Method for producing a sensor comprising materials for enhancing the upconversion of near-infrared and / or visible radiation

Abstract

Method for producing a sensor comprising a layer system (100) for the upconversion of near-infrared and / or visible radiation, the method comprising: - forming a, preferably two-dimensional, photonic crystal (110) having a first (111) and a second side (112) by means of nanoimprint lithography; - applying an upconversion material (120) to the first side (111) and / or the second side (112) of the photonic crystal (110), wherein the upconversion material (120) contains a first lanthanide, wherein the first lanthanide is preferably neodymium or ytterbium; and wherein the upconversion material (120) contains a second lanthanide, wherein the second lanthanide is preferably selected from the group consisting of erbium, thulium and holmium.

Description

Technical area

[0001] The invention lies in the field of upconversion materials. Previously known state of the art

[0002] Upconversion, or photon upconversion, is a method in which multiple photons are absorbed by an upconversion material, resulting in the emission of higher-frequency or shorter-wavelength radiation compared to the absorbed radiation. This effect opens up a wide range of potential applications, for example, in bioanalytics, security technology, and photovoltaics.

[0003] US 2013 / 0000698 A1 describes a light convergence device, a manufacturing method therefor, and a solar cell battery system. Shi, Y. et al. describe “Upconversion fluorescence enhancement of NaYF4: Yb / Re nanoparticles by coupling with SiO2 opal photonic crystals,” in J. Mater. Sci, Vol. 54, 2019, No. 11, pp. 8461-8471 (ISSN 0022-2461). Tan, Y. et al. describe “Simultaneous Visualization and Quantitation of Multiple Steroid Hormones Based on Signal-Amplified Biosensing with Duplex Molecular Recognition,” in Chem. Eur. J., Vol. 23, 2017, No. 44, pp. 10683-10689 (ISSN 1521-3765). Lu, D. et al. describes “Plasmon Enhancement Mechanism for the Upconversion Processes in NaYF4: Yb 3+ , He 3+ Nanoparticles: Maxwell versus Förster,” in ACS Nano, Vol. 8, 2014, No. 8, pp. 7780-7792 (ISSN 1936-0851). Disadvantages of the state of the art

[0004] State-of-the-art upconversion materials only result in low upconversion efficiencies and intensities. Increasing the emission intensities of upconversion materials (or upconversion intensities) has so far been achieved primarily by increasing the irradiation intensity, particularly by using intense lasers. The use of intense lasers results in high costs and high hazard potential. Problem

[0005] In view of the above, there is a need for further improvements. It is therefore an object of the present invention to provide a method for manufacturing a sensor comprising a system for upconverting near-infrared and / or visible radiation, which enables an increase in upconversion efficiency and intensity. Inventive solution

[0006] This object is achieved by a method for producing a sensor comprising a layer system according to claim 1. Further embodiments, modifications and improvements will become apparent from the following description and the appended claims.

[0007] According to one embodiment, a layer system for upconverting near-infrared and / or visible radiation is provided. The layer system comprises a, preferably two-dimensional, photonic crystal with a first and a second side and an upconversion material arranged on the first side and / or the second side. The upconversion material contains a first lanthanide, wherein the first lanthanide is preferably neodymium or ytterbium. The upconversion material further contains a second lanthanide, wherein the second lanthanide is preferably selected from the group consisting of erbium, thulium, and holmium. The photonic crystal is produced by nanoimprint lithography.

[0008] The photonic crystal can be a two-dimensional or a three-dimensional photonic crystal. The second side of the photonic crystal can be arranged opposite the first side. For example, the first side can also be considered an upper side and the second side a lower side. The photonic crystal extends along or substantially parallel to the first side and has a small extension from the first side to the second side.

[0009] According to one embodiment, the photonic crystal has an extension of at least 20 nm, preferably at least 60 nm, and / or at most 5000 nm, preferably at most 500 nm, from the first side to the second side.

