Optical filter, infrared sensor, and light emitting device

Abstract

An optical filter (1) includes a matrix (10) composed of an inorganic substance having a solubility of 0.4 g / 100 g-H2O or less in water, and a wavelength-selective absorbing material (20) dispersed in the matrix (10). The optical filter (1) absorbs a light component having any one of wavelength bands in a target wavelength band of 0.8 μm to 20 μm. When heated at a rate of 10°C / min from 100°C in air, the temperature at which the mass reduction rate of the wavelength-selective absorbing material (20) reaches 10 mass% is 900°C or less. The apparent density of the optical filter (1) is 70% or more relative to the true density of the matrix (10). In the target wavelength band, the wavelength bandwidth for which the straight transmittance per 1 mm thickness of the optical filter (1) is 30% or more is 50 nm or more.

Description

Technical Field

[0001] This invention relates to optical filters, infrared sensors, and light-emitting devices. Background Technology

[0002] In the past, infrared sensors have been used in applications such as flame sensors or human body sensors. These sensors detect the presence of flames or people by exposing them to infrared light of specific wavelengths emitted by the flame or person. However, infrared sensors can also detect light components emitted by substances other than the detected objects, at wavelengths different from those wavelengths. Therefore, to remove the light components that cause noise, optical filters that selectively transmit only specific wavelengths of infrared light are used in infrared sensors.

[0003] As such an optical filter, Patent Document 1 discloses a particle-dispersed composite infrared bandpass filter, which includes a resin and inorganic compound particles uniformly dispersed in the resin and selectively transmitting infrared light only in a specific wavelength band.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 63-073203 Summary of the Invention

[0007] In the prior art, bandpass filters with a wide range of transmittance wavelengths are easily manufactured by selecting a combination of resin and inorganic compound particles. However, it is known that resins deteriorate when exposed to ultraviolet light, etc. Therefore, existing bandpass filters have concerns about changes in optical properties over time and limitations in application environments.

[0008] The present invention was made in view of the technical problems existing in the prior art. Furthermore, the object of the present invention is to provide optical filters, infrared sensors, and light-emitting devices having excellent durability and an inorganic matrix.

[0009] To address the aforementioned technical problems, the optical filter of the first embodiment of the present invention comprises a matrix composed of an inorganic substance with a solubility in water of 0.4 g / 100 g H₂O or less, and a wavelength-selective absorbing material dispersed within the matrix. The optical filter absorbs light components of any wavelength band within a target wavelength range of 0.8 μm to 20 μm. When heated in air at a rate of 10 °C / min starting from 100 °C, the temperature at which the mass reduction rate of the wavelength-selective absorbing material reaches 10% by mass is 900 °C or less. The apparent density of the optical filter relative to the true density of the matrix is ​​70% or more. Within the target wavelength range, the wavelength bandwidth of the optical filter with a linear transmittance of 30% or more per 1 mm thickness is 50 nm or more.

[0010] The infrared sensor of the second aspect of the present invention includes the aforementioned optical filter.

[0011] The third-party light-emitting device of the present invention includes the aforementioned optical filter. Attached Figure Description

[0012] Figure 1 A cross-sectional view is shown to schematically illustrate one example of the optical filter of this embodiment.

[0013] Figure 2 To enlarge Figure 1 A cross-sectional view of the optical filter.

[0014] Figure 3 A cross-sectional view is shown to schematically illustrate one example of an infrared sensor according to this embodiment.

[0015] Figure 4 This is a schematic diagram illustrating one example of the light-emitting device according to this embodiment.

[0016] Figure 5 The infrared spectra of the test samples of Example 1 and Reference Example 1 were determined using the transmission method.

[0017] Figure 6 This is the TG curve of melamine.

[0018] Figure 7 The infrared spectra of the test samples of Examples 2 to 6 and Reference Example 2 were determined by means of the transmission method.

[0019] Figure 8 To enlarge Figure 7 A portion of the infrared spectrum.

[0020] Figure 9 The infrared spectra of the test samples of Example 2, Example 7 and Reference Example 2 were determined by means of the transmission method.

[0021] Figure 10 To enlarge Figure 9 A portion of the infrared spectrum.

[0022] Figure 11 To determine the infrared spectra of PTFE powder and PVDF powder using the ATR method.

[0023] Figure 12 The TG curves are for PTFE and PVDF. Detailed Implementation

[0024] The optical filter, infrared sensor, light-emitting device, and manufacturing method of the optical filter according to this embodiment will be described in detail below with the aid of accompanying drawings. Furthermore, the dimensions in the drawings are exaggerated for ease of explanation and may sometimes differ from the actual dimensions.

[0025] [Optical Filter]

[0026] The optical filter 1 in this embodiment is as follows: Figure 1 The diagram shows a matrix 10 and a wavelength-selective absorbing material 20.

[0027] The matrix 10 is composed of inorganic materials. Therefore, compared with the use of resin, the matrix 10 is less prone to deterioration over time, and an optical filter 1 with high infrared transmittance can be obtained.

[0028] The inorganic substance constituting matrix 10 has a solubility of 0.4 g / 100 g H₂O or less in water. Because the solubility of the inorganic substance in water is below this value, the optical filter 1 can be used stably even in high humidity environments or underwater environments. Furthermore, the solubility was measured at 1 atm and 25°C. The unit of solubility, "g / 100 g H₂O," refers to the mass of the inorganic substance dissolved in 100 g of water.

[0029] The inorganic material constituting matrix 10 contains at least one metallic element selected from alkali metals, alkaline earth metals, transition metals, base metals, and semimetals. In this specification, alkaline earth metals include beryllium and magnesium in addition to calcium, strontium, barium, and radium. Base metals include aluminum, zinc, gallium, cadmium, indium, tin, mercury, thallium, lead, bismuth, and polonium. Semimetals include boron, silicon, germanium, arsenic, antimony, and tellurium. Preferably, the inorganic material contains at least one metallic element selected from alkali metals such as lithium, zinc, aluminum, and magnesium. As described later, the inorganic material containing these metallic elements can readily form bonding portions 12 from the inorganic material using a pressure heating method.

[0030] The inorganic substance constituting matrix 10 preferably contains at least one compound selected from, for example, fluorides, oxides, nitrides, hydroxides, oxyhydroxides, sulfides, borides, carbides, and halides of the aforementioned metal element. More preferably, the inorganic substance contains the aforementioned compound as a main component. Furthermore, a main component refers to the inorganic substance containing 50 mol% or more of the aforementioned compound. Preferably, the inorganic substance contains 80 mol% of the aforementioned compound, more preferably 90 mol% or more. In addition, the oxides of the aforementioned metal element may include phosphates, silicates, aluminates, and borates, in addition to compounds in which only oxygen is bonded to the metal element. Furthermore, the inorganic substance constituting matrix 10 may also be a complex anionic compound containing the aforementioned metal element. A complex anionic compound is a substance containing multiple anions in a single compound; examples include acyl fluorides, acyl chlorides, and nitrogen oxides.

