Optical control element

Abstract

To provide a novel optical control element.SOLUTION: An optical control element 10 comprises: a substrate 12; and a plurality of inorganic particles 14 formed of phase transition material that makes a phase transition according to environmental changes which are one or more of temperature change and light absorption, having an average particle diameter of 1 nm or more and 1000 μm or less, having variations in one or more of the particle diameter and the particle shape, and spaced apart from each other on a surface 12a of the substrate 12, and its optical characteristics, which are one or more of light transmission characteristics and light reflection characteristics, change according to the environmental changes.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a light control element. [Background technology]

[0002] Previously, UV sensors have been proposed that use elements with vanadium dioxide films formed on the surfaces of alumina or silicon substrates and realize multilevel memory functions by controlling the UV irradiation conditions (Non-Patent Document 1). Vanadium dioxide is a phase-transition material that undergoes a phase transition from the low-temperature monoclinic (M1) phase to the high-temperature rutile (R) phase at approximately 341 K, and is said to exhibit a rapid change in resistance and significant optical switching in the infrared region during the phase transition process. Furthermore, since the proportion of the monoclinic phase in vanadium dioxide films decreases with increasing UV irradiation, it is believed that these properties can be utilized to realize multilevel memory functions. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] G. Li et al., “Photo-induced non-volatile VO2 phase transition for neuromorphic ultraviolet sensors”, Nature Communications (2022) 13:1729. Summary of the Invention [Problem to be solved by the invention]

[0004] However, in Non-Patent Document 1, vanadium dioxide, which is a phase transition material, is formed as a film, and when used in a light control element, the desired change in optical properties may not be obtained.

[0005] The present disclosure has been made to solve such problems, and a main object of the disclosure is to provide a novel light control element. [Means for solving the problem]

[0006] As a result of intensive research to achieve the above-mentioned object, the inventors discovered that when a phase transition material is separated and arranged as nano- to micro-sized particles with varying particle diameters and shapes, rather than as a film, it exhibits the desired change in optical properties, and have thus completed the invention of the present disclosure.

[0007] That is, the light control element of the present disclosure is A substrate; a plurality of inorganic particles formed of a phase transition material that undergoes a phase transition in response to an environmental change, which is at least one of a temperature change and light absorption, and having an average particle size of 1 nm to 1000 μm and varying in at least one of particle size and particle shape, and arranged separately from one another on the surface of the substrate; Equipped with The environmental change causes a change in optical characteristics, which may be one or more of light transmission characteristics and light reflection characteristics. [Effects of the Invention]

[0008] The present disclosure provides a novel light control element. For example, it can provide a light control element that exhibits a change in optical properties different from that observed when a phase transition material is formed into a film. The reason for this effect is presumed to be as follows. For example, when a phase transition material is formed into nano- to micro-sized particles, it is thought that the material exhibits a change in optical properties different from that observed when the material is formed into a film due to a difference in the surface condition (e.g., the amount of oxygen defects on the surface that become crystal nuclei and the distortion of the crystal structure) compared to when the material is formed into a film. Furthermore, when the particles have different particle sizes or shapes, the surface condition differs for each particle, resulting in a different change in optical properties for each particle. Therefore, by adjusting the particle size, particle shape, distribution, etc., it is possible to finely adjust the change in optical properties, thereby providing a novel light control element that exhibits a desired change in optical properties. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is an explanatory diagram showing the outline of the configuration of the light control element 10. [Figure 2] FIG. 10 is an explanatory diagram of curves showing changes in optical properties when the temperature is increased and decreased. [Figure 3] Confocal microscope photograph of Experimental Example 1 at a sample temperature of 18°C. [Figure 4] Confocal microscope photographs of the sample in Experimental Example 1 as the temperature was increased. [Figure 5] FIG. 5 is an explanatory diagram showing the results of image analysis of FIG. 4. [Figure 6] Confocal microscope photographs of the sample of Experimental Example 1 as the temperature was lowered. [Figure 7] FIG. 7 is an explanatory diagram showing the results of image analysis of FIG. 6. [Figure 8] Electron microscope photographs of samples from Experimental Examples 2 to 6. [Figure 9] 1 is a histogram showing the particle size distribution of samples from Experimental Examples 2 to 6. [Figure 10] FIG. 10 is an explanatory diagram of the complex refractive index measurement results of Experimental Example 7. [Figure 11] FIG. 11 is an explanatory diagram of the results of numerical calculations based on the measurement results of Experimental Example 7. DETAILED DESCRIPTION OF THE INVENTION