[0010] According to one embodiment, the layer system or the photonic crystal has an extension of at least 1 mm, preferably at least 1 cm, and more preferably at least 3 cm along the first side. Parallel to the first side, the layer system or the photonic crystal can have an extension of more than 10 cm. 2 , preferably several 10 cm 2 , have.

[0011] Advantageously, nanoimprint lithography enables the production of photonic crystals with the dimensions disclosed above with short production times and low costs.

[0012] The layer system according to embodiments of the present disclosure enables applications that require large-area (layer) systems and / or (layer) systems in large numbers. According to one embodiment, the layer system is used for an assay or a bioassay. Typically, assays or bioassays require dimensions of more than 10 cm 2 or even several 10 cm 2 .

[0013] The photonic crystal may comprise a first material, wherein the first material may be selected from the group consisting of oxides, nitrides, carbides, III / V semiconductors, germanium, and silicon. In a preferred embodiment, the first material is silicon.

[0014] The photonic crystal can have a substantially periodic arrangement of holes or elevations parallel to the first side and / or the second side. The holes can each be regarded as a depression that is substantially perpendicular to the first or second side and extends from the first or second side. The holes can extend completely from the first to the second side. Typically, the holes extend over a section perpendicular to the first and / or second side. The elevations can be substantially perpendicular to the first and / or second side and extend completely or partially between the first side and the second side. Top sides and bottom sides of the elevations can form the first side and the second side, respectively. In one embodiment, the holes or elevations are arranged substantially hexagonally.

[0015] The holes or protrusions can have an average spacing of at least 100 nm, preferably at least 300 nm and / or at most 3 µm, preferably at most 1.5 µm. The holes or protrusions can have an average diameter of at least 20 nm, preferably at least 50 nm and / or at most 3 µm, preferably at most 1.5 µm.

[0016] The layer system further comprises an upconversion material arranged on the first and / or second side. The upconversion material can also enclose the photonic crystal and / or fill air spaces of the photonic crystal. The upconversion material contains at least a first lanthanide and at least a second lanthanide. The first lanthanide is preferably neodymium or ytterbium, or a combination of neodymium and ytterbium. The second lanthanide is preferably selected from the group consisting of erbium, thulium, and holmium, and combinations thereof. Lanthanide refers to lanthanide ions, for example erbium. 3+ .

[0017] The first lanthanide can be selected such that radiation in a specific spectral range, particularly in the near-infrared and / or visible spectral range, is absorbed by the first lanthanide. Absorption of radiation by the first lanthanide leads to emission of radiation through the layer system of shorter wavelengths compared to the radiation absorbed by the first lanthanide.

[0018] The first lanthanide may be present in a higher particle ratio than the second lanthanide. The particle ratio between the first lanthanide and the second lanthanide is at most 99:1 and / or at least 1:1.

[0019] The upconversion material can further comprise a support matrix. The first lanthanide and the second lanthanide can be applied to the support matrix or incorporated into the support matrix. The support matrix can comprise one selected from the group consisting of a nanoparticle, a microparticle, a film, a membrane, and combinations thereof. In one embodiment, the support matrix preferably comprises fluorinated materials, such as NaYF4, CaF, BaF, SrF. The support matrix or a component of the support matrix can contain the first lanthanide or the second lanthanide, for example in the case of NaYbF4. In one embodiment, the support matrix comprises SiO2. In another embodiment, the support matrix comprises a polymer. In one embodiment, the support matrix comprises nanoparticles or microparticles and a film, wherein the nanoparticles or microparticles are embedded in the film.Multiple support matrices can be combined, for example, lanthanide-containing NaYF4 nanoparticles embedded in a polymer. In embodiments in which the support matrix comprises nanoparticles or microparticles, the percentage ratio between the first lanthanide, the second lanthanide, and the replaced atoms of the nanoparticles or microparticles can be, for example, 10%:1%:89% or 20%:2%:78%. For example, NaYF4:2% Er:20% Yb means that 2% of the Na atoms have been replaced by Er, and another 20% by Yb.

