Layer structure as an optical component for angle-independent spectral response and use thereof as an interference filter and / or as an interference mirror

Abstract

The invention relates to a layer structure (10) for the wavelength-selective filtering and / or reflection of light, comprising at least two sub-layer structures (12a, 12b), with each sub-layer structure (12) comprising at least two layers (14a, 14b), the layers (14) within one layer structure (12) having a high or a low refractive index and the at least two layers (14a, 14b) of a sub-layer structure (12) being arranged alternately in relation to the refractive index within the respective sub-layer structure (12), and at least one absorption layer (16), with the absorption layer (16) being arranged between the two sub-layer structures (12a, 12b) and the absorption layer (16) having a material resonance such that an absorption spectrum of the absorption layer (16) has an absorption edge (42) that drops off towards longer wavelengths, with a wavelength of the absorption edge (42) at ±10% of a longer-wave end of a stop band (18) of the layer structure (10) being at an angle of incidence of 0 degrees. The invention also relates to the use of the aforementioned layer structure (10) as an interference filter and / or as an interference mirror.

Description

[0001] Layer structure as an optical component for angle-independent spectral response and its use as an interference filter and / or as an interference mirror

[0002] Description

[0003] Interference filters and interference mirrors are optical components that utilize the effect of interference in thin layers to filter or reflect light depending on the frequency. The designation of the component as a filter or mirror depends on whether the transmitted or reflected light is used. Well-known interference filters and interference mirrors include Bragg mirrors, which consist of alternating thin layers with different refractive indices.

[0004] Known interference filters and interference mirrors exhibit angular dispersion, meaning the optical components exhibit different reflection and transmission coefficients for different angles of incidence of the light. This is due to the angular dependence of the reflection and transmission coefficients and thus of the interference effect. This makes the use of such optical components difficult in sensitive optical applications. The presence of angular dispersion requires precise alignment of the interference filter / interference mirror and makes optical systems using such optical components susceptible to temporal drift. If the light passing through the interference filter or the light being reflected by the interference mirror also exhibits a distribution of angular components, as is the case with most light sources, the wavelength selectivity of the interference filter / interference mirror is also impaired.For example, the transmitted or reflected light of a bandpass filter is spectrally broadened in an uncontrolled manner, instead of producing a narrow spectral line as desired for this component. The transmitted or reflected line shape is often severely distorted at angles of incidence that deviate significantly from the normal, meaning it broadens considerably and can also exhibit different behavior depending on the polarization of the incident light.

[0005] The document DE 10 2020 125 597 A1 relates to an interference filter for wavelength-selective filtering of light, with a stack arrangement of layer structures which has two partially transparent mirror layer structures and an intermediate layer structure arranged between the two partially transparent mirror layer structures, wherein the two partially transparent mirror layer structures form an optical resonator with a characteristic resonator wavelength A.

[0006] Document US 2005 / 0237134 A1 describes a dielectric filter provided with a dielectric multilayer structure formed by stacking two or more dielectric layers with different relative permittivities. At least one feed electrode is provided between the dielectric layers or within the dielectric layers of the dielectric multilayer structure, as well as a shielding portion covering the outer surface of the dielectric multilayer structure and made of a conductive material positioned to fit the outer surface without a gap.

[0007] Based on this, it is the object of the invention to provide measures to reduce the angular dispersion of interference filters and interference mirrors.

[0008] The object is achieved according to the invention by the features of the independent claims. Advantageous embodiments of the invention are specified in the subclaims. According to the invention, a layer structure for wavelength-selective filtering and / or reflection of light is provided, comprising at least two sublayer structures, each sublayer structure comprising at least two layers, the layers within a sublayer structure having a high or a low refractive index, and the at least two layers of a sublayer structure being arranged alternately with respect to the refractive index within the respective sublayer structure, at least one absorption layer, the absorption layer being arranged between the two sublayer structures, and the absorption layer having a material resonance such thatthat an absorption spectrum of the absorption layer has a decreasing absorption edge towards longer wavelengths, wherein a wavelength of the absorption edge lies at ±10% of a longer wavelength end of a stop band of the layer structure at an angle of incidence of 0 degrees.,

