Optical filters and sterilizers

Abstract

To provide an optical filter having an ultraviolet transmittance that is less susceptible to deterioration even when irradiated with strong ultraviolet light.SOLUTION: An optical filter 1 is provided, comprising a transparent base material 2 made of glass and a dielectric multilayer film 3 provided on the transparent base material 2, the optical filter 1 having a moisture content of 0.15 mm-1 or greater in terms of β-OH.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical filter that can selectively transmit light in a specific wavelength range, and a sterilization device using the optical filter. [Background technology]

[0002] Optical filters capable of selectively transmitting light in a specific wavelength range have been widely used in various applications. A known example of such an optical filter is a bandpass filter using a dielectric film.

[0003] Recently, a sterilization device has been proposed that selectively inactivates DNA in the cells of target organisms such as bacteria by applying ultraviolet light without harming human cells. This sterilization device uses an interference filter as an optical filter to transmit light emitted from a light source with a wavelength range of 190 nm to 230 nm and to cut light with wavelengths outside the above range.

[0004] For example, the following Patent Document 1 discloses a microorganism inactivation treatment device that inactivates target microorganisms by irradiating light emitted from a light source through an optical filter. Patent Document 1 describes that when light emitted from a light source is incident at an incident angle of 0°, the optical filter transmits at least a portion of ultraviolet light in the range of 190 nm to 230 nm and at least a portion of ultraviolet light greater than 230 nm and less than 237 nm, and blocks the transmission of ultraviolet light outside the wavelength range of 190 nm to 237 nm. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-115525 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, optical filters such as those described in Patent Document 1 become colored when exposed to strong ultraviolet light, which can result in a problem of reduced ultraviolet light transmittance in the wavelength range of 190 nm to 230 nm, which selectively inactivates cells of organisms to be sterilized.

[0007] An object of the present invention is to provide an optical filter whose ultraviolet ray transmittance is unlikely to decrease even when exposed to strong ultraviolet rays, and a sterilization device using said optical filter. [Means for solving the problem]

[0008] The optical filter according to the present invention is an optical filter comprising a transparent substrate made of glass and a dielectric multilayer film provided on the transparent substrate, wherein the amount of moisture in the optical filter is 0.15 mm or less in terms of β-OH value. -1 The present invention is characterized in that:

[0009] In the present invention, the amount of moisture in the optical filter is 0.80 mm in terms of β-OH value. -1 It is preferable that:

[0010] In the present invention, it is preferable that the dielectric multilayer film has a high refractive index film having a relatively high refractive index and a low refractive index film having a relatively low refractive index, and the low refractive index film is a film containing silicon oxide.

[0011] In the present invention, the high refractive index film is preferably a film containing hafnium oxide.

[0012] In the present invention, the high refractive index film is preferably a film containing cubic hafnium oxide crystals.

[0013] The sterilization device of the present invention is a sterilization device for inactivating target microorganisms, and is characterized by comprising a light source that emits light with a wavelength in the wavelength range of 190 nm to 230 nm, and an optical filter constructed according to the present invention. Effect of the Invention

[0014] According to the present invention, it is possible to provide an optical filter whose ultraviolet ray transmittance is unlikely to decrease even when irradiated with strong ultraviolet rays, and a sterilization device using the optical filter. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an optical filter according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic cross-sectional view showing an optical filter according to a second embodiment of the present invention. [Diagram 3] FIG. 3 is a schematic diagram showing a sterilization device according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Preferred embodiments will be described below. However, the following embodiments are merely examples, and the present invention is not limited to the following embodiments. In addition, in each drawing, components having substantially the same functions may be referred to by the same reference numerals.

[0017] [Optical filters] (First embodiment) Fig. 1 is a schematic cross-sectional view showing an optical filter according to a first embodiment of the present invention. As shown in Fig. 1, the optical filter 1 includes a transparent substrate 2 and a dielectric multilayer film 3. The dielectric multilayer film 3 is provided on the transparent substrate 2.

[0018] In this embodiment, the transparent base material 2 has a rectangular plate shape. However, the transparent base material 2 may have a shape such as a disk shape, and the shape is not particularly limited.

[0019] The transparent substrate 2 is made of glass. In particular, the transparent substrate 2 is preferably made of glass that is transparent in the wavelength range used by the optical filter 1. More specifically, the transparent substrate 2 preferably has an average light transmittance of 80% or more in the ultraviolet wavelength range of 220 nm to 225 nm.