[0020] In embodiments in which the carrier matrix comprises nanoparticles, the nanoparticles can have an average particle size of at least 1 nm and / or at most 100 nm. The average particle size is preferably determined by means of transmission electron spectroscopy. In embodiments in which the carrier matrix comprises microparticles, the microparticles can have an average particle size of at least 0.1 µm and / or at most 100 µm. The nanoparticles and / or the microparticles can each have a core and a shell, wherein the first lanthanide and / or the second lanthanide can each be arranged in the core and / or in the shell. For example, the nanoparticles and / or the microparticles can each have cores with lanthanides and a shell without lanthanides. In another exemplary embodiment, the nanoparticles and / or the microparticles can each have cores with Yb 3+ and He3+ , and bowls with Nd 3+ and Yb 3+ or nuclei with Yb 3+ and He 3+ , and shells without lanthanides.

[0021] The upconversion material can form a film on the first side and / or the second side of the photonic crystal, partially or substantially completely covering the first side and / or the second side, or enclosing the photonic crystal. The upconversion material can have a layer thickness of at most 1 mm, preferably at most 300 nm. In one embodiment, the upconversion material is arranged in the form of particles on the first side and / or the second side.

[0022] According to one embodiment, a passivation layer can be arranged on the upconversion material and / or on the first side and / or on the second side. The passivation layer can represent a protective layer for the upconversion material and / or the photonic crystal. The passivation layer can comprise a polymer or SiO2.

[0023] Advantageously, the layer system comprising the photonic crystal and the upconversion material arranged on the photonic crystal enables a substantial increase in upconversion efficiencies and intensities compared to upconversion materials known from the prior art. With the photonic crystal, optical resonances or optical field strength increases occur in a limited spectral range, in particular additionally at a limited angle of incidence. The photonic crystal can be selected or manufactured such that the absorption band of the upconversion material substantially coincides with or partially overlaps the spectral range of the optical resonances or optical field strength increases of the photonic crystal.The production of photonic crystals in which optical resonances or optical field strength increases occur in a limited spectral range, in particular additionally at a limited angle of incidence, is known to those skilled in the art. For example, reference is made to Photonic Crystals, Molding the Flow of Light, 2nd edition by John D. Joannopoulos, Steven G. Johnson, Joshua N. Winn, Robert D. Meade, Princeton University Press. Without being bound by any theory, it is assumed that within the photonic crystal, and in particular near or in the region of the first and / or second side of the photonic crystal, the field strength is locally increased and an interaction with the upconversion material occurs. This higher field strength can be used to increase the efficiency of an energy transfer mechanism from the first lanthanide to the second lanthanide.As a result, a substantial increase in the upconversion efficiencies and intensities can be achieved for the layer system according to the present disclosure compared to an upconversion material without the use of a photonic crystal or compared to upconversion materials known from the prior art.

[0024] The layer system according to embodiments of the present disclosure enables efficient upconversion of low-intensity radiation. Particularly in the field of security technology (security applications) or when using the layer system for an assay or bioassay (bioanalytics), this enables the use of low-power excitation sources, in particular lasers. Advantageously, applications become more cost-effective and human safety is increased. Low power of the excitation source reduces negative influences on the layer system. For example, the risk of overheating or other degradation of the layer system caused by the excitation source is reduced.The use of the layer system according to the present disclosure for a sensor for detecting neutral or ionic analytes or an assay or a bioassay enables the lowering of detection limits compared to previously used upconversion materials due to the efficient upconversion.

[0025] Furthermore, the layer system according to embodiments of the present disclosure enables control of the color impression of the radiation emitted by the layer system. Without being bound by any theory, it is assumed that the upconversion efficiencies and intensities depend on the local field strength. The color impression of the radiation emitted by the layer system can be controlled by selecting or producing a photonic crystal such that the local increase in field strength is suitable for the increased upconversion of a desired wavelength range of the emitted radiation. The production of photonic crystals in which optical resonances or optical field strength increases occur in a limited spectral range, in particular additionally at a limited angle of incidence, is known as such to the person skilled in the art. For example, see Photonic Crystals, Molding the Flow of Light, 2.Edition by John D. Joannopoulos, Steven G. Johnson, Joshua N. Winn, Robert D. Meade, Princeton University Press.