[0009] One aspect of the invention is that the absorption layer, with its absorption spectrum, is tuned to the stop band of the layer structure such that the wavelength of the absorption edge lies at ±10% of the longer-wavelength end of the stop band at a perpendicular angle of incidence—i.e., 0 degrees. This has the consequence that, due to a coupling of a vibration mode of the layer structure with the material resonance of the absorption layer, the angular dispersion is greatly reduced, and the layer structure can be used as a substantially angle-independent interference filter and / or angle-independent interference mirror. The layer structure according to the invention thus preferably has a transmission within the stop band that is less than 10% of the maximum transmission outside the stop band, for all angles of incidence between 0 degrees (perpendicular) and ±80 degrees.

[0010] The layer structure comprises at least two sublayer structures, which in turn each comprise two or more layers. The layers within the sublayer structure have a high or low refractive index and are arranged alternately with respect to the refractive index within the respective sublayer structure. In other words, within a sublayer structure, a layer with a high refractive index is followed by a layer with a low refractive index and / or vice versa. In other words, this also means that within a sublayer structure no two layers with the same refractive index are arranged directly next to each other. Due to the multiple alternating layers of the sublayer structures with low and high refractive indices, the layer structure has a stop band. Light whose wavelength lies within the stop band can not pass through the layer structure or can only pass through it to a small extent.The longer-wavelength end of the stop band refers to the end of the stop band at a high wavelength. Light with a wavelength longer than the longer-wavelength end of the stop band can propagate and pass through the layered structure at an angle of incidence of 0 degrees. The layered structure therefore preferably has a transmission outside the stop band that is more than 50% of the maximum transmission within the stop band. This can preferably apply to all angles of incidence between 0 degrees (perpendicular) and ± 80 degrees.

[0011] The absorption layer is arranged between the two sublayer structures. It is possible for the absorption layer to be directly adjacent to the sublayer structures and to be in contact with them. Alternatively, it is possible for further elements of the layer structure to be arranged between the absorption layer and the at least two sublayer structures. For example, a layer structure can be constructed as follows: H / L / A / H / L or H / L / A / L / H or H / L / H / A / H / L, where H stands for the layer with a high refractive index, L stands for the layer with a low refractive index, and A stands for the absorption layer.

[0012] The falling absorption edge is a sudden transition from strong to weak absorption that occurs at a specific wavelength in the absorption spectrum of the absorption layer. A falling absorption edge towards longer wavelengths specifically means that light with a wavelength longer than the absorption edge is weakly or not at all absorbed by the absorption layer, and light with a wavelength shorter than the absorption edge is strongly absorbed by the absorption layer due to the material resonance. Particularly preferably, the wavelength of the absorption edge is determined such that, for a standardized absorption spectrum with a maximum absorption of 1, the falling absorption edge lies at the wavelength at which the absorption has dropped to a value of 1 / 3, starting from the maximum towards longer wavelengths.Preferably, the spectral distance between the absorption edge and the absorption maximum of the absorption layer is less than 100 nm, particularly preferably less than 50 nm.

[0013] The term “light” in the context of this application is not limited to the visible spectral range (VIS) of the electromagnetic spectrum, but also includes the adjacent spectral ranges such as infrared (IR), ultraviolet (UV) and terahertz (THz).

[0014] According to a preferred development of the invention, the sublayer structures and the absorption layer are matched to one another in such a way that a strong coupling exists between the longer-wavelength sidebands of the stop band and the material resonance. Due to the multiple alternating layers with low and high refractive indices, the layer structure not only has a stop band, but also sidebands directly adjacent to the ends of the stop band, with reflectances and transmittances that vary in a wave-like manner relative to the wavelength axis. Therefore, an absorption layer that exhibits a material resonance with high oscillator strength in the spectral range of the longer-wavelength sideband of the stop band is preferably used.Due to the strong coupling of the longer-wavelength sidebands and the material resonances, the angle dependence of the layered structure is significantly reduced, resulting in angle-stable optical behavior while retaining the advantages of the layered structure, such as high optical density and high transmission. In other words, the angle-independent behavior of the layered structure is based on a coherent interplay of light and matter resonances. Strong coupling, rather than weak coupling between light and material resonance, is preferred. In the weak coupling region, no energy exchange occurs between the sideband mode and the material resonance mode. In contrast, in the strong coupling region, a coherent interaction occurs between the sideband mode and the material resonance mode.This process requires an interaction strength between the sideband mode and the material resonance mode that exceeds the loss mechanisms for both the sideband mode, where losses due to emission, parasitic absorption, and / or scattering are present, and the material resonance mode, where losses due to non-radiative recombination dominate. The coherent interaction between the sideband mode and the material resonance mode leads to the lifting of the energetic degeneracy, which can also be described as hybridization of the photon resonance mode and the material resonance mode, manifesting as an energetic splitting into a lower-energy and a higher-energy state of the hybrid mode.This combination allows the combination of the advantages of known interference filters and pure absorption filters and offers significantly better transmission and reflection properties with a lower overall thickness compared to the latter, as well as compared to an incoherent combination of known interference and absorption filters.

