CN116068793A - A photonic crystal structural color thin film based on phase change material and its preparation method - Google Patents

Abstract

The invention discloses a photonic crystal structure color film based on a phase change material, which has the structure that: (HP) ^s L(PH) ^s The structure of the film is a symmetrical structure taking L as a center, wherein H represents a high-refractive-index dielectric layer, P represents a phase-change layer, L represents a low-refractive-index dielectric layer, each group (HP) or (PH) forms an equivalent high-refractive-index unit, each group of equivalent high-refractive-index units is formed by stacking the high-refractive-index dielectric layer H and the phase-change layer P, s represents the repeated stacking times of the equivalent high-refractive-index units, and s is a positive integer. The invention also provides a phase change material-based materialAccording to the preparation method of the photonic crystal structure color film, the prepared film can have a structure color with larger chromatic aberration before and after phase change through phase change of the phase change layer.

Description

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

Technical Field

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

Background Art

Phase-changeable materials refer to materials whose physical structure can be changed by changing their temperature within a certain temperature range, and have an almost fixed phase change temperature. The working principle of phase-change materials is that when the ambient temperature is higher than the phase change temperature, they store heat; when the ambient temperature is lower than the phase change temperature, they release the stored energy. Currently, phase-change materials have been widely used in energy storage, medical fields, data storage, etc. In the field of optical films, phase-change materials have been mostly used in heat absorption and insulation in the aerospace field and mid- and far-infrared camouflage in the military field.

From the working principle of phase-changeable materials, we know that the main phase change methods are to heat the object directly or indirectly. The phase change can be completed by high-temperature annealing process, electric heating, and light stimulation (laser pulse phase change). In order to measure the phase change performance of a material, the phase change goodness of man (FOM) is usually used to define the quality of its phase change ability. The larger the FOM value, the greater the refractive index difference between the two materials in the amorphous and crystalline states; at the same time, the smaller the extinction coefficient of the film in the crystalline state, the better. In order to make the photonic crystal film show better phase change performance, higher saturation and greater phase change chromatic aberration, phase change materials are needed, but there are relatively few studies based on phase change materials in the optical field.

Typical phase change materials include chalcogenide semiconductor materials represented by Ge2Sb2Te5 (GST for short). GST materials can achieve sub-nanosecond phase change through electrical pulses and optical pulses. Since its phase change can be switched quickly and repeatedly, its optical and electrical properties can also present two different states, which makes it a reliable material for making non-volatile memory. Although GST materials are widely used in photonic devices such as non-volatile displays, optical switches, photonic memories, and all-optical computers, they are rarely used in the field of phase-changeable thin film structural colors.

Doping and modification are performed on the basis of GST, a classic phase change material (PCM). Experiments have shown that replacing part of Te in Ge2Sb2Te5 with Se can reduce the extinction coefficient of the material in the visible light region, thereby enhancing the brightness of the film structure color, but too much Se will also cause the material to lose its phase change ability. Ge2Sb2Se4Te1 (GSST for short) is a critical material that ensures its phase change ability while minimizing material absorption as much as possible.

As a new material with significant optical performance advantages over the classic phase change material GST, GSST has been used to make silicon-based three-dimensional waveguide mode optical switches (CN114995010A), multi-parameter tunable filters based on phase change Bragg gratings (CN216248399U), programmable arbitrary power dividers based on DBS algorithms (CN113191115A), etc. However, in the field of phase-changeable thin film structural colors, GSST still has great application prospects.

The Chinese invention patent with patent number CN202011061690 discloses a resonant cavity film system and a preparation method that have non-volatility, multi-structural colors, multi-levels and high transmittance contrast. The composite dual-cavity film system uses two different PCM materials to achieve the goals of high transmittance and multi-levels, 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 a structural color with high brightness, high saturation and large phase change difference for this film system.

At present, some new electrochromic materials have been proposed, such as an electrochromic structural color designed in CN202211003546. By adjusting the size and direction of the applied voltage, the metal particles can be deposited and dissolved on the transparent electrode, thereby changing the thickness of its film structure to change it from transparent color to a certain color. The color change that can be achieved by this adjustment method is very limited, and its phase change color is also relatively single. How to design a film that can complete a large color phase change without changing the structure of the generated film is a hot topic of research at this stage.

Summary of the invention

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 difference before and after the phase change by causing phase change in the phase change layer.

In order to achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is: a photonic crystal structural 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 of (HP) or (PH) constitutes an equivalent high refractive index unit, and each group of equivalent high refractive index units is formed by stacking 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.