[0026] According to one embodiment, the photonic crystal can be selected or manufactured such that a substantial increase in field strength occurs at certain incident angles. The layer system can be configured to efficiently upconvert near-infrared radiation at a predefined incident angle. In one embodiment, the layer system can be configured to very efficiently upconvert near-infrared radiation at a substantially perpendicular incident angle. The layer system can be configured to emit upconverted radiation isotropically or directionally.

[0027] Advantageously, an angular dependence of the amplification of the electromagnetic field strength of the photonic crystal near or in the region of the upconversion material and / or the emission properties of the layer system leads to an increase in the upconversion efficiencies and intensities, for example, when using the layer system for an assay or a bioassay. The angular dependence of the amplification of the upconversion efficiency and / or the emission properties of the layer system enables an additional coding dimension when using the layer system for security applications. Furthermore, an increase in the efficiency of the upconversion material and / or the emission properties of the layer system allows conclusions to be drawn about the field strength within the photonic crystal. The layer system can advantageously be used for a sensor for determining electromagnetic field strengths in photonic structures.

[0028] According to one embodiment, the layer system comprises a substrate arranged on the second side. The substrate can be removably applied to the second side. The substrate can be a membrane or a film.

[0029] The substrate is preferably transparent. Transparent here means, in particular, transparent to radiation in the visible spectral range, or transparent to radiation in the visible spectral range and the near-infrared spectral range up to 1000 nm. The substrate can be made of a material that has a lower refractive index than the first material of the photonic crystal. Preferably, the substrate comprises one of the following materials: a glass, a transparent polymer, and cellulose.

[0030] The layer system comprising the transparent substrate arranged on the second side enables application for transmission measurements, particularly when the layer system is used for an assay or bioassay. Advantageously, a transparent substrate enables the absorption of radiation by the upconversion material at any angle of incidence and the emission of radiation by the layer system at any angle.

[0031] According to one embodiment, the layer system comprises biomolecules, preferably antibodies, oligonucleotides (DNA, RNA) or aptamers, between the first side of the, preferably two-dimensional, photonic crystal and the upconversion material and / or between the second first side of the, preferably two-dimensional, photonic crystal and the upconversion material.

[0032] According to one embodiment, the upconversion material can comprise a dye. For example, the dye can be an organic dye, an analyte-sensitive dye, or an environment-sensitive dye. The dye can be coupled to the first lanthanide and / or the second lanthanide. For example, the dye can be applied to the surface of the nanoparticles or the dye can be embedded in the carrier matrix. The carrier matrix can be permeable to analytes. The layer system can be used for a biosensor and / or a biosensor can be provided that comprises the layer system. The coupling between the dye and the first lanthanide and / or the second lanthanide can enable a radiationless or radiative energy transfer between the first lanthanide and / or the second lanthanide and the dye.Emission from the dye can serve as a detection signal or to determine the concentration of an analyte. In another embodiment, the dye can serve as an indicator. The dye can absorb the radiation emitted by the first lanthanide and / or the second lanthanide. An emission spectrum of the layer system altered by the absorption of the dye can serve to detect an analyte. The analytes can be, for example, metal ions or organic molecules. The environment-sensitive dyes can be sensitive to environmental properties such as viscosity, pH, and temperature.

[0033] According to one embodiment, a layer system for the upconversion of near-infrared and / or visible radiation is provided. The layer system comprises a, preferably two-dimensional, photonic crystal with a first and a second side and an upconversion material arranged on the first side. The upconversion material contains a first lanthanide, wherein the first lanthanide is preferably neodymium or ytterbium. The upconversion material further contains a second lanthanide, wherein the second lanthanide is preferably selected from the group consisting of erbium, thulium, and holmium. The layer system has a substrate arranged on the second side. Optionally, the substrate is detachably applied to the second side. The substrate is preferably a membrane or a film.