[0015] Particularly preferably, the material resonance is configured as an excitonic material resonance. Due to its high oscillator strength, this has been shown to be particularly suitable for achieving strong coupling with the sideband mode.

[0016] According to a further preferred development of the invention, the material resonance is such that the absorption spectrum of the absorption layer covers the entire stop band of the layer structure at an angle of incidence of 0 degrees. In this case, it is therefore preferably provided that the absorption layer exhibits continuous absorption within the stop band of the layer structure at an angle of incidence of 0 degrees. For example, if the stop band extends from 400 nm to 500 nm at an angle of incidence of 0 degrees, this means that the absorption layer preferably absorbs in the range from 400 nm to 500 nm, with the longer-wavelength absorption edge lying at 450 nm to 550 nm.

[0017] According to an alternative development of the invention, however, it can also be provided that the absorption spectrum has at least one transmission window within the stop band of the layer structure at an angle of incidence of 0 degrees. In other words, in this alternative embodiment, the absorption spectrum of the absorption layer does not cover the entire range of the stop band.

[0018] With regard to the absorption layer, according to a further preferred development of the invention, the absorption layer comprises one or more organic molecules, and preferably one or more organic dyes selected from the group comprising coumarin dyes, phthalocyanines, fluorene, polyfluorene, Spiro-TTB, BSBCz, C545T, SubPc, BODIPY, rylene dyes, in particular rylene monoimide derivatives or rylene diimide derivatives, and non-fullerene acceptors (NF As) such as Y5. These dyes have proven to be particularly suitable because they display particularly strong material resonances, in particular excitonic resonances, in suitable spectral ranges and are easy to process. The dye SpiroTTB is the dye 2,2',7,7'-tetrakis(N,N'-di-p-methylphenylamino)-9,9'-spirobifluorene with the CAS no. 515834-67-0. The dye BSBCz is 4,4'-bis[(N-carbazole)styryl]biphenyl.C545T, also known as Coumarin 545T, refers to the dye 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-l,l,7,7-tetramethyl-lH,5H,l lH-(l)benzopyropyrano(6,7-8-1,j)quinolizin-11-one with CAS No. 155306-71-1. SubPc is boron subphthalocyanine chloride with CAS No. 36530-06-0. BODIPY refers to the dye 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene with CAS No. 138026-71-8.

[0019] With regard to the layers of the sublayer structure, it is preferably provided that they are dielectric layers. According to a further preferred embodiment of the invention, it is also preferably provided that the layers of the sublayer structure comprise metal oxides, semimetal oxides, and / or transition metal oxides. More preferably, they are layers of silicon dioxide (SiO2) and / or tantalum(V) oxide (Ta2O5).

[0020] In this context, according to a preferred development of the invention, the layers of the sublayer structure have a thickness of V(4*n) ±20%, where n is the central wavelength of the stop band and n is the refractive index of the respective layer. Alternatively, the layers can have an integer multiple of this intended layer thickness. For use in the visible spectral range, these layer thicknesses are preferably in the range of 50 nm to 200 nm. The layers are therefore thin layers, which are preferably produced using different coating processes. The layers are preferably produced by physical vapor deposition processes such as sputtering or vapor deposition. Alternatively, chemical vapor deposition or sol-gel processes are used to produce the layers.