Furthermore, the high refractive index medium layer H is a material film layer with 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 range of the high refractive index medium layer H is 20-500nm.

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 range of the phase change layer P is 5-30nm.

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 to 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.

Furthermore, the number of repeated stacking times s of the equivalent high refractive index unit is in the range of 1 to 5; when the number s is 2 to 5, the s high refractive index medium layers H in (HP) ^s are made of exactly the same material or at least two layers of the same material or completely different materials, and the s phase change layers P in (HP) ^s are made of exactly the same material or at least two layers of the same material or completely different materials.

The present invention also provides a method for preparing a photonic crystal structure color film based on a phase change material, comprising the following steps:

Step 1. Design a photonic crystal structural 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 medium layer, P represents a phase change layer, and L represents a low refractive index medium layer. Each group of (HP) or (PH) constitutes an equivalent high refractive index unit. Each group of equivalent high refractive index units is formed by stacking 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.

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

Step 3, determining the structural parameters required for preparing the film according to the design results;

Step 4, using a flat surface object as a substrate and placing it in the film forming equipment cavity; when the film does not need to be demolded, perform step 5; when the film needs to be demolded, perform step 6;

Step 5, growing the first layer, the second layer, ... 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 to the 2s layer, the middle layer is the low refractive index medium layer L, and the middle layer to the last layer are grown symmetrically with L as the center; 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 stacked in sequence according to the number s, the middle layer is the low refractive index medium layer L, and the middle 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.

Furthermore, the step 2 specifically includes:

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

Step 22, determining different temperature thresholds according to the materials used by the s-layer phase change layer P in (HP) ^s . 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 goes 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 goes to step 24; if the phase change layers P in the s-layer have both GSST materials and GST materials, the temperature thresholds are determined to be T2, T1 and T3, and the process goes to step 25;

Step 23, recording the first color presented by the film within a temperature range less than T1, then performing a phase change treatment on the film so that the temperature of the film rises to a temperature range not less than T1, and again recording the second color presented by the film at this time, and comparing the color changes before and after the phase change. If the color difference changes greatly, it means that the thickness and material of each layer in the structure of the designed film are reasonable; if the color difference changes little, entering step 21 to readjust the thickness and material of each layer in the structure of the film;

Step 24, recording the first color presented by the film within a temperature range less than T2, then performing 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 T3, again recording the second color presented by the film at this time, then performing phase change treatment on the film so that the temperature of the film rises to a temperature range not less than T3, again recording the third color presented by the film at this time, and comparing 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, entering step 21 to readjust the thickness and material of each layer in the structure of the film;

Step 25, recording the first color presented by the film within a temperature range less than T2, then performing 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 recording again the second color presented by the film at this time, then performing 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 recording again the third color presented by the film at this time, then performing phase change treatment on the film so that the temperature of the film rises to a temperature range not less than T3, and recording again the fourth color presented by the film at this time; comparing 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, entering step 21 to readjust the thickness and material of each layer in the structure of the film.

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.

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.

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 polyvinylidene fluoride; the material of the demolding agent is fluoride, chloride or water-soluble organic material that is easily soluble in water.

By adopting the above-mentioned technical scheme, 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 remain unchanged 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, and only heats the phase change layer through high temperature or laser pulses or irradiates the phase change layer with laser light, 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.

And by designing a symmetrical film system structure, a structural color film that can be used for device coating and can achieve a large color phase change is produced. On the basis of this design structure, phase-changeable films of various colors such as red, orange, yellow, green, blue, indigo, and purple can be prepared. This structure applies the sulfide phase-changeable material GSST to the field of thin film structural color, which not only innovatively proposes the application of this material in the field of tunable structural color, but also can improve some problems of traditional phase change materials such as GST in the application of tunable structural color, such as insufficient color display ability and unclear phase change effect. Not only that, it is precisely because this design structure can produce very rich colors, which provides a new tunable solution for its application in the field of color printing and micro-nano color display. As a semiconductor material, GSST is also widely used in optical devices. Combining its electrical and optical properties, it can realize a variety of color displays on some special optical devices, so that its electrical and other properties can provide visual feedback for its phase change in the application scenario. Compared with previous studies, the method proposed in the present invention has the advantages of many tunable structures, good tunable effects, and easy 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

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative work.

FIG1 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).

FIG2 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).

FIG3 is a flow chart of a method for preparing a photonic crystal structural color film based on phase change material provided by the present invention.