[0034] The above embodiment can be arbitrarily combined with the features of all previously disclosed embodiments.

[0035] According to one embodiment, a layer system for the upconversion of near-infrared and / or visible radiation is provided. The layer system is obtainable by the steps of: producing a, preferably two-dimensional, photonic crystal having a first and a second side by means of nanoimprint lithography and applying an upconversion material to the first side and / or the second side of the photonic crystal. The upconversion material contains a first lanthanide, wherein the first lanthanide is preferably neodymium or ytterbium. The upconversion material contains a second lanthanide, wherein the second lanthanide is preferably selected from the group consisting of erbium, thulium, and holmium.

[0036] The above embodiment can be arbitrarily combined with the features of all previously disclosed embodiments.

[0037] According to one embodiment, a method for producing a layer system for upconverting near-infrared and / or visible radiation is provided. The method comprises forming a, preferably two-dimensional, photonic crystal having a first and a second side by means of nanoimprint lithography and applying an upconversion material to the first side and / or the second side of the photonic crystal. The upconversion material contains a first lanthanide, wherein the first lanthanide is preferably neodymium or ytterbium. The upconversion material contains a second lanthanide, wherein the second lanthanide is preferably selected from the group consisting of erbium, thulium, and holmium.

[0038] In one embodiment, the photonic crystal is formed according to published patent application DE 10 2011 111 629 A1 and / or according to published patent application WO / 2013 / 027123 A1, and / or according to C. Becker, P. Wyss, D. Eisenhauer, J. Probst, V. Preidel, M. Hammerschmidt and S. Burger, Scientific Reports 4, 5886 (2014), which is hereby incorporated by reference.

[0039] Forming the preferably two-dimensional photonic crystal can comprise structuring a master substrate using nanoimprint lithography. Subsequently, a first material can be applied by physical vapor deposition. In particular, the first material can be applied in amorphous form. For example, the first material can be silicon. Subsequently, thermal heating can be performed, whereby the first material at least partially crystallizes. Furthermore, forming the two-dimensional photonic crystal can comprise removing non-crystalline material, in particular by chemical etching and / or mechanical abrasion.

[0040] Advantageously, both physical vapor deposition and nanoimprint lithography enable the fabrication of photonic crystals with a large size at short fabrication times and low costs.

[0041] In one embodiment, the upconversion material is applied by a method selected from the group consisting of spin coating, spray coating, drop coating, dip coating, or sol-gel method.

[0042] The method may comprise applying a substrate to the second side of the photonic crystal. Applying the substrate may occur at any time. According to one embodiment, the method comprises applying the substrate after applying the upconversion material. According to one embodiment, the master substrate is the substrate.

[0043] According to one embodiment, the method can be an assay or a bioassay. The assay can comprise, between the step of forming a, preferably two-dimensional, photonic crystal with a first and a second side by means of nanoimprint lithography and the step of applying an upconversion material to the first side and / or the second side of the photonic crystal, a step of applying biomolecules, preferably antibodies, oligonucleotides (DNA, RNA), or aptamers, to the first side and / or the second side of the photonic crystal.

[0044] The layer systems according to one of the embodiments of the present disclosures can be used for one selected from the group consisting of a display screen; a nanolamp; a photovoltaic system; and a sensor, in particular a sensor for determining electromagnetic field strengths in photonic structures, a sensor for determining a radiation intensity of a radiation source, a humidity sensor, a pressure sensor, a temperature sensor, a sensor for detecting water, a biosensor, in particular a biosensor for detecting ionic and / or neutral analytes or a biosensor for detecting environmental properties, such as viscosity, pH value and temperature, an assay, or a bioassay. Brief description of the characters

