embodiments of the invention, comprising a protective composition which may function as an encapsulant. 
           [0028]      FIG. 4  is a schematic side view of a light emitting arrangement according to embodiments of the invention, comprising a light source, a wavelength converting layer and a protective layer. 
           [0029]      FIG. 5  is a cross-sectional side view of a light emitting arrangement according to embodiments of the invention, comprising a plurality of light sources arranged in a reflective chamber, and a protective layer. 
           [0030]      FIG. 6  shows a side view of a bulb replacement lamp that may comprise a light emitting arrangement according to embodiments of the invention. 
           [0031]      FIG. 7  shows a perspective view of a luminaire that may comprise a light emitting arrangement according to embodiments of the invention. 
       
    
    
       [0032]    As illustrated in the figures, the sizes of layers and regions are exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of embodiments of the present invention. Like reference numerals refer to like elements throughout. 
       DETAILED DESCRIPTION 
       [0033]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person. 
         [0034]    The present invention is based on the realization that an organometallic getter capable of forming a crystal complex with sulfur can be used for capturing H 2 S gas. Thereby adverse effects of this gas can be reduced, in particular in light emitting arrangements. Advantageously the organometallic getter can also form a crystal complex with selenium and thereby also capture H 2 Se gas. Several metals can form crystal complexes with sulfur and/or selenium, even nanocrystals, that have no or only low light absorption. 
         [0035]    Examples of suitable metals of the organometallic getter include copper, iron, cadmium, lead and zinc. Zinc may be particularly advantageous since zinc sulfide nanoparticles have almost no light absorption and also because zinc is non-toxic. 
         [0036]    The organic moiety of the organometallic getter is an organic anion, typically the anion of an organic salt. Examples of suitable anions include acetonate anions, carboxylate anions, phthalate anions, and sulfonate anions that may form metal complexes (typically salts). Examples of such salts include zinc acetate, cadmium acetate, zinc benzoate, lead naphtalate, iron(II)acetate, ferric acetonate and zinc trifluoromethane sulfonate. 
         [0037]    In general, the reaction between an organometallic getter including a metal ion and sulfide gas may be as follows (Equation I): 
         [0000]      H 2 S+MX→MS+XH 2    Equation I
 
         [0000]    in which M represents the metal atom of the organometallic getter and X represents the organic anions of the organometallic getter. Depending on the oxidation states of the metal and the organic anion Formula I may have to be adapted with respect to the relative amounts of M, X and H 2 S. The corresponding equation for the reaction between the organometallic getter and selenide gas may be as follows (Equation II): 
         [0000]      H 2 Se+MX→MSe+XH 2    Equation II
 
         [0000]    in which M represents the metal atom of the organometallic getter and X represents the organic anions of the organometallic getter. Depending on the oxidation states of the metal and the organic anion Formula I may have to be adapted with respect to the relative amounts of M, X and H 2  Se. 
         [0038]    As an example, the reaction between an organometallic getter comprising zinc(II) and H 2 S may be as follows (Equation Ia): 
         [0000]      H 2 S+ZnX→ZnS+XH 2    Equation Ia
 
         [0000]    in which X represents the organic anions of the organometallic getter. The corresponding reaction between zinc and selenide gas may be as follows (Equation IIa): 
         [0000]      H 2 Se+ZnX→ZnSe+XH 2    Equation IIa
 
         [0000]    in which X represents the organic anions of the organometallic getter. 
         [0039]    For instance, the reaction between zinc acetate as the organometallic getter and H 2 S is as follows (Equation Ib): 
         [0000]      H 2 S+Zn(CH 3 CO 2 ) 2 →ZnS+(CH 3 CHO 2 ) 2    Equation Ib.
 