[0021] With respect to the absorption layer, according to a further preferred embodiment of the invention, a layer thickness of the absorption layer corresponds to 50% to 400% of the thickness of a layer of the sublayer structure. Thus, the thickness of the absorption layer is preferably between k / (8*n) and X / n, and more preferably for use in the visible spectral range between 25 nm and 800 nm.

[0022] In principle, the layer structure can comprise exactly one absorption layer and exactly two sublayer structures. However, according to a preferred development of the invention, the layer structure comprises a plurality of absorption layers and one or more further sublayer structures, wherein each of the plurality of absorption layers is arranged between two sublayer structures. In other words, no two absorption layers of the plurality of absorption layers are located directly adjacent to one another, but are separated from one another by at least one sublayer structure with at least two layers. The transmission and reflection behavior of the layer structure can be adapted particularly easily by the plurality of absorption layers and the plurality of further sublayer structures.

[0023] In this context, according to a further preferred development, it is provided that the multiple absorption layers are of similar design. In other words, the absorption layers have similar absorption spectra. In a preferred alternative, however, it is provided that the multiple absorption layers are at least partially different from one another. In this case, preferably at least one absorption layer has a different absorption spectrum from the other absorption layers.

[0024] According to a further preferred development of the invention, with differently configured absorption layers, the multiple absorption layers are configured so that they differ from one another that the sum of the absorption spectra covers at least the entire stop band of the layer structure at an angle of incidence of 0 degrees. It can therefore also preferably be provided that the sum of the absorption spectra covers a spectral range that is larger than the stop band of an individual sublayer structure or the layer structure.

[0025] Alternatively, it can also be provided that the plurality of absorption layers are designed differently such that the sum of the absorption spectra has at least one transmission window within the stop band of the layer structure at an angle of incidence of 0 degrees.

[0026] The multiple sublayer structures can also preferably be in the form that the layer structure has multiple stop bands. For this purpose, it is preferably provided that each sublayer structure has layers with a high and a low refractive index, but the value of the identical refractive index in the respective sublayer structures differs from one another. For example, a first sublayer structure can be formed according to H / L / H / L... and a further sublayer structure according to H' / L' / H' / L' . . ., where L and L' denote the layers with a low refractive index and H and H' denote the layers with a high refractive index, wherein the value of the refractive index of L and L' and of H and H' is not the same. Alternatively or additionally, multiple stop bands can be achieved by the thicknesses of the layers in the respective sublayer structures differing from one another.

[0027] In this regard, according to a further preferred development of the invention, the layer structure has a plurality of stop bands and a plurality of absorption layers, and the absorption layers differ from one another in such a way that the wavelength of the respective absorption edge lies at ±10% of the respective longer-wavelength end of each stop band of the layer structure at an angle of incidence of 0 degrees. In other words, a first absorption layer is tuned with its absorption spectrum to the longer-wavelength end of a first stop band, a second absorption layer is tuned with its absorption spectrum to the longer-wavelength end of a second stop band, and so on.

[0028] Furthermore, according to a further preferred development of the invention, the layer structure comprises a plurality of stop bands and a plurality of absorption layers, wherein the plurality of absorption layers are configured so as to differ from one another that the sum of the absorption spectra exhibits at least one transmission window between the stop bands of the layer structure at an angle of incidence of 0 degrees. Thus, transmission at wavelengths between the stop bands is also not hindered by absorption by the absorption layers of the layer structure. Accordingly, a substantially angle-independent transmission bandpass filter can be provided in this way.

[0029] As already mentioned, the sublayer structures have at least two layers which are arranged alternately with respect to their refractive index within the respective sublayer structure. In this context, according to a preferred development of the invention, the absorption layer is preferably arranged between two sublayer structures in such a way that two layers of the sublayer structure with the same refractive index are present above and below the absorption layer. In other words, arrangements in the form of H / L / A / L / H or L / H / A / H / L or H / L / A / L' / H' or L / H / A / H' / L' are preferred over arrangements in the form of H / L / A / H / L or L / H / A / L / H or H / L / A / H' / L' or L / H / A / L' / H'. It has been shown that such an arrangement leads to particularly angle-independent behavior of the layer structure.