[0045] The accompanying drawings illustrate embodiments and, together with the description, serve to explain the principles of the invention. The elements of the drawings are relative to one another and are not necessarily to scale. Like reference numerals designate similar parts. Fig. 1A schematically shows a section of a photonic crystal, according to embodiments of the present disclosure. Fig. 1B schematically shows a section of a photonic crystal, according to embodiments of the present disclosure. Fig. 2 schematically shows a section of a layer system according to embodiments of the present disclosure. Fig. 3 schematically shows a section of a layer system according to embodiments of the present disclosure. Fig. 4 schematically shows a section of a layer system according to embodiments of the present disclosure. Fig. 5 shows a measurement of a section of a photonic crystal, according to embodiments of the present disclosure. Fig. 6 shows a measurement of a section of a layer system, according to embodiments of the present disclosure. Fig. 7 shows a measurement of a section of a layer system, according to embodiments of the present disclosure. Fig. 8 shows a measurement of a section of a layer system, according to embodiments of the present disclosure. Fig. 9A shows a measurement of a layer system, according to embodiments of the present disclosure. Fig. 9B shows a measurement of a layer system, according to embodiments of the present disclosure. Fig. 10A shows a measurement of a layer system, according to embodiments of the present disclosure. Fig. 10B shows a measurement of a layer system, according to embodiments of the present disclosure. Detailed description

[0046] Fig. 1A schematically shows a section of a two-dimensional photonic crystal 110 according to one embodiment. The photonic crystal 110 has a first side 111 and a second side 112. In the Fig. 1A, only the first side 111 is visible. The two-dimensional photonic crystal 110 has Fig. 1A has a substantially periodic arrangement of holes 113 parallel to the first side 111. The holes 113 are arranged substantially hexagonally.

[0047] Fig. Figure 1B schematically shows a section of the two-dimensional photonic crystal 110 according to one embodiment. The photonic crystal 110 has the first side 111 and the second side 112. In the Fig. 1B, only the first side 111 is visible. The two-dimensional photonic crystal 110 has Fig. 1B has a substantially periodic arrangement of elevations 114 parallel to the first side 111. The elevations 114 are arranged substantially hexagonally.

[0048] Fig. Figure 2 schematically shows a section of the layer system 100 according to one embodiment. The layer system 100 comprises the two-dimensional photonic crystal 110 with the first side 111 and the second side 112. The two-dimensional photonic crystal 110 comprises Fig. 2 parallel to the first side 111 a substantially periodic arrangement of elevations 114. The upper sides of the elevations each form the first side 111. Furthermore, the layer system 100 has an upconversion material 120 arranged on the first side 111. The upconversion material 120 has a carrier matrix. The upconversion material 120 contains a first lanthanide and a second lanthanide. The first lanthanide and the second lanthanide are incorporated in the carrier matrix. The carrier matrix is ​​in Fig. 2 is a film. The layer system 100 has a substrate 130 arranged on the second side 112. The substrate 130 is a film.

[0049] Fig. Figure 3 schematically shows a section of the layer system 100 according to one embodiment. The layer system 100 comprises the two-dimensional photonic crystal 110 with the first side 111 and the second side 112. The two-dimensional photonic crystal 110 comprises Fig. 3 parallel to the first side 111, a substantially periodic arrangement of elevations 114. The upper sides of the elevations each form the first side 111. Furthermore, the layer system 100 has the upconversion material 120 arranged on the first side 111. The upconversion material 120 has the carrier matrix. The upconversion material 120 contains a first lanthanide and a second lanthanide. The first lanthanide and the second lanthanide are incorporated in the carrier matrix. The carrier matrix is ​​in Fig. 3 a nanoparticle.

[0050] Fig. Figure 4 schematically shows a section of the layer system 100 according to one embodiment. The layer system 100 comprises the two-dimensional photonic crystal 110 with the first side 111 and the second side 112. The two-dimensional photonic crystal 110 comprises Fig. 4 parallel to the first side 111 a substantially periodic arrangement of elevations 114. The upper sides of the elevations each form the first side 111. Furthermore, the layer system 100 has the upconversion material 120 arranged on the first side 111. The upconversion material 120 has the carrier matrix. The upconversion material 120 contains a first lanthanide and a second lanthanide. The first lanthanide and the second lanthanide are incorporated in the carrier matrix. The carrier matrix is ​​in Fig. 4, a nanoparticle. The layer system 100 has the substrate 130 arranged on the second side 112. The substrate 130 is a film.