         [0040]    The metal sulfide or metal selenide reaction product formed by reaction of the organometallic getter with sulfide gas or selenide gas, respectively, may be present in the form of crystals, for example nanocrystals. Advantageously, such crystals, in particular nanocrystals, may have high transparency and may have low or no light absorption. Nanocrystals are particularly advantageous as the absorption band shifts to lower wavelengths with decreasing particle size. 
         [0041]    According to embodiments of the invention, the reaction between an organometallic getter comprising cadmium and H 2 S gas may be as outlined in  FIG. 1 . Before reaction with H 2 S, the organometallic getter comprises cadmium benzoate bound to an acrylate polymer network. Upon reaction with H 2 S, cadmium sulfide (CdS) nanocrystals are formed, surrounded by the polymer matrix containing benzoic acid linked to the acrylate polymer network. 
         [0042]    The organometallic getter is typically incorporated in a carrier matrix, which may be a polymer matrix or a siloxane-based matrix. Suitably the matrix material may be capable of forming a complex with the metal ion of the organometallic getter. Examples of matrix materials contemplated for use in embodiments of the present invention include polysiloxane-based materials, such as poly(dimethyl siloxane) and derivatives thereof. A polysiloxane-based material may be crosslinked. For instance, the following material are capable of forming complexes with zinc and are therefore advantageously used in combination with an organometallic getter comprising zinc: carboxydecyldimethyl terminated poly(dimethyl siloxane), carboxypropyl terminated poly(dimethyl siloxane), trimethyl silylpropionic acid, 1,3-bis(3-carboxypropyl)tetramethyldisiloxane, and 2-(trimethyl silyl)acetic acic. 
         [0043]    Typically, the matrix material may be a material that can be formed in to a layer, optionally a self-supporting sheet. A composition of matrix material, including the organometallic getter, can be applied onto a surface, such as the surface of an LED or the surface of a wavelength converting element or layer, to form a coating layer using conventional surface coating techniques. Alternatively, the composition can be extruded, injection molded or compression molded. The composition may form a functional optical component such as a dome, a lens or a collimator optionally in direct contact with an LED. Optionally the composition typically in the form of a layer may be combined with one or more other functional layers such as a wavelength converting layer or a reflective layer, thus forming a layer assembly. For example, the composition comprising the organometallic getter and the matrix may be applied, e.g. by screen printing, or other conventional coating technique on top of a wavelength converting layer or a reflective layer. In the case of packaged LEDs, the matrix carrying the organometallic getter can be brought in liquid form (typically, not completely polymerized) into the cup containing the LEDs, followed by curing of the matrix by polymerization and/or cross-linking. 
         [0044]    The organometallic getter, optionally incorporated in a carrier matrix, may be provided as a protective layer covering or encapsulating at least a part of or a component of a light emitting arrangement.  FIG. 2  schematically illustrates a light emitting arrangement comprising a protective layer according to an embodiment of the invention. In  FIG. 2 , which is a cross-sectional side view, is shown a light emitting diode (LED) package  200  comprising an LED  201  arranged in a reflective cup  202 . The bottom of the reflective cup, on which the LED is mounted, has a reflective silver layer  203 . The reflective silver layer  203  and the LED  201  are covered with a thin protective layer  204  of substantially uniform thickness, comprising an organometallic getter typically distributed in a carrier matrix as described above. The protective layer may be transparent or translucent. The organometallic getter of the protective layer  204  is capable of capturing H 2 S gas and/or H 2 Se gas released from the wavelength converting layer or otherwise present within the light emitting arrangement. 
         [0045]      FIG. 3  shows another embodiment of a light emitting arrangement, similar to the embodiment shown in  FIG. 2  but instead of the thin protective layer  204  having a thicker layer  205  of the protective composition filling the interior of the reflective cup  202 , thus functioning as an encapsulant. 
         [0046]    It is contemplated that in a so-called chip-on-board package, a plurality of LED arranged on a printed circuit board mounted on the reflective layer (instead of the single LED  201  shown in  FIGS. 1 and 2 ) may be covered with a protective layer of suitable thickness, uniform or non-uniform. 
         [0047]    A composition comprising the organometallic getter, typically incorporated in a matrix, may further comprise at least one wavelength converting material, commonly known as a phosphor. Such a composition may thus form a protective layer which also has wavelength converting properties. Additionally or alternatively, a composition comprising the organometallic getter may comprise scattering element, for example scattering particles such as particles of Al 2 O 3  or TiO 2 . In general, the wavelength converting material used in embodiments of the present invention may be an inorganic wavelength converting material or an organic wavelength converting material. Examples of inorganic wavelength converting materials may include, but are not limited to, cerium (Ce) doped yttrium aluminum garnet (Y 3 Al 5 O 12 :Ce 3+ , also referred to as YAG:Ce or Ce doped YAG) or lutetium aluminum garnet (LuAG, Lu 3 Al 5 O 12 ), α-SiAlON:Eu 2+  (yellow), and M 2 Si 5 N 8 :Eu 2+  (red) wherein M is at least one element selected from calcium Ca, Sr and Ba. Furthermore, a part of the aluminum of YAG:Ce may be substituted with gadolinium (Gd) or gallium (Ga), wherein more Gd results in a red shift of the yellow emission. Other suitable wavelength converting materials may include (Sr 1−x−y Ba x Ca y ) 2−z Si 5−a Al a N 8−a Oa:Eu 2+  wherein 0≦a&lt;5, 0≦x≦1, 0≦y≦1 and 0&lt;z≦1, and (x+y)≦1, such as Sr 2 Si 5 N 8 :Eu 2+  which emits light in the red range. 