[0010] The light control element of the present disclosure includes a substrate and a plurality of inorganic particles formed on the surface of the substrate. The inorganic particles may be formed on only one surface of the substrate, or may be formed on two opposing surfaces, for example. The inorganic particles are arranged separately from one another on the surface of the substrate. "Separately arranged" means that the inorganic particles are arranged apart from one another without contacting each other.

[0011] The substrate is, for example, a flat substrate, preferably a plane-parallel substrate. The substrate may be, for example, a glass substrate such as fused silica glass or synthetic quartz glass, a ceramic substrate, or a resin substrate. The substrate is preferably light-transmitting, and is preferably transparent.

[0012] The inorganic particles are made of a phase-transition material that undergoes a phase transition in response to an environmental change, which may be one or more of a temperature change and light absorption. When a phase-transition material undergoes a phase transition in response to an environmental change, it is thought that the dielectric constant changes, the interaction with incident light changes, and optical properties such as transmitted light characteristics and reflected light characteristics change. The temperature change also includes a temperature change caused by the inorganic particles absorbing light. The phase-transition material may be a solid-solid phase-transition material whose crystalline structure changes in response to a change in environmental conditions, or a metal-dielectric phase-transition material. The phase-transition material may be a metal oxide or a metal sulfide. The phase-transition material may be a strongly correlated insulator or a Mott insulator, such as vanadium dioxide (VO2) or chromium hollandite (K2Cr8O 16 ), or iron-based spin ladder material (BaFe2S3). These may be doped with other atoms or may not be doped; for example, vanadium dioxide may be undoped vanadium dioxide, tungsten-doped vanadium dioxide, or chromium-doped vanadium dioxide.

[0013] The inorganic particles are preferably formed of vanadium dioxide. Vanadium dioxide changes from a dielectric state to a metallic state when the temperature is changed from low to high, and from the metallic state to a dielectric state when the temperature is changed from high to low. In this way, the real part of the relative dielectric constant of vanadium dioxide is inverted before and after the phase transition due to the temperature change. Furthermore, when vanadium dioxide is irradiated with light, it absorbs the incident light and converts it into heat, causing a temperature change.

[0014] The inorganic particles are preferably composed of nanoparticles having a nano-sized particle size (1 nm or more but less than 1000 nm) or microparticles having a micro-sized particle size (1 μm or more but less than 1000 μm). The average particle size of the inorganic particles is 1 nm or more but less than 1000 μm. The average particle size of the inorganic particles may be 10 nm or more, 100 nm or more, 300 nm or more, or 500 nm or more. The average particle size of the inorganic particles is preferably 1 / 10 or more of the target wavelength, and considering applications from visible light to near-infrared wavelengths, 40 nm or more is desirable. The average particle size of the inorganic particles may be 1000 nm or less, 700 nm or less, or 650 nm or less. The particle size of the inorganic particles is the equivalent circle diameter (the diameter of a circle having the same area as the projected area of ​​the particle) determined by image analysis using an optical microscope or electron microscope. The average particle size of the inorganic particles is the average particle size based on the number of particles.

[0015] The shape of the inorganic particles may be, for example, a circular or elliptical shape when the light control element is viewed from above, or a shape in which multiple such shapes are connected together.The shape of the inorganic particles may be, for example, a spherical shape, an ellipsoidal shape, a partially missing sphere shape, or a partially missing ellipsoidal shape.Furthermore, the shape of the inorganic particles may be a secondary particle shape in which multiple primary particles such as spheres, ellipsoids, partially missing spheres, or partially missing ellipsoidal spheres are connected together.