[0051] Fig. Figure 5 shows a measurement of a section of the two-dimensional photonic crystal 110, according to embodiments of the present disclosure, taken with a scanning electron microscope. The photonic crystal 110 has the first side 111, which is Fig. 4, and the second side 112. The two-dimensional photonic crystal 110 has a substantially periodic arrangement of holes 113 parallel to the first side 111. The holes 113 are arranged essentially hexagonally.

[0052] Fig. Figure 6 shows a measurement of a section of the layer system 100, according to embodiments of the present disclosure, taken with a scanning electron microscope. The layer system 100 has the upconversion material 120 arranged on the first side 111 of the two-dimensional photonic crystal 110. The photonic crystal 110 of the Fig. The layer system shown in Figure 6 has an extension of 65 nm from the first side 111 to the second side 112. The photonic crystal 110 comprises a first material consisting of silicon. The upconversion material 120 comprises the carrier matrix and contains the first lanthanide and the second lanthanide. The carrier matrix comprises nanoparticles and a film, with the nanoparticles embedded in the film. The first lanthanide and the second lanthanide are incorporated into the nanoparticles. The film comprises a polymer. The nanoparticles have an average particle size of 25 nm. The average particle size was determined using transmission electron spectroscopy. The nanoparticles consist of NaYF4 doped with 18% Yb. 3+ and 2% He 3+ The nanoparticles are embedded in a film containing polymethyl methacrylate.

[0053] Fig. Figure 7 shows a measurement of a section of the layer system 100, according to embodiments of the present disclosure, taken with an atomic force microscope. The layer system 100 comprises the two-dimensional photonic crystal 110 with the first side 111 and the second side 112. The two-dimensional photonic crystal 110 has Fig. 7, parallel to the first side 111, a substantially periodic arrangement of holes 113. The holes 113 are arranged substantially hexagonally. Furthermore, the layer system 100 comprises the upconversion material 120 arranged on the first side 111. The upconversion material 120 comprises individual NaYF4 nanoparticles containing the first lanthanide and the second lanthanide. The first lanthanide is ytterbium, and the second lanthanide is erbium. The nanoparticles have an average particle size of 25 nm.

[0054] Fig. 8 shows a measurement of a section of a layer system 100 according to embodiments of the present disclosure, taken with a scanning electron microscope. For the Fig. 6 and Fig. The same layer system was used for the measurements shown in Figure 8.

[0055] Fig. Figure 9A shows an angle-dependent and excitation wavelength-dependent transmission measurement of the photonic crystal 110. The photonic crystal 110 of Fig. 9A corresponds to the Fig. 6. Regions of low transmission indicate spectral positions of modes of the photonic crystal 110, which can be used for emission amplification.

[0056] Fig. Figure 9B shows the angle-dependent enhancement of the emission of the layer system made of Fig. 6. The layer system was excited by a radiation source with a wavelength of 976 nm. The emission amplification corresponds to the ratio of the emission of the layer system to Fig. 6 (each at a specific angle) and the emission of a non-inventive layer system. The non-inventive layer system has the same properties as the layer system shown in Fig. 6, in particular with regard to the upconversion material, with the difference that there is no photonic crystal, but a layer of silicon, which has the same extension from the first side 111 to the second side 112 (65 nm) as the layer system shown in Fig. 6. The layer system according to the invention can increase the upconversion efficiency by a factor of more than one hundred compared to the layer system not according to the invention.

[0057] Fig. 10A shows a transmission measurement under the same test conditions as in Fig. 9A, with the difference that the photonic crystal 110 has an extension of 120 nm from the first side 111 to the second side 112.

[0058] Fig. Figure 10B shows the angle-dependent enhancement of the emission under the same experimental conditions as in Fig. 9B, with the difference that both the photonic crystal 110 of the layer system according to the invention and the silicon layer of the layer system not according to the invention have an extension of 120 nm from the first side 111 to the second side 112.