[0020] Examples of the glass constituting the transparent substrate 2 include quartz glass and borosilicate glass. The quartz glass may be synthetic quartz glass or fused quartz glass. The borosilicate glass preferably contains, in mass %, 55% to 75% SiO2, 1% to 10% Al2O3, 10% to 30% B2O3, 0% to 5% CaO, 0% to 5% BaO, and 1.0% to 15% Li2O+Na2O+K2O, and more preferably contains 0% to 0.001% TiO2, 0% to 0.001% Fe2O3, and 0.5% to 2.0% F.

[0021] The thickness of the transparent base material 2 is not particularly limited and can be appropriately set depending on the light transmittance, etc. The thickness of the transparent base material 2 can be, for example, about 0.1 mm to 30 mm.

[0022] The transparent substrate 2 has a first main surface 2a and a second main surface 2b that face each other. A dielectric multilayer film 3 is provided on the first main surface 2a of the transparent substrate 2 as a filter section.

[0023] The dielectric multilayer film 3 is a multilayer film having a high refractive index film 4 having a relatively high refractive index and a low refractive index film 5 having a relatively low refractive index. In this embodiment, the high refractive index film 4 and the low refractive index film 5 are alternately laminated in this order on the first main surface 2a of the transparent substrate 2 to form the multilayer film.

[0024] In this embodiment, the high refractive index film 4 is made of hafnium oxide and is a film containing hafnium oxide as a main component. However, the high refractive index film 4 may be a film containing aluminum oxide or the like as a main component. These materials for the high refractive index film 4 may be used alone or in combination.

[0025] The low refractive index film 5 is made of silicon oxide and is a film containing silicon oxide as a main component. However, the low refractive index film 5 may be a film containing magnesium fluoride or the like as a main component. These materials for the low refractive index film 5 may be used alone or in combination.

[0026] In this specification, a film containing a material as a main component refers to a film containing 50% or more of that material, although it may of course be a film containing 100% of that material.

[0027] The thickness of each layer of the high refractive index film 4 is not particularly limited, but is preferably 5 nm or more, more preferably 10 nm or more, and is preferably 60 nm or less, more preferably 50 nm or less.

[0028] The thickness of each layer of the low refractive index film 5 is not particularly limited, but is preferably 5 nm or more, more preferably 10 nm or more, and is preferably 80 nm or less, more preferably 60 nm or less.

[0029] The total thickness of the dielectric multilayer film 3 is not particularly limited, but is preferably 1000 nm or more, more preferably 1500 nm or more, preferably 3000 nm or less, more preferably 2000 nm or less.

[0030] The number of layers constituting the dielectric multilayer film 3 is preferably 20 or more, more preferably 30 or more, and is preferably 100 or less, more preferably 80 or less.

[0031] The optical filter 1 is a bandpass filter that includes such a dielectric multilayer film 3 and is designed to selectively transmit light in a specific wavelength range by optical interference.

[0032] In the optical filter 1, the minimum value of the spectral transmittance in the wavelength range of 220 nm to 225 nm is preferably 50% or more, more preferably 60% or more, and further preferably 70% or more. In this case, ultraviolet light useful for sterilization treatment such as sterilization treatment of skin can be transmitted more effectively. The upper limit of the minimum value of the spectral transmittance in the wavelength range of 220 nm to 225 nm is not particularly limited, but can be, for example, 95%.

[0033] In addition, in the optical filter 1, the maximum value of the spectral transmittance in the wavelength range of 237 nm to 280 nm is preferably 10% or less, more preferably 5% or less, further preferably 3% or less, and particularly preferably 1% or less. In this case, the transmission of ultraviolet rays that are harmful to the human body can be more effectively suppressed. The lower limit of the maximum value of the spectral transmittance in the wavelength range of 237 nm to 280 nm is not particularly limited, but can be, for example, 0.2%.

[0034] In this specification, the spectral transmittance can be determined by, for example, using a spectral transmittance meter (manufactured by Hitachi High-Tech Science Corporation, product number "U4150") to measure the spectral transmittance of the entire optical filter 1. The measurement conditions can be, for example, from the main surface 1a side of the optical filter 1, and the measurement wavelength can be set to 190 nm to 400 nm.

[0035] In the optical filter 1 of this embodiment, the amount of moisture in the optical filter 1 is 0.15 mm in terms of β-OH value. -1 As a result, even when exposed to strong ultraviolet light, the ultraviolet transmittance is unlikely to decrease, and the optical filter 1 is therefore highly reliable.