[0016] Inorganic particles vary in one or more of particle size and particle shape. When inorganic particles vary in particle size or particle shape, the phase transition temperature varies due to differences in the surface condition (e.g., the amount of oxygen defects on the surface that become crystal nuclei or the distortion of the crystal structure). Therefore, by providing variation in one or more of particle size and particle shape, the phase transition temperature differs for each particle, and it is believed that the optical properties can be changed to a multi-value or continuous value exceeding two. When inorganic particles vary in particle size, the standard deviation of the particle size may be 500 nm or less, 400 nm or less, or 300 nm or less. The standard deviation of the particle size may be 100 nm or more, or 200 nm or more. Note that variation in particle size and particle shape means that the particle size and particle shape are not constant, and two or more particle sizes and particle shapes are sufficient.

[0017] The inorganic particles may be formed over 10% or more of the substrate surface, i.e., the coverage of the substrate surface with the inorganic particles may be 10% or more. This coverage may be 15% or more, or 20% or more. Also, this coverage may be 90% or less, 80% or less, 70% or less, or 65% or less.

[0018] The optical control element may be fabricated, for example, by forming the raw material of the phase transition material or the phase transition material into a film or particles on a substrate and, if necessary, heat-treating the material under a predetermined atmosphere. Examples of phase transition materials include the aforementioned vanadium dioxide, chromium hollandite, and iron-based spin ladder materials. Examples of raw materials for the phase transition material include metals such as vanadium, tungsten, chromium, iron, potassium, and barium, as well as compounds containing these metals. Methods for forming the film or particles include physical vapor deposition (PVD) such as sputtering, vacuum deposition, and ion plating, and chemical vapor deposition (CVD) such as thermal CVD and plasma CVD. When forming the film, the film thickness may be, for example, 1 nm or more, 10 nm or more, or 20 nm or more. The film thickness may be, for example, 300 nm or less, 200 nm or less, or 100 nm or less. Examples of heat-treatment atmospheres include oxygen-containing atmospheres, sulfur-containing atmospheres, and vacuum atmospheres. The heat treatment atmosphere may be, for example, 0.1 Pa or more, or 20 Pa or more. The heat treatment atmosphere may be, for example, 100 Pa or less, or 30 Pa or less. The heat treatment temperature may be, for example, 150°C or more, or 300°C or more. The heat treatment temperature may be, for example, 600°C or less, or 400°C or less. The heat treatment time may be, for example, 1 minute to 180 minutes, 5 minutes to 120 minutes, or 10 minutes to 90 minutes. By appropriately adjusting these conditions, the particle size, particle shape, coverage, etc. of the inorganic particles can be adjusted to exhibit the desired change in optical properties.

[0019] The light control element may be used, for example, in a window material such as a smart window, or in an optical system for writing to an optical medium such as a CD.

[0020] FIG. 1 shows an example of a light control element. FIG. 1 is an explanatory diagram illustrating the outline of the configuration of a light control element 10. FIG. 1A is a schematic top view of the light control element 10, and FIG. 1B is a schematic cross-sectional view of the light control element cut along a plane perpendicular to a substrate 12. As shown in FIG. 1, the light control element 10 includes a substrate 12 and a plurality of inorganic particles 14 arranged separately from one another on a surface 12a of the substrate 12. The inorganic particles 14 are formed of a phase transition material such as VO2, have an average particle size of 1 nm to 1000 μm, and exhibit variation in one or more of particle size and particle shape. In this light control element, environmental changes, such as temperature change and / or light absorption, change the optical properties, such as one or more of light transmission characteristics and light reflection characteristics. By adjusting the particle size, particle shape, and coverage of the inorganic particles, the desired optical property changes can be achieved.