[0031] Furthermore, the inorganic material constituting the matrix 10 preferably includes at least one selected from fluorides, oxides, and hydroxides. Because this inorganic material has low solubility in water, the optical filter 1 can be used stably even in high humidity environments or underwater environments. Examples of fluorides include magnesium fluoride and lithium fluoride. For example, when the inorganic material includes lithium fluoride, it can provide an optical filter 1 with high transmittance and high density in the wavelength band below 10 μm. Examples of oxides include aluminum oxide, zinc oxide, magnesium oxide, cerium oxide, and yttrium oxide.

[0032] like Figure 2 As shown, the matrix 10 may further comprise a plurality of inorganic particles 11. Each of the plurality of inorganic particles 11 is bonded to the others. The inorganic particles 11 may be in point contact or in surface contact. Furthermore, the matrix 10 may also include bonding portions 12 that bond the plurality of inorganic particles 11 together. Adjacent inorganic particles 11 are bonded through the bonding portions 12, resulting in three-dimensional bonding between the inorganic particles 11, thus obtaining an optical filter 1 with high mechanical strength. The bonding portions 12 preferably have direct contact with the inorganic particles 11. Furthermore, the bonding portions 12 preferably cover at least a portion of the surface of each of the plurality of inorganic particles 11, more preferably covering the entire surface of each of the plurality of inorganic particles 11. Therefore, since the inorganic particles 11 are firmly bonded to the bonding portions 12, an optical filter 1 with excellent density and mechanical strength can be obtained. In addition to existing between adjacent inorganic particles 11, the bonding portion 12 can also exist between inorganic particles 11 and wavelength-selective absorbing material 20, as well as between adjacent wavelength-selective absorbing materials 20.

[0033] Inorganic particles 11 can be composed of the same inorganic material as the inorganic material constituting the matrix 10 described above.

[0034] The inorganic material constituting the inorganic particles 11 can be crystalline or amorphous. From the viewpoint of gas barrier properties or durability, the inorganic material constituting the inorganic particles 11 is preferably crystalline. Furthermore, from the viewpoint of light transmittance, the inorganic material constituting the inorganic particles 11 is preferably amorphous. Moreover, when the inorganic material is crystalline, the inorganic particles 11 are more preferably crystalline inorganic particles containing at least one metallic element selected from alkali metals, alkaline earth metals, transition metals, base metals, and half-metals.

[0035] Furthermore, from the viewpoint of gas barrier properties or durability, the inorganic particles 11 are preferably crystalline particles containing at least one selected from oxides, nitrides, hydroxides, hydroxide oxidants, sulfides, borides, carbides, and halides of the aforementioned metallic elements. More preferably, the inorganic particles 11 are crystalline particles whose main component is at least one selected from oxides, nitrides, hydroxides, hydroxide oxidants, sulfides, borides, carbides, and halides of the aforementioned metallic elements. The inorganic particles 11 preferably contain at least 80 mol% of at least one selected from oxides, nitrides, hydroxides, hydroxide oxidants, sulfides, borides, carbides, and halides of the aforementioned metallic elements, more preferably at least 90 mol%, and even more preferably at least 95 mol%. In addition, the inorganic material can be monocrystalline or polycrystalline.

[0036] The average particle size of the plurality of inorganic particles 11 is preferably 50 nm or more and 50 μm or less. With an average particle size of 50 μm or less, the transmittance of the optical filter 1 is improved. Furthermore, with an average particle size of 11 within this range, the inorganic particles 11 are firmly bonded together, which improves the strength of the optical filter 1. Additionally, with an average particle size of 11 within this range, as described later, since the proportion of pores present inside the optical filter 1 reaches 30% or less, the strength of the optical filter 1 can be improved. From the viewpoint of improving the transmittance of the optical filter 1, the average particle size of the plurality of inorganic particles 11 is more preferably 30 μm or less, further preferably 20 μm or less, and particularly preferably 10 μm or less. Moreover, unless otherwise specified, the value referred to as "average particle size" in this specification is calculated as the average particle size of particles observed in several to dozens of fields of view using observation methods such as scanning electron microscopy (SEM) or transmission electron microscopy (TEM).

[0037] The shape of the inorganic particles 11 is not particularly limited; for example, they can be spherical. Alternatively, the inorganic particles 11 can also be whisker-like (needle-like) particles or scale-like particles. Compared to spherical particles, whisker-like or scale-like particles have increased contact with other particles, thus improving the overall strength of the optical filter 1.

[0038] The bonding portion 12 preferably comprises an amorphous inorganic compound. Specifically, the bonding portion 12 may be a site formed solely of an amorphous inorganic compound, or it may be a site formed by a mixture of an amorphous inorganic compound and a crystalline inorganic compound. Alternatively, the bonding portion 12 may be a site formed by a crystalline inorganic compound dispersed within an amorphous inorganic compound. When an amorphous inorganic compound and a crystalline inorganic compound are mixed, the amorphous inorganic compound and the crystalline inorganic compound may have the same chemical composition or they may have different chemical compositions.

[0039] The inorganic particles 11 and the bonding portion 12 preferably contain the same metallic element, and this metallic element is at least one selected from alkali metals, alkaline earth metals, transition metals, base metals, and half-metals. That is, the inorganic compound constituting the inorganic particles 11 and the amorphous inorganic compound constituting the bonding portion 12 preferably contain at least the same metallic element. In addition, the inorganic compound constituting the inorganic particles 11 and the amorphous inorganic compound constituting the bonding portion 12 may have the same chemical composition or different chemical compositions.

[0040] Wavelength-selective absorbing material 20 is dispersed within the matrix 10. The wavelength-selective absorbing material 20 can exist between adjacent inorganic particles 11 or within the bonding portions 12. By dispersing the wavelength-selective absorbing material 20 within the matrix 10, the dependence on the incident angle of light is low, and even at large incident angles, an optical filter 1 with high light transmittance can be obtained. That is, even when light is irradiated onto the optical filter 1 from an oblique direction, the optical filter 1 can absorb specific light components and transmit other light components. Furthermore, since the gas barrier properties of the inorganic substances constituting the matrix 10 are higher than those of resin, the oxidation of the wavelength-selective absorbing material 20 can be suppressed by dispersing it within the matrix 10. Therefore, materials such as oxidants and reducing agents that are unstable in air can also be used as the wavelength-selective absorbing material 20.

[0041] Furthermore, in interference filters where multiple multilayer films of dielectrics with different refractive indices are stacked on the substrate surface, there is concern that the transmitted wavelength varies with the angle of light incidence. Therefore, it is recommended to transmit light in a direction perpendicular to the incident surface of the interference filter. However, in the optical filter 1 of this embodiment, the wavelength-selective absorption material 20 is dispersed in the matrix 10. Therefore, the transmitted wavelength is less dependent on the incident angle, and even if light is incident from an oblique direction relative to the surface of the optical filter 1, the effect on the transmitted wavelength is minimal. Thus, the optical filter 1 according to this embodiment can be applied to applications that are not feasible in interference filters.

