A photonic crystal structure color film based on phase change material and its preparation method

Abstract

The present invention discloses a photonic crystal structure color film based on phase change material, the structure of the film is: (HP) s L(PH) s The film has a symmetrical structure centered around L, where H represents a high-refractive-index dielectric layer, P represents a phase-change layer, and L represents a low-refractive-index dielectric layer. Each group (HP) or (PH) constitutes an equivalent high-refractive-index unit, and each group of equivalent high-refractive-index units is composed of a stack of high-refractive-index dielectric layers H and phase-change layers P. s represents the number of times the equivalent high-refractive-index units are stacked, and s is a positive integer. The present invention also provides a method for preparing a photonic crystal structural color film based on a phase-change material. By causing a phase change in the phase-change layer, the prepared film can exhibit structural colors with large color differences before and after the phase change.

Description

Technical Field

[0001] The present invention relates to the field of optical technology, and in particular to a photonic crystal structured color film based on phase change material and a preparation method thereof. Background Art

[0002] Phase-change materials are materials whose physical structure changes by varying their temperature within a certain temperature range, with a nearly fixed phase transition temperature. The working principle of phase-change materials is that when the ambient temperature is above the phase transition temperature, they store heat; when the ambient temperature is below the phase transition temperature, they release the stored energy. Currently, phase-change materials are widely used in energy storage, medicine, data storage, and other fields. In the field of optical thin films, phase-change materials have been widely used for heat absorption and insulation in the aerospace field, as well as mid- and far-infrared camouflage in the military field.

[0003] The working principles of phase-changeable materials reveal that the primary phase-change methods involve direct or indirect heating of the object. Phase change can be achieved through high-temperature annealing, electrical heating, or optical stimulation (laser pulse phase change). To measure a material's phase-change performance, the Form of Merit (FOM) is often used to define its phase-change ability. A larger FOM value indicates a greater difference in refractive index between the amorphous and crystalline states of the two materials. Furthermore, a smaller extinction coefficient in the crystalline state is also desirable. Phase-change materials are required to achieve superior phase-change performance, high saturation, and greater phase-change chromatic aberration in photonic crystal films. However, current research on phase-change materials in the optical field is relatively limited.

[0004] Typical phase-change materials include chalcogenide semiconductors such as Ge2Sb2Te5 (GST). GST materials can achieve sub-nanosecond phase transitions through electrical and optical pulses. Because their phase transitions can be switched rapidly and repeatedly, their optical and electrical properties can exhibit two distinct states, making them a reliable material for non-volatile memory. While GST materials are widely used in photonic devices such as non-volatile displays, optical switches, photonic memories, and all-optical computers, their application in the field of phase-changeable thin-film structural color is relatively limited.

[0005] Doping and modification are performed on the classic phase change material (PCM) Ge2Sb2Te5. Experiments have shown that replacing some of the Te in Ge2Sb2Te5 with Se can reduce the material's extinction coefficient in the visible light region, thereby enhancing the brightness of the resulting thin film's structural color. However, excessive Se also causes the material to lose its phase change ability. Ge2Sb2Se4Te1 (GSST) is a critical material that ensures phase change capability while minimizing absorption.

[0006] GSST, a novel material with significant optical performance advantages over the classic phase-change material GST, has been used in the manufacture of silicon-based three-dimensional waveguide mode optical switches (CN114995010A), multi-parameter tunable filters based on phase-change Bragg gratings (CN216248399U), and programmable arbitrary power dividers based on DBS algorithms (CN113191115A). However, GSST holds great promise in the field of phase-changeable thin-film structural color.

[0007] The Chinese invention patent with patent number CN202011061690 discloses a resonant cavity film system and preparation method that combines non-volatility, multi-structural colors, multiple gears and high transmittance contrast. The composite dual-cavity film system uses two different PCM materials to achieve the goals of high transmittance and multiple gears, and the two PCM materials must adopt the elemental composition of (GeTe)x(Sb2Te3)1-x. Considering that the FOM values ​​of GeTe and Sb2Te3 are not as good as GST and GSST, it is difficult to design structural colors with high brightness, high saturation and large phase change differences for this film system.

[0008] Currently, some new electrochromic materials have been proposed, such as the electrochromic structural color designed in CN202211003546. By adjusting the magnitude and direction of the applied voltage, the deposition and dissolution of metal particles on the transparent electrode can be controlled, thereby changing the thickness of the film structure, so that it changes from transparent to a certain color in visible light. The color transformation that can be achieved by this adjustment method is very limited, and the phase change color is also relatively single. How to design a film that can achieve a large color phase change without changing the existing film structure is a hot topic of research at this stage. Summary of the Invention

[0009] In view of this, the purpose of the present invention is to propose a photonic crystal structural color film based on phase change material, which can achieve structural colors with large color differences before and after the phase change by causing phase change in the phase change layer.

[0010] In order to achieve the above technical objectives, the technical solution adopted by the present invention is: a photonic crystal structure color film based on phase change material, the structure of the film is: (HP) s L (PH) s The structure of the film is a symmetrical structure centered on L, wherein H represents a high refractive index medium layer, P represents a phase change layer, and L represents a low refractive index medium layer. Each group (HP) or (PH) constitutes an equivalent high refractive index unit, and each group of equivalent high refractive index units is stacked by a high refractive index medium layer H and a phase change layer P. s represents the number of times the equivalent high refractive index unit is repeatedly stacked, and s is a positive integer.

[0011] Furthermore, the high-refractive-index dielectric layer H is a film layer of a material having a refractive index greater than or equal to 1.55 in the range of 400nm to 780nm, and is made of lanthanum titanate, amorphous silicon, indium tin oxide, titanium dioxide, tantalum pentoxide, hafnium dioxide, zirconium dioxide, zinc sulfide or silicon monoxide; the thickness of the high-refractive-index dielectric layer H is in the range of 20-500nm.

[0012] Furthermore, the phase change layer P adopts GSST material or GST material, and the GSST material has two different crystalline states at different temperatures, namely, an amorphous state and a crystalline state; the GST material has three different crystalline states at different temperatures, namely, an amorphous state, a metastable state and a crystalline state; the thickness of the phase change layer P ranges from 5 to 30 nm.

[0013] Furthermore, the low-refractive-index medium layer L is a material film layer with a refractive index less than 1.55 in the range of 400nm~780nm, and is made of silicon dioxide, magnesium fluoride, cerium fluoride, lanthanum fluoride, sodium aluminum fluoride, neodymium fluoride, banknote fluoride, barium fluoride, calcium fluoride or lithium fluoride; the thickness of the low-refractive-index medium layer L is in the range of 20nm~600nm.

[0014] Furthermore, the number of times s that the equivalent high refractive index unit is repeatedly stacked ranges from 1 to 5; when the number s is 2 to 5, (HP) s The s layers of high refractive index medium H in the (HP) are made of the same material or at least two layers of the same material or completely different materials. s The s phase change layers P in the embodiment are made of the same material or at least two layers of the same material or completely different materials.

