WO2024135592A1 - Optical filter, sterilizing device, and uv ray detecting device - Google Patents

Abstract

Provided is an optical filter that can effectively transmit UV rays of a wide wavelength range and that can increase transmittance of the same.　An optical filter 1 comprises: a transparent base material 2 that is composed of glass and has a thickness of 1.0 mm or less; and dielectric multilayer films 3A, 3B that are provided on main surfaces 2a, 2b of at least one side of the transparent base material 2 and that contain a hafnium oxide. The minimum value of the spectral transmittance at wavelengths of 240-300 nm is 92% or greater, and the wavelength λ₆₀ at which the spectral transmittance is 60% is 230 nm or less.

Description

Optical filters, sterilizers, and ultraviolet detectors

The present invention relates to an optical filter that can transmit light in a specific wavelength range, as well as a sterilization device and an ultraviolet detection device that use the optical filter.

Optical filters that can transmit light in a specific wavelength range have been widely used in a variety of applications. For example, ultraviolet transmission filters are used in water sterilization devices, curing devices used to harden ultraviolet-curable resins, ultraviolet sensors, and other applications.

The following Patent Document 1 discloses an ultraviolet transmission filter having a glass plate with a spectral transmittance of 70% or more at a wavelength of 254 nm at a thickness of 0.5 mm, and a protective film provided on the main surface of the glass plate. Patent Document 1 also describes that the average transmittance of the ultraviolet transmission filter at wavelengths of 200 nm to 300 nm is 60% or less.

Patent Document 2 below discloses a microorganism inactivation treatment device that inactivates the microorganisms to be treated by irradiating light emitted from a light source through an optical filter. Patent Document 2 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 with a wavelength of 190 nm or more and 230 nm or less, and at least a portion of ultraviolet light with a wavelength of more than 230 nm and 237 nm or less, and blocks the transmission of ultraviolet light outside the wavelength range of 190 nm or more and 237 nm or less.

International Publication No. 2018/100991 JP 2019-115525 A

However, the optical filters in Patent Documents 1 and 2 selectively transmit ultraviolet light in a specific wavelength range, which limits the types of objects to be treated, such as viruses. In addition, the optical filters in Patent Documents 1 and 2 do not have sufficient ultraviolet light transmittance, so there are cases in which the sterilization effect cannot be fully enhanced, and there is also the problem that it takes time to inactivate the objects to be treated. Against this background, there is a demand for optical filters that can effectively transmit ultraviolet light in a wide wavelength range and can also increase the transmittance.

The object of the present invention is to provide an optical filter that can effectively transmit ultraviolet light over a wide wavelength range and increase the transmittance, as well as a sterilization device and an ultraviolet light detection device that use the optical filter.

This article describes various aspects of an optical filter that solves the above problems, as well as a sterilization device and an ultraviolet detection device that use the optical filter.

The optical filter according to a first aspect of the present invention comprises a transparent substrate made of glass and having a thickness of 1.0 mm or less, and a dielectric multilayer film containing hafnium oxide and provided on at least one main surface of the transparent substrate, the optical filter being characterized in that the minimum value of the spectral transmittance in the wavelength range of 240 nm to 300 nm is 92% or more, and the wavelength λ ₆₀ at which the spectral transmittance becomes 60% is 230 nm or less.

In the optical filter according to aspect 2, in aspect 1, the dielectric multilayer film has a high refractive index film with a relatively high refractive index and a low refractive index film with a relatively low refractive index, and it is preferable that the high refractive index film contains hafnium oxide.

In the optical filter according to aspect 3, in aspect 2, it is preferable that the thickness of the high refractive index film of the outermost layer, which is the furthest from the transparent substrate, among the plurality of high refractive index films, is thicker than the thickness of the high refractive index film of the innermost layer, which is the closest to the transparent substrate.

In the optical filter according to aspect 4, in aspect 3, it is preferable that the ratio of the thickness of the high refractive index film of the outermost layer to the thickness of the high refractive index film of the innermost layer (outermost layer/innermost layer) is 2 or more.

In the optical filter according to aspect 5, in any one of aspects 1 to 4, it is preferable that the number of layers of the dielectric multilayer film provided on one main surface of the transparent substrate is 10 or less.

In the optical filter according to aspect 6, in any one of aspects 2 to 5, it is preferable that the total thickness of the high refractive index films constituting the dielectric multilayer film is 500 nm or less.

In the optical filter according to aspect 7, in any one of aspects 1 to 6, it is preferable that the dielectric multilayer film is provided on both main surfaces of the transparent substrate.

In the optical filter according to aspect 8, in any one of aspects 1 to 7, it is preferable that the transparent substrate has a dome shape.

In the optical filter according to aspect 9, in any one of aspects 1 to 8, it is preferable that the ratio of the height of the dome-shaped openings to the spacing (height/spacing of openings) is 0.1 or more.

The sterilization device according to aspect 10 of the present invention is a sterilization device for inactivating a processing object, and is characterized in that it comprises a light source that emits light having a wavelength in the ultraviolet wavelength range, and an optical filter according to any one of aspects 1 to 9, and that the light source and the optical filter are arranged so that the processing object is inactivated by irradiating the light emitted from the light source through the optical filter.

The ultraviolet detection device according to aspect 11 of the present invention is an ultraviolet detection device for detecting ultraviolet light, and is characterized by comprising an optical filter according to any one of aspects 1 to 9, and an ultraviolet light receiving element.