[0042] Furthermore, in colored glass filters, since an absorbing material that absorbs light components with specific wavelengths is dispersed within the glass, the transmitted wavelength is less dependent on the incident angle. However, in colored glass filters, the molding temperature used to disperse the glass in the absorbing material is high. Therefore, only materials capable of withstanding such molding temperatures can be used, resulting in low design freedom. In contrast, the optical filter 1 of this embodiment, as described below, can be manufactured at low temperatures because the wavelength-selective absorbing material 20 can be dispersed within the matrix 10 using a pressure heating method.

[0043] When heated in air at a rate of 10°C / min from 100°C, the temperature at which the mass reduction rate of the wavelength-selective absorbing material 20 reaches 10% by mass is below 900°C. Since the optical filter 1 can be manufactured at low temperatures, even if the wavelength-selective absorbing material 20 is a compound with low heat resistance, or a material such as an oxidizing agent or reducing agent that is unstable in air, the wavelength-selective absorbing material 20 can be dispersed within the matrix 10. The temperature at which the mass reduction rate reaches 10% by mass can also be below 600°C, or even below 300°C. Furthermore, the temperature at which the mass reduction rate reaches 10% by mass can also be above 100°C. Moreover, the mass reduction rate can be measured using TG (thermogravimetric analysis).

[0044] The wavelength-selective absorption material 20 can absorb light components with wavelengths ranging from 0.8 μm to 20 μm within a target wavelength band. By absorbing such light components with the wavelength-selective absorption material 20, light components that would otherwise become noise can be removed when the optical filter 1 is used, for example, in an infrared sensor. Furthermore, the target wavelength band can be 1 μm or more, 2 μm or more, 3 μm or more, 7 μm or more, or 8 μm or more. Additionally, the target wavelength band can be 15 μm or less, 10 μm or less, or 6 μm or less.

[0045] The wavelength-selective absorbing material 20 may further comprise at least one selected from inorganic compounds, organic compounds, and deuterated derivatives of these compounds having hydrogen replaced by deuterium. Inorganic compounds may comprise at least one selected from hydroxides, nitrates, sulfates, hypophosphites such as calcium hypophosphite, and boric acid. Organic compounds may comprise at least one selected from fluoropolymers, azo metal complexes, triarylmethane compounds, anthocyanin compounds, squaric acid cyanide compounds, phthalocyanine compounds, dithiol complex pigments, diammonium salt compounds, naphthoquinone compounds, anthraquinone compounds, and amino compounds such as melamine. Fluoropolymers may, for example, comprise at least one selected from polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), perfluoroalkoxy fluoropolymer (PFA), ethylene tetrafluoride-propylene hexafluoride copolymer (FEP), ethylene-ethylene tetrafluoride copolymer (ETFE), and ethylene-chlorotrifluoroethylene copolymer (ECTFE). In addition, fluoropolymers can also be polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE). These fluoropolymers are readily available because they are widely used.

[0046] The average particle size of the wavelength-selective absorbing material 20 can be below 500 nm. When the average particle size of the wavelength-selective absorbing material 20 is below 500 nm, light scattering can be suppressed. There is no particular limitation on the lower limit of the average particle size of the wavelength-selective absorbing material 20; the average particle size of the wavelength-selective absorbing material 20 can be above 1 nm. The average particle size of the wavelength-selective absorbing material 20 can also be above 10 nm or above 100 nm. In addition, the average particle size of the wavelength-selective absorbing material 20 can also be below 400 nm or below 300 nm.

[0047] The refractive index difference between the material constituting the matrix 10 and the material constituting the wavelength-selective absorption material 20 can be 0.1 or less. When the refractive index difference is 0.1 or less, light scattering can be suppressed. There is no particular limitation on the lower limit of the refractive index difference; it is acceptable as long as the refractive index difference is 0 or more. The refractive index difference can be 0.01 or more, or 0.02 or more. In addition, the refractive index difference can also be 0.08 or less, or 0.04 or less.

[0048] The apparent density of the optical filter 1 is 70% or more relative to the true density (hereinafter also referred to as "relative density") of the matrix 10. With a relative density of 70% or more, the optical filter 1 becomes denser, increasing the amount of light transmitted through it. Furthermore, the density of the optical filter 1 also increases its strength, thus improving its machinability. Additionally, since cracking of the optical filter 1, originating from pores, can be suppressed, its flexural strength can be improved. More preferably, the relative density of the optical filter 1 is 80% or more; even more preferably, 90% or more; and particularly preferably, 95% or more.

[0049] The porosity of the cross-section of the optical filter 1 is preferably 30% or less. That is, when observing the cross-section of the optical filter 1, the average proportion of pores per unit area is preferably 30% or less. When the porosity is 30% or less, the amount of light transmitted through the optical filter 1 increases. In addition, when the porosity is 30% or less, the optical filter 1 becomes denser, and its strength increases. Therefore, the machinability of the optical filter 1 can be improved. Furthermore, when the porosity is 30% or less, cracking of the optical filter 1 starting from pores can be suppressed, thereby improving the bending strength of the optical filter 1. Moreover, the porosity of the cross-section of the optical filter 1 is more preferably 20% or less, further preferably 10% or less, and particularly preferably 5% or less. The smaller the porosity of the cross-section of the optical filter 1, the more effectively cracking starting from pores can be suppressed, thereby improving the strength of the optical filter 1.

[0050] In this specification, porosity can be calculated as follows. First, the cross-section of the optical filter 1 is observed to identify the matrix 10 and the pores. Then, the area per unit area and the area of ​​the pores within that unit area are measured, and the proportion of pores per unit area is obtained, which is taken as the porosity. More preferably, for the cross-section of the optical filter 1, after obtaining the proportion of pores per unit area at multiple locations, the average value of the proportion of pores per unit area is taken as the porosity. When observing the cross-section of the optical filter 1, an optical microscope, a scanning electron microscope (SEM), or a transmission electron microscope (TEM) can be used. Furthermore, the area per unit area and the area of ​​the pores within that unit area can be measured by binarizing the image observed using a microscope.

[0051] The size of the pores present inside the optical filter 1 is not particularly limited, but is preferably as small as possible. Because the pores are small, cracking originating from the pores can be suppressed, thereby improving the strength and machinability of the optical filter 1. Furthermore, the small pore size suppresses light scattering, thus increasing transmittance. Moreover, the size of the pores in the optical filter 1 is preferably 5 μm or less, more preferably 1 μm or less, and even more preferably 100 nm or less. The size of the pores present inside the optical filter 1, like the porosity described above, can be calculated by observing the cross-section of the optical filter 1 using a microscope.