[0015] The present invention also provides a method for preparing a photonic crystal structured color film based on a phase change material. The method is based on the above-mentioned photonic crystal structured color film based on a phase change material and comprises the following steps:

[0016] Step 1: Design a photonic crystal structured color film based on phase change material according to user needs. The structure of the film is: (HP) s L (PH) s The structure of the film is a symmetrical structure centered on L, wherein H represents a high-refractive-index dielectric layer, P represents a phase-change layer, and L represents a low-refractive-index dielectric layer. Each group (HP) or (PH) constitutes an equivalent high-refractive-index unit, and each group of equivalent high-refractive-index units is stacked by a high-refractive-index dielectric layer H and a phase-change layer P. s represents the number of times the equivalent high-refractive-index units are repeatedly stacked, and s is a positive integer.

[0017] Step 2: adjusting the thickness and material of each layer in the structure of the film, so that the film exhibits different color changes in different temperature ranges;

[0018] Step 3: determining the structural parameters required for preparing the film according to the design results;

[0019] Step 4: Place the flat surface object as a substrate in the film forming equipment chamber; if the film does not require demolding, proceed to step 5; if the film requires demolding, proceed to step 6;

[0020] Step 5: Growing the first layer, the second layer, and so on until the last layer of the thin film on the substrate according to the structural parameters, wherein the high refractive index medium layer H and the phase change layer P are stacked in sequence according to the number s between the first layer and the second layer, and the middle layer is the low refractive index medium layer L. The first layer to the last layer are grown symmetrically with L as the center; thus completing the preparation of the thin film;

[0021] Step 6: Then grow a layer of release agent on the substrate; grow the first layer, the second layer... until the last layer of the thin film on the release agent according to the structural parameters; between the first layer to the 2s layer, the high refractive index medium layer H and the phase change layer P are cross-stacked in sequence according to the number s, the middle layer is the low refractive index medium layer L, and the first layer to the last layer are grown symmetrically with L as the center; use the solvent corresponding to the release agent to dissolve the release agent, so that the thin film is separated from the release agent to obtain the separate thin film, thereby completing the preparation of the thin film.

[0022] Furthermore, the step 2 specifically includes:

[0023] Step 21, designing the thickness and material of each layer in the structure of the film;

[0024] Step 22, according to (HP) s The materials used for the phase change layer P in the s layer determine different temperature thresholds. If the phase change layers P in the s layer are all GSST materials, the temperature threshold is determined to be T1, and the process proceeds to step 23; if the phase change layers P in the s layer are all GST materials, the temperature thresholds are determined to be T2 and T3, and the process proceeds to step 24; if the phase change layers P in the s layer are both GSST materials and GST materials, the temperature thresholds are determined to be T2, T1, and T3, and the process proceeds to step 25;

[0025] Step 23: Record the first color of the film within a temperature range less than T1, then perform a phase change treatment on the film so that the temperature of the film is raised to a temperature range not less than T1, and again record the second color of the film at this time. Compare the color changes before and after the phase change. If the color difference is large, it indicates that the thickness and material of each layer in the structure of the film are designed appropriately. If the color difference is small, proceed to step 21 to readjust the thickness and material of each layer in the structure of the film.

[0026] Step 24: Record the first color of the film within a temperature range less than T2, then perform a phase change treatment on the film so that the temperature of the film is raised to a temperature range not less than T2 and less than T3, and again record the second color of the film at this time. Then, perform a phase change treatment on the film so that the temperature of the film is raised to a temperature range not less than T3, and again record the third color of the film at this time. Compare the color changes during the phase change process. If the color difference changes greatly, it indicates that the thickness and material of each layer in the designed structure of the film are reasonable. If the color difference changes little, proceed to step 21 to readjust the thickness and material of each layer in the structure of the film.

[0027] Step 25: Record the first color of the film within a temperature range less than T2, then perform phase change treatment on the film so that the temperature of the film rises to a temperature range not less than T2 and less than T1, and again record the second color of the film at this time; then perform phase change treatment on the film so that the temperature of the film rises to a temperature range not less than T1 and less than T3, and again record the third color of the film at this time; then perform phase change treatment on the film so that the temperature of the film rises to a temperature range not less than T3, and again record the fourth color of the film at this time; compare the color changes during the phase change process; if the color difference changes greatly, it means that the thickness and material of each layer in the designed structure of the film are reasonable; if the color difference changes little, proceed to step 21 to readjust the thickness and material of each layer in the structure of the film.

[0028] Furthermore, the phase change process of the phase change layer P is completed by a high temperature annealing process, electric heating or laser pulse phase change.

[0029] Furthermore, the structural parameters include the total number of layers, the material used for each layer, the thickness of each layer and the distribution between the layers; the temperature threshold T1 is 310 degrees, the temperature threshold T2 is 220 degrees, and the temperature threshold T3 is 400 degrees.

[0030] Furthermore, the material of the substrate is polished glass, polished stainless steel, polished mirror aluminum, polyethylene terephthalate, cellulose triacetate, polymethyl methacrylate, polycarbonate / polymethyl methacrylate composite material, polyimide, polypropylene, polyvinyl chloride, polyvinyl butyral, ethylene vinyl acetate copolymer, polyurethane elastomer, polytetrafluoroethylene, fluoroethyl propylene or polyvinyl difluoride; the material of the release agent is fluoride, chloride or water-soluble organic material that is easily soluble in water.

[0031] By adopting the above-mentioned technical solution, the present invention has the following beneficial effects compared with the prior art: the present invention is based on the optical properties of phase change materials to produce a photonic crystal thin film structural color device that can maintain the film structure in the visible light region without changing the film structure, and uses phase changeable materials (GSST or GST) to prepare a phase change layer without changing the film structure, only through high temperature or laser pulse heating or laser irradiation to cause a phase change, thereby changing the color of the film. Ultimately, the prepared film can have a structural color with a large color difference before and after the phase change.

[0032] By designing a symmetrical film structure, a structural color thin film capable of large color phase transitions, suitable for device coating, was fabricated. This design allows for the production of phase-change thin films in a variety of colors, including red, orange, yellow, green, blue, indigo, and violet. This structure applies the chalcogenide phase-change material GSST to thin-film structural color applications, innovatively proposing its application in tunable structural color. It also addresses the shortcomings of conventional phase-change materials, such as GST, in tunable structural color applications, such as insufficient color display and weak phase transition effects. Furthermore, the rich variety of colors that can be produced by this design provides a novel tunable solution for applications in color printing and micro-nano color displays. As a semiconductor material, GSST is widely used in optical devices. Combining its electrical and optical properties, it can achieve diverse color displays in specialized optical devices, allowing its electrical and other properties to provide visual feedback for phase transitions in specific applications. Compared to previous research, the method proposed in this paper offers advantages such as a wide range of tunable structures, excellent tunability, and ease of large-scale production. These advantages make this non-volatile, high-saturation color filter have broad application potential in color display panels, photodetectors, car paint, color printing and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 This is a schematic structural diagram of a photonic crystal structural color film based on phase change material provided by the present invention (including a substrate).