         [0048]    Examples of inorganic wavelength converting materials include quantum dots or quantum rods. Quantum dots are small crystals of semiconducting material generally having a width or diameter of only a few nanometers. When excited by incident light, a quantum dot emits light of a color determined by the size and material of the crystal. Light of a particular color can therefore be produced by adapting the size of the dots. Most known quantum dots with emission in the visible range are based on cadmium selenide (CdSe) with a shell such as cadmium sulfide (CdS) and zinc sulfide (ZnS). Cadmium free quantum dots such as indium phosphode (InP), and copper indium sulfide (CuInS2) and/or silver indium sulfide (AgInS2) can also be used. Quantum dots show very narrow emission band and thus they show saturated colors. Furthermore the emission color can easily be tuned by adapting the size of the quantum dots. 
         [0049]    Any type of quantum dot known in the art may be used in the present invention. However, it may be preferred for reasons of environmental safety and concern to use cadmium-free quantum dots or at least quantum dots having a very low cadmium content. 
         [0050]    Examples of suitable organic phosphor materials are organic luminescent materials based on perylene derivatives, for example compounds sold under the name Lumogen® by BASF. Examples of suitable compounds include, but are not limited to, Lumogen® Red F305, Lumogen® Orange F240, Lumogen® Yellow F083, and Lumogen® F170. 
         [0051]    In embodiments of the invention, narrow band emitting materials, including sulfide based wavelength converting materials, optionally europium doped, may be used to great advantage. 
         [0052]    In fact, incorporation of a wavelength converting material into a composition comprising the organometallic getter may be particularly advantageous when the wavelength converting material contains sulfur and/or selenide and hence may give rise to sulfide and/or selenide gas. Examples of such wavelength converting materials include phosphors based on, for example, calcium sulfide, strontium sulfide, calcium strontium sulfide, calcium selenide sulfide, and calcium strontium selenide sulfide. 
         [0053]    Another embodiment of the invention is schematically depicted in  FIG. 4 . This figure shows a side view of the general layer structure of a light emitting arrangement  400  including a solid state light source  401  and a layer assembly  402  comprising a wavelength converting layer  403  and a protective layer  404 . The light source  401  is adapted to emit primary light in the direction of the wavelength converting layer  403 . The wavelength converting layer  403  receives light emitted by the light source  401  and converts this light into secondary, converted light. 
         [0054]    The protective layer  404  comprises an organometallic getter  406 , typically distributed in a matrix as described above. The wavelength converting layer, which may contain a wavelength converting material comprising sulfur and/or selenium, may be arranged between the light source  401  and the protective layer  404 . Hence, the protective layer is arranged on the light output side of the wavelength converting layer, i.e. on the side intended to face a viewer of the light emitting arrangement  400 . Optionally, the wavelength converting layer may be partly or fully covered, or even embedded, by the protective composition. 
         [0055]    The organometallic getter of the protective layer  404  is capable of capturing H 2 S gas  407  and optionally H 2 Se gas released from the wavelength converting layer or otherwise present adjacent the protective layer. 
         [0056]    Although not shown in  FIG. 4 , a light emitting arrangement may include a reflective cup as shown in  FIGS. 2 and 3 , and may be sealed, optionally by the protective layer  404 . In embodiments of the invention, schematically illustrated in  FIG. 5 , a light emitting arrangement  500  may comprise a plurality of solid state light sources  501  arranged within a reflective chamber  505 , also referred to as a light mixing chamber, defined by at least one reflective wall  506 . A protective layer  502  comprising an organometallic getter  508  as described above forms part of a light exit window  507  of the light mixing chamber  505 . In the embodiment of  FIG. 5 , a wavelength converting layer  503  is provided directly on top of each light source  501 , but alternatively or additionally a wavelength converting material may be included within the protective layer, or arranged as a wavelength converting layer adjacent the protective layer  502 . Indeed, in embodiments of the invention, the layer assembly  402 , the wavelength converting layer  403 ,  503  and/or the protective layer  404 ,  502  may form part of the light exit window through which light may exit a light mixing chamber. 
         [0057]    Referring again to  FIG. 4 , the layer assembly  402  comprises at least a protective layer as described above. Typically it also comprises at least one additional layer, which may be a wavelength converting layer  403 . Alternatively, in embodiments where the protective layer also contains wavelength converting material as described above, the additional layer may be another optically functional layer, such as a scattering layer. In some embodiments of the invention, the at least one additional layer may comprise a support layer, e.g. comprising matrix material without any organometallic getter. The at least one additional layer may be positioned on any suitable side of the protective layer  404 . 
         [0058]    In embodiments of the invention, the layer assembly may comprise the protective layer and the at least one additional layer arranged in direct contact with each other, thus forming a multilayer structure. In other embodiments however the layer assembly may comprise at least two layers mutually spaced apart. For example, as shown in  FIG. 4 , the protective layer  404  and the wavelength converting layer  403  may be arranged at a distance from each other, separated by a gap. Alternatively, in embodiments comprising more than two layers, for example a protective layer, a wavelength converting layer and a further layer, any two of these layers may be arranged in direct contact with each other while the third layer may be spaced apart from the two layers. 