[0021] The light control element described above includes inorganic particles formed of a phase transition material that undergoes a phase transition in response to environmental changes, such as temperature and / or light absorption. This phase transition occurs in response to environmental changes, resulting in changes in optical properties, such as one or more of light transmission and reflection. For example, the light transmission and reflection characteristics change in a direction perpendicular to the substrate or along the substrate. Furthermore, because the inorganic particles vary in one or more of their particle size and shape, the phase transition temperature varies depending on the particle size and shape, resulting in a multi-value change in optical properties exceeding two. The multi-value change may be a gradual or continuous change. When the light control element is actually used, the optical change may be gradual or continuous, resulting in a multi-value change of two or more values, such as by gradually changing the environment, or abruptly changing the environment, resulting in a binary optical change. The phase transition of inorganic particles depends on the probability of transition nucleation during the crystal phase transition and is thought to be triggered primarily by distortion of the crystalline structure near the surface of the inorganic particles or oxygen defects, which are missing oxygen atoms in the crystal lattice. In other words, inorganic particles, whose surface conditions vary depending on the particle size and particle shape, undergo phase transitions under different environmental conditions, and it is thought that gradual changes in environmental conditions result in multi-value changes, or at the limit of these multi-value changes, in a continuous change in the relative dielectric constant.

[0022] This light control element may have a hysteresis width ΔT in a curve showing changes in optical properties during temperature rise and fall that is wider than the hysteresis width typically observed during a phase transition of vanadium dioxide. The hysteresis width ΔT is calculated from the area S of the hysteresis range (the shaded area in FIG. 2 ) in a curve with temperature on the horizontal axis and optical property values ​​(e.g., the amount of reflected light or the amount of transmitted light) on the vertical axis, where ΔR is the difference between the maximum value Rmax and the minimum value Rmin of the optical property, using the formula ΔT = S / ΔR. FIG. 2 shows an example of a curve showing changes in optical properties during temperature rise and fall. In FIG. 2 , the change in optical property is represented by a change in reflectance. The hysteresis width ΔT is preferably 10°C or more, more preferably 15°C or more. The hysteresis width ΔT may be 20°C or more, 30°C or more, or 35°C or more. Moreover, the hysteresis width ΔT may be set to 90° C. or less, 80° C. or less, or 70° C. or less.

[0023] In this light control element, the inorganic particles are made of a phase-transition material and undergo a phase transition in response to an environmental change, such as a temperature change or light absorption. It is believed that only a portion of the inorganic particles undergo a phase transition when a predetermined environmental change occurs. For example, as shown in Figure 2, during the temperature rise process, if the maximum temperature is raised to a range below a predetermined threshold (phase transition onset temperature) Ta1, no inorganic particles undergo a phase transition (e.g., all remain dielectric), whereas if the maximum temperature exceeds a predetermined threshold Ta2, all of the inorganic particles undergo a phase transition (e.g., all become metallic). If the maximum temperature is raised to an intermediate value, such as between Ta1 and Ta2, it is believed that only a portion of the inorganic particles undergo a phase transition (e.g., some remain dielectric and the rest become metallic). Furthermore, during the temperature drop process, if the minimum temperature is dropped within a range exceeding a predetermined threshold Tb1, no inorganic particles will undergo a phase transition (e.g., all will remain metallic). If the minimum temperature is dropped below a predetermined threshold Tb2, all of the inorganic particles will undergo a phase transition (e.g., all will become dielectric). If the minimum temperature is dropped to an intermediate value, such as between Tb2 and Tb1, only a portion of the inorganic particles will undergo a phase transition (e.g., some will remain metallic and the rest will become dielectric). This is thought to enable the optical properties to be changed into multiple values. Note that in Figure 2, Ta1 and Tb2 are the same, and Ta2 and Tb1 are the same, but these values ​​do not have to be the same.

[0024] It goes without saying that the present disclosure is not limited to the above-described embodiments, and can be implemented in various forms as long as they fall within the technical scope of the present disclosure.