[0030] According to a further preferred development of the invention, the absorption layer is arranged between two sublayer structures in such a way that the absorption layer directly abuts at least one, preferably two, sublayer structures. In other words, it is preferably provided that no further element of the layer structure is arranged between the absorption layer and the sublayer structure, and the absorption layer thus abuts in contact with at least one, and preferably both, sublayer structures. This makes the construction and manufacture of the sublayer structure particularly simple.

[0031] In an alternative preferred development of the invention, however, it is provided that the absorption layer does not directly adjoin two sublayer structures, but rather a further element is arranged between the absorption layer and at least one of the two sublayer structures. In this regard, and according to a further preferred development of the invention, it is provided that the layer structure comprises one or more metal layers. Preferably, the layer structure comprises two metal layers for each absorption layer. It has been shown that a layer structure with dielectric layers and with metal layers is particularly advantageous, especially for narrowband transmission filters.

[0032] The metal layers are further preferably thin metal layers whose thickness is of the same order of magnitude as the layers of the sublayer structure. In this context, according to a preferred embodiment of the invention, the metal layer has a thickness of less than 50 nm.

[0033] In connection with the metal layers, according to a further preferred embodiment of the invention, the absorption layer is directly adjacent to one and preferably directly to two metal layers. Thus, layer structures of the form H / L / M / A / L / H (one metal layer) or H / L / M / A / M / L / H (two metal layers) are preferably provided, where M stands for the metal layer. These offer advantages for narrowband transmission filters.

[0034] According to a further preferred embodiment of the invention, the layer structure comprises a carrier onto which at least one sublayer structure is applied. The carrier is preferably a mechanically flexible carrier such as parylene, in particular Parlyen-C, or PET.

[0035] Furthermore, it is advantageously provided that the layer structure is an interference filter for filtering light and / or an interference mirror for reflecting light from at least one of the following spectral ranges:

[0036] UV range (about 200 - 380 nm),

[0037] VIS range (about 380 - 780 nm),

[0038] NIR range (about 780 - 3 pm),

[0039] IR range (about 3pm - 1mm) and

[0040] THz range (about 30 pm - 3 mm).

[0041] The invention also relates to the use of the layer structure described above as an interference filter and / or as an interference mirror.

[0042] The invention will be explained below by way of example with reference to the accompanying drawings using preferred embodiments, wherein the features presented below can represent an aspect of the invention both individually and in combination. They show:

[0043] Fig. 1 shows an interference filter known from the prior art for wavelength-selective filtering of light, as well as its angle-resolved transmission spectrum,

[0044] Fig. 2 shows a layer structure for wavelength-selective filtering of light according to a first preferred embodiment of the invention, as well as its angle-resolved transmission spectrum,

[0045] Fig. 3 shows a refractive index profile for a layer structure according to a further preferred embodiment of the invention, Fig. 4 shows a layer structure with a refractive index profile according to Figure 3, its angle-resolved transmission spectrum, as well as sections through the transmission spectrum,

[0046] Fig. 5 shows a refractive index curve for a layer structure according to another preferred embodiment of the invention,

[0047] Fig. 6 a layer structure with refractive index profile according to Figure 5, as well as its angle-resolved transmission spectrum,

[0048] Fig. 7 shows a layer structure for wavelength-selective filtering of light according to another preferred embodiment of the invention, as well as its angle-resolved transmission spectrum, and

[0049] Fig. 8 schematically shows the normalized absorption spectra of the dyes BSBCz, Spiro-TTB, C545T and SubPc, which can be contained in the layer structures according to preferred embodiments.

[0050] Figure 1 shows a schematic representation of a prior art interference filter 1' for wavelength-selective filtering of light, as well as its angle-resolved transmission spectrum. The interference filter 1' is designed as a Bragg mirror and has several alternating layers 2a', 2b' with low and high refractive indices. Layers 2a' and 2b' are Ta20s and SiCh layers, respectively.

[0051] The interference filter 1' shown in Figure 1 has the following structure in relation to the number of layers and their thicknesses: (10x (53 nm Ta20s | 77 nm SiCL)) | 53 nm Ta20s. The normalized angle-resolved transmission spectrum shows the wavelength in nm on the x-axis 3' and the angle of incidence from 0 to 80 degrees on the y-axis 4'. This shows that the stop band 5' of the interference filter 1', which lies between 400 nm and 500 nm at an angle of incidence of 0 degrees (vertical), is shifted to lower wavelengths—i.e., into the blue—at higher angles of incidence. The interference filter 1' exhibits strong angular dispersion.