[0052] In the optical filter 1, it is preferable that the volume ratio of the plurality of inorganic particles 11 is 30% or more. In this case, the resulting optical filter 1 becomes a structure that readily utilizes the properties of the inorganic particles 11. In the optical filter 1, the volume ratio of the plurality of inorganic particles 11 is more preferably 40% or more, and even more preferably 50% or more. The volume ratio of the inorganic particles 11 is preferably greater than the volume ratio of the bonding portion 12.

[0053] While the volume percentage of the wavelength-selective absorbing material 20 in the optical filter 1 depends on factors such as the transmission characteristics of the optical filter 1, it is preferably 0.1% by volume or more and 30% by volume or less. Having a volume percentage of 0.1% or more for the wavelength-selective absorbing material 20 increases the amount of light absorbed by the optical filter 1. Furthermore, having a volume percentage of 30% or less for the wavelength-selective absorbing material 20 improves the mechanical properties of the optical filter 1. A more preferable volume percentage is 0.2% by volume or more, and even more preferably 0.5% by volume or more. Furthermore, a more preferable volume percentage is 15% by volume or less, even more preferably 10% by volume or less, and particularly preferably 5% by volume or less.

[0054] The optical filter 1 absorbs light components with wavelengths ranging from 0.8 μm to 20 μm within a target wavelength band. By absorbing these light components, the optical filter 1 can remove light components that would otherwise become noise when used in applications such as sensors. Furthermore, the target wavelength band can be 1 μm or more, 2 μm or more, or 3 μm or more. Additionally, the target wavelength band can be 15 μm or less, 10 μm or less, or 6 μm or less.

[0055] Within the target wavelength band of 0.8 μm to 20 μm, the optical filter 1 has a wavelength bandwidth of 50 nm or more with a linear transmittance of 30% or more per 1 mm thickness. Due to this characteristic, the optical filter 1 can cut off a portion of the light component in the target wavelength band while allowing another portion to pass through. Therefore, when the optical filter 1 is used in, for example, an infrared sensor, it removes light components that would otherwise become noise, allowing the desired light component to reach the infrared sensor. Thus, an infrared sensor with low noise and high sensitivity can be obtained. Furthermore, the wavelength bandwidth with a linear transmittance of 30% or more can also be 100 nm or more, 300 nm or more, or 500 nm or more. Additionally, the wavelength bandwidth with a linear transmittance of 30% or more can be 5000 nm or less, 3000 nm or less, or 1000 nm or less. Furthermore, the linear transmittance can also be 35% or more, or 40% or more. There is no particular upper limit to the linear transmittance; for example, it can be 100%.

[0056] Within the target wavelength range of 0.8 μm to 20 μm, it is preferable that the wavelength bandwidth of the optical filter 1, with a linear transmittance of 1% or less per 1 mm thickness, is 50 nm or more. Because the optical filter 1 possesses this characteristic, when used in applications such as infrared sensors, it can significantly cut off light components that would otherwise become noise. Therefore, an infrared sensor with low noise and high sensitivity can be obtained. Furthermore, the wavelength bandwidth with a linear transmittance of 1% or less can also be 100 nm or more, 300 nm or more, or 500 nm or more. Additionally, the wavelength bandwidth with a linear transmittance of 1% or less can be 10000 nm or less, 5000 nm or less, 3000 nm or less, or 1000 nm or less. Furthermore, the linear transmittance can also be 0.5% or less, or 0.2% or less. The lower limit of the linear transmittance is not particularly limited, for example, it can be 0%.

[0057] Specifically, in the target wavelength band of 3μm to 10μm, the wavelength bandwidth with a linear transmittance of 30% or more is preferably 300nm or more. Furthermore, in the target wavelength band of 3μm to 10μm, the wavelength bandwidth with a linear transmittance of 1% or less is preferably 300nm or more. Additionally, in the target wavelength band of 3μm to 10μm, it is even more preferable that the wavelength bandwidth with a linear transmittance of 30% or more is 300nm or more, and the wavelength bandwidth with a linear transmittance of 1% or less is also 300nm or more. This optical filter 1 is useful as a bandpass filter or a bandstop filter.

[0058] Furthermore, in optical filter 1, the overall linear transmittance of the 8μm to 20μm wavelength band can be 10% or less. This optical filter 1 can be used as a filter that cuts off the wavelength of the long wavelength band. This filter can reduce noise in the long wavelength region, and therefore, when used in infrared sensors, for example, it can suppress false detections. In addition, by cutting off this wide wavelength band, the design freedom of machines such as infrared sensors can be increased. The overall linear transmittance of the 8μm to 20μm wavelength band can also be 8% or less, 5% or less, 2% or less, or 1% or less.

[0059] Furthermore, in optical filter 1, the overall linear transmittance of the wavelength band from 7μm to 20μm can be 10% or less. Therefore, an optical filter 1 that further cuts off the wavelength of the aforementioned long wavelength band can be provided. The overall linear transmittance of the wavelength band from 7μm to 20μm can also be 9% or less, 6% or less, 4% or less, or 1% or less.

[0060] The inorganic material may include fluorides, and the wavelength-selective absorption material 20 may include fluoropolymers. This allows for the provision of, for example, an optical filter 1 that cuts off wavelengths in the aforementioned long-wavelength band. Fluoropolymers have CF bonds and absorb light in the 8μm to 9μm wavelength band; therefore, by combining them with the fluoride matrix 10, an optical filter 1 that cuts off specific wavelengths in the aforementioned long-wavelength band can be provided. The fluoride can be, for example, lithium fluoride. Alternatively, the fluoropolymer can be, for example, polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE). Furthermore, since PVDF absorbs light components in the 8μm to 9μm wavelength band, the fluoropolymer can be PVDF.

[0061] Linear transmittance can be obtained by measuring optical filter 1 using a FT-IR (Fourier Transform Infrared Spectrometry) device via transmittance measurement. The linear transmittance of the infrared transmission spectrum is calculated according to Beer-Lambert's law, taking the linear transmittance as the thickness of 1 mm. Furthermore, the wavelength bandwidth can be obtained by measuring the wavelength bandwidth within the target wavelength band where the linear transmittance reaches or falls below a predetermined value. The wavelength bandwidth can be the wavelength bandwidth where the linear transmittance continuously reaches or falls below the predetermined value, or it can be the total wavelength bandwidth where the linear transmittance continuously and intermittently reaches or falls below the predetermined value. That is, the wavelength bandwidth is the total wavelength bandwidth within the target wavelength band where the linear transmittance reaches or falls above the predetermined value, or the total wavelength bandwidth where the linear transmittance falls below the predetermined value. Therefore, when the linear transmittance intermittently reaches or falls below the predetermined value, the wavelength bands where the linear transmittance reaches or falls below the predetermined value can be separate within the target wavelength band. Furthermore, the wavelength bandwidth is preferably the wavelength bandwidth where the linear transmittance continuously reaches or falls below the predetermined value. Specifically, within the target wavelength band, the wavelength bandwidth in which the linear transmittance of optical filter 1 is continuously 30% or more per 1 mm thickness can be 50 nm or more. Furthermore, within the target wavelength band, the wavelength bandwidth in which the linear transmittance is continuously 1% or less can be 300 nm or more.