[0035] Figure 2 This is a schematic structural diagram of a photonic crystal structural color film based on phase change material provided by the present invention (including a substrate and a release agent).

[0036] Figure 3 This is a flow chart of a method for preparing a photonic crystal structured color film based on phase change material provided by the present invention.

[0037] Figure 4 This is a schematic structural diagram of a photonic crystal structural color film based on phase change material provided by the present invention (without substrate and release agent, the number of s is 1).

[0038] Figure 5 This is a schematic structural diagram of a photonic crystal structural color film based on phase change material provided by the present invention (without substrate and release agent, the number of s is 2).

[0039] FIG6 shows the optical constants of the amorphous state of the GSST phase change material provided by the present invention in the visible light range.

[0040] Figure 7 It is the optical constant of the crystalline state of the GSST phase change material provided by the present invention in the visible light range.

[0041] Figure 8 This is the reflection spectrum of the amorphous state of Example 1 under vertical incidence.

[0042] Figure 9 This is the reflection spectrum of the crystal of Example 1 under vertical incidence.

[0043] Figure 10 1 is a chromaticity coordinate diagram of the amorphous state of Example 1 under vertical incidence.

[0044] Figure 11 1 is a chromaticity coordinate diagram of the crystal state of Example 1 under vertical incidence.

[0045] Figure 12 This is the reflection spectrum of the amorphous state of Example 2 under vertical incidence.

[0046] Figure 13 This is the reflection spectrum of the crystal of Example 2 under vertical incidence.

[0047] Figure 14 1 is a chromaticity coordinate diagram of the amorphous state of Example 2 under vertical incidence.

[0048] Figure 15 2 is a chromaticity coordinate diagram of the crystal state of Example 2 under vertical incidence.

[0049] Figure 16 This is the reflection spectrum of the amorphous state of Example 3 under vertical incidence.

[0050] Figure 17 This is the reflection spectrum of the crystal of Example 3 under vertical incidence.

[0051] Figure 18This is the chromaticity coordinate diagram of the amorphous state of Example 3 under vertical incidence.

[0052] Figure 19 This is the chromaticity coordinate diagram of the crystal state of Example 3 under vertical incidence.

[0053] Figure 20 This is the reflection spectrum of the amorphous state of Example 4 under vertical incidence.

[0054] Figure 21 This is the reflection spectrum of the crystal of Example 4 under vertical incidence.

[0055] Figure 22 This is the chromaticity coordinate diagram of the amorphous state of Example 4 under vertical incidence.

[0056] Figure 23 This is the chromaticity coordinate diagram of the crystal state of Example 4 under vertical incidence.

[0057] Figure 24 This is the reflection spectrum of the amorphous state of Example 5 under vertical incidence.

[0058] Figure 25 This is the reflection spectrum of the crystalline state of Example 5 under vertical incidence.

[0059] Figure 26 This is the chromaticity coordinate diagram of the amorphous state of Example 5 under vertical incidence.

[0060] Figure 27 This is the chromaticity coordinate diagram of the crystal state of Example 5 under vertical incidence.

[0061] Figure 28 This is the reflection spectrum of the amorphous state of Example 6 under vertical incidence.

[0062] Figure 29 This is the reflection spectrum of the metastable state of Example 6 under vertical incidence.

[0063] Figure 30 This is the reflection spectrum of the crystalline state of Example 6 under vertical incidence.

[0064] Figure 31 3 is the chromaticity coordinate diagram of the amorphous state of Example 6 under vertical incidence.

[0065] Figure 32 3 is the chromaticity coordinate diagram of the metastable state of Example 6 under vertical incidence.

[0066] Figure 33 This is the chromaticity coordinate diagram of the crystalline state of Example 6 under vertical incidence.

[0067] Figure 34 This is the reflection spectrum of Example 7 at room temperature under vertical incidence.

[0068] Figure 35 This is the reflection spectrum of Example 7 after annealing to 220°C under vertical incidence.

[0069] Figure 36 This is the reflection spectrum of Example 7 at 310°C under vertical incidence.

[0070] Figure 37 This is the reflection spectrum of Example 7 after annealing to 400°C under vertical incidence.

[0071] Figure 38 This is the chromaticity coordinate diagram of Example 7 at normal temperature under vertical incidence.

[0072] Figure 39 This is the chromaticity coordinate diagram of Example 7 after annealing to 220°C under vertical incidence.

[0073] Figure 40 This is the chromaticity coordinate diagram of Example 7 after annealing to 310°C under vertical incidence.

[0074] Figure 41 This is the chromaticity coordinate diagram of Example 7 annealed to 400°C under vertical incidence. DETAILED DESCRIPTION

[0075] The present invention will be described in further detail below with reference to the accompanying drawings and examples. It is particularly noted that the following examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. Similarly, the following examples are only some embodiments of the present invention and are not intended to be exhaustive. All other embodiments obtained by those of ordinary skill in the art without creative effort are intended to fall within the scope of protection of the present invention.

[0076] See Figure 1 、 Figure 2 、 Figure 4 and Figure 5 The present invention relates to a photonic crystal structure color film based on phase change material, the structure of the film is: (HP) s L (PH) s The structure of the film is a symmetrical structure centered on L, wherein H represents a high refractive index medium layer, P represents a phase change layer, and L represents a low refractive index medium layer. Each group (HP) or (PH) constitutes an equivalent high refractive index unit, and each group of equivalent high refractive index units is stacked by a high refractive index medium layer H and a phase change layer P. s represents the number of times the equivalent high refractive index unit is repeatedly stacked, and s is a positive integer.

[0077] In this embodiment, the high-refractive-index dielectric layer H is a material film layer having a refractive index greater than or equal to 1.55 in the range of 400 nm to 780 nm, and is made of lanthanum titanate (H4), amorphous silicon (a-Si), indium tin oxide (ITO), titanium dioxide (TiO2), tantalum pentoxide (Ta2O5), hafnium dioxide (HfO2), zirconium dioxide (ZrO2), zinc sulfide (ZnS) or silicon monoxide (SiO); the thickness of the high-refractive-index dielectric layer H is in the range of 20-500 nm.

[0078] In this embodiment, the phase change layer P uses GSST material (the phase change layer P uses chalcogenide phase change material, among which GSST (Ge2Sb2Se4Te1) is the preferred material) or GST material. The GSST material has two different crystalline states at different temperatures, namely, an amorphous state and a crystalline state; the GST material has three different crystalline states at different temperatures, namely, an amorphous state, a metastable state and a crystalline state; the thickness of the phase change layer P ranges from 5 to 30 nm.