The present invention provides an optical filter that can effectively transmit ultraviolet light over a wide wavelength range and increase the transmittance, as well as a sterilization device and an ultraviolet light detection device that use the optical filter.

FIG. 1 is a schematic front view showing an optical filter according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing an optical filter according to one embodiment of the present invention. 3A to 3C are schematic cross-sectional views for explaining a film forming method for an optical filter according to one embodiment of the present invention. FIG. 4 is a schematic cross-sectional view showing a sterilization device according to one embodiment of the present invention. FIG. 5 is a schematic cross-sectional view showing an ultraviolet detection device according to an embodiment of the present invention. FIG. 6 is a diagram showing the transmission spectra of the optical filter obtained in Example 1 and the glass substrate of Comparative Example 1 in the wavelength range of 200 nm to 400 nm. FIG. 7 is an enlarged view of the transmission spectrum in the wavelength range of 200 nm to 300 nm in FIG. FIG. 8 is a diagram showing the transmission spectra of the optical filters obtained in Examples 2 to 7 at wavelengths of 200 nm to 400 nm. FIG. 9 is an enlarged view of the transmission spectrum in the wavelength range of 200 nm to 300 nm in FIG.

Below, preferred embodiments are described. 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.

[Optical Filter]
Fig. 1 is a schematic front view showing an optical filter according to one embodiment of the present invention. Fig. 2 is a schematic cross-sectional view showing an optical filter according to one embodiment of the present invention. Fig. 2 is a schematic cross-sectional view assuming that the optical filter in Fig. 1 is flat. In Fig. 2, the dielectric multilayer film is shown enlarged for explanation.

As shown in FIG. 1, the optical filter 1 comprises a transparent substrate 2, a first dielectric multilayer film 3A, and a second dielectric multilayer film 3B.

The transparent substrate 2 is made of glass. The thickness of the transparent substrate 2 is 1.0 mm or less. The transparent substrate 2 also has a first main surface 2a and a second main surface 2b that face each other.

A first dielectric multilayer film 3A containing hafnium oxide is provided on the first main surface 2a of the transparent substrate 2. A second dielectric multilayer film 3B containing hafnium oxide is provided on the second main surface 2b of the transparent substrate 2. In this embodiment, the first dielectric multilayer film 3A and the second dielectric multilayer film 3B (hereinafter also referred to as dielectric multilayer films 3A and 3B) are multilayer films having the same configuration.

In this embodiment, the dielectric multilayer films 3A and 3B have a high refractive index film with a relatively high refractive index and a low refractive index film with a relatively low refractive index. The high refractive index film also contains hafnium oxide.

The optical filter 1 is an anti-reflection filter designed to prevent reflection of ultraviolet light by optical interference by including dielectric multilayer films 3A and 3B. More specifically, the minimum value of the spectral transmittance of the optical filter 1 in the wavelength range of 240 nm to 300 nm is 92% or more. Moreover, the wavelength λ ₆₀ at which the spectral transmittance of the optical filter 1 is 60% is 230 nm or less.

The spectral transmittance can be determined, for example, by measuring the spectral transmittance of the entire optical filter 1 using a spectral transmittance meter. For example, a model UH4150 manufactured by Hitachi High-Tech Science Corporation can be used as the spectral transmittance meter. The spectral transmittance can be measured under the conditions of an incident angle of 0° and a measurement wavelength of 200 nm to 800 nm.

The optical filter 1 of this embodiment has the above-mentioned configuration, and therefore can effectively transmit ultraviolet light in a wide wavelength range and can increase the transmittance. Therefore, when used in a sterilization device, for example, the optical filter 1 can improve the sterilization effect by increasing the types of objects to be treated (microorganisms, viruses, etc.) that can be treated and shortening the time required for inactivation treatment of the objects to be treated. Furthermore, when used in an ultraviolet detection device, the optical filter 1 can detect ultraviolet light in a wide wavelength range with high sensitivity.

In this embodiment, the minimum value of the spectral transmittance of the optical filter 1 at wavelengths of 240 nm to 300 nm is 92% or more, preferably 93% or more, more preferably 94% or more, even more preferably 96% or more, and particularly preferably 97% or more. In this case, ultraviolet light in a wide wavelength range can be transmitted more effectively. The upper limit of the minimum value of the spectral transmittance at wavelengths of 240 nm to 300 nm is not particularly limited, but can be, for example, 99.5%.

The wavelength λ ₆₀ at which the spectral transmittance of the optical filter 1 is 60% is 230 nm or less, preferably 225 nm or less, and more preferably 220 nm or less. In this case, ultraviolet rays in a wide wavelength range can be transmitted more effectively. The lower limit of the wavelength λ ₆₀ at which the spectral transmittance of the optical filter 1 is 60% is not particularly limited, but can be, for example, 200 nm.

In this embodiment, the optical filter 1 has a dome shape. In this case, the planar shape of the optical filter 1 may be approximately circular or approximately rectangular. When the optical filter 1 has a dome shape, the effective irradiation area of the ultraviolet light transmitted through the optical filter 1 can be made larger. However, the optical filter 1 may have a rectangular plate shape or a disk shape, and the shape is not particularly limited.

The components that make up the optical filter 1 are explained in detail below.

(Transparent substrate)
The transparent substrate 2 has a dome shape. In this case, the planar shape of the transparent substrate 2 may be substantially circular or substantially rectangular. When the transparent substrate 2 has a dome shape, the effective irradiation area of the ultraviolet light transmitted through the optical filter 1 can be increased. However, the transparent substrate 2 may have a rectangular plate shape or a disk shape, and the shape is not particularly limited.