[0052] Figure 2 shows a schematic representation of a layer structure 10 for wavelength-selective filtering of light according to a preferred embodiment of the invention, as well as its angle-resolved normalized transmission spectrum. The layer structure 10 has at least two sublayer structures 12a, 12b, wherein each sublayer structure 12a, 12b in turn comprises at least two layers 14a and 14b. In the present case, the sublayer structures 12a, 12b each comprise more than two layers 14. The layers 14 within a sublayer structure 12 each have a high refractive index or a low refractive index, wherein in the present case, the layers 14a have a high refractive index and the layers 14b have a low refractive index. With respect to the refractive index, the layers 14 within the sublayer structure 12 are arranged alternately. The layers 14 are Ta20s and SiCE layers in the present case.

[0053] An absorption layer 16 is arranged between the sublayer structures 12a and 12b. The absorption layer 16 has a material resonance such that an absorption spectrum of the absorption layer 16 has a decreasing absorption edge toward longer wavelengths, with a wavelength of the absorption edge lying at ±10% of a longer-wavelength end of a stop band 18 of the layer structure 10 at an angle of incidence of 0 degrees. In the present case, the absorption layer 16 comprises the organic dye Coumarin 545T.

[0054] The layer structure 10 shown in Figure 2 has the following structure in relation to the number of layers and their thicknesses: (5x (53 nm Ta2Os | 77 nm SiC>2)) | 53 nm Ta2C>5 | 75 nm Coumarin 545T | (5x (53 nm Ta2Os | 77 nm SiO2)) | 53 nm Ta2Os. The normalized angle-resolved transmission spectrum of the layer structure 10 shows the wavelength in nm on the x-axis 20 and the angle of incidence from 0 to 80 degrees on the y-axis 22. This shows that the stop band 18 of the layer structure 10 lies between 400 nm and 500 nm at an angle of incidence of 0 degrees (vertical). The wavelength of the absorption edge of the absorption layer 16 is therefore between 450 nm (corresponding to 500 nm - 50 nm) and 550 nm (500 nm + 50 nm). The transmission spectrum of the layer structure 10 also shows that the stop band 18 is essentially angle-independent and lies between 400 nm and 500 nm even at higher angles of incidence.

[0055] Figure 3 shows a refractive index curve for a layer structure 10 according to another preferred embodiment of the invention. The y-axis 24 of Figure 3 shows the depth perpendicular to the planes of the layers 14 in nm, while the x-axis 26 shows the refractive index for the wavelength 450 nm. Figure 3 shows that the refractive index in the very first layer 14a (at a depth of 0 nm) has a value of 2.2, drops to a value of 1.4 for the second layer 14b, and then behaves alternately. The layers 14 in this case are Ta20s and SiCE layers.

[0056] It can also be seen that the layer structure 10 in this exemplary embodiment has four sublayer structures 12a, 12b, 12c, and 12d and three absorption layers 16. It can also be seen that the absorption layer 16 is directly adjacent to two sublayer structures 12, and that two layers 14 of the sublayer structure 12 with a similar refractive index—in this case, layer 14a with a high refractive index—are located directly above and below the absorption layer 16. The absorption layer 16 comprises the dye Coumarin 545T.

[0057] Figure 4 shows a layer structure 10 with the refractive index profile shown in Figure 3, its angle-resolved normalized transmission spectrum, and sections through the transmission spectrum. From the transmission spectrum and the sections at the angles of incidence of 0 degrees, 20 degrees, 40 degrees, and 60 degrees, it can be seen that the stop band 18 remains essentially stable between 400 nm and 500 nm, even for high angles of incidence. In the graphic in Figure 4, which shows the sections through the transmission spectrum, the x-axis 20 represents the wavelength in nm, and the y-axis 28 represents the normalized transmittance.

[0058] The layer structure 10 shown in Figures 3 and 4 has, in concrete terms with regard to the number of layers and their thicknesses, the following structure specified in Table 1, wherein the absorption layers with Coumarin 545T are highlighted in bold for better clarity.