[0062] The thickness t of the optical filter 1 is not particularly limited, and can be, for example, 100 μm or more. The optical filter 1 of this embodiment can be formed using a pressure heating method as described later. Therefore, a thick optical filter 1 can be easily obtained. Furthermore, the thickness of the optical filter 1 can be 500 μm or more, 1 mm or more, or 1 cm or more. The upper limit of the thickness of the optical filter 1 is not particularly limited, and can be, for example, 50 cm.

[0063] As described above, the optical filter 1 comprises a matrix 10 made of an inorganic substance with a solubility of 0.4 g / 100 g H₂O or less in water, and a wavelength-selective absorbing material 20 dispersed within the matrix 10. The optical filter 1 absorbs light components of any wavelength range within the target wavelength band of 0.8 μm to 20 μm. When heated in air at a rate of 10 °C / min from 100 °C, the temperature at which the mass reduction rate of the wavelength-selective absorbing material 20 reaches 10% by mass is 900 °C or less. The apparent density of the optical filter 1 relative to the true density of the matrix 10 is 70% or more. In the target wavelength band, the wavelength bandwidth of the optical filter 1 with a linear transmittance of 30% or more per 1 mm thickness is 50 nm or more. As described above, the optical filter 1 exhibits excellent durability due to the presence of the inorganic matrix 10.

[0064] Furthermore, the matrix 10 is composed of an inorganic material with higher gas barrier properties than resin, and the wavelength selective absorbing material 20 is dispersed within the matrix 10. Additionally, the matrix 10 has a high relative density compared to the apparent density of the optical filter 1, and is dense. Therefore, the optical filter 1 of this embodiment can protect the wavelength selective absorbing material 20 from the influence of air and other elements present in the external space. Thus, it is possible to use materials that were previously unusable and have low stability to oxygen or water as the wavelength selective absorbing material 20.

[0065] Infrared sensor

[0066] Next, use Figure 3 This embodiment describes the infrared sensor 100. The infrared sensor 100 is as follows: Figure 3 The optical filter 1 described above is shown. In addition, the infrared sensor 100 includes an infrared detection element 110, an IC element 120, a substrate 130, and a metal housing 150.

[0067] Infrared detection element 110 and IC element 120 are mounted on substrate 130 via chip bonding material 131. Infrared detection element 110 and IC element 120 are electrically connected to each other via wire 140. In addition, infrared detection element 110 is connected to a circuit wiring (not shown) on substrate 130 via wire 140.

[0068] Infrared detection element 110 receives infrared light, converts the thermal energy of the received infrared light into electrical energy, and outputs an electrical signal corresponding to the amount of infrared light received to IC element 120. Infrared detection element 110 can be a thermoelectric element, a thermopile type infrared detection element, or a thermal radiation type infrared detection element, or a quantum type infrared detection element.

[0069] IC element 120 includes an amplification circuit that amplifies the electrical signal output by infrared detection element 110, and a determination circuit that determines the presence of a flame when the amplified electrical signal exceeds a threshold.

[0070] A metal housing 150 is mounted on a substrate 130. The metal housing 150 surrounds the infrared detection element 110 and the IC element 120, sealing them together with the substrate 130. The metal housing 150 includes an upper wall 151 and a side wall 152. An opening is provided in the upper wall 151, which is covered by an optical filter 1. The optical filter 1 is arranged facing the infrared detection element 110, and the infrared detection element 110 is mounted on the substrate 130 in a manner that it receives infrared light passing through the optical filter 1. The side wall 152 connects the edge of the upper wall 151 to the edge of the substrate 130.

[0071] Infrared radiation emitted by a flame or similar source passes through an optical filter 1 and is received by an infrared detection element 110. The infrared detection element 110 outputs an electrical signal corresponding to the amount of infrared radiation received to an IC element 120. The IC element 120 determines the presence of a flame based on the electrical signal. In this way, the infrared sensor 100 can detect a flame using infrared radiation emitted by the flame.

[0072] Furthermore, this embodiment describes an example of using an infrared sensor 100 in a flame sensor for detecting flames, but the application of the infrared sensor 100 is not limited to this method. The infrared sensor 100 can also be used in human body sensors, biosensors, security sensors, gas sensors, non-contact thermometers, solid-state imaging devices, or camera assemblies, etc.

[0073] [Light-emitting device]

[0074] Next, use Figure 4 The light-emitting device 200 of this embodiment will be described. The light-emitting device 200 is as follows: Figure 4 The device shown includes the aforementioned optical filter 1. Additionally, the light-emitting device 200 includes a light source 210 that illuminates the optical filter 1 with light including infrared radiation. The light source 210 may include an LED, a xenon lamp, a laser diode, or a combination thereof.

[0075] Since the light-emitting device 200 is equipped with an optical filter 1, a portion of the infrared light irradiated by the light source 210 can be blocked using the optical filter 1. Therefore, the light-emitting device 200 according to this embodiment can irradiate light with a specific wavelength. The light-emitting device 200 can be used, for example, in light-emitting devices for inspection, light-emitting devices for surveillance cameras, light-emitting devices for hair removal, and light-emitting devices for curing infrared-curable resins.

[0076] [Manufacturing methods for optical filters]

[0077] Next, the manufacturing method of the optical filter 1 of this embodiment will be described. The optical filter 1 can be manufactured by pressurizing and heating a mixture of inorganic material particles and wavelength-selective absorbing material in a solvent-containing state. By using this pressurization and heating method, since part of the inorganic material dissolves and the inorganic materials bond to each other, an optical filter 1 in which wavelength-selective absorbing material 20 is internally dispersed can be formed.

[0078] Specifically, the inorganic powder is first mixed with the wavelength-selective absorbing material powder to prepare a mixed powder. The mixing method between the inorganic powder and the wavelength-selective absorbing material powder is not particularly limited and can be carried out dry or wet. Furthermore, the inorganic powder and the wavelength-selective absorbing material powder can also be mixed in air or in an inert gas environment. As a method for preparing the mixture, the wavelength-selective absorbing material and a solvent are first mixed. The wavelength-selective absorbing material may or may not be dissolved in the solvent. Then, by adding the inorganic powder to the mixture of the wavelength-selective absorbing material and the solvent, a mixture containing the inorganic substance, the wavelength-selective absorbing material, and the solvent can be prepared.