When the transparent substrate 2 has a dome shape, the height H of the openings shown in FIG. 1 is preferably 0.5 mm or more, more preferably 0.6 mm or more, and preferably 1.5 mm or less, more preferably 1.2 mm or less. The spacing R of the openings is preferably 2.0 mm or more, more preferably 2.5 mm or more, and preferably 6.0 mm or less, more preferably 5.5 mm or less. Note that, for example, when the planar shape of the transparent substrate 2 is approximately circular, the spacing R of the openings corresponds to the diameter of the openings.

The ratio of the height H to the spacing R of the dome-shaped openings (height H/spacing R of openings) is preferably 0.1 or more, more preferably 0.15 or more, even more preferably 0.2 or more, and is preferably 0.6 or less, more preferably 0.5 or less, even more preferably 0.4 or less. When the ratio (height H/spacing R of openings) is within the above range, the effective irradiation area of the ultraviolet light transmitted through the optical filter 1 can be made larger.

The transparent substrate 2 is made of glass. In particular, the transparent substrate 2 is preferably 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 200 nm to 400 nm.

Examples of the glass constituting the transparent substrate 2 include quartz glass, borosilicate glass, etc. The quartz glass may be synthetic quartz glass or fused quartz glass. The borosilicate glass preferably contains, in mass %, 50%-80% SiO ₂ , 0%-10% Al ₂ O ₃ , 5%-30% B ₂ O ₃ , 0%-5% CaO, 0%-5% BaO, and 0%-15% Li ₂ O + Na ₂ O + K ₂ O, and more preferably contains, in mass %, 55%-75% SiO _{2 ,} 1%-10% Al ₂ O ₃ , 10%-30% B ₂ O ₃ , 0%-5% CaO, 0%-5% BaO, and 1.0%-15% Li ₂ O + Na ₂ O + K ₂ O.

SiO ₂ is a component that forms a glass network and also significantly increases the light transmittance from the ultraviolet wavelength region to the visible region. In particular, in the case of high refractive index glass, the effect of increasing the light transmittance is easily obtained. SiO ₂ is also a component that improves heat resistance and weather resistance. The content of SiO ₂ is preferably 50% to 80%, more preferably 55% to 75%, and even more preferably 58% to 70%. If the content of SiO ₂ is too small, it is difficult to obtain the above effects. In addition, when the film-attached transparent substrate is heat-treated after the film is formed, it is likely to soften and deform. On the other hand, if the content of SiO ₂ is too large, the softening point becomes high and it becomes difficult to mold the transparent substrate 2.

Al ₂ O ₃ is a component that forms a glass network and also increases the light transmittance from the ultraviolet wavelength region to the visible region. In particular, in the case of high refractive index glass, the effect of increasing the light transmittance is easily obtained. The content of _{Al 2} O ₃ is preferably 0% to 10%, more preferably 1% to 10%, even more preferably 3% to 10%, even more preferably 4% to 9.5%, and particularly preferably more than 4% to 9%. If the content of Al ₂ O ₃ is too small, it is difficult to obtain the above effect. In addition, when the transparent substrate with the film after the film formation is heat-treated, it is likely to soften and deform. On the other hand, if the content of Al ₂ O ₃ is too large, the softening point becomes high, making it difficult to mold the transparent substrate 2.

B ₂ O ₃ is a component that forms a glass network and also increases the light transmittance from the ultraviolet wavelength region to the visible region. In particular, in the case of high refractive index glass, the effect of increasing the light transmittance is easily obtained. The content of B ₂ O ₃ is preferably 5% to 30%, more preferably 10% to 30%, and even more preferably 12% to 28%. If the content of B ₂ O ₃ is too low, it becomes difficult to obtain the above effect. On the other hand, if the content of B ₂ O ₃ is too high, the transparent substrate with the film is easily softened and deformed when the transparent substrate with the film is heat-treated after the film is formed.

The glass composition may contain MgO, CaO, SrO, BaO and ZnO. MgO, CaO, SrO, BaO and ZnO are components that act as fluxes. In addition, MgO, CaO, SrO, BaO and ZnO are also components that suppress devitrification and improve weather resistance. The content of MgO+CaO+SrO+BaO+ZnO is preferably 0% to 10%, more preferably 0.1% to 9%, even more preferably 0.5% to 8%, even more preferably 1% to 7%, even more preferably 1.5% to 6%, and particularly preferably 2% to 5%. On the other hand, if the content of MgO, CaO, SrO, BaO and ZnO is too high, devitrification is likely to occur during molding and sintering. In addition, the light transmittance is likely to decrease.

The content of MgO, CaO, SrO, BaO and ZnO is preferably 0% to 10%, more preferably 0.1% to 9%, even more preferably 0.5% to 8%, even more preferably 1% to 7%, even more preferably 1.5% to 6%, and particularly preferably 2% to 5%.

Li ₂ O, Na ₂ O, and K ₂ O are components that lower the softening point. The content of Li ₂ O + Na ₂ O + K ₂ O is preferably 0.1% to 15%, more preferably 0.5% to 10%, and even more preferably 1 to 5%. If the content of Li ₂ O, Na ₂ O, or K ₂ O is too small, it becomes difficult to obtain the above effects. On the other hand, if the content of Li ₂ O, Na ₂ O, or K ₂ O is too large, the weather resistance and refractive index tend to decrease, and the light transmittance tends to decrease.

Furthermore, in addition to the above components, the borosilicate glass more preferably contains, as a glass composition, 0% to 0.001% TiO ₂ , 0% to 0.001% Fe ₂ O ₃ , and 0.5% to 2.0% F.