[0036] Conventionally, optical filters have been known to become colored when exposed to strong ultraviolet light, resulting in a problem of reduced transmittance of ultraviolet light with wavelengths of 190 nm to 230 nm, which selectively inactivates cells of organisms to be sterilized.

[0037] The present inventors focused on the amount of moisture in the optical filter 1 and estimated the amount of moisture in the optical filter 1 to be 0.15 mm -1 It has been found that by doing so, even when irradiated with strong ultraviolet light, the optical filter 1 is less likely to be colored, and a decrease in ultraviolet light transmittance can be suppressed.

[0038] In the present invention, the amount of moisture in the optical filter 1 is preferably 0.18 mm -1 More preferably, 0.20 mm -1 More than 0.80mm, preferably 0.80mm -1 Less than or equal to 0.50 mm, preferably -1 When the moisture content in the optical filter 1 is within the above range, the optical filter 1 is more resistant to coloration, and the decrease in ultraviolet ray transmittance can be more effectively prevented.

[0039] The amount of moisture in the optical filter 1 converted into the β-OH value can be determined by a Fourier transform infrared spectrophotometer (FT-IR). Specifically, the amount of moisture can be determined by measuring the FT-IR spectrum of the optical filter 1 and using the following formula (1).

[0040] β-OH=(1 / t)log 10 (T1 / T2) …Equation (1)

[0041] In formula (1), t is the thickness (mm) of the optical filter 1, T1 is the transmittance of the reference wavenumber, and T2 is the transmittance of the hydroxyl group absorption wavenumber. For example, when the reference wavenumber is 3846 cm -1 (wavelength 2600 nm) and the hydroxyl group absorption wave number is 3600 cm -1 It is possible to achieve a minimum transmittance near the wavelength of 2800 nm.

[0042] The moisture content in the optical filter 1 calculated as a β-OH value can be adjusted, for example, by the glass constituting the transparent substrate 2. For example, it can be adjusted by the melting temperature, humidity, and melting atmosphere when producing the glass.

[0043] In the present invention, it is preferable that the dielectric multilayer film 3 contains hafnium oxide crystals. More specifically, it is preferable that the high refractive index film 4 constituting the dielectric multilayer film 3 contains hafnium oxide crystals, and more preferably contains cubic hafnium oxide crystals. In this case, the spectral transmittance at wavelengths of 220 nm to 225 nm can be further increased.

[0044] In this specification, whether or not cubic hafnium oxide crystals are contained can be confirmed by whether or not a diffraction peak due to the (1,1,1) crystal plane derived from cubic hafnium oxide crystals is observed in an X-ray diffraction measurement.

[0045] In this specification, the X-ray diffraction measurement can be performed by a wide-angle X-ray diffraction method. For example, an X-ray diffraction measurement device manufactured by Rigaku Corporation, product number "SmartLab" can be used. Furthermore, a CuKα ray can be used as a radiation source. In the X-ray diffraction measurement, the entire optical filter 1 is measured from the main surface 1a side.

[0046] In the present invention, in the X-ray diffraction measurement, it is preferable that the diffraction peak due to the (1,1,1) crystal plane originating from the cubic hafnium oxide crystal is larger than the diffraction peak due to the (-1,1,1) crystal plane originating from the monoclinic hafnium oxide crystal. In this case, the spectral transmittance at wavelengths of 220 nm to 225 nm can be further increased, while the maximum value of the spectral transmittance at wavelengths of 237 nm to 280 nm can be further decreased.

[0047] In the present invention, the ratio Ic / Im of the peak area intensity Ic of the diffraction peak due to the (1,1,1) crystal plane derived from the cubic hafnium oxide crystal to the peak area intensity Im of the diffraction peak due to the (-1,1,1) crystal plane derived from the monoclinic hafnium oxide crystal is preferably 0.1 or more, more preferably 1 or more. When the ratio Ic / Im is equal to or more than the lower limit, the spectral transmittance at wavelengths of 220 nm to 225 nm can be further increased, while the maximum value of the spectral transmittance at wavelengths of 237 nm to 280 nm can be further reduced. The upper limit of the ratio Ic / Im is not particularly limited, but can be, for example, 10,000.

[0048] In the present invention, an anti-reflection film may be provided on the second main surface 2b of the transparent substrate 2. In this case, the spectral transmittance at wavelengths of 220 nm to 225 nm can be further increased.