FIG4 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 s is 1).

FIG5 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, and the number of s is 2).

FIG. 6 shows the optical constants of the amorphous state of the GSST phase change material provided by the present invention in the visible light range.

FIG. 7 shows the optical constants of the crystalline state of the GSST phase change material provided by the present invention in the visible light range.

FIG8 is a reflection spectrum diagram of the amorphous state of Example 1 under vertical incidence.

FIG. 9 is a reflection spectrum diagram of the crystalline state of Example 1 under vertical incidence.

FIG. 10 is a chromaticity coordinate diagram of the amorphous state of Example 1 under vertical incidence.

FIG. 11 is a chromaticity coordinate diagram of the crystal state of Example 1 under vertical incidence.

FIG. 12 is a reflection spectrum diagram of the amorphous state of Example 2 under vertical incidence.

FIG. 13 is a reflection spectrum diagram of the crystalline state of Example 2 under vertical incidence.

FIG. 14 is a chromaticity coordinate diagram of the amorphous state of Example 2 under vertical incidence.

FIG. 15 is a chromaticity coordinate diagram of the crystal state of Example 2 under vertical incidence.

FIG. 16 is a reflection spectrum diagram of the amorphous state of Example 3 under vertical incidence.

FIG. 17 is a reflection spectrum diagram of the crystalline state of Example 3 under vertical incidence.

FIG. 18 is a chromaticity coordinate diagram of the amorphous state of Example 3 under vertical incidence.

FIG. 19 is a chromaticity coordinate diagram of the crystal state of Example 3 under vertical incidence.

FIG. 20 is a reflection spectrum diagram of the amorphous state of Example 4 under vertical incidence.

FIG. 21 is a reflection spectrum diagram of the crystalline state of Example 4 under vertical incidence.

FIG. 22 is a chromaticity coordinate diagram of the amorphous state of Example 4 under vertical incidence.

FIG. 23 is a chromaticity coordinate diagram of the crystal state of Example 4 under vertical incidence.

FIG. 24 is a reflection spectrum diagram of the amorphous state of Example 5 under vertical incidence.

FIG. 25 is a reflection spectrum diagram of the crystalline state of Example 5 under vertical incidence.

FIG. 26 is a chromaticity coordinate diagram of the amorphous state of Example 5 under vertical incidence.

FIG. 27 is a chromaticity coordinate diagram of the crystal state of Example 5 under vertical incidence.

FIG. 28 is a reflection spectrum diagram of the amorphous state of Example 6 under vertical incidence.

FIG. 29 is a reflection spectrum diagram of the metastable state of Example 6 under vertical incidence.

FIG30 is a reflection spectrum diagram of the crystalline state of Example 6 under vertical incidence.

FIG. 31 is a chromaticity coordinate diagram of the amorphous state of Example 6 under vertical incidence.

FIG. 32 is a chromaticity coordinate diagram of the metastable state of Example 6 under vertical incidence.

FIG. 33 is a chromaticity coordinate diagram of the crystalline state of Example 6 under vertical incidence.

FIG34 is a reflection spectrum diagram of Example 7 at room temperature under vertical incidence.

FIG35 is a reflection spectrum diagram of Example 7 after annealing to 220° C. under vertical incidence.

FIG36 is a reflection spectrum diagram of Example 7 at 310° C. under vertical incidence.

FIG37 is a reflection spectrum diagram of Example 7 after annealing to 400° C. under vertical incidence.

FIG38 is a chromaticity coordinate diagram of Example 7 at room temperature under vertical incidence.

FIG. 39 is a chromaticity coordinate diagram of Example 7 after annealing to 220° C. under vertical incidence.

FIG. 40 is a chromaticity coordinate diagram of Example 7 after annealing to 310° C. under vertical incidence.

FIG. 41 is a chromaticity coordinate diagram of Example 7 annealed to 400° C. under vertical incidence.

DETAILED DESCRIPTION

The present invention will be further described in detail below in conjunction with the accompanying drawings and examples. It is particularly noted that the following examples are only used to illustrate the present invention, but are not intended to limit the scope of the present invention. Similarly, the following examples are only partial embodiments of the present invention rather than all embodiments, and all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present invention.

Please refer to Figures 1, 2, 4 and 5. The present invention is a photonic crystal structural 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 of (HP) or (PH) constitutes an equivalent high refractive index unit, and each group of equivalent high refractive index units is formed by stacking 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.

In this embodiment, the high refractive index medium layer H is a material film layer with a refractive index greater than or equal to 1.55 in the range of 400nm to 780nm, 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 medium layer H is in the range of 20-500nm.