When the glass contains a large amount of Fe as an impurity (for example, 20 ppm or more), _TiO2 tends to significantly reduce the light transmittance and the softening point tends to increase. Therefore, the content of _TiO2 is preferably 1% or less, more preferably 0.5% or less, even more preferably 0.1% or less, even more preferably 0.01% or less, and particularly preferably 0.001% or less.

_Fe2O3 tends to significantly reduce _the light transmittance and also tends to increase the softening point. Therefore, the content _{of Fe2O3 is} preferably 1% or less, more preferably 0.5% or less, even more preferably 0.1% or less, even more preferably 0.01% or less, and particularly preferably 0.001% or less.

F is a component that lowers the softening point. In addition, F is a component that significantly increases the light transmittance in the ultraviolet region. The F content is preferably 0% to 5%, more preferably 0.1% to 4.5%, even more preferably 0.2% to 5%, even more preferably 0.3% to 4%, even more preferably 0.4% to 3%, and particularly preferably 0.5% to 2%. If the F content is too high, the weather resistance and resistance to devitrification are likely to deteriorate.

The thickness of the transparent substrate 2 is preferably 0.5 mm or less, more preferably 0.3 mm or less, and even more preferably 0.2 mm or less. In this case, shapes such as a dome shape can be easily formed. The lower limit of the thickness of the transparent substrate 2 is not particularly limited, but from the viewpoint of making it easier to form the dielectric multilayer films 3A and 3B on the transparent substrate 2, it is preferably 0.05 mm or more, and more preferably 0.1 mm or more.

(Dielectric multilayer film)
The dielectric multilayer films 3A and 3B are dielectric multilayer films having the same configuration. However, the dielectric multilayer films 3A and 3B may be dielectric multilayer films having different configurations, and are not particularly limited.

The dielectric multilayer film used for the dielectric multilayer films 3A and 3B is a multilayer film having a high refractive index film 4 with a relatively high refractive index and a low refractive index film 5 with a relatively low refractive index. In this embodiment, the multilayer film is formed by alternately stacking the high refractive index film 4 and the low refractive index film 5 in this order on the main surfaces 2a and 2b on both sides of the transparent substrate 2, respectively.

In this embodiment, the high refractive index film 4 is made of hafnium oxide and is a film whose main component is hafnium oxide. However, as long as the effect of the present invention is not hindered, a part of the high refractive index film 4 may be a film whose main component is aluminum oxide or the like.

The low refractive index film 5 is made of silicon oxide and is a film containing silicon oxide as its main component. However, the low refractive index film 5 may also be a film containing aluminum oxide, zirconium oxide, tin oxide, magnesium fluoride, or silicon nitride as its main component. These materials for the low refractive index film 5 may be used alone or in combination.

In this specification, a film containing a material as a main component refers to a film containing 50% or more by mass of the material. In a film containing a material as a main component, it is preferable that the material be contained in the film at 80% or more by mass, and more preferably at 90% or more by mass. Naturally, a film containing a material as a main component may be a film containing 100% by mass of the material.

In this embodiment, the total thickness of the dielectric multilayer films 3A and 3B is not particularly limited, but is preferably 160 nm or more, more preferably 200 nm or more, and is preferably 700 nm or less, more preferably 600 nm or less, even more preferably 500 nm or less, and particularly preferably 400 nm or less. When the total thickness of the dielectric multilayer films 3A and 3B is within the above range, ultraviolet rays in a wider wavelength range can be effectively transmitted, and the transmittance can be further increased. In particular, when the total thickness of the dielectric multilayer films 3A and 3B is equal to or less than the above upper limit, the wavelength λ ₆₀ at which the spectral transmittance of the optical filter 1 is 60% can be shifted to the lower wavelength side.

The total thickness of the high refractive index film 4 (the sum of the thicknesses of the high refractive index films 4) is preferably 70 nm or more, more preferably 80 nm or more, even more preferably 90 nm or more, preferably 500 nm or less, more preferably 480 nm or less, even more preferably 350 nm or less, and particularly preferably 240 nm or less. When the total thickness of the high refractive index film 4 is within the above range, ultraviolet rays in a wider wavelength range can be effectively transmitted, and the transmittance can be further increased. In particular, when the total thickness of the high refractive index film 4 is equal to or less than the above upper limit, the wavelength λ ₆₀ at which the spectral transmittance of the optical filter 1 becomes 60% can be shifted to the lower wavelength side.

The thickness of each layer of the high refractive index film 4 is not particularly limited, but is preferably 1.0 nm or more, more preferably 2.0 nm or more, even more preferably 4.0 nm or more, and is preferably 220 nm or less, more preferably 200 nm or less, even more preferably 150 nm or less.

In this embodiment, it is preferable that the thickness of the high refractive index film 4B, which is the outermost layer and is the furthest from the transparent substrate 2, is thicker than the thickness of the high refractive index film 4A, which is the innermost layer and is closest to the transparent substrate 2. In this case, ultraviolet light in a wider wavelength range can be effectively transmitted, and the transmittance can be further increased. It is preferable that the high refractive index film 4 has a film thickness gradient structure in which the thickness increases from the innermost high refractive index film 4A to the outermost high refractive index film 4B. In this case, the minimum value of the spectral transmittance of the optical filter 1 in the wavelength range of 240 nm to 300 nm can be further increased.