[0049] The anti-reflection film is not particularly limited, and may be, for example, a multilayer film having a high refractive index film with a relatively high refractive index and a low refractive index film with a relatively low refractive index. The multilayer film may be configured by alternately providing a high refractive index film and a low refractive index film in this order. The high refractive index film may be, for example, a film mainly composed of hafnium oxide. The low refractive index film may be, for example, a film mainly composed of silicon oxide, aluminum oxide, zirconium oxide, tin oxide, silicon nitride, or the like. The number of layers constituting the multilayer film may be, for example, 4 layers or more and 100 layers or less.

[0050] As long as the effects of the present invention are not impaired, a film other than an antireflection film may be laminated on the second main surface 2b of the transparent substrate 2. As long as the effects of the present invention are not impaired, a film other than the dielectric multilayer film 3 may also be provided on the first main surface 2a of the transparent substrate 2. In this case, a film may be provided between the transparent substrate 2 and the dielectric multilayer film 3, or a film may be provided on the dielectric multilayer film 3.

[0051] An example of a method for manufacturing the optical filter 1 will now be described in detail.

[0052] (Method of manufacturing optical filters) Film-coated transparent substrate formation process; First, a transparent substrate 2 is prepared. Next, a dielectric multilayer film 3 is formed on a first main surface 2a of the transparent substrate 2. The dielectric multilayer film 3 can be formed by alternately laminating a high refractive index film 4 and a low refractive index film 5 in this order on the first main surface 2a of the transparent substrate 2. The high refractive index film 4 and the low refractive index film 5 can each be formed by a sputtering method.

[0053] The temperature of the substrate when forming the high refractive index film 4 is preferably 300° C. or less, more preferably 270° C. or less. In this case, in the obtained optical filter 1, the spectral transmittance at wavelengths of 220 nm to 225 nm can be further increased, while the maximum value of the spectral transmittance at wavelengths of 237 nm to 280 nm can be further decreased. The lower limit of the substrate temperature when forming the high refractive index film 4 can be, for example, 20° C.

[0054] The high refractive index film 4 can be formed, for example, by using a target of the material constituting the high refractive index film 4, setting the flow rate of an inert gas such as argon gas as a carrier gas to 50 sccm to 500 sccm, and applying power of 0.5 kW to 40 kW.

[0055] The low refractive index film 5 can be formed, for example, by using a target of the material constituting the low refractive index film 5, setting the flow rate of an inert gas such as argon gas as a carrier gas to 50 sccm to 500 sccm, and applying power of 0.5 kW to 40 kW.

[0056] Heat treatment process; Next, the obtained film-attached transparent substrate is heat-treated at a temperature of 500°C or higher. This allows the optical filter 1 to be obtained. In particular, since the film-attached transparent substrate is heated at a temperature of 500°C or higher, the content of cubic hafnium oxide crystals can be relatively increased. Therefore, in the obtained optical filter 1, the spectral transmittance at wavelengths of 220nm to 225nm can be further increased, while the maximum value of the spectral transmittance at wavelengths of 237nm to 280nm can be further reduced.

[0057] The heat treatment temperature for the film-attached transparent substrate is preferably 500° C. or higher, more preferably 550° C. or higher, and preferably 800° C. or lower, more preferably 750° C. or lower. When the heat treatment temperature is within the above range, the spectral transmittance at wavelengths of 220 nm to 225 nm can be further increased, while the maximum value of the spectral transmittance at wavelengths of 237 nm to 280 nm can be further decreased.

[0058] The time for the heat treatment of the film-attached transparent substrate is not particularly limited, but can be, for example, 10 minutes or more and 120 minutes or less.

[0059] In the present invention, it is preferable that the intensity of the diffraction peak due to the (-1,1,1) crystal plane derived from the monoclinic hafnium oxide crystal is small in the X-ray diffraction measurement of the film-attached transparent substrate before the heat treatment. It is preferable that the intensity of the diffraction peak due to the (-1,1,1) crystal plane derived from the monoclinic hafnium oxide crystal is at the microcrystalline level, and more preferably, the height of the peak intensity is within three times the height of the peak intensity of the amorphous halo. In this case, the heat treatment can further increase the peak area intensity Ic of the diffraction peak due to the (1,1,1) crystal plane derived from the cubic hafnium oxide crystal to the peak area intensity Im of the diffraction peak due to the (-1,1,1) crystal plane derived from the monoclinic hafnium oxide crystal. Therefore, in the obtained optical filter 1, the spectral transmittance at wavelengths of 220 nm to 225 nm can be further increased, while the maximum value of the spectral transmittance at wavelengths of 237 nm to 280 nm can be further reduced.