[0025] The present disclosure may be any of the following [1] to [8]. [1] A light control element comprising: a substrate; and a plurality of inorganic particles formed of a phase transition material that undergoes a phase transition in response to an environmental change, which is one or more of a temperature change and light absorption, the inorganic particles having an average particle size of 1 nm to 1000 μm and varying in one or more of particle size and particle shape, and arranged separately from one another on the surface of the substrate; wherein the optical characteristics, which are one or more of light transmission characteristics and light reflection characteristics, change in response to the environmental change. [2] The light control element according to [1], wherein the phase transition material is vanadium dioxide. [3] The light control element according to [1] or [2], wherein the inorganic particles have an average particle size of 700 nm or less. [4] The light control element according to any one of [1] to [3], wherein the inorganic particles are formed over an area of ​​20% to 65% of the surface of the substrate. [5] The light control element according to any one of [1] to [4], wherein when an environmental change under a predetermined condition occurs as the environmental change, only a part of the inorganic particles undergoes a phase transition. [6] The light control element according to any one of [1] to [5], wherein the optical characteristics change in multiple values ​​exceeding two values. [7] The light control element according to any one of [1] to [6], wherein the inorganic particles have a standard deviation of particle size of 200 nm or more and 300 nm or less. [8] The optical control element according to any one of [1] to [7], wherein the environmental change is a temperature change, and the hysteresis width of a curve showing the change in optical characteristics during temperature rise and temperature fall is 15°C or more. [Example]

[0026] Examples in which the light control element of the present disclosure has been specifically examined will be described below. Experimental Examples 1 to 6 correspond to working examples of the present disclosure, and Experimental Examples 7 and 8 correspond to reference examples.

[0027] 1. Examination of changes in optical characteristics [Experimental Example 1] Vanadium was sputtered onto a fused quartz substrate to a thickness of 60 nm, and then baked under controlled oxygen partial pressure to produce an optical control element with nanoparticles formed on the substrate surface. Specifically, the base vacuum in the chamber was set at 1×10 -3After evacuation to below 100 Pa, a mixed gas of argon and oxygen was used as the sputtering gas. The ratio of argon to oxygen was 99.5% and the gas pressure was 0.5 Pa. The substrate temperature during film formation was 350°C. After sputtering, when the substrate temperature fell to below 50°C, the chamber was purged with nitrogen gas and the sample was released into the atmosphere. The firing conditions after sputtering were as follows: the furnace was evacuated to a base vacuum of 2 Pa or less, and then oxygen gas was introduced into the furnace, maintaining the oxygen gas pressure in the furnace at 20 Pa. Then, firing was performed at 600°C for 90 minutes. When the temperature in the furnace fell to below 50°C, the sample was released into the atmosphere. This was the sample for Experimental Example 1.

[0028] [Results and Discussion] Figure 3 shows a confocal microscope photograph of the sample in Experimental Example 1 taken at 18°C, specifically an image of the pixels corresponding to the red component in RGB decomposition. It was found that VO2 nanoparticles with an average particle size of about several hundred nm were dispersed on the substrate surface.

[0029] Figure 4 shows the changes in confocal microscope photographs as the temperature of the sample in Experimental Example 1 was increased. Figure 4 is an enlarged view of the center of Figure 3, and shows images taken with a confocal microscope at each stage, starting from 18°C, then increasing the temperature from 40°C to 60°C in 10°C increments, and then increasing the temperature from 65°C to 95°C in 3°C increments. The number of particles that began to darken increased from 68°C, and by 92°C, almost all particles had darkened. Although individual particles showed a sudden change in brightness, the overall result was that the brightness changed gradually.

[0030] Figure 5 shows the results of image analysis of Figure 4. Figure 5 shows the count of the number of particles whose brightness changed from the image at the previous temperature in a circular area with a diameter of 25 micrometers. A distribution with two peaks was obtained between 65°C and 95°C.