In this embodiment, the thickness ratio of the high refractive index film 4B of the outermost layer to the high refractive index film 4A of the innermost layer (outermost layer/innermost layer) is preferably 2 or more, more preferably 3 or more, even more preferably 5 or more, even more preferably 8 or more, even more preferably 10 or more, even more preferably 15 or more, and preferably 120 or less, more preferably 100 or less, even more preferably 80 or less, even more preferably 60 or less, even more preferably 50 or less, even more preferably 30 or less, and particularly preferably 20 or less. In this case, ultraviolet rays in a wider wavelength range can be effectively transmitted, and the transmittance can be further increased. In particular, when the thickness ratio of the high refractive index film 4B of the outermost layer to the high refractive index film 4A of the innermost layer (outermost layer/innermost layer) is equal to or greater than the above lower limit, the minimum value of the spectral transmittance of the optical filter 1 at wavelengths of 240 nm to 300 nm can be further increased.

The thickness of the innermost high refractive index film 4A is preferably 1.0 nm or more, more preferably 2.0 nm or more, more preferably 4.0 nm or more, preferably 20 nm or less, more preferably 10 nm or less. The thickness of the outermost high refractive index film 4B is preferably 20 nm or more, more preferably 30 nm or more, preferably 220 nm or less, more preferably 110 nm or less.

The total thickness of the low refractive index film 5 (the sum of the thicknesses of each low refractive index film 5) is preferably 60 nm or more, more preferably 80 nm or more, even more preferably 100 nm or more, preferably 500 nm or less, more preferably 450 nm or less, even more preferably 320 nm or less.

The thickness of each layer of the low refractive index film 5 is not particularly limited, but is preferably 1.0 nm or more, more preferably 2.0 nm or more, even more preferably 3.0 nm or more, and is preferably 130 nm or less, more preferably 100 nm or less.

The total thickness of the dielectric multilayer films 3A and 3B, the high refractive index film 4, and the low refractive index film 5 is the total thickness of the films provided on one main surface (the first main surface 2a or the second main surface 2b) of the transparent substrate 2.

In this embodiment, the number of layers constituting the dielectric multilayer films 3A and 3B is preferably 4 or more, preferably 14 or less, more preferably 10 or less, and even more preferably 4 or less. When the number of layers constituting the dielectric multilayer films 3A and 3B is within the above range, ultraviolet rays in a wider wavelength range can be effectively transmitted, and the transmittance can be further increased. In particular, when the number of layers constituting the dielectric multilayer films 3A and 3B is equal to or less than the upper limit value, the wavelength _λ60 at which the spectral transmittance of the optical filter 1 becomes 60% can be shifted to the lower wavelength side.

The number of layers constituting the high refractive index film 4 is preferably 1 or more, preferably 7 or less, more preferably 2 or less. The number of layers constituting the low refractive index film 5 is preferably 1 or more, preferably 7 or less, more preferably 2 or less.

The number of layers constituting the dielectric multilayer films 3A and 3B, the high refractive index film 4, and the low refractive index film 5 is the number of layers provided on one main surface (the first main surface 2a or the second main surface 2b) of the transparent substrate 2.

In this embodiment, it is preferable that the dielectric multilayer films 3A and 3B contain hafnium oxide crystals. More specifically, it is preferable that the high refractive index film 4 constituting the dielectric multilayer films 3A and 3B contains hafnium oxide crystals, and more preferably contains one or more types selected from cubic hafnium oxide crystals and tetragonal hafnium oxide crystals. In this case, the wavelength λ ₆₀ at which the spectral transmittance of the optical filter 1 becomes 60% can be shifted to the lower wavelength side.

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

In addition, in this specification, X-ray diffraction measurement can be performed by wide-angle X-ray diffraction. For example, an X-ray diffraction device manufactured by Rigaku Corporation, model number "SmartLab" can be used. Furthermore, CuKα radiation can be used as the radiation source. In addition, in the X-ray diffraction measurement, the entire optical filter 1 is subjected to measurement from the main surface side of the dielectric multilayer films 3A and 3B.

In the present invention, in an X-ray diffraction measurement, it is preferable that the diffraction peak due to the (1,1,1) crystal plane originating from a cubic hafnium oxide crystal or a tetragonal hafnium oxide crystal is larger than the diffraction peak due to the (-1,1,1) crystal plane originating from a monoclinic hafnium oxide crystal. In this case, the wavelength _λ60 at which the spectral transmittance of the optical filter 1 becomes 60% can be shifted to the lower wavelength side.

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 cubic hafnium oxide crystal or tetragonal hafnium oxide crystal to the peak area intensity Im of the diffraction peak due to the (-1,1,1) crystal plane derived from monoclinic hafnium oxide crystal is preferably 0.1 or more, more preferably 1 or more, even more preferably 2 or more, particularly preferably 2.5 or more, and most preferably 3 or more. When the ratio Ic/Im is equal to or more than the lower limit, the wavelength λ ₆₀ at which the spectral transmittance of the optical filter 1 becomes 60% can be shifted to the lower wavelength side. The upper limit of the ratio Ic/Im is not particularly limited, but can be set to, for example, 10,000.

In this embodiment, the dielectric multilayer films 3A, 3B are provided on both main surfaces 2a, 2b of the transparent substrate 2. In this way, in the present invention, it is preferable that the dielectric multilayer films 3A, 3B are provided on both main surfaces 2a, 2b of the transparent substrate 2, but it is sufficient that the dielectric multilayer films 3A, 3B are provided on one of the first main surface 2a and the second main surface 2b of the transparent substrate 2.