[0079] The amorphous-formation ability of GSST is enhanced compared to GST, which increases the thermal stability of the amorphous state, prolongs the phase change shelf life of the film layer, and also increases the maximum usable thickness of the phase-change material. But on the other hand, due to the enhanced thermal stability of its amorphous state, GSST also loses the metastable face-centered cubic (FCC) phase of GST, and directly transforms into the final stable hexagonal phase after high-temperature annealing at 310°C. That is to say, its phase transition temperature has increased to a great extent, which also makes it possible for the film system to be used in special high-temperature scenarios. Experiments have shown that GSST maintains an amorphous structure before 310°C, and its single-layer optical constants such as Figure 6 After annealing at 310℃, the GSST structure transforms into a hexagonal crystal state, and its optical constants are as follows: Figure 7 shown.

[0080] This structure can also use phase change material GST, which will show an amorphous state at room temperature, a metastable state at 220℃, and a crystalline state after annealing at 400℃. This can be used in the structure of this design to show three color changes. In addition, the structure of this design can also use different phase change layers P using GSST and GST mixed and matched, and by controlling different annealing temperatures, it can show more phase change colors. For example, when s is 2, (HP) s There are two phase change layers P structure, where P 1 and P 2 The material can be selected from different GSST or GST materials, such as P 1 GSST material is selected and P 2 Choose GST material or P 1GST material is selected and P 2 GSST material is selected.

[0081] In this embodiment, the low-refractive-index dielectric layer L is a film layer of a material with a refractive index less than 1.55 in the range of 400nm to 780nm. The low-refractive-index dielectric layer L is phase-matched with the high-refractive-index dielectric layer H. Silicon dioxide (SiO2), magnesium fluoride (MgF2), cerium fluoride (CeF3), lanthanum fluoride (LaF3), sodium aluminum fluoride (Na3AIF or NasAlFA), neodymium fluoride (NdF3), silver fluoride (SmF3), barium fluoride (BaF2), calcium fluoride (CaF2), or lithium fluoride (LiF) are used. The thickness of the low-refractive-index dielectric layer L ranges from 20nm to 600nm. In this embodiment, the number of times s of repeated stacking of the equivalent high-refractive-index unit ranges from 1 to 5. The greater the number of s, the less obvious the change in structural color before and after the phase transition. When the number of s is 2 to 5, (HP) s The s layers of high refractive index medium H in the (HP) are made of the same material or at least two layers of the same material or completely different materials. s The s phase change layers P in the invention are made of the same material or at least two layers of the same material or completely different materials. The invention can design structural color films of different colors by adjusting the material and thickness of each layer.

[0082] This embodiment is described with s being 1. The specific structure is as follows Figure 4 As shown in the figure, the film structure, from the base upward, consists of a high-refractive-index dielectric layer H, a phase-change layer P, an intermediate dielectric layer L, a phase-change layer P, and a high-refractive-index dielectric layer H. Because the material required for the phase-change layer P is easily oxidized, it cannot be placed directly on the surface in contact with air. Therefore, the phase-change layer P is positioned between the high-refractive-index dielectric layer H and the intermediate dielectric layer L. Due to the symmetrical design of the film system, the two high-refractive-index dielectric layers H, symmetrical above and below the intermediate dielectric layer L, are made of the same thickness and material. The phase-change layers P, symmetrical above and below the intermediate dielectric layer L, are also made of the same thickness and material.

[0083] The FP thin film filter is a simple narrowband filter developed based on the Fabry-Perot interferometer. This filter consists primarily of a parallel central cavity layer and high-reflectivity layers at either end. Depending on the materials used in these layers, it can be categorized into two types: metal-dielectric and all-dielectric. A metal-dielectric FP filter primarily consists of two parallel metal layers with a dielectric spacer layer between them. The following calculations describe the key parameters of the FP filter based on thin-film reflection and transmission theory.

[0084] Among the various performance parameters of the filter, the main ones that describe its characteristics include the center wavelength, the full width at half maximum (FWHM) of the peak, and the transmittance at the center wavelength. And Free Spectral Range (FSR).

[0085] FP filter transmittance expression:

[0086]

[0087] Where, 、 、 and are the transmittance and reflectance of the two metal reflective layers respectively (for example, the transmittance and reflectance of the first metal reflective layer are and , the transmittance and reflectance of the second metal reflective layer are and );

[0088] ,in is the phase thickness of the spacer layer, and and are the reflection phases of the two layers of reflection respectively.

[0089] The wavelength at maximum transmittance, that is, the central wavelength expression:

[0090]

[0091] The free spectral range (FSR) of an FP thin film filter represents the spectral range between two maximum transmission peaks. In optics, it is mainly used to indicate the maximum wavelength difference between sub-wavelengths that prevents the overlap of interference fringes of different levels. The specific calculation formula is:

[0092]

[0093] The full width at half maximum (FWHM) is referred to as the half-peak width. It represents the passband width at half the transmission or reflection peak of the filter waveform, representing the width of the passband. The calculation formula is:

[0094]

[0095] in , ,in, and are the reflectivities of the dielectric layer and the reflective layer, respectively.

[0096] because , Absorption is approximately constant. To improve the overall reflectivity of the film system, conventional FP thin-film filters for structural color require reducing transmittance, based on the transmittance expression. This is done by increasing the reflectivity of the two metal layers and adjusting the phase thickness of the intermediate dielectric layer. However, due to the inherently high absorption of metals and the phase matching requirements of the intermediate dielectric layer to control the full width at half maximum (FWHM) of the spectral peak and the free spectral range, achieving high reflectivity and a variety of colors with conventional FP thin-film filters for structural color is difficult.

[0097] The present invention utilizes the interference effect of dielectric films and the equivalent characteristics of the refractive index and phase thickness of symmetrical film structures. Through computer optimization design, the required refractive index can be achieved by changing the material type and physical thickness of the high refractive index dielectric layer and the intermediate dielectric layer. We know that when the refractive index is On the substrate

[0098] The optical thickness of the coating is The high refractive index ( ) film, the reflectivity can be greatly increased due to the phase of the reflected light at the air / film and film / substrate interfaces. , the admittance of the equivalent combination of a single-layer film and a substrate is , the reflectivity at vertical incidence is:

[0099]

[0100] Among them, in the film system of this design, each group (HP) or (PH) constitutes an equivalent high refractive index unit, and each layer is alternately formed with high and low refractive index layers. The multilayer film can obtain higher reflectivity. This is because the light beams reflected from all interfaces have the same phase when they return to the interface, thus generating constructive interference. According to this theory, different reflectivities can be obtained. The refractive index of the high refractive index layer is expressed by Represents the refractive index of the low refractive index layer. Then at the center wavelength The equivalent interface admittance of the entire membrane structure

[0101] Y is:

[0102]

[0103] Where 2s+1 is the number of layers of the multilayer film, and the central wavelength is The reflectivity, that is, the maximum reflectivity, is:

[0104]

[0105] According to the film layer designed in this structure, the absorption formula of the outermost layer with high refractive index film layer is selected, and its absorption loss is:

[0106]

[0107] The reason why the outermost layer is a high refractive index film layer is that compared to the outermost layer with a low refractive index film layer, according to its absorption formula, it will have greater absorption, resulting in a lower reflectivity. H is the extinction coefficient of the high refractive index medium layer, k L is the extinction coefficient of the low-refractive-index layer. The formulas for absorption and maximum reflectivity show that the refractive index and extinction coefficient of the high-refractive-index dielectric layer H and the phase-change layer P in this structure jointly influence the reflectivity at the center wavelength. By varying the physical thickness of the high-refractive-index dielectric layer H and the phase-change layer P, the maximum reflectivity of the film can be positioned at different center wavelengths, thereby changing the film's color. and Different ratios also change the maximum reflectivity at the center wavelength, so choosing different materials can also change the peak reflectivity in this design. Annealing the prepared film at 310°C causes the GSST in the phase change layer P to transition from an amorphous state to a crystalline state, altering both its refractive index and extinction coefficient. Based on the reflectivity formula above, it's clear that the reflectivity at the center wavelength changes, thereby altering the structural color exhibited by the film system, achieving the color change function after the film is prepared.

[0108] Considering that the designed thin film can later be used in other devices to realize various color-related functions, the present invention has designed a symmetrical film structure that can be peeled from the preparation substrate and then used for device coating. The advantage of this structure is that the thin film structural color can show the designed color whether viewed from the front or back. Unlike other traditional structural color film systems based on FP thin film filters, the structure requires a thick metal bottom layer as a reflective layer. Although a thick metal bottom layer can provide higher peak reflectivity, it also poses different challenges for its application scenarios and preparation process.

[0109] like Figure 3 As shown, the present invention also provides a method for preparing a photonic crystal structured color film based on a phase change material. The preparation method is based on the above-mentioned photonic crystal structured color film based on a phase change material, and includes the following steps:

[0110] Step 1: Design a photonic crystal structured color film based on phase change material according to user needs. The structure of the film is: (HP) s L (PH) sThe structure of the film is a symmetrical structure centered on L, wherein H represents a high-refractive-index dielectric layer, P represents a phase-change layer, and L represents a low-refractive-index dielectric layer. Each group (HP) or (PH) constitutes an equivalent high-refractive-index unit, and each group of equivalent high-refractive-index units is stacked by a high-refractive-index dielectric layer H and a phase-change layer P. s represents the number of times the equivalent high-refractive-index units are repeatedly stacked, and s is a positive integer.

[0111] Step 2: Adjust the thickness and material of each layer in the structure of the thin film so that the thin film exhibits different color changes in different temperature ranges; the phase change layer P adopts phase change material, and is produced according to the optical properties of the phase change material so as not to change the structure of the thin film in the visible light region. A phase changeable material (GSST or GST) is used to prepare a photonic crystal thin film structure color device that changes the color of the thin film only by heating the phase change layer at high temperature or laser pulses or irradiating the phase change layer without changing the structure of the thin film, thereby finally enabling the prepared thin film to have a structure with a large color difference before and after the phase change.

[0112] Depending on whether a colored object absorbs light, its color can be divided into two types: pigment color and structural color. Pigment color primarily involves absorption involving coordination field effect transitions, and the resulting color is also called chemical color. Structural color primarily includes physical optical effects such as gratings, single-layer films, multilayer films, photonic crystals, Rayleigh scattering, and Mie scattering, and the resulting color is called structural color.

[0113] Photonic crystal structural color films realized using GSST materials have not been developed and researched. Considering that the films prepared by this method have the advantages of fast phase change speed, good non-volatility, low absorption, large phase change range, diverse colors, and simple design structure, it has important application prospects in optical devices, color printing, optical display, and other fields.

[0114] In this embodiment, step 2 specifically includes:

[0115] Step 21, designing the thickness and material of each layer in the structure of the film;

[0116] Step 22, according to (HP) s The materials used for the phase change layer P in the s layer determine different temperature thresholds. If the phase change layers P in the s layer are all GSST materials, the temperature threshold is determined to be T1, and the process proceeds to step 23; if the phase change layers P in the s layer are all GST materials, the temperature thresholds are determined to be T2 and T3, and the process proceeds to step 24; if the phase change layers P in the s layer are both GSST materials and GST materials, the temperature thresholds are determined to be T2, T1, and T3, and the process proceeds to step 25;

[0117] Step 23: Record the first color of the film within a temperature range less than T1, then perform a phase change treatment on the film so that the temperature of the film is raised to a temperature range not less than T1, and again record the second color of the film at this time. Compare the color changes before and after the phase change. If the color difference is large, it indicates that the thickness and material of each layer in the structure of the film are designed to be reasonable. At this time, if the temperature is lowered to a temperature range less than T1, the color will return to the first color. If the color difference is small, proceed to step 21 to readjust the thickness and material of each layer in the structure of the film.

[0118] Step 24: Record the first color of the film within a temperature range less than T2, then perform a phase change treatment on the film so that the temperature of the film is increased to a temperature range not less than T2 and less than T3, and again record the second color of the film at this time. Then, perform a phase change treatment on the film so that the temperature of the film is increased to a temperature range not less than T3, and again record the third color of the film at this time. Compare the color changes during the phase change process. If the color difference changes greatly, it indicates that the thickness and material of each layer in the designed structure of the film are reasonable. At this time, if the temperature is lowered to a temperature range not less than T2 and less than T3, the color will return to the second color. If the temperature is lowered to a temperature range less than T2, the color will return to the first color. If the color difference changes little, proceed to step 21 to readjust the thickness and material of each layer in the structure of the film.

[0119] Step 25: Record the first color of the film within a temperature range less than T2, then perform a phase change treatment on the film so that the temperature of the film is increased to a temperature range not less than T2 and less than T1, and again record the second color of the film at this time. Then, perform a phase change treatment on the film so that the temperature of the film is increased to a temperature range not less than T1 and less than T3, and again record the third color of the film at this time. Then, perform a phase change treatment on the film so that the temperature of the film is increased to a temperature range not less than T3, and again record the fourth color of the film at this time. Compare the color changes during the phase change process. If the color difference is large, it indicates that the thickness and material of each layer in the structure of the designed film are reasonable. At this time, if the temperature is reduced to a temperature range not less than T1 and less than T3, the color will return to the third color. If the temperature is reduced to a temperature range not less than T2 and less than T1, the color will return to the second color. If the temperature is reduced to a temperature range less than T2, the color will return to the first color. If the color difference is small, proceed to step 21 to readjust the thickness and material of each layer in the structure of the film.