[0079] Next, a solvent is added to the mixed powder. There are no particular limitations on the solvent; for example, a solvent capable of dissolving a portion of the inorganic substance when the mixed powder is pressurized and heated can be used. Alternatively, a solvent capable of reacting with the inorganic substance to generate an inorganic substance different from the inorganic substance can also be used. As such a solvent, at least one selected from acidic aqueous solutions, alkaline aqueous solutions, water, alcohols, ketones, and esters can be used. As an acidic aqueous solution, an aqueous solution with a pH of 1 to 3 can be used. As an alkaline aqueous solution, an aqueous solution with a pH of 10 to 14 can be used. An aqueous solution of an organic acid is preferred as the acidic aqueous solution. Furthermore, an alcohol with 1 to 12 carbon atoms is preferred as the alcohol.

[0080] Next, a mixture comprising inorganic matter, wavelength-selective absorbing material, and solvent is filled into the interior of a metal mold. After filling the metal mold with the mixture, the mold can be heated as needed. Then, by applying pressure to the mixture inside the metal mold, the interior of the mold becomes a high-pressure state. At this time, while the inorganic matter and wavelength-selective absorbing material are densified, the particles of the inorganic matter bond together.

[0081] Here, when a solvent that dissolves a portion of the inorganic substance is used as a solvent, the inorganic compound constituting the inorganic substance dissolves in the solvent under high pressure. The dissolved inorganic compound permeates into the gaps between the inorganic substance and the wavelength-selective absorbing material, the gaps between inorganic substances, and the gaps between the wavelength-selective absorbing material. Furthermore, by removing the solvent from the mixture under these conditions, connections originating from the inorganic substance are formed between the inorganic substance and the wavelength-selective absorbing material, between inorganic substances, and between the wavelength-selective absorbing material. Alternatively, when a solvent that reacts with the inorganic substance to generate an inorganic substance different from the inorganic substance is used as a solvent, the inorganic compound constituting the inorganic substance reacts with the solvent under high pressure. Furthermore, other inorganic substances generated through the reaction are filled into the gaps between the inorganic substance and the wavelength-selective absorbing material, the gaps between inorganic substances, and the gaps between the wavelength-selective absorbing material, forming connections originating from other inorganic substances.

[0082] The heating and pressurizing conditions for the mixture comprising inorganic substances, wavelength-selective absorbing materials, and solvent are not particularly limited when using a solvent that dissolves part of the inorganic substances as the solvent, as long as the dissolution of the inorganic substances occurs on the surface. Furthermore, when using a solvent that reacts with the inorganic substances to generate inorganic substances different from the inorganic substances, the heating and pressurizing conditions for the mixture are not particularly limited when using a solvent that reacts with the inorganic substances to generate inorganic substances different from the inorganic substances, as long as the reaction between the inorganic substances and the solvent occurs. For example, it is preferable to heat the mixture comprising inorganic substances, wavelength-selective absorbing materials, and solvent to 50–300°C and then pressurize it at a pressure of 10–600 MPa. Furthermore, the temperature for heating the mixture comprising inorganic substances, wavelength-selective absorbing materials, and solvent is more preferably 80–250°C, and even more preferably 100–200°C. Furthermore, the pressure for pressurizing the mixture comprising inorganic substances, wavelength-selective absorbing materials, and solvent is more preferably 50–600 MPa.

[0083] Furthermore, by removing the molded body from inside the metal mold, the optical filter 1 can be obtained. In addition, the connection portion formed between the inorganic material and the wavelength selective absorbing material, between the inorganic materials, and between the wavelength selective absorbing materials is preferably the aforementioned bonding portion 12.

[0084] Here, sintering is a known method for manufacturing mechanical parts made of ceramics. Sintering is a method of obtaining a sintered body by heating an aggregate of solid powders formed from inorganic materials at a temperature below their melting point. However, in sintering, the solid powders are heated to, for example, 1000°C or higher. Therefore, even if one wants to obtain a composite component formed from inorganic materials and wavelength-selective absorbing materials using sintering, the wavelength-selective absorbing material carbonizes due to the high temperature, making it impossible to obtain the composite component. However, according to the manufacturing method of the optical filter 1 of this embodiment, since the mixture of powders of inorganic materials and powders of wavelength-selective absorbing materials is heated at a low temperature below 300°C, carbonization of the wavelength-selective absorbing material is less likely to occur. Therefore, the wavelength-selective absorbing material 20 can be stably dispersed within the matrix 10 formed from inorganic materials.

[0085] Furthermore, according to the manufacturing method of this embodiment, since the mixture of powdered inorganic material and powdered wavelength-selective absorbing material is heated and pressurized, the inorganic material agglomerates to form a dense matrix 10. As a result, since the porosity inside the matrix 10 is reduced, an optical filter 1 with high strength can be obtained while suppressing the oxidative degradation of the wavelength-selective absorbing material 20.

[0086] Thus, the manufacturing method of the optical filter 1 includes the following steps: a step of mixing powdered inorganic material and powdered wavelength-selective absorbing material to obtain a mixture; and a step of adding a solvent for dissolving inorganic material or a solvent that reacts with inorganic material to the mixture, followed by pressurizing and heating the mixture. Alternatively, the manufacturing method of the optical filter 1 includes the following steps: a step of mixing wavelength-selective absorbing material in a solvent for dissolving inorganic material or a solvent that reacts with inorganic material; a step of mixing powdered inorganic material in a solvent containing wavelength-selective absorbing material to obtain a mixture; and a step of pressurizing and heating the mixture. Furthermore, the heating and pressurizing conditions of the mixture are preferably a temperature of 50 to 300°C and a pressure of 10 to 600 MPa. According to the manufacturing method of this embodiment, since the optical filter 1 is formed under such low-temperature conditions, the carbonization of the wavelength-selective absorbing material 20 can be suppressed, and a colored ceramic component can be obtained. In addition, in the above method, a solvent for dissolving inorganic material or a solvent that reacts with inorganic material is added to the mixture. However, the optical filter 1 of this embodiment may also be produced without adding the solvent for dissolving inorganic substances or the solvent that reacts with inorganic substances to the mixture. That is, the optical filter 1 can also be obtained by pressurizing and heating a mixture of powdered inorganic substances and powdered wavelength-selective absorption materials. For example, when lithium fluoride is used as the inorganic substance, since it undergoes plastic deformation at high temperatures, a dense optical filter 1 can be manufactured by pressurizing it above the temperature at which plastic deformation occurs.

[0087] Example

[0088] The present embodiment will be described in more detail below with reference to examples and reference examples, but the present embodiment is not limited to these examples.