In addition, other films such as antifouling films may be laminated on the main surfaces 2a and 2b of the transparent substrate 2 as long as the effects of the present invention are not impaired.

Below, an example of a method for manufacturing the optical filter 1 is described in detail.

(Method of Manufacturing Optical Filter)
A film-attached transparent substrate forming step;
First, as shown in Fig. 3(a), a transparent substrate base material 22 is prepared, and the transparent substrate base material 22 is fixed to a film forming jig 26 using a fixing member 27. A base material having a plurality of dome-shaped portions 22A arranged thereon can be used as the transparent substrate base material 22. Although not shown in the drawings, in this embodiment, the transparent substrate base material 22 has a flat plate shape, and the dome-shaped portions 22A are arranged in both the length direction and the width direction in a plan view. Also, a tape such as a polyimide tape can be used as the fixing member 27.

Next, a dielectric multilayer film 3A (not shown in Figs. 3(a) to (c)) is formed on the first main surface 22a of the transparent substrate base material 22 on the apex side of the dome shape. The dielectric multilayer film 3A can be formed by alternately stacking a high refractive index film 4 and a low refractive index film 5 in this order on the first main surface 22a of the transparent substrate base material 22. The high refractive index film 4 and the low refractive index film 5 can be formed by deposition, sputtering, CVD, or the like. In particular, the high refractive index film 4 and the low refractive index film 5 are preferably formed by a RAS (Radical Assisted Sputtering) sputtering method from the viewpoint of controlling the thickness of each layer with higher precision and forming a denser film.

The temperature of the transparent substrate base material 22 when forming the high refractive index film 4 is preferably 300°C or less, and more preferably 150°C or less. The lower limit of the temperature of the transparent substrate base material 22 when forming the high refractive index film 4 can be, for example, 20°C (room temperature).

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

The temperature of the transparent substrate base material 22 when forming the low refractive index film 5 is preferably 300°C or less, and more preferably 270°C or less. The lower limit of the temperature of the transparent substrate base material 22 when forming the low refractive index film 5 can be, for example, 20°C (room temperature).

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

Next, as shown in FIG. 3(b), a concave surface forming jig 28 is attached to the film forming jig 26 to prepare a film forming jig 29 with holes in the same arrangement as the dome-shaped portion 22A.

Next, as shown in FIG. 3(c), the transparent substrate base material 22 is placed so that the first main surface 22a on the apex side of the dome shape is positioned on the hole side of the film-forming jig 29, and the transparent substrate base material 22 is fixed to the film-forming jig 29 using the fixing member 27.

Next, in the transparent substrate base material 22, a dielectric multilayer film 3B (not shown in FIGS. 3(a) to (c)) is formed on the second main surface 22b opposite the apex of the dome shape to form a film-coated transparent substrate base material. The dielectric multilayer film 3B can be formed in the same manner as the dielectric multilayer film 3A. Next, the film-coated transparent substrate base material 22 can be divided into individual pieces to obtain a film-coated transparent substrate.

Heat treatment process;
Next, the obtained film-attached transparent substrate is heat-treated. As a result, the optical filter 1 can be obtained. The temperature of the heat treatment can be, for example, 450° C. or higher. In particular, when the film-attached transparent substrate is heated at a temperature of 450° C. or higher, the content of cubic hafnium oxide crystals can be relatively increased. Therefore, in the obtained optical filter 1, the wavelength λ ₆₀ at which the spectral transmittance becomes 60% can be shifted to the lower wavelength side.

The temperature of the heat treatment of the film-coated transparent substrate is preferably 450° C. or higher, more preferably 500° C. or higher, even 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 wavelength λ ₆₀ at which the spectral transmittance of the optical filter 1 becomes 60% can be shifted to the shorter wavelength side.

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

In the obtained optical filter 1, the minimum value of the spectral transmittance in the wavelength range of 240 nm to 300 nm is 92% or more. In the obtained optical filter 1, the wavelength λ ₆₀ at which the spectral transmittance becomes 60% is 230 nm or less.

The minimum value of the spectral transmittance of the optical filter 1 at wavelengths of 240 nm to 300 nm can be increased, for example, by increasing the ratio of the thickness of the outermost high refractive index film 4B to the thickness of the innermost high refractive index film 4A.

Furthermore, the wavelength _λ60 at which the spectral transmittance of the optical filter 1 becomes 60% can be shifted to a shorter wavelength side, for example, by reducing the number of laminated films constituting the dielectric multilayer films 3A and 3B, by reducing the total thickness of the dielectric multilayer films 3A and 3B, or by reducing the total thickness of the high refractive index film 4.

In addition, after the film-coated transparent substrate forming process, a heat treatment process may be subsequently performed, and then the base material of the film-coated transparent substrate may be divided into individual pieces to obtain the film-coated transparent substrate.

In addition, after the base material of the transparent substrate with the film is divided into individual pieces, an optical filter may be obtained without carrying out a heat treatment.

[Sterilization device]
FIG. 4 is a schematic cross-sectional view showing a sterilization device according to one embodiment of the present invention.

The sterilization device 30 shown in FIG. 4 is a sterilization device for inactivating objects to be treated (microorganisms, viruses, etc.) that are attached to or contained in the sterilization object P. The sterilization device 30 includes a light source 32, a reflector 33, a housing 34, and an optical filter 1.

The sterilization device 30 is equipped with the dome-shaped optical filter 1 described above. The optical filter 1 is arranged on the housing 34 such that the first main surface 2a at the apex side of the dome shape is disposed on the outside (the side of the object to be sterilized P). In the sterilization device 30, the emitted light emitted from the light source 32 is irradiated onto the object to be sterilized P via the optical filter 1.