[0031] Figure 6 shows the changes in confocal microscope photographs as the temperature of the sample in Experimental Example 1 was lowered. Figure 6 is an enlarged view of the center of Figure 3, and shows images taken with a confocal microscope after the temperature was lowered from 80°C, then from 70°C to 49°C in 3°C increments, and then from 45°C to 35°C in 5°C increments.

[0032] Figure 7 shows the results of image analysis of the results in Figure 6. Figure 7 shows the count of the number of particles whose brightness changed from the image at the previous temperature in a circular area with a diameter of 25 micrometers. Most particles showed changes in the temperature range from 67°C to 55°C.

[0033] Comparing Figures 5 and 7, the phase transition occurred mainly between 68°C and 89°C during heating (Figure 5), whereas the phase transition occurred in the range of 67°C to 55°C during cooling (Figure 7). The difference in the phase transition temperature ranges during heating and cooling is called hysteresis, and is commonly observed during phase transitions in vanadium dioxide.

[0034] 2. Examination of particle morphology [Experimental Examples 2-6] A vanadium sputtering target was used on a 25 mm fused quartz substrate. A 100 nm vanadium film was deposited at a substrate temperature of 350°C under conditions of Ar (99%) and O2 (1%). The film was then baked at 600°C for 30 minutes under controlled oxygen partial pressure P (P > 20 Pa). This produced samples in which VO2 nano- and microparticles were dispersed on the substrate, with the particle state gradually changing radially from the center. The sample located approximately 0 mm from the substrate center was designated as Experimental Example 2. The sample located approximately 2.5 mm from the substrate center was designated as Experimental Example 3. The sample located approximately 5.0 mm from the substrate center was designated as Experimental Example 4. The sample located approximately 7.5 mm from the substrate center was designated as Experimental Example 5. The sample located approximately 10 mm from the substrate center was designated as Experimental Example 6.

[0035] [Results and Discussion] Figure 8 shows electron microscope images of samples from Experimental Examples 2 to 6. Figure 8A shows electron microscope images of samples from Experimental Example 2, Figure 8B shows electron microscope images of samples from Experimental Example 3, Figure 8C shows electron microscope images of samples from Experimental Example 4, Figure 8D shows electron microscope images of samples from Experimental Example 5, and Figure 8E shows electron microscope images of samples from Experimental Example 6. Note that electron microscope observations were performed under low vacuum to protect the samples. As shown in Experimental Examples 2 to 6, it was found that the particle morphology can be changed, for example, by changing the distance from the substrate center. The reason for this change in particle morphology depending on the distance from the substrate center is presumed to be due to slight non-uniformity in the vanadium film thickness caused by the substrate position during sputtering deposition and the high pressure (>20 Pa) during heat treatment. Note that in Experimental Examples 2 to 6, the coverage (filling rate) of the inorganic particles on the substrate surface was approximately 30 to 45%, and no significant difference was observed.

[0036] Figure 9 shows a histogram representing the particle size distribution of the samples of Experimental Examples 2 to 6. Table 1 summarizes the average particle size, standard deviation of particle size, and hysteresis width ΔT of the samples of Experimental Examples 2 to 6. As shown in Figure 9 and Table 1, when the average particle size of VO2 particles is 1000 nm or less, the hysteresis width ΔT can be expanded to approximately 10°C. When the average particle size of VO2 particles is 700 nm or less, the hysteresis width ΔT can be expanded to approximately 20°C, which is more preferable. Furthermore, when the standard deviation of particle size is 100 nm or more and 500 nm or less, the hysteresis width ΔT can be expanded to approximately 10°C. When the standard deviation of particle size is 200 nm or more and 300 nm or less, the hysteresis width ΔT can be expanded to approximately 20°C, which is more preferable from the perspective of multi-value response.