         [0059]    Furthermore, in embodiments of the invention, a layer assembly comprising a protective layer as described above and at least one additional layer may be arranged directly on top of a light source, such as an LED. Alternatively one or more layers of the layer assembly, and optionally the whole layer assembly, may be arranged at a distance from the light source. 
         [0060]    Similarly, embodiments of the invention where the protective layer comprises a wavelength converting material in addition to the organometallic getter, the protective layer may be arranged directly on a light source, or at a distance from a light source, typically an LED. 
         [0061]    A light emitting arrangement according to embodiments of the invention may typically comprise a solid state light source. The solid state light source may be a light emitting diode (LED) or a laser diode. Alternatively the light source may be an organic light emitting diode (OLED). In some embodiments the solid state light source may be a blue light emitting LED, such as GaN or InGaN based LED, for example emitting primary light of the wavelength range from 440 to 460 nm. Alternatively, the solid state light source may emit UV or violet light. Blue, violet or UV LEDs can be combined with one or more wavelength converting material such that light source light is converted into light of longer wavelength(s) by the wavelength converting material(s). 
         [0062]    The protective layer and the light emitting arrangement according to embodiments of the invention described herein may be employed in a variety of lighting applications and devices. For example a light emitting arrangement according to embodiments of the invention may be used in an LED based bulb replacement lamp, for replacement of conventional light incandescent bulbs. A bulb replacement lamp typically comprises a light emitting arrangement, which may be a light emitting arrangement as described herein.  FIG. 6  shows a side view of a bulb replacement lamp  600  comprising a base member  601  adapted to allow electrical connection to the light source, including a fitting for a conventional socket. On the top surface of the base member a light emitting arrangement is mounted (not shown). Typically, the light emitting arrangement may comprise a plurality of light sources, usually LEDs. A transparent or translucent cover  602 , optionally shaped like a conventional bulb, may be attached to the base member  601  to cover the light emitting arrangement. A protective layer or the layer assembly according to embodiments of the invention may be arranged at any suitable position between the light source(s) and the cover  602 . It is contemplated that the protective layer or layer assembly according to embodiments of the invention may be arranged on an inner surface of the transparent or translucent cover  602 . 
         [0063]    Furthermore, the protective layer or the light emitting arrangement according to embodiments of the invention may be employed in a luminescent tube replacement lamp, also referred to as a TL replacement lamp or tube. A TL replacement lamp usually comprises an elongated, e.g. tubular, at least partially transparent or translucent enclosure enclosing a light emitting arrangement which may be a light emitting arrangement as described herein. The elongated enclosure is typically provided with electrical contacts allowing electrical connection to the light source(s) Typically, the light emitting arrangement may comprise a plurality of light sources, usually LEDs. A protective layer or the layer assembly according to embodiments of the invention may be arranged at any suitable position between the light source(s) and the enclosure. It is contemplated that the protective layer or layer assembly according to embodiments of the invention may be arranged on an inner surface of the enclosure. 
         [0064]    Furthermore, the protective layer or the light emitting arrangement according to embodiments of the invention may also be employed in luminaires comprising solid-state light sources, such as LED-based luminaires. Such a luminaire may have any suitable design and be fitted for being suspended from above (e.g. a ceiling, as in  FIG. 7 ), mounted on a wall or standing on a surface.  FIG. 7  shows a perspective view of a suspended luminaire  700 , comprising a frame  701  and a light exit window  702 . Arrows indicate the direction of light emission from the luminaire  700 . A light emitting arrangement (not shown) including at least one light source, typically a plurality of LEDs, may be mounted within the frame, behind the light exit window to emit light in the direction of the light exit window  702 . A protective layer or the layer assembly according to embodiments of the invention may be arranged at any suitable position between the light source(s) and the light exit window  702 . It is contemplated that the protective layer or layer assembly according to embodiments of the invention may be arranged on an inner surface of the light exit window or form part of the light exit window. 
         [0065]    The light emitting arrangement according to embodiments of the invention may also be employed in LED modules intended for any type of lighting application. 
         [0066]    The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, any embodiment of a light emitting arrangement according to the invention may comprise a plurality of solid state light sources. Furthermore, a protective layer comprising the organometallic getter need not be the only protective layer of e.g. a light emitting arrangement. Indeed, the protective layer may be contained in a hermetically or pseudo-hermetically sealed compartment, typically together with other components such as a light source, a reflector, a wavelength converting material, etc. Sealing may be achieved by one or more additional sealing material(s) or sealing layer(s) known in the art. 
         [0067]    Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.