A light source 32 and a reflector 33 are arranged inside the housing 34. The light source 32 is a light source that emits light with a wavelength in the ultraviolet wavelength range (for example, a wavelength range of 200 nm to 400 nm). The reflector 33 is capable of diffusing the light emitted from the light source over a wide range. The light source 32 is arranged facing the concave surface of the optical filter 1.

As the light source 32, 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 300 nm. As such an excimer lamp, for example, a KrCl excimer lamp can be used. The excimer lamp may be a KrF excimer lamp. In addition, multiple UV-LEDs with different peak wavelengths in the range of 250 nm to 320 nm may be used.

By using the sterilization device 30, it is possible to inactivate the objects to be sterilized (microorganisms, viruses, etc.) that are attached to the object to be sterilized P and are contained therein. The sterilization device 30 can efficiently transmit ultraviolet light, which is useful for sterilization, and therefore can efficiently perform ultraviolet sterilization on the object to be sterilized P. For example, in ultraviolet sterilization, ultraviolet light can be applied to the DNA within the cells of microorganisms such as bacteria to selectively inactivate the microorganisms, or ultraviolet light can be applied to viruses to selectively inactivate them.

The sterilization device 30 of this embodiment is equipped with the optical filter 1, which allows ultraviolet light in a wide wavelength range to pass effectively and increases the transmittance. Therefore, when the optical filter 1 is used in a sterilization device, it can improve the sterilization effect by broadening the range of applicable treatment objects (microorganisms, viruses, etc.) and shortening the time required for inactivation treatment.

Furthermore, in the sterilization device 30 of this embodiment, the optical filter 1 is provided in a dome shape. Therefore, emitted light with a small angle of incidence can be made to be incident not only near the center of the optical filter 1 located above the light source 32, but also in a portion of the optical filter 1 located diagonally above the light source 32 and away from the center. Therefore, according to the sterilization device 30, even if the effective irradiation area of the light emitted from the light source 32 is increased, ultraviolet light useful for sterilization processing can be efficiently transmitted.

In the sterilization device 30 of this embodiment, as shown in FIG. 4, it is preferable that the optical filter 1 is arranged concentrically around the light source 32 in a cross-sectional view along the thickness direction. In this case, it is possible to increase the effective irradiation area of the emitted light while more efficiently transmitting ultraviolet light that is useful for sterilization processing.

In the present embodiment, the sterilization device 30 uses one light source 32, but multiple light sources 32 emitting light with different wavelength ranges may be used. In this case, by using a light source 32 capable of emitting light in a corresponding wavelength range for each of multiple processing objects having different wavelength ranges that enhance the sterilization effect, multiple processing objects can be sterilized simultaneously. In addition, the multiple light sources 32 may be arranged in the same housing 34, or may be arranged individually in multiple housings 34.

[Ultraviolet Detector]
FIG. 5 is a schematic cross-sectional view showing an ultraviolet detection device according to an embodiment of the present invention.

The ultraviolet detection device 40 shown in FIG. 5 includes a base 42, an ultraviolet light receiving element 41, and an optical filter 1. In the ultraviolet detection device 40, ultraviolet light from the outside enters the base 42 through the optical filter 1. The ultraviolet light that enters the base 42 can then be detected by the ultraviolet light receiving element 41.

The ultraviolet detection device 40 of this embodiment is equipped with an optical filter 1, so it can transmit ultraviolet light in a wide wavelength range and can increase the transmittance. Therefore, the ultraviolet detection device 40 can detect ultraviolet light in a wide wavelength range with high sensitivity.

The present invention will now be described in more detail with reference to specific examples. The present invention is not limited to the following examples, and can be modified as appropriate without departing from the spirit of the invention.

Example 1
First, a borosilicate glass substrate having a thickness of 0.2 mm (manufactured by Nippon Electric Glass Co., Ltd., product number "BU-41", dimensions: 100 mm x 100 mm x 0.2 mm) was prepared. Next, the prepared glass substrate was processed into a dome shape by press molding to prepare a transparent base material (spacing of openings: 4.0 mm, height: 1.0 mm). The glass substrate may be processed into a dome shape by heating and thermal deformation.

Next, a dielectric multilayer film was formed on one main surface of the transparent substrate processed into a dome shape by a sputtering method of the RAS method. Specifically, first, argon gas and oxygen gas were used as carrier gases to sputter a hafnium target, and a hafnium oxide film (HfO ₂ film) was formed on one main surface of the transparent substrate. At this time, the flow rate of argon gas was set to 500 sccm, the flow rate of oxygen gas was set to 156 sccm, and the target applied power (film forming power) was set to 4.5 kW. Next, argon gas and oxygen gas were used as carrier gases to sputter a silicon target, and a silicon oxide film (SiO ₂ film) was formed on the HfO ₂ film. At this time, the flow rate of argon gas was set to 600 sccm, the flow rate of oxygen gas was set to 240 sccm, and the target applied power (film forming power) was set to 5.0 kW. By repeating this operation, a dielectric multilayer film having a total of four layers of films, in which HfO ₂ films and SiO ₂ films are alternately stacked one by one in this order, was formed on one main surface of the transparent substrate. In the same manner, a dielectric multilayer film having a total of four layers of films, in which HfO ₂ films and SiO ₂ films are alternately stacked one by one in this order, was formed on the other main surface of the transparent substrate, and a transparent substrate with a film was obtained. Note that during the film formation, the atmosphere temperature was room temperature (20 ° C.) without external heating. Next, the transparent substrate with a film was heat-treated at a temperature of 600 ° C. for 60 minutes in an air atmosphere to obtain an optical filter.