[0037] [Table 1]

[0038] 3. Examination of phase transitions [Experimental Example 7] Experimental Examples 1 to 6 demonstrated that a multi-value variable element whose value gradually changes in response to changes in environmental conditions can be realized by using a nanoparticle dispersion element dispersed on a substrate. In Experimental Example 7, the physical properties used in the calculations to provide estimates by numerical calculation in Experimental Example 8, described below, were experimentally determined. The measured sample was a flat film of vanadium dioxide, and the complex refractive index was determined by spectroscopic ellipsometry at different measurement temperatures.

[0039] [Results and Discussion] Figure 10 shows the complex refractive index measurement results for Experimental Example 7. Figure 10A shows the real part during heating, Figure 10B shows the real part during cooling, Figure 10C shows the imaginary part during heating, and Figure 10D shows the imaginary part during cooling. The real part of the complex refractive index is related to the dielectric constant of the object being measured; a larger positive value indicates a more dielectric, and a larger negative value indicates a more metallic. The imaginary part of the complex refractive index is related to the amount of light absorbed by the object being measured; a larger value of the imaginary part indicates a greater amount of absorption. Figure 10 shows that as the temperature increases, the amount of light absorption increases as the object changes from a dielectric to a metal, and as the temperature decreases, the amount of light absorption decreases as the object changes from a metal to a dielectric. We also found that the temperature at which the phase transition occurs changes between heating and cooling, and that the amount of light absorption changes with the same trend.

[0040] 4. Examination of the relationship between the dielectric / metal distribution of inorganic particles and their optical properties [Experimental Example 8] Figure 11 shows the results of numerical calculations based on the measurement results of Experimental Example 7 as Experimental Example 8. For the calculations, the dielectric constant measured in Experimental Example 7 was applied to a model (e.g., Figure 11B) in which nine VO2 particles were dispersed on a glass substrate and different combinations of dielectric (D) and metal (M) were used, and the rates of transmission (forward scattering), reflection (backward scattering), and absorption when light was irradiated from below were calculated. Figure 11A is a graph showing the results of the numerical calculations, Figure 11B is an explanatory diagram showing an example of the model used in the numerical calculations, and Figure 11C is an example display of the calculation results.

[0041] [Results and Discussion] As shown in Figure 11, it was found that as the proportion of metal particles increases, the proportion of transmitted light increases and the proportion of reflected light decreases. It is thought that a change in the dielectric constant of the nanoparticles increases forward scattering due to Mie scattering, which increases transmittance. This also shows that by varying the particle size of the inorganic particles, it is possible to change the optical properties into multiple values.

[0042] It goes without saying that the present disclosure is not limited to the above-described embodiments, and can be implemented in various forms as long as they fall within the technical scope of the present disclosure. [Explanation of symbols]

[0043] 10 light control element, 12 substrate, 12a surface, 14 inorganic particles.

Claims

1. A substrate; a plurality of inorganic particles formed of a phase transition material that undergoes a phase transition in response to an environmental change, which is at least one of a temperature change and light absorption, and having an average particle size of 1 nm to 1000 μm and varying in at least one of particle size and particle shape, and arranged separately from one another on the surface of the substrate; Equipped with A light control element in which optical characteristics, which are at least one of light transmission characteristics and light reflection characteristics, change due to the environmental change.

2. 2. The light control element of claim 1, wherein the phase change material is vanadium dioxide.

3. 3. The light control element according to claim 1, wherein the inorganic particles have an average particle size of 700 nm or less.

4. 3. The light control element according to claim 1, wherein the inorganic particles are formed over an area of ​​20% to 65% of the surface of the substrate.

5. 3. The light control element according to claim 1, wherein when an environmental change of a predetermined condition occurs as the environmental change, only a part of the inorganic particles undergoes a phase transition.

6. The light control element according to claim 1 or 2, wherein the optical characteristics change in more than two values.

7. 3. The light control element according to claim 1, wherein the inorganic particles have a standard deviation of particle size of 200 nm or more and 300 nm or less.

8. 3. The light control element according to claim 1, wherein the environmental change is a temperature change, and a hysteresis width of a curve showing changes in optical characteristics during temperature rise and temperature fall is 15[deg.] C. or more.

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