[0060] In the present invention, the transmittance of ultraviolet light at wavelengths of 220 nm to 225 nm and the transmittance of ultraviolet light at wavelengths of 237 nm to 280 nm can be adjusted, for example, by the total number, film thickness, and material of the films constituting the dielectric multilayer film 3, and the heat treatment temperature of the film-coated transparent substrate. In particular, by adjusting the heat treatment temperature of the film-coated transparent substrate, in the obtained optical filter 1, the spectral transmittance at wavelengths of 220 nm to 225 nm can be further increased, while the maximum value of the spectral transmittance at wavelengths of 237 nm to 280 nm can be further decreased.

[0061] Second Embodiment Fig. 2 is a schematic cross-sectional view showing an optical filter according to a second embodiment of the present invention. As shown in Fig. 2, in an optical filter 21, an outermost layer 26 of a dielectric multilayer film 23 is a high refractive index film 4 made of hafnium oxide. Other points are the same as those of the first embodiment.

[0062] In the optical filter 21, the amount of moisture in the optical filter 21 is 0.15 mm in terms of β-OH value. -1 As a result, even when exposed to strong ultraviolet light, the ultraviolet transmittance is unlikely to decrease, and the optical filter 21 is therefore highly reliable.

[0063] However, when using an excimer lamp or the like that emits ultraviolet light in the wavelength range of 220 nm to 225 nm, the irradiated light can deteriorate the device components and generate acidic gases, which can corrode the film of the optical filter, causing the optical characteristics to change and making it impossible to meet the required characteristics.

[0064] In contrast, when the outermost layer 26 is made of hafnium oxide, as in the case of the optical filter 21, corrosion by acid gases can be further suppressed, and changes in optical characteristics can be further suppressed.

[0065] Furthermore, the thickness of the outermost layer 26 is preferably 1 nm or more, more preferably 2 nm or more, and preferably 10 nm or less, and more preferably 7 nm or less. When the thickness of the outermost layer 26 is equal to or more than the above lower limit, erosion by acidic gases can be further suppressed, and changes in optical properties can be further suppressed. On the other hand, when the thickness of the outermost layer 26 is equal to or less than the above upper limit, the spectral transmittance at wavelengths of 220 nm to 225 nm can be further increased, while the maximum value of the spectral transmittance at wavelengths of 237 nm to 280 nm can be further reduced.

[0066] [Sterilizer] Figure 3 is a schematic diagram showing a sterilization device according to one embodiment of the present invention. As shown in Figure 3, sterilization device 31 comprises a housing 32, a light source 33, and an optical filter 1. The light source 33 is disposed inside the housing 32. The light source 33 and the optical filter 1 are disposed to face each other. In the sterilization device 31, light emitted from the light source 33 is irradiated onto an object 34 to be sterilized via the optical filter 1.

[0067] As the light source 33, for example, an excimer lamp can be used. As the excimer lamp, it is preferable to use an excimer lamp that emits ultraviolet light with a wavelength in the range of 220 nm to 225 nm. As such an excimer lamp, for example, a KrCl excimer lamp can be used. The excimer lamp may be a KrBr excimer lamp.

[0068] The sterilization device 31 of this embodiment uses the optical filter 1 described above, so even when strong ultraviolet light is irradiated, the ultraviolet light transmittance is unlikely to decrease, and ultraviolet sterilization can be performed on the sterilization target 34. In ultraviolet sterilization, ultraviolet light can be applied to DNA in the cells of the organisms to be sterilized, such as bacteria, to selectively inactivate them.

[0069] The present invention will be described in more detail below with reference to specific examples. The present invention is not limited to the following examples, and can be modified as appropriate within the scope of the present invention.