In this embodiment, the phase change layer P adopts 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, amorphous state, metastable state and crystalline state; the thickness range of the phase change layer P is 5-30nm.

The amorphous amorphous forming 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 use 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, its phase transition temperature has been greatly increased, which also provides the possibility for the use of this film system in special high-temperature scenarios. Experiments have shown that GSST maintains an amorphous structure before 310°C, and its single-layer optical constants are shown in Figure 6. After high-temperature annealing at 310°C, the GSST structure is transformed into a hexagonal crystal state, and its optical constants are shown in Figure 7.

The structure can also use the phase change material GST, which will present an amorphous state at room temperature, a metastable state at a high temperature of 220°C, and a crystalline state after high temperature annealing at 400°C. This can be applied to the structure of this design to present three color changes. In addition, the structure in this design can also mix and match different phase change layers P using GSST and GST, and allow it to present more phase change colors by controlling different annealing temperatures. For example, when s is 2, (HP) ^s has a 2-layer phase change layer P structure, in which the materials of ^P1 and ^P2 can be selected from different GSST or GST materials, such as ^P1 using GSST material and ^P2 using GST material, or ^P1 using GST material and ^P2 using GSST material.

In this embodiment, 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 to 780nm, and the low refractive index medium layer L is admittance matched with the high refractive index medium layer H; silicon dioxide ( _SiO2 ), magnesium fluoride ( _MgF2 ), cerium fluoride ( _CeF3 ), lanthanum fluoride ( _LaF3 ), sodium aluminum fluoride ( _Na3AIF or NasAlFA), neodymium fluoride ( _NdF3 ), silicon dioxide ( _SmF3 ), barium fluoride ( _BaF2 ), calcium fluoride ( _CaF2 ) or lithium fluoride (LiF) are used; the thickness of the low refractive index medium layer L is in the range of 20nm to 600nm. In this embodiment, the equivalent high refractive index unit is repeatedly stacked for a number of times s ranging from 1 to 5. The greater the number of s, the less obvious the structural color change before and after the phase change. When the number of s is 2 to 5, the s layers of high refractive index medium layers H in (HP) ^s are made of the same material or at least two layers of the same material or completely different materials, and the s layers of phase change layers P in (HP) ^s are made of the same material or at least two layers of the same material or completely different materials. The present invention can design structural color films of different colors by adjusting the material and thickness of each layer.

This embodiment is described with s being 1, and the specific structure is shown in FIG4 . The film layer structure is a high refractive index medium layer H, a phase change layer P, an intermediate medium layer L, a phase change layer P, and a high refractive index medium layer H from the substrate upward. Since the material required for the phase change layer P is easily oxidized, the phase change layer P cannot be placed directly on the surface in contact with the air, so the phase change layer P is between the high refractive index medium layer H and the intermediate medium layer L. According to the symmetrical design of the film system, the thickness and material of the two layers of high refractive index medium layers H symmetrically arranged above and below the intermediate medium layer L are the same, and the thickness and material of the phase change layers P symmetrically arranged above and below the intermediate medium layer L are the same.

The F-P thin film filter is a simple narrowband filter, which is improved on the basis of the Fabry-Perot interferometer. This filter is mainly composed of a parallel cavity layer in the middle and high reflectivity layers at both ends. According to the materials of the high reflective layers at both ends, it can be divided into two types: metal-dielectric structure and full dielectric structure. The metal-dielectric F-P filter is mainly composed of two parallel metal layers and a dielectric spacer layer in the middle. The main parameters of the F-P filter are calculated based on the thin film reflection and transmission theory.

Among the various performance parameters of the filter, the main ones that describe its characteristics include the central wavelength λ ₀ , the full width at half maximum (FWHM) of the peak, the transmittance T of the central wavelength and the free spectral range (FSR).

F-P filter transmittance expression:

Wherein, T ₁ , T ₂ , R ₁ and R ₂ are the transmittance and reflectance of the two metal reflective layers respectively (eg, the transmittance and reflectance of the first metal reflective layer are T ₁ and R ₁ respectively, and the transmittance and reflectance of the second metal reflective layer are T ₂ and R ₂ respectively);

其中

为间隔层的位相厚度，而

和

分别为两层反射的反射位相。

in

is the phase thickness of the spacer layer, and

and

They are the reflection phases of the two layers of reflection.