Claims

[1] Method for producing a sensor comprising a layer system (100) for the upconversion of near-infrared and / or visible radiation, the method comprising: - forming a, preferably two-dimensional, photonic crystal (110) having a first (111) and a second side (112) by means of nanoimprint lithography; - applying an upconversion material (120) to the first side (111) and / or the second side (112) of the photonic crystal (110), wherein the upconversion material (120) contains a first lanthanide, wherein the first lanthanide is preferably neodymium or ytterbium; and wherein the upconversion material (120) contains a second lanthanide, wherein the second lanthanide is preferably selected from the group consisting of erbium, thulium and holmium. [2] The method according to claim 1, wherein the particle ratio between the first lanthanide and the second lanthanide is at most 99:1 and / or at least 1:

1. [3] Method according to one of the preceding claims, wherein the upconversion material (120) has a layer thickness of at most 1 mm, preferably at most 300 nm. [4] Method according to one of the preceding claims, wherein the upconversion material (120) further comprises a carrier matrix, wherein the first lanthanide and the second lanthanide are arranged on or in the carrier matrix, in particular wherein the carrier matrix comprises one selected from the group consisting of a nanoparticle, a microparticle, a film, a membrane, and combinations thereof. [5] The method according to claim 4, wherein the nanoparticles have an average particle size of at least 1 nm and / or at most 100 nm, or the microparticles have an average particle size of at least 0.1 µm and / or at most 100 µm. [6] Method according to one of the preceding claims, wherein an extension of the photonic crystal (110) from the first side (111) to the second side (112) is at least 20 nm, preferably at least 60 nm, and / or at most 5000 nm, preferably at most 500 nm. [7] Method according to one of the preceding claims, wherein the photonic crystal (110) comprises a first material, wherein the first material is selected from the group consisting of oxides, nitrides, carbides, III / V semiconductors, germanium and silicon, preferably the first material is silicon. [8] Method according to one of the preceding claims, wherein the photonic crystal (110) has a substantially periodic arrangement of holes (113) or elevations (114) parallel to the first side (111), wherein preferably the holes (113) or elevations (114) are arranged substantially hexagonally. [9] Method according to one of the preceding claims, wherein the holes (113) or elevations (114) have an average spacing of at least 100 nm, preferably at least 300 nm and / or at most 3 µm, preferably at most 1.5 µm and / or wherein the holes (113) or elevations (114) have an average diameter of at least 20 nm, preferably at least 50 nm and / or at most 3 µm, preferably at most 1.5 µm. [10] Method according to one of the preceding claims, wherein the layer system is further configured to absorb near-infrared radiation at a substantially perpendicular angle of incidence, and / or further configured to emit up-converted radiation isotropically or directionally. [11] Method according to one of the preceding claims, wherein along the first side (111) the layer system, in particular the photonic crystal (110), has an extension of at least 1 mm, preferably at least 1 cm, and more preferably at least 3 cm. [12] Method according to one of the preceding claims, wherein the upconversion material (120) is applied by means of a process selected from the group consisting of spin coating, spray coating, drop coating, dip coating or sol-gel process. [13] The method of any preceding claim, wherein forming the photonic crystal (110) comprises depositing a first material by physical vapor deposition. [14] Method according to one of the preceding claims, further comprising the step: - Applying a substrate (130) to the second side (112) of the photonic crystal, wherein optionally the substrate (130) is detachably applied to the second side (112), preferably wherein the substrate (130) is a membrane or a film. [15] The method of claim 14, wherein the substrate (130) is transparent and / or wherein the substrate (130) comprises one of the group consisting of a glass, a transparent polymer and cellulose. [16] Method according to one of the preceding claims, wherein the sensor is one selected from the group consisting of a sensor for determining electromagnetic field strengths in photonic structures, a sensor for determining a radiation intensity of a radiation source, a humidity sensor, a pressure sensor, a temperature sensor, a sensor for detecting water, a biosensor, and a bioassay.

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