[0070] Example 1 First, a fused quartz glass substrate (manufactured by USTRON, product number "FLH311") was prepared as a transparent substrate. This fused quartz glass substrate was formed in a humidified state. Next, a dielectric multilayer film was formed by sputtering on one main surface of the prepared transparent substrate. Specifically, first, a hafnium target was sputtered using argon gas and oxygen gas as carrier gases, and a hafnium oxide film (HfO2 film) was formed on one main surface of the transparent substrate. At this time, the flow rates of the argon gas and oxygen gas were each set to 100 sccm, and the target applied power (film forming power) was set to 4 kW. Next, a silicon target was sputtered using argon gas and oxygen gas as carrier gases, and a silicon oxide film (SiO2 film) was formed on the HfO2 film. At this time, the flow rates of the argon gas and oxygen gas were set to 100 sccm, and the target applied power (film forming power) was set to 4 kW. By repeating this operation, a dielectric multilayer film having a total of 38 layers, in which HfO2 films and SiO2 films were alternately stacked one by one, was formed on one main surface of the transparent substrate, and a transparent substrate with a film was obtained. Note that the substrate temperature was kept at room temperature (20°C) during the film formation. Next, the transparent substrate with the film was heat-treated at a temperature of 600°C for 60 minutes in an air atmosphere to produce an optical filter.

[0071] Comparative Example 1 An optical filter was produced in the same manner as in Example 1, except that the fused silica glass substrate was changed to one that had been molded in a non-humidified state.

[0072] [evaluation] (β-OH value) The moisture content in the optical filters obtained in Example 1 and Comparative Example 1 was calculated based on the β-OH value. The FT-IR was measured using a Thermo Fisher Scientific Co., Ltd. product number "Nicolet iS10" at a measurement wave number of 4000 cm. -1 ~400cm -1The measurement was performed with a scan count of 16. Using the obtained FT-IR spectrum, the β-OH value was calculated according to the following formula (1).

[0073] β-OH=(1 / t)log 10 (T1 / T2) …Equation (1)

[0074] (In formula (1), t is the thickness of the optical filter (mm), and T1 is the reference wave number of 3846 cm -1 (wavelength 2600 nm), and T2 is the hydroxyl group absorption wavenumber 3600 cm -1 (The transmittance is minimal at a wavelength of around 2800 nm.)

[0075] (Transmittance reduction amount) The optical filters obtained in Example 1 and Comparative Example 1 were irradiated with a KrCl excimer lamp for 1150 hours, and the difference in spectral transmittance at a wavelength of 222 nm before and after the irradiation was determined.

[0076] The spectral transmittance of the optical filters obtained in Example 1 and Comparative Example 1 was measured using a spectral transmittance meter (manufactured by Hitachi High-Tech Science Corporation, product number "U4150") Specifically, the incident angle was set to 0°, and the measurement wavelength was set to 190 nm to 400 nm.

[0077] The spectral transmittance at a wavelength of 222 nm was measured before and after the irradiation, and the amount of decrease in transmittance was calculated from the difference between the spectral transmittance at a wavelength of 222 nm before and after the irradiation.

[0078] The results are shown in Table 1 below.

[0079] [Table 1]

[0080] As is clear from Table 1, the amount of moisture in the optical filter is 0.15 mm in terms of β-OH value. -1 In the optical filter of Example 1, the β-OH value is converted to 0.15 mm -1It can be seen that, compared to the optical filter of Comparative Example 1, in which the transmittance is less than 100%, the decrease in the ultraviolet ray transmittance due to irradiation with strong ultraviolet rays is suppressed. [Explanation of symbols]

[0081] 1,21...Optical filter 1a…main surface 2...Transparent base material 2a…First main surface 2b…Second main surface 3,23...Dielectric multilayer film 4...High refractive index film 5...Low refractive index film 26…Outermost layer 31...Sterilizer 32…Housing 33…Light source 34...Objects to be sterilized

Claims

1. A transparent substrate made of glass; A dielectric multilayer film provided on the transparent substrate; An optical filter comprising: the dielectric multilayer film has a high refractive index film having a relatively high refractive index and a low refractive index film having a relatively low refractive index, the high refractive index film is a film containing cubic hafnium oxide crystals, The amount of moisture in the optical filter is 0.15 mm in terms of β-OH value. －１ That's it, the optical filter.

2. The amount of moisture in the optical filter is 0.80 mm in terms of β-OH value. －１ 2. The optical filter of claim 1 , wherein:

3. An optical filter as described in claim 1 or 2, wherein the low refractive index film is a film containing silicon oxide.

4. A sterilization apparatus for inactivating a microorganism to be treated, comprising: A light source having an emitted light wavelength in a wavelength range of 190 nm to 230 nm; An optical filter according to any one of claims 1 to 3; A sterilization apparatus comprising:

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