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

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

Δλ _FSR =λ ² /(2nd)

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

其中，R₁和R₂分别为介质层和反射层的反射率。in

Wherein, _R1 and _R2 are the reflectivity of the dielectric layer and the reflective layer respectively.

Since R+T+A=1, the absorption of A is approximately a constant. In order to improve the overall reflectivity performance of the film system, the traditional F-P thin film filter structural color film needs to reduce the transmittance according to the transmittance expression. One is to increase the reflectivity of the two metal layers, and the other is to adjust the phase thickness of the intermediate dielectric layer. However, due to the inherent large absorption of the metal itself and the phase matching requirements of the intermediate dielectric layer to control the half-maximum full width of the spectral peak and the free spectral range, it is difficult for the traditional F-P thin film filter structural color to achieve multiple colors with high reflectivity.

膜层后，由于空气/膜层和膜层/基片界面的反射光同位相，使反射率能够大大增加。对于中心波长λ₀，单层膜和基片的等效组合的导纳为n₁ ²/n_g，垂直入射的反射率为：The present invention utilizes the interference effect of dielectric film and the equivalent characteristics of the refractive index and phase thickness of the symmetrical film structure. 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 through computer optimization design. We know that when a high refractive index with an optical thickness of λ ₀ /4 is plated on a substrate with a refractive index of n _g ,

After the film layer is formed, the reflectivity can be greatly increased because the reflected light at the air/film layer and film layer/substrate interface is in phase. For the central wavelength λ ₀ , the admittance of the equivalent combination of a single film and substrate is n ₁ ² / _ng , and the reflectivity at vertical incidence is:

Among them, in the film system of this design, each group (HP) or (PH) constitutes an equivalent high refractive index unit, and a multilayer film with high and low refractive index layers alternating for each layer of λ ₀ /4 can obtain a 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. In this structure, n _H is used to represent the refractive index of the high refractive index layer, and n _L is used to represent the refractive index of the low refractive index layer. Then the equivalent interface admittance Y of the entire film system structure at the center wavelength λ ₀ is:

Where 2s+1 is the number of layers of the multilayer film, and the reflectivity of the central wavelength λ ₀ , i.e., the maximum reflectivity, is:

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

The reason why the outermost layer is selected as a high refractive index film layer is that compared with the outermost layer of a low refractive index film layer, according to its absorption formula, it will have greater absorption, resulting in a lower reflectivity. In the formula, _kH is the extinction coefficient of the high refractive index medium layer, _{and kL} is the extinction coefficient of the low refractive index layer. It can be seen from the absorption and maximum reflectivity formulas that the refractive index and extinction coefficient of the high refractive index medium layer H and the phase change layer P in this structure jointly affect the reflectivity of the central wavelength. By changing the physical thickness of the high refractive index medium layer H and the phase change layer P, the maximum reflectivity of the film layer can also be located at different central wavelength positions, thereby changing the color of the film layer. The difference in the ratio of _nH to _nL will also change the maximum value of the central wavelength reflectivity, so choosing different materials can also change the peak reflectivity size in this design structure. Annealing the prepared film at 310°C can change the GSST in the phase change layer P from an amorphous state to a crystalline state, and its refractive index and extinction coefficient will change. According to the characteristics of the above reflectivity formula, it can be clearly seen that the reflectivity of the central wavelength will change, thereby changing the structural color of the film system, achieving the function of color change after the film is prepared.

Considering that the designed thin film can be used in other devices to realize various color-related functions, the present invention designs a symmetrical film structure that can be peeled off from the preparation substrate and can be used for device coating. The advantage of this structure is that the thin film structural color can show the designed color whether it is observed from the front or back. Unlike other traditional structural color film systems based on the F-P thin film filter structure, which requires a thick metal layer at the bottom as a reflective layer, although a thick metal layer at the bottom can provide a higher peak reflectivity, it also provides different difficulties for its application scenarios and preparation process.

As shown in FIG. 3 , the present invention also provides a method for preparing a photonic crystal structural color film based on a phase change material, comprising the following steps:

Step 1, designing a photonic crystal structural color film based on phase change material according to user needs, wherein 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 of (HP) or (PH) constitutes an equivalent high refractive index unit, and each group of equivalent high refractive index units is formed by stacking 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;

Step 2, adjust the thickness and material of each layer in the structure of the film, so that the film shows 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. On the basis of not changing the film structure in the visible light region, a photonic crystal thin film structural color device is prepared using a phase changeable material (GSST or GST) to change the color of the film by heating the phase change layer only by high temperature or laser pulses or laser irradiation without changing the film structure. Finally, the prepared film can have a structure with a large color difference before and after the phase change.