The thickness of each layer in the dielectric multilayer film is as shown in Table 1 below.

(Examples 2 to 7)
An optical filter was obtained in the same manner as in Example 1, except that the dielectric multilayer film was formed to have the structure and thickness as shown in Table 1 above and that no heat treatment was performed after film formation.

(Comparative Example 1)
A borosilicate glass substrate having a thickness of 0.2 mm (manufactured by Nippon Electric Glass Co., Ltd., product number "BU-41", dimensions: 100 mm x 100 mm x 0.2 mm) was prepared. Next, the prepared glass substrate was processed into a dome shape (spacing of openings: 4.0 mm, height: 1.0 mm) by press molding to prepare a transparent base material, which was used as it was without forming a dielectric multilayer film.

[evaluation]
(Spectral transmittance)
The spectral transmittance was measured using a spectral transmittance meter (manufactured by Hitachi High-Tech Science Corporation, product number "UH4150") for the optical filter of Example 1 and the transparent substrate of Comparative Example 1. Specifically, the angle of incidence (AOI) was set to 0°, and the measurement wavelength was set to 200 nm to 400 nm.

FIG. 6 is a diagram showing the transmission spectra at wavelengths of 200 nm to 400 nm of the optical filter obtained in Example 1 and the glass substrate of Comparative Example 1. FIG. 7 is a diagram showing an enlarged view of the transmission spectra at wavelengths of 200 nm to 300 nm in FIG. 6. Note that in FIGS. 6 and 7, the transmission spectrum of the optical filter (after firing) obtained in Example 1 is shown by a solid line, and the transmission spectrum of the optical filter obtained in Example 1 before firing is shown by a dashed line. Also, the transmission spectrum of the glass substrate of Comparative Example 1 is shown by a dashed line.

As shown in Figures 6 and 7, in Example 1, the transmittance of ultraviolet light is increased over a wide wavelength range, and in particular, the spectral transmittance in the wavelength range of 240 nm to 300 nm is higher than that of the transparent substrate itself in Comparative Example 1.

Furthermore, Fig. 8 shows the transmission spectra of the optical filters obtained in Examples 2 to 7 at wavelengths of 200 nm to 400 nm. Also, Fig. 9 shows an enlarged view of the transmission spectra of Fig. 8 at wavelengths of 200 nm to 300 nm.

As shown in Figures 8 and 9, Examples 2 to 7 show improved transmittance of ultraviolet light over a wide wavelength range.

DESCRIPTION OF SYMBOLS 1...Optical filter 2... Transparent substrate 2a, 22a...First main surface 2b, 22b...Second main surface 3A, 3B...First and second dielectric multilayer films 4...High refractive index film 4A...Innermost high refractive index film 4B...Outermost high refractive index film 5...Low refractive index film 22...Transparent substrate base material 22A...Dome-shaped portion 26, 29...Film-forming jig 27...Fixing member 28...Concave surface forming jig 30...Sterilization device 32...Light source 33...Reflector 34...Housing 40...Ultraviolet light detection device 41...Ultraviolet light receiving element 42...Substrate P...Object to be sterilized

Claims (11)

1. A transparent substrate made of glass and having a thickness of 1.0 mm or less;
   a dielectric multilayer film provided on at least one main surface of the transparent substrate and containing hafnium oxide;
   Equipped with
   The minimum spectral transmittance in the wavelength range of 240 nm to 300 nm is 92% or more;
   An optical filter having a wavelength _λ60 at which the spectral transmittance is 60% being 230 nm or less.
2. 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 optical filter of claim 1 , wherein the high refractive index film comprises hafnium oxide.
3. The optical filter according to claim 2, wherein the thickness of the high refractive index film of the outermost layer, which is the furthest from the transparent substrate, is greater than the thickness of the high refractive index film of the innermost layer, which is the closest to the transparent substrate.
4. The optical filter according to claim 3, wherein the ratio of the thickness of the high refractive index film of the outermost layer to the thickness of the high refractive index film of the innermost layer (outermost layer/innermost layer) is 2 or more.
5. The optical filter according to any one of claims 1 to 4, wherein the number of layers of the dielectric multilayer film provided on one main surface of the transparent substrate is 10 or less.
6. The optical filter according to any one of claims 2 to 4, wherein the total thickness of the high refractive index films constituting the dielectric multilayer film is 500 nm or less.
7. The optical filter according to any one of claims 1 to 4, wherein the dielectric multilayer film is provided on both main surfaces of the transparent substrate.
8. The optical filter according to any one of claims 1 to 4, wherein the transparent substrate has a dome shape.
9. The optical filter of claim 8, wherein the ratio of the height of the dome-shaped openings to the spacing between them (height/spacing between openings) is 0.1 or greater.
10. A sterilization apparatus for inactivating an object to be treated, comprising:
    A light source that emits light having a wavelength in the ultraviolet wavelength range;
    An optical filter according to any one of claims 1 to 4;
    Equipped with
    A sterilization device, wherein the light source and the optical filter are arranged so that the object to be treated is inactivated by irradiating the object with light emitted from the light source via the optical filter.
11. An ultraviolet detection device for detecting ultraviolet light, comprising:
    An optical filter according to any one of claims 1 to 4;
    An ultraviolet light receiving element;
    An ultraviolet detection device comprising:

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