[0089] [Preparation of test samples]

[0090] (Example 1)

[0091] First, lithium fluoride powder (Fujifilm and Koko Pure Chemical Industries, Ltd., Special Grade Reagent) with a solubility of 0.134 g / 100 mL in water and an average particle size of 5 μm was prepared as inorganic particles. Additionally, melamine powder (Fujifilm and Koko Pure Chemical Industries, Ltd., Special Grade Reagent) was prepared as a wavelength-selective absorption material. Next, acetone was added to the lithium fluoride powder and melamine powder in a mass ratio of 99:1 (volume ratio of 98.3:1.7) using an agate mortar and agate rod to obtain a mixed powder.

[0092] Next, the mixed powder was placed inside a cylindrical metal mold (Φ10) with an internal space. Then, the mixed powder was heated and pressurized at 180°C, 400 MPa, for 30 minutes. This yielded a cylindrical test sample as described in this example.

[0093] (Refer to Example 1)

[0094] Except for the absence of wavelength-selective absorbing material, the test samples were prepared in the same manner as in Example 1. That is, the lithium fluoride powder used in Example 1 was heated and pressurized in the same way as in Example 1.

[0095] [evaluate]

[0096] (Linear transmittance)

[0097] First, the test sample obtained above was measured using an FT-IR instrument via the transmission method to obtain... Figure 5 The infrared transmission spectrum is shown. Furthermore, the linear transmittance of the infrared transmission spectrum is calculated based on Beer-Lambert's law, using the method of converting the linear transmittance to a thickness of 1 mm.

[0098] like Figure 5 As shown, compared with the test sample of Reference Example 1, the linear transmittance of the test sample in Example 1 decreased in several bands, and infrared radiation with specific wavelengths was absorbed by the wavelength-selective absorbing material. This indicates that the wavelength-selective absorbing material did not decompose but remained in the test sample.

[0099] In addition, by Figure 5As shown in the infrared spectrum, the maximum transmittance of the test sample in Example 1 is 56% at a wavelength of 5.71 μm. In addition, the band with linear transmittance of 1 / 2 (28%) of the maximum transmittance is 5.13 μm to 5.84 μm, and the full width at half maximum (FWHM) is 705 nm.

[0100] Furthermore, the band with a linear transmittance of 30% or more is in the range of 5.21 μm to 5.83 μm, with a bandwidth of 621 nm. Additionally, the linear transmittance is consistently around 0.4% at least in the range of 9.60 μm to 10.00 μm, with a wavelength bandwidth of 400 nm. Furthermore, the linear transmittance is intermittently around 0.6% at least in the range of 6.00 to 7.00 μm. These results demonstrate that the test sample of Example 1 is useful as an optical filter.

[0101] (TG (Thermogravimetric Analysis))

[0102] The mass reduction rate of melamine was determined by TG (thermometry). Furthermore, 7.1 mg of the sample was placed in an aluminum container, air was introduced at a rate of 50 mL / min, and the temperature was measured from 100°C to 560°C at a heating rate of 10°C / min. The TG curve obtained by the determination is shown below. Figure 6 middle.

[0103] like Figure 6 As shown, melamine begins to decrease in mass around 240°C, reaches a 5% mass reduction rate at 279°C, and a 10% mass reduction rate at 292°C. Therefore, the results indicate that when melamine is heated in air at a rate of 10°C starting from 100°C, the temperature at which a 10% mass reduction rate is achieved is below 300°C. This example demonstrates that by heating and pressurizing the mixed powder at 180°C, 400 MPa, and for 30 minutes, even materials with low heat resistance, such as melamine, can be dispersed within an inorganic matrix.

[0104] (Relative density)

[0105] The relative density of the test samples of Example 1 and Reference Example 1 was determined. Specifically, the volume and mass of the test samples were first measured, and the apparent density of the test samples was calculated. Then, the relative density of the test samples was calculated by dividing the apparent density of the test samples by the true density of lithium fluoride, which serves as the matrix.

[0106] The relative density calculated above shows that the relative density of the test sample in Example 1 is 89%, and the relative density of the test sample in Reference Example 1 is 90%. This suggests that the porosity of the test sample in Example 1 is 11%, and the porosity of the test sample in Reference Example 1 is 10%. These results indicate that the test samples have low porosity, resulting in a dense structure.

[0107] Next, test samples from Examples 2 to 7 and Reference Example 2 were prepared and evaluated.

[0108] [Preparation of test samples]

[0109] (Example 2)

[0110] First, lithium fluoride powder with a solubility of 0.134 g / 100 mL in water and an average particle size of 1 μm was prepared as inorganic particles. PVDF was prepared as a wavelength-selective absorption material. Next, acetone was added to and the lithium fluoride powder and PVDF powder were mixed using an agate mortar and agate rod at a mass ratio of 99:1 (volume ratio of 98.5:1.5) to obtain a mixed powder.

[0111] Furthermore, lithium fluoride powder was prepared as follows: First, 8.9 g of LiCl (Fujifilm Wako Pure Chemicals Co., Ltd. Wako Tokugi) was dissolved in 35 ml of ion-exchanged water to prepare a LiCl solution. Separately, 12.2 g of KF (Fujifilm Wako Pure Chemicals Co., Ltd. Wako Tokugi) was dissolved in 35 ml of ion-exchanged water to prepare a KF solution. Next, the total volumes of the LiCl and KF solutions were mixed at room temperature and stirred for 3 minutes using a magnetic stirrer. The stirred solution was then filtered through a 0.1 μm pore size filter membrane, and the residue was dried to obtain lithium fluoride powder.

[0112] The PVDF used was Sigma-Aldrich PVDF (average Mw ~534,000, powder obtained by GPC). The average particle size of PVDF is approximately 200 nm. Furthermore, lithium fluoride has a refractive index of 1.39, while PVDF has a refractive index of 1.42, therefore the refractive index difference between lithium fluoride and PVDF is 0.03.

[0113] Next, the mixed powder was placed inside a cylindrical metal mold (Φ12) with an internal space. Then, the mixed powder was heated and pressurized at 200°C, 400 MPa for 10 minutes. This yielded a cylindrical test sample for this example. Furthermore, the thickness of the test sample was 1053 μm.

[0114] (Example 3)

[0115] Except that the mass ratio of lithium fluoride powder to PVDF powder in the mixed powder was 98:2 (volume ratio 97.1:2.9), the test samples were prepared in the same manner as in Example 2. Furthermore, the thickness of the test samples was 1057 μm.

[0116] (Example 4)

[0117] Except that the mass ratio of lithium fluoride powder to PVDF powder in the mixed powder was 97:3 (volume ratio 95.6:4.4), the test samples were prepared in the same manner as in Example 2. Furthermore, the thickness of the test samples was 1017 μm.

[0118] (Example 5)

[0119] Except that the mass ratio of lithium fluoride powder to PVDF powder in the mixed powder was 96:4 (volume ratio 94.2:5.8), the test samples were prepared in the same manner as in Example 2. Furthermore, the thickness of the test samples was 1014 μm.