According to whether the colored object absorbs light or not, the color of the colored object can be divided into two types: pigment color and structural color. Pigment color mainly includes the absorption involving coordination field effect transition, and the color it reflects is also called chemical color. Structural color mainly includes physical optical effects such as gratings, single-layer films, multi-layer films, photonic crystals, Rayleigh scattering, Mie scattering, etc., and the color it reflects is called structural color.

Photonic crystal structural color films made 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, small 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.

In this embodiment, step 2 specifically includes:

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

Step 22, determining different temperature thresholds according to the materials used by the s-layer phase change layer P in (HP) ^s . 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 goes 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 goes to step 24; if the phase change layers P in the s-layer have both GSST materials and GST materials, the temperature thresholds are determined to be T2, T1 and T3, and the process goes to step 25;

Step 23, recording the first color presented by the film within a temperature range less than T1, then performing a phase change treatment on the film so that the temperature of the film rises to a temperature range not less than T1, and recording the second color presented by the film again, and comparing the color changes before and after the phase change. If the color difference changes greatly, it means that the thickness and material of each layer in the structure of the designed film are reasonable. At this time, if the temperature is lowered to a temperature range less than T1, the color will be restored to the first color; if the color difference changes little, entering step 21 to readjust the thickness and material of each layer in the structure of the film;

Step 24, recording the first color presented by the film within a temperature range less than T2, then performing 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 recording the second color presented by the film at this time, then performing 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 recording the third color presented by the film at this time, and comparing the color change during the phase change process, if the color difference changes greatly, it means that the thickness and material of each layer in the structure of the designed film are reasonable, and at this time, if the temperature is reduced to a temperature range not less than T2 and less than T3, the color will be restored to the second color, and if the temperature is reduced to a temperature range less than T2, the color will be restored to the first color; if the color difference changes little, then entering step 21 to readjust the thickness and material of each layer in the structure of the film;

Step 25, recording the first color presented by the film within a temperature range less than T2, then performing 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 recording the second color presented by the film at this time again, then performing 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 recording the third color presented by the film at this time again, then performing phase change treatment on the film so that the temperature of the film is increased to a temperature range not less than T3, and recording the fourth color presented by the film at this time again; comparing 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 structure of the designed film are reasonable, and at this time, if the temperature is reduced to a temperature range not less than T1 and less than T3, the color will be restored to the third color, if the temperature is reduced to a temperature range not less than T2 and less than T1, the color will be restored to the second color, and if the temperature is reduced to a temperature range less than T2, the color will be restored to the first color; if the color difference changes little, entering step 21 to readjust the thickness and material of each layer in the structure of the film.

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.

Step 3, determining the structural parameters required for preparing the film according to 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;

Step 4, using a flat surface object as a substrate and placing it in the film forming equipment cavity; when the film does not need to be demolded, perform step 5; when the film needs to be demolded, perform step 6;

In this embodiment, the material of the substrate is 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);

Step 5, growing the first layer, the second layer, ... 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 to the 2s layer, the middle layer is the low refractive index medium layer L, and the middle layer to the last layer are grown symmetrically with L as the center; completing the preparation of the thin film;

Step 6, then grow a layer of release agent on the substrate, the material of the release agent adopts 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 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 stacked in sequence according to the number s, the middle layer is the low refractive index medium layer L, and the middle 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 film is separated from the release agent, and the separate film is obtained, thereby completing the preparation of the film.

Step 7, after the film is prepared, the film is coated on the outer surface of the device. At this time, the outer surface of the device has different colors at different temperatures; if the phase change layer P only uses GSST material, then within the temperature range of less than 310 degrees, the outer surface of the device presents the first color. The specific color is determined by the thickness and material of each layer. The transformation from the crystalline state to the amorphous state can be achieved by high-temperature annealing to a temperature range of not less than 310 degrees. The outer surface of the device presents the second color. The presentation of different colors is achieved by the specific design requirements and conditions of steps 1-2. After the second color is presented at not less than 310 degrees, the heat is continued to be supplied so that the temperature is slowly reduced to room temperature. The structure of the film will not change, and the color will continue to be the second color; if the second color is to be restored to the first color, the film can be heated to a temperature higher than 310 degrees and then quickly cooled to room temperature. This process can be achieved by the laser pulse method. In this way, the film structure can be changed from the color after the phase change to the structural color before the phase change, and repeated structural color phase change adjustment can be achieved. Similarly, if the phase change layer P is made of GST material only, then within a temperature range of less than 220 degrees, the outer surface of the device presents a first color. The specific color is determined by the thickness and material of each layer. After high-temperature annealing to a temperature range of not less than 220 degrees to less than 400 degrees, the outer surface of the device presents a second color. After high-temperature annealing to a temperature range of not less than 400 degrees, the outer surface of the device presents a third color. The presentation of different colors is achieved by the specific design requirements and conditions of steps 1-2. After the third color is presented at not less than 400 degrees, the temperature is slowly reduced to room temperature by continuing to supply heat. The structure of the film will not change, and the color will continue to be the third color; if the third color is to be restored to the first color, the film can be heated to a temperature above 400 degrees and then quickly cooled to room temperature. Rapid cooling can be achieved by laser pulse method. In this way, the film structure can be changed from the color after the phase change to the structural color before the phase change, and repeated structural color phase change adjustment can be achieved.