[0120] In this embodiment, the phase change process of the phase change layer P is completed by high temperature annealing process, electric heating or laser pulse phase change; the temperature threshold T1 is 310 degrees, the temperature threshold T2 is 220 degrees, and the temperature threshold T3 is 400 degrees.

[0121] Step 3: Determine the structural parameters required for preparing the film based on the design results, wherein the structural parameters include the total number of layers, the material used for each layer, the thickness of each layer, and the distribution between the layers;

[0122] Step 4: Place the flat surface object as a substrate in the film forming equipment chamber; if the film does not require demolding, proceed to step 5; if the film requires demolding, proceed to step 6;

[0123] In this embodiment, the substrate is made of polished glass, polished stainless steel, polished mirror aluminum, polyethylene terephthalate (PET), triacetyl cellulose (TAC), polymethyl methacrylate (PMMA), polycarbonate / polymethyl methacrylate composite (PC / PMMA), polyimide (PI), polypropylene (PP), polyvinyl chloride (PVC), polyvinyl butyral (PVB), ethylene vinyl acetate copolymer (EVA), polyurethane elastomer (TPU), polytetrafluoroethylene (PTFE), fluoroethyl propylene (FEP) or polyvinyl difluoride (PVDF);

[0124] Step 5: Growing the first layer, the second layer, and so on until the last layer of the thin film on the substrate according to the structural parameters, wherein the high refractive index medium layer H and the phase change layer P are stacked in sequence according to the number s between the first layer and the second layer, and the middle layer is the low refractive index medium layer L. The first layer to the last layer are grown symmetrically with L as the center; thus completing the preparation of the thin film;

[0125] Step 6: Then grow a layer of release agent on the substrate, the material of the release agent is fluoride, chloride or water-soluble organic material that is easily soluble in water; grow the first layer, the second layer... until the last layer of the thin film on the release agent according to the structural parameters; between the first layer to the 2s layer, the high refractive index medium layer H and the phase change layer P are cross-stacked in sequence according to the number s, the middle layer is the low refractive index medium layer L, and the first layer to the last layer are grown symmetrically with L as the center; use the solvent corresponding to the release agent to dissolve the release agent, so that the thin film is separated from the release agent to obtain the separate thin film, and complete the preparation of the thin film.

[0126] Step 7: After the film is prepared, it is applied to the outer surface of the device. The outer surface of the device now exhibits different colors at different temperatures. If the phase change layer P is made solely of GSST material, the outer surface of the device exhibits a first color within a temperature range below 310°C. The specific color displayed depends on the thickness and material of each layer. Transitioning from a crystalline state to an amorphous state can be achieved by high-temperature annealing to a temperature range of no less than 310°C, at which point the outer surface of the device exhibits a second color. The different colors are achieved based on the specific design requirements and circumstances of steps 1-2. After exhibiting the second color at no less than 310°C, continued heating is continued until the temperature is slowly lowered to room temperature. The film's structure remains unchanged, and the color remains at the second color. To restore the second color back to the first, the film can be heated to above 310°C and then rapidly cooled to room temperature. This process can be achieved using laser pulses. This allows the film structure to change from a post-phase change color to a pre-phase change structural color, achieving repeatable structural color phase change modulation. Similarly, if the phase change layer P is made solely of GST material, within a temperature range of less than 220°C, the device's outer surface exhibits a first color, with the specific color determined by the thickness and material of each layer. After high-temperature annealing to a temperature range of no less than 220°C and no more than 400°C, the device's outer surface exhibits a second color. Further high-temperature annealing to a temperature range of no less than 400°C results in a third color. The different colors are determined by the specific design requirements and circumstances of steps 1-2. After exhibiting the third color at no less than 400°C, continued heating and slow cooling to room temperature will maintain the third color without changing the film's structure. To restore the third color back to the first, the film can be heated to above 400°C and then rapidly cooled to room temperature. Rapid cooling can be achieved using laser pulses. This allows the film structure to transition from a post-phase change color back to its pre-phase change structural color, enabling repeatable structural color phase change modulation.

[0127] The present invention will be further described below with reference to the accompanying drawings.

[0128] Example 1

[0129] like Figure 4As shown, the structural color device consists of a substrate (not shown), a high-refractive-index dielectric layer H (TiO2) on the substrate, a phase-change layer P (GSST), a low-refractive-index dielectric layer L (MgF2), a phase-change layer P (GSST), and a high-refractive-index dielectric layer H (TiO2). The substrate is made of a thin film deposited on K9 glass with a diameter of 80 mm, a thickness of 2 mm, and a surface quality of 20 / 10. The specific thickness of each layer is given in Table 1. Using the thickness values ​​given in Table 1, a color that appears red at temperatures below 310°C and turns purple-red after high-temperature annealing to a crystalline state at a temperature of at least 310°C can be produced. Figure 8 、 Figure 9 This is the reflection spectrum of Example 1 in the amorphous state less than 310 degrees and the crystalline state not less than 310 degrees. Figure 10 、 Figure 11 The chromaticity coordinates of the amorphous and crystalline states of Example 1 at normal incidence are shown in the figure. The figure shows a significant change in the reflectance spectrum after the phase transition, with the maximum reflectance decreasing from 74% to 56%, while the reflectance at 300nm increases from 10% to 30%. The chromaticity coordinates also shift significantly, from (0.37, 0.5) to (0.38, 0.45), demonstrating excellent color change characteristics.

[0130] Table 1

[0131]

[0132] Example 2

[0133] Example 2 maintains the same materials as Example 1, but by varying the thicknesses of the high-refractive-index dielectric layer H and the low-refractive-index dielectric layer L, different colors are exhibited before and after the phase change. This structural color device comprises a substrate Sub, a high-refractive-index dielectric layer H (TiO2) on the substrate, a phase change layer P (GSST), a low-refractive-index dielectric layer L (MgF2), a phase change layer P (GSST), and a high-refractive-index dielectric layer H (TiO2). The substrate is a thin film deposited on K9 glass with a diameter of 80 mm, a thickness of 2 mm, and a surface quality of 20 / 10. The specific thicknesses of each layer are listed in Table 2. Using the thickness values ​​listed in Table 2, a device can be produced that appears orange when observed at temperatures below 310°C, and gray-purple when annealed at a temperature of at least 310°C and crystallized. Figure 12 、 Figure 13 This is the reflection spectrum of Example 2 in the amorphous state less than 310 degrees and the crystalline state not less than 310 degrees. Figure 14 、 Figure 15The chromaticity coordinates for the amorphous and crystalline states of Example 2 at normal incidence are shown in the figure. The figure shows that after the phase change, the position of the maximum reflectance in the visible light range shifts from 735nm to 400nm, and the chromaticity coordinates also move from (0.33, 0.51) to (0.24, 0.4). This significant shift demonstrates good color change characteristics.