[0059] Figure 5 shows a refractive index curve for a layer structure 10 according to another preferred embodiment of the invention. Analogous to Figure 3, the y-axis 24 of Figure 5 shows the depth perpendicular to the planes of the layers 14 in nm, while the x-axis 26 shows the refractive index for the wavelength 450 nm. Figure 5 shows that the refractive index in the very first layer 14a (at a depth of 0 nm) has a value of 2.2, drops to a value of 1.4 for the second layer 14b, and then behaves alternately. The layers 14 in this case are Ta20s and SiCh layers.

[0060] It can also be seen that the layer structure 10 in this exemplary embodiment has five sublayer structures 12a, 12b, 12c, 12d, and 12e and four absorption layers 16. In contrast to Figure 3, the absorption layers 16 are not all of the same design. Instead, two absorption layers 16a contain the dye Spiro-TTB, and two absorption layers 16b contain the dye Coumarin 545T.

[0061] Figure 6 shows a layer structure 10 with the refractive index profile shown in Figure 4 and its angle-resolved normalized transmission spectrum. The transmission spectrum of the layer structure 10 shows that the stop band 18 is essentially angle-independent and lies between 300 nm and 500 nm even at higher angles of incidence.

[0062] The layer structure 10 shown in Figures 5 and 6 has, in concrete terms with regard to the number of layers and their thicknesses, the following structure specified in Table 2, wherein the absorption layers with Spiro-TTB and Coumarin 545T are highlighted in bold for better clarity.

[0063] Figure 7 shows a layer structure 10 according to another preferred embodiment of the invention, as well as its simulated angle-resolved normalized transmission spectrum. In this embodiment, the layer structure 10 has two stop bands 18a, 18b. Furthermore, the layer structure has differently configured absorption layers 16, with a first absorption layer 16 comprising the dye BSBCz and a second absorption layer 16 comprising the dye SubPc. The dyes have absorption spectra such that the sum of the absorption spectra of the absorption layers has a transmission window 30 between the two stop bands 18a, 18b of the layer structure 10.

[0064] The simulated transmission spectrum of the layer structure 10 shows that the first stop band 18a extends essentially angle-independently up to a wavelength of 400 nm, followed by the only weakly angle-dependent transmission window 30, and from 600 nm onwards the second stop band 18b.

[0065] Figure 8 schematically shows the normalized absorption spectra of the dyes BSBCz 32, Spiro-TTB 34, C545T 36, and SubPc 38. The wavelength in nm is plotted on the x-axis 20, and the y-axis 40 shows the normalized absorbance. Absorption spectra 32, 34, 36, and 38 each exhibit an absorption edge 42 toward longer wavelengths. For C545T (absorption spectrum 36), the wavelength of the absorption edge 42—that is, the wavelength at which the absorption has dropped to a value of 1 / 3 from the maximum absorption to longer wavelengths—is approximately 510 nm. Thus, with respect to the layer stack 10 shown in Figure 2, the wavelength of the absorption edge 42 is ±10% of the longer-wavelength end of the stop band 18 at an angle of incidence of 0 degrees of the layer structure 10 from Figure 2.

[0066] The invention originates from funded research projects within the framework of the EU funding MSCA (Marie Sklodowska-Curie Actions) Fellowship with the funding number D-74322-A, as well as within the framework of the Alexander von Humboldt Professorship AvH Gather of the Alexander von Humb ol dt Foundation.

[0067] Reference symbol

[0068] 1 ' Interference filter (state of the art)

[0069] 2' layer (state of the art)

[0070] 3' x-axis, wavelength in nm (state of the art)

[0071] 4' y-axis, angle of incidence in degrees (state of the art)

[0072] 5' stop band (state of the art)