The present invention will be further described below in conjunction with the accompanying drawings.

Example 1

As shown in FIG4 , the structural color device is composed of a substrate Sub (not shown), a high refractive index dielectric layer H (TiO ₂ ) on the substrate, a phase change layer P (GSST), a low refractive index dielectric layer L (MgF ₂ ), a phase change layer P (GSST), and a high refractive index dielectric layer H (TiO ₂ ). The substrate is a K9 glass deposited film 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. According to the thickness values given in Table 1, a color that is observed as red at a temperature less than 310 degrees and observed as purple-red after high temperature annealing to a crystalline state at a temperature not less than 310 degrees can be prepared. FIG8 and FIG9 are reflection spectra of Example 1 in an amorphous state less than 310 degrees and a crystalline state not less than 310 degrees, and FIG10 and FIG11 are chromaticity coordinate diagrams of the amorphous state and the crystalline state of Example 1 at a vertical incident angle. It can be seen from the figure that after the phase change, the maximum reflectivity of the reflectance spectrum dropped from 74% to 56%, and the reflectivity at 300nm increased from 10% to 30%, which is a significant change. The movement of the chromaticity coordinate point is large, from (0.37, 0.5) to (0.38, 0.45), showing good color change characteristics.

Table 1

Example 2

Example 2: The same materials as Example 1 are maintained, and different colors are presented before and after the phase change by changing the thickness of the high refractive index medium layer H and the low refractive index medium layer L. The structural color device is composed of a substrate Sub, a high refractive index medium layer H (TiO ₂ ) on the substrate, a phase change layer P (GSST), a low refractive index medium layer L (MgF ₂ ), a phase change layer P (GSST), and a high refractive index medium layer H (TiO ₂ ). The substrate is a K9 glass deposition film 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 2. According to the thickness values given in Table 2, a device can be prepared that is observed as orange at less than 310 degrees, and is observed as gray-purple after high-temperature annealing at a temperature not less than 310 degrees and changes to a crystalline state. Figures 12 and 13 are reflection spectra of Example 2 in the amorphous state less than 310 degrees and the crystalline state not less than 310 degrees, and Figures 14 and 15 are chromaticity coordinates of the amorphous state and the crystalline state at a vertical incident angle of Example 2. It can be seen from the figure that after the phase change, the position of the maximum reflectivity of the reflection spectrum in the visible light range is transferred from 735nm to 400nm, and the chromaticity coordinates are also moved from (0.33, 0.51) to (0.24, 0.4). The movement of the point is large, showing good color change characteristics.

Table 2

Example 3

Example 3 uses completely different materials from the high and low refractive index dielectric layers of Example 1. The 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 (SiO ₂ ), a phase change layer P (GSST), and a high refractive index dielectric layer H (ZnS). The substrate is the same material as previously used. The specific thickness of each layer is given in Table 3. According to the thickness values given in Table 3, a yellow color can be prepared that is observed at less than 310 degrees, and brown after being annealed at high temperature and heated to not less than 310 degrees and then changed to a crystalline state. Figures 16 and 17 are reflection spectra of Example 3 in an amorphous state of less than 310 degrees and a crystalline state of not less than 310 degrees, and Figures 18 and 19 are chromaticity coordinate diagrams of the amorphous and crystalline states of Example 3 at vertical incidence angles. It can be seen from the figure that after the phase change, the position of the maximum reflectivity of the reflection spectrum in the visible light range is transferred from 600nm to 631nm, and the peak value of the reflectivity has also changed to a great extent.