[0134] Table 2

[0135]

[0136] Example 3

[0137] Example 3 uses completely different materials for the high- and low-refractive-index dielectric layers than Example 1. This structural color device consists of a substrate Sub, a high-refractive-index dielectric layer H (ZnS) on the substrate, a phase-change layer P (GSST), a low-refractive-index dielectric layer L (SiO2), a phase-change layer P (GSST), and a high-refractive-index dielectric layer H (ZnS). The substrate is made of the same material as previously used. The specific thicknesses of each layer are given in Table 3. Using the thickness values ​​given in Table 3, a device can be produced that appears yellow when observed at temperatures below 310°C, and brown when crystalline after high-temperature annealing to a temperature of at least 310°C. Figure 16 、 Figure 17 This is a reflection spectrum diagram of Example 3 in an amorphous state less than 310 degrees and a crystalline state not less than 310 degrees. Figure 18 、 Figure 19 The chromaticity coordinates of the amorphous and crystalline states at normal incidence are shown in Example 3. The figure shows that after the phase change, the position of the maximum reflectivity in the visible light range shifts from 600 nm to 631 nm, and the magnitude of the reflectivity peak also changes significantly.

[0138] Table 3

[0139]

[0140] Example 4

[0141] Example 4 consists of a substrate Sub, a high-refractive-index dielectric layer H (Ta2O5) on the substrate, a phase-change layer P (GSST), a low-refractive-index dielectric layer L (SiO2), a phase-change layer P (GSST), and a high-refractive-index dielectric layer H (Ta2O5). The substrate is made of the same material as previously used. The specific thicknesses of each layer are given in Table 4. Using the thickness values ​​given in Table 4, a product can be produced that appears pink when observed at temperatures below 310°C, and then changes to a blue-purple color after high-temperature annealing to a temperature of at least 310°C and crystallization. Figure 20 、 Figure 21 This is a reflection spectrum diagram of Example 4 in an amorphous state less than 310 degrees and a crystalline state not less than 310 degrees. Figure 22 、 Figure 23 The chromaticity coordinate diagram of the amorphous and crystalline states in Example 4 at a vertical incident angle is shown. The color change can be clearly seen from the chromaticity coordinate diagram, with the coordinates moving from (0.31, 0.45) to (0.18, 0.26).

[0142] Table 4

[0143]

[0144] Example 5

[0145] The materials used in Example 5 are the same as those in Example 1, with only minor adjustments to the thickness of each layer. The material comprises a substrate Sub, a high-refractive-index dielectric layer H (TiO2) on the substrate, a phase-change layer P (GSST), a low-refractive-index dielectric layer L (MgF2), a phase-change layer P1 (GSST), and a high-refractive-index dielectric layer H1 (TiO2). The substrate is made of the same material as previously used. The specific thicknesses of each layer are given in Table 5. Using the thickness values ​​given in Table 5, a product can be produced that appears purple when observed at temperatures below 310°C, and blue when crystalline after high-temperature annealing to a temperature of at least 310°C. Figure 24 、 Figure 25 This is the reflection spectrum of Example 5 in the amorphous state less than 310 degrees and the crystalline state not less than 310 degrees. Figure 26 、 Figure 27 The chromaticity coordinate diagram of the amorphous and crystalline states of Example 5 at a vertical incident angle.

[0146] Table 5

[0147]

[0148] Example 6

[0149] The phase change layer P in Example 6 uses GST material. It consists of a substrate Sub, a high-refractive-index dielectric layer H (Ta2O5) on the substrate, a phase change layer P (GST), a low-refractive-index dielectric layer L (SiO2), a phase change layer P (GST), and a high-refractive-index dielectric layer H (Ta2O5). The substrate is made of the same material as previously used. The specific thicknesses of each layer are given in Table 6. Using the thickness values ​​given in Table 6, a product can be produced that is orange when observed at temperatures below 220°C, orange-yellow after being heated to a temperature of at least 220°C and below 400°C, and brown after being crystalline after annealing at a temperature of at least 400°C. Figure 28 、 Figure 29 、 Figure 30 The reflection spectra of Example 6 are shown in the amorphous state of less than 220 degrees, the metastable state of not less than 220 degrees and less than 400 degrees, and the crystalline state of not less than 400 degrees. Figure 31 、 Figure 32 、 Figure 33This is the chromaticity coordinate diagram of the amorphous, metastable, and crystalline states of Example 6 at a vertical incident angle.

[0150] Table 6

[0151]

[0152] Example 7

[0153] The phase-change layer P in Example 7 uses a combination of GST and GSST. It consists of a substrate Sub, a high-refractive-index dielectric layer H (Ta2O5) on the substrate, a phase-change layer P (GSST), a high-refractive-index dielectric layer H (Ta2O5), a phase-change layer P (GST), a low-refractive-index dielectric layer L (SiO2), a phase-change layer P (GST), a high-refractive-index dielectric layer H (Ta2O5), a phase-change layer P (GSST), and a high-refractive-index dielectric layer H (Ta2O5). The substrate is made of the same material as previously used. The specific thickness of each layer is given in Table 7. Using the thickness values ​​given in Table 7, a product can be produced that is yellow-green when observed at temperatures below 220°C, emerald green after high-temperature annealing at 220-310°C, brown after high-temperature annealing at 310-400°C, and brown after high-temperature annealing at 400°C and crystallization. Figure 34 、 Figure 35 、 Figure 36 、 Figure 37 The reflection spectra of Example 7 after high temperature annealing at less than 220, 220-310, 310-400, and not less than 400 degrees are shown. Figure 38 、 Figure 39 、 Figure 40 、 Figure 41 These are the chromaticity coordinate diagrams of Example 7 at vertical incident angles after high-temperature annealing at less than 220 degrees, 220-310 degrees, 310-400 degrees, and not less than 400 degrees.

[0154] Table 7

[0155]

[0156] The above descriptions are only some embodiments of the present invention and do not limit the scope of protection of the present invention. Any equivalent device or equivalent process transformation made by using the contents of the description and drawings of the present invention, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A photonic crystal structure color film based on phase change material, characterized in that: The structure of the film is: (HP) s L (PH) s The structure of the film is a symmetrical structure centered on L, wherein H represents a high-refractive-index dielectric layer, P represents a phase-change layer, and L represents a low-refractive-index dielectric layer. Each group (HP) or (PH) constitutes an equivalent high-refractive-index unit, and each group of equivalent high-refractive-index units is stacked by a high-refractive-index dielectric layer H and a phase-change layer P. s represents the number of times the equivalent high-refractive-index units are repeatedly stacked, and s is a positive integer. The high-refractive-index dielectric layer H is a film layer of a material having a refractive index greater than or equal to 1.55 in the range of 400 nm to 780 nm, and is made of lanthanum titanate, amorphous silicon, indium tin oxide, titanium dioxide, tantalum pentoxide, hafnium dioxide, zirconium dioxide, zinc sulfide, or silicon monoxide; the thickness of the high-refractive-index dielectric layer H is in the range of 20-500 nm; The phase change layer P is made of GSST material or GST material. The GSST material has two different crystalline states at different temperatures, namely, an amorphous state and a crystalline state; the GST material has three different crystalline states at different temperatures, namely, an amorphous state, a metastable state, and a crystalline state. The thickness of the phase change layer P is in the range of 5-30 nm. The low-refractive-index medium layer L is a material film layer with a refractive index less than 1.55 in the range of 400nm~780nm, and is made of silicon dioxide, magnesium fluoride, cerium fluoride, lanthanum fluoride, sodium aluminum fluoride, neodymium fluoride, banknote fluoride, barium fluoride, calcium fluoride or lithium fluoride; the thickness of the low-refractive-index medium layer L ranges from 20nm to 600nm.