[0120] (Example 6)

[0121] Except that the mass ratio of lithium fluoride powder to PVDF powder in the mixed powder was 92:8 (volume ratio of 88.6:11.4), the test samples were prepared in the same manner as in Example 2. Furthermore, the thickness of the test samples was 1064 μm.

[0122] (Example 7)

[0123] The test samples were prepared in the same manner as in Example 2, except that PTFE powder (Kitamura KTL-1N Co., Ltd.) was used instead of PVDF powder. Specifically, the mass ratio of lithium fluoride powder to PTFE powder in the mixed powder was 99:1 (volume ratio of 98.4:1.6). Furthermore, the thickness of the test sample was 1147 μm.

[0124] (See Example 2 for reference)

[0125] Except that the mass ratio of lithium fluoride powder to PVDF powder in the mixed powder was 100:0, the test sample was prepared in the same manner as in Example 2. Furthermore, the thickness of the test sample was 1064 μm.

[0126] [evaluate]

[0127] (Linear transmittance)

[0128] The test sample obtained above was measured using an FT-IR instrument via transmission method. Figures 7-10 The infrared transmission spectrum is shown. Furthermore, the linear transmittance of the infrared transmission spectrum is calculated based on Beer-Lambert's law, using the method of converting the linear transmittance to a thickness of 1 mm.

[0129] like Figures 7-10 As shown, in the test samples of Examples 2 to 7, compared with the test sample of Reference Example 2, the linear transmittance decreased in several bands, and infrared radiation with specific wavelengths was absorbed by the wavelength-selective absorbing material. This indicates that the wavelength-selective absorbing material did not decompose but remained in the test samples.

[0130] In addition, by Figure 7 and Figure 8 As shown, the test samples of Examples 2 to 7 exhibited a linear transmittance of 30% or more per 1 mm thickness within the target wavelength band of 0.8 μm to 20 μm, with a wavelength bandwidth of 50 nm or more. These results demonstrate that the test samples of Examples 2 to 7 are useful as optical filters.

[0131] Furthermore, in the test samples of Examples 2 to 7, the linear transmittance was less than 10% across the entire wavelength band of 8 μm to 20 μm. It was further observed that the more fluoropolymer added, the lower the linear transmittance. Additionally, it was found that when PVDF was used as the fluoropolymer, the linear transmittance in the wavelength band of 7 μm to 8 μm could be reduced compared to using the same amount of PTFE. These results demonstrate that the test samples of Examples 2 to 7 are useful as filters that cut off wavelengths in the long wavelength band.

[0132] When using an FT-IR apparatus to determine the PTFE and PVDF powders used in the examples using the ATR method, it was confirmed that... Figure 11 The absorption spectra shown confirm that PTFE has an absorption peak in the wavelength range of 8 μm to 9 μm. Furthermore, it was confirmed that PVDF, in addition to the 8 μm to 9 μm wavelength range, also exhibits multiple absorption peaks around this range. These results suggest that a portion of the light transmitted through the matrix is ​​absorbed by the fluoropolymer, resulting in a decrease in the overall linear transmittance of the 8 μm to 20 μm wavelength band.

[0133] (TG (Thermogravimetric Analysis))

[0134] The mass loss rate of PTFE and PVDF was determined by thermogravimetric analysis (TG). Furthermore, samples were prepared by placing 5.5 mg of PTFE or 6.2 mg of PVDF in an aluminum container, with air flowing in at a rate of 50 mL / min, and heating from 30°C to 600°C at a rate of 10°C / min. The TG curves obtained by the determination are shown below. Figure 12 The results showed that the temperature at which PTFE achieved a 10% mass reduction was 456℃, and the temperature at which PVDF achieved a 10% mass reduction was 400℃.

[0135] (Relative density)

[0136] The relative densities of the test samples from Examples 2 to 7 and Reference Example 2 were measured in the same manner as described above. The results showed that the relative density of any one test sample was 90% or higher. This indicates that the test samples had low porosity and a dense structure.

[0137] This document quotes the full contents of Japanese Special Application No. 2021-025009 (application date: February 19, 2021).

[0138] The above describes this embodiment, but this embodiment is not limited to these. Various modifications can be made within the scope of the main idea of ​​this embodiment.

[0139] Industrial availability

[0140] According to this disclosure, optical filters, infrared sensors, and light-emitting devices with excellent durability and an inorganic matrix can be provided.

[0141] Symbol Explanation

[0142] 1 Optical Filter

[0143] 10 Matrix

[0144] 20 Wavelength-selective absorption materials

[0145] 100 Infrared Sensor

[0146] 200 Light-emitting devices

Claims

1. An optical filter comprising a substrate composed of an inorganic substance having a solubility of 0.4 g / 100 g-H20 or less in water, and a wavelength-selective absorbing material dispersed in the substrate, the optical filter absorbing a light component having any one of wavelength bands in a subject wavelength band of 0.8 μm to 20 μm, a temperature at which a mass reduction rate of the wavelength-selective absorbing material reaches 10 mass% is 900°C or less when heating at a rate of 10°C / min from 100°C in air, an apparent density of the optical filter is 70% or more relative to a true density of the substrate, in the subject wavelength band, a wavelength bandwidth in which a straight transmittance per 1 mm thickness of the optical filter is 30% or more is 50 nm or more.

2. The optical filter of claim 1, wherein, the temperature at which the mass reduction rate reaches 10 mass% is 600°C or less.

3. The optical filter according to claim 1 or 2, wherein, the temperature at which the mass reduction rate reaches 10 mass% is 300°C or less.

4. The optical filter of claim 1 or 2, wherein, the inorganic substance constituting the substrate contains at least one selected from the group consisting of a fluoride, an oxide, and an oxyhydroxide.

5. The optical filter of claim 1 or 2, wherein, in a subject wavelength band of 3 μm to 10 μm, a wavelength bandwidth in which the straight transmittance is 30% or more is 300 nm or more.

6. The optical filter of claim 1 or 2, wherein, in a subject wavelength band of 3 μm to 10 μm, a wavelength bandwidth in which the straight transmittance is 1% or less is 300 nm or more.

7. The optical filter of claim 1 or 2, wherein, in a subject wavelength band of 3 μm to 10 μm, a wavelength bandwidth in which the straight transmittance is 30% or more is 300 nm or more, and a wavelength bandwidth in which the straight transmittance is 1% or less is 300 nm or more.

8. The optical filter of claim 1 or 2, wherein, the inorganic substance contains lithium fluoride.

9. The optical filter of claim 1 or 2, wherein, the inorganic substance contains a fluoride, and the wavelength-selective absorbing material contains a fluororesin.

10. The optical filter of claim 1 or 2, wherein, in the entire wavelength band of 8 μm to 20 μm, the straight transmittance is 10% or less.

11. An infrared sensor comprising the optical filter according to any one of claims 1 to 10.

12. A light-emitting device comprising the optical filter according to any one of claims 1 to 10.

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