[0073] 10 Layer structure

[0074] 12 Sublayer structure

[0075] 14a layer with high refractive index

[0076] 14b Low refractive index layer

[0077] 16 Absorption layer

[0078] 18 stop band

[0079] 20 x-axis, wavelength in nm

[0080] 22 y-axis, angle of incidence in degrees

[0081] 24 y-axis, depth in nm

[0082] 26 x-axis, refractive index at 450 nm

[0083] 28 standardized transmittance

[0084] 30 transmission windows

[0085] 32 Absorption spectrum of BSBCz

[0086] 34 Absorption spectrum of Spiro-TTB

[0087] 36 Absorption spectrum of C545T

[0088] 38 Absorption spectrum of SubPc

[0089] 40 y-axis, normalized absorbance

[0090] 42 Absorption edge

Claims

P a t e n t a n s p r ü c h e 1. A layer structure (10) for wavelength-selective filtering and / or reflection of light, comprising at least two sublayer structures (12a, 12b), each sublayer structure (12) comprising at least two layers (14a, 14b), the layers (14) within a sublayer structure (12) having a high or a low refractive index, and the at least two layers (14a, 14b) of a sublayer structure (12) being arranged alternately with respect to the refractive index within the respective sublayer structure (12), at least one absorption layer (16), the absorption layer (16) being arranged between the two sublayer structures (12a, 12b), and the absorption layer (16) having a material resonance such that an absorption spectrum of the absorption layer (16) has a decreasing absorption edge (42) towards longer wavelengths,wherein a wavelength of the absorption edge (42) is ±10% of a longer wavelength end of a stop band (18) of the layer structure (10) at an angle of incidence of 0 degrees., 2. Layer structure (10) according to claim 1, wherein the sublayer structures (12) and the absorption layer (16) are matched to one another in such a way that there is a strong coupling between longer-wavelength sidebands of the stop band (18) and the material resonance.

3. Layer structure (10) according to one of the preceding claims, wherein the material resonance is such that the absorption spectrum (32, 34, 36, 38) of the absorption layer (16) covers the entire stop band (18) of the layer structure (10) at an angle of incidence of 0 degrees.

4. Layer structure (10) according to one of the preceding claims, wherein the absorption layer (16) comprises one or more organic molecules, and preferably one or more organic dyes selected from the group comprising coumarin dyes, phthalocyanines, fluorene, polyfluorene, spiro-TTB, BSBCz, C545T, SubPc, BODIPY, rylene dyes, in particular rylene monoimide derivatives or rylene diimide derivatives, and non-fullerene acceptors (NF As) such as Y5.

5. Layer structure (10) according to one of the preceding claims, wherein the layers (14) of the sublayer structure (14) comprise metal oxides, semi-metal oxides and / or transition metal oxides.

6. Layer structure (10) according to one of the preceding claims, comprising a plurality of absorption layers (16a, 16b) and one or more further sub-layer structures (12), wherein each of the plurality of absorption layers (16) is arranged between two sub-layer structures (12).

7. Layer structure (10) according to claim 6, wherein the plurality of absorption layers (16) are formed differently from one another such that the sum of the absorption spectra (32, 34, 36, 38) covers at least the entire stop band (18) of the layer structure (10) at an angle of incidence of 0 degrees.

8. Layer structure (10) according to claim 6, wherein the layer structure (10) has a plurality of stop bands (18, 18b), wherein the plurality of absorption layers (16a, 16b) are formed differently from one another such that the sum of the absorption spectra (32, 34, 36, 38) has at least one transmission window (30) between the stop bands (18a, 18b) of the layer structure (10) at an angle of incidence of 0 degrees.

9. Layer structure (10) according to one of the preceding claims, wherein the absorption layer (16) is arranged between two sublayer structures (12) in such a way is that above and below the absorption layer (16) there are two layers (14) of the sublayer structure (12) with the same refractive index.

10. Layer structure (10) according to one of the preceding claims, wherein the absorption layer (16) is arranged between two sub-layer structures (12) such that the absorption layer (16) lies directly against at least one, preferably two, sub-layer structures (12).

11. Layer structure (10) according to one of the preceding claims, wherein the layer structure (10) comprises one or more metal layers.

12. Layer structure according to claim 11, wherein the absorption layer (16) directly adjoins one and preferably directly two metal layers.

13. Layer structure (10) according to one of the preceding claims, wherein a layer thickness of the absorption layer (61) corresponds to 50% to 400% of a thickness of a layer (14) of the sub-layer structure (12).

14. Layer structure (10) according to one of the preceding claims, comprising a carrier on which at least one sublayer structure (12) is applied.

15. Use of a layer structure (10) according to one of the preceding claims as an interference filter and / or as an interference mirror.

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