2. The photonic crystal structure color film based on phase change material according to claim 1, characterized in that: The number of times s of repeated stacking of the equivalent high refractive index unit is in the range of 1 to 5; when the number s is 2 to 5, (HP) s The s layers of high refractive index medium H in the (HP) are made of the same material or at least two layers of the same material or completely different materials. s The s phase change layers P in the embodiment are made of the same material or at least two layers of the same material or completely different materials.

3. A method for preparing a photonic crystal structure color film based on phase change material, characterized in that: The preparation method needs to be based on a photonic crystal structured color film based on a phase change material as claimed in any one of claims 1 to 2, comprising the following steps: Step 1: Design a photonic crystal structured color film based on phase change material according to user needs. The structure of the film is: (HP) s L (PH) s The structure of the film is a symmetrical structure centered on L, wherein H represents a high-refractive-index dielectric layer, P represents a phase-change layer, and L represents a low-refractive-index dielectric layer. Each group (HP) or (PH) constitutes an equivalent high-refractive-index unit, and each group of equivalent high-refractive-index units is stacked by a high-refractive-index dielectric layer H and a phase-change layer P. s represents the number of times the equivalent high-refractive-index units are repeatedly stacked, and s is a positive integer. Step 2: adjusting the thickness and material of each layer in the structure of the film, so that the film exhibits different color changes in different temperature ranges; Step 3: determining the structural parameters required for preparing the film according to the design results; Step 4: Place the flat surface object as a substrate in the film forming equipment chamber; if the film does not require demolding, proceed to step 5; if the film requires demolding, proceed to step 6; Step 5: Growing the first layer, the second layer, and so on until the last layer of the thin film on the substrate according to the structural parameters, wherein the high refractive index medium layer H and the phase change layer P are stacked in sequence according to the number s between the first layer and the second layer, and the middle layer is the low refractive index medium layer L. The first layer to the last layer are grown symmetrically with L as the center; thus completing the preparation of the thin film; Step 6: Then grow a layer of release agent on the substrate; grow the first layer, the second layer... until the last layer of the thin film on the release agent according to the structural parameters; between the first layer to the 2s layer, the high refractive index medium layer H and the phase change layer P are cross-stacked in sequence according to the number s, the middle layer is the low refractive index medium layer L, and the first layer to the last layer are grown symmetrically with L as the center; use the solvent corresponding to the release agent to dissolve the release agent, so that the thin film is separated from the release agent to obtain the separate thin film, thereby completing the preparation of the thin film.

4. The method for preparing a photonic crystal structured color film based on a phase change material according to claim 3, wherein: The step 2 specifically includes: Step 21, designing the thickness and material of each layer in the structure of the film; Step 22, according to (HP) s The materials used for the phase change layer P in the s layer determine different temperature thresholds. If the phase change layers P in the s layer are all GSST materials, the temperature threshold is determined to be T1, and the process proceeds to step 23; if the phase change layers P in the s layer are all GST materials, the temperature thresholds are determined to be T2 and T3, and the process proceeds to step 24; if the phase change layers P in the s layer are both GSST materials and GST materials, the temperature thresholds are determined to be T2, T1, and T3, and the process proceeds to step 25; Step 23: Record the first color of the film within a temperature range less than T1, then perform a phase change treatment on the film so that the temperature of the film is raised to a temperature range not less than T1, and again record the second color of the film at this time. Compare the color changes before and after the phase change. If the color difference is large, it indicates that the thickness and material of each layer in the structure of the film are designed appropriately. If the color difference is small, proceed to step 21 to readjust the thickness and material of each layer in the structure of the film. Step 24: Record the first color of the film within a temperature range less than T2, then perform a phase change treatment on the film so that the temperature of the film is raised to a temperature range not less than T2 and less than T3, and again record the second color of the film at this time. Then, perform a phase change treatment on the film so that the temperature of the film is raised to a temperature range not less than T3, and again record the third color of the film at this time. Compare the color changes during the phase change process. If the color difference changes greatly, it indicates that the thickness and material of each layer in the designed structure of the film are reasonable. If the color difference changes little, proceed to step 21 to readjust the thickness and material of each layer in the structure of the film. Step 25: Record the first color of the film within a temperature range less than T2, then perform phase change treatment on the film so that the temperature of the film rises to a temperature range not less than T2 and less than T1, and again record the second color of the film at this time; then perform phase change treatment on the film so that the temperature of the film rises to a temperature range not less than T1 and less than T3, and again record the third color of the film at this time; then perform phase change treatment on the film so that the temperature of the film rises to a temperature range not less than T3, and again record the fourth color of the film at this time; compare the color changes during the phase change process; if the color difference changes greatly, it means that the thickness and material of each layer in the designed structure of the film are reasonable; if the color difference changes little, proceed to step 21 to readjust the thickness and material of each layer in the structure of the film.

5. The method for preparing a photonic crystal structured color film based on phase change material according to claim 3, characterized in that: The phase change process of the phase change layer P is completed by a high temperature annealing process, electric heating or laser pulse phase change.

6. The method for preparing a photonic crystal structured color film based on phase change material according to claim 4, characterized in that: The structural parameters include the total number of layers, the material used for each layer, the thickness of each layer, and the distribution between the layers; the temperature threshold T1 is 310 degrees, the temperature threshold T2 is 220 degrees, and the temperature threshold T3 is 400 degrees.

7. The method for preparing a photonic crystal structured color film based on phase change material according to claim 3, characterized in that: The material of the substrate is polished glass, polished stainless steel, polished mirror aluminum, polyethylene terephthalate, cellulose triacetate, polymethyl methacrylate, polycarbonate / polymethyl methacrylate composite material, polyimide, polypropylene, polyvinyl chloride, polyvinyl butyral, ethylene vinyl acetate copolymer, polyurethane elastomer, polytetrafluoroethylene, fluoroethyl propylene or polyvinyl difluoride; the material of the demolding agent is fluoride, chloride or water-soluble organic material that is easily soluble in water.

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