Table 3

Example 4

Example 4 is composed of a substrate Sub, a high refractive index medium layer H (Ta ₂ O ₅ ) on the substrate, a phase change layer P (GSST), a low refractive index medium layer L (SiO ₂ ), a phase change layer P (GSST), and a high refractive index medium layer H (Ta ₂ O ₅ ). The substrate is the same material as previously used. The specific thickness of each layer is given in Table 4. According to the thickness values given in Table 4, a material can be prepared that is pink when observed at less than 310 degrees, and blue-purple when observed after high-temperature annealing and heating to not less than 310 degrees and changing to a crystalline state. Figures 20 and 21 are reflection spectra of Example 4 in an amorphous state of less than 310 degrees and a crystalline state of not less than 310 degrees. Figures 22 and 23 are chromaticity coordinate diagrams of the amorphous state and the crystalline state of Example 4 at a vertical incident angle. The color change can be clearly seen from the chromaticity coordinate diagram, and the coordinate moves from (0.31, 0.45) to (0.18, 0.26).

Table 4

Example 5

The materials of Example 5 are the same as those of Example 1, and only the thickness of each layer is adjusted to a certain extent. It is composed of a substrate Sub, a high refractive index medium layer H (TiO ₂ ) on the substrate, a phase change layer P (GSST), a low refractive index medium layer L (MgF ₂ ), a phase change layer P1 (GSST), and a high refractive index medium layer H1 (TiO ₂ ), and the substrate is the same as the material used before. The specific thickness of each layer is given in Table 5. According to the thickness values given in Table 5, a material can be prepared that is observed as purple at a temperature less than 310 degrees, and is observed as blue after being annealed at high temperature and heated to not less than 310 degrees and then changed to a crystalline state. Figures 24 and 25 are reflection spectra of Example 5 in an amorphous state less than 310 degrees and a crystalline state not less than 310 degrees, and Figures 26 and 27 are chromaticity coordinate diagrams of the amorphous and crystalline states of Example 5 at vertical incidence angles.

Table 5

Example 6

The phase change layer P of Example 6 is made of GST material. It is composed of a substrate Sub, a high refractive index medium layer H (Ta ₂ O ₅ ) on the substrate, a phase change layer P (GST), a low refractive index medium layer L (SiO ₂ ), a phase change layer P (GST), and a high refractive index medium layer H (Ta ₂ O ₅ ). The substrate is the same material as previously used. The specific thickness of each layer is given in Table 6. According to the thickness values given in Table 6, a material can be prepared that is orange when observed at less than 220 degrees, orange-yellow after being heated to not less than 220 degrees and less than 400 degrees, and brown when observed after being annealed at a high temperature of not less than 400 degrees and changing to a crystalline state. Figures 28, 29 and 30 are reflection spectra of Example 6 in an amorphous state less than 220 degrees, a metastable state not less than 220 degrees and less than 400 degrees, and a crystalline state not less than 400 degrees. Figures 31, 32 and 33 are chromaticity coordinate diagrams of Example 6 in amorphous, metastable and crystalline states at vertical incident angles.

Table 6

Example 7

The phase change layer P of Example 7 uses a combination of GST and GSST. It consists of a substrate Sub, a high refractive index medium layer H (Ta ₂ O ₅ ) on the substrate, a phase change layer P (GSST), a high refractive index medium layer H (Ta ₂ O ₅ ), a phase change layer P (GST), a low refractive index medium layer L (SiO ₂ ), a phase change layer P (GST), a high refractive index medium layer H (Ta ₂ O ₅ ), a phase change layer P (GSST) and a high refractive index medium layer H (Ta ₂ O ₅ ), and the substrate is the same as the material used before. The specific thickness of each layer is given in Table 7. According to the thickness values given in Table 7, a yellow-green color can be prepared when observed at less than 220 degrees, emerald green after high-temperature annealing to 220-310 degrees, brown after high-temperature annealing to 310-400 degrees, and brown after high-temperature annealing to 400 degrees Celsius and changing to a crystalline state. Figures 34, 35, 36 and 37 are reflection spectra of Example 7 after high-temperature annealing at less than 220, 220-310, 310-400 and not less than 400 degrees. Figures 38, 39, 40 and 41 are chromaticity coordinate diagrams of Example 7 at vertical incident angles after high-temperature annealing at less than 220, 220-310, 310-400 and not less than 400 degrees.

Table 7

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

Claims (10)

1. The photonic crystal structure color film based on the phase change material is characterized in that the structure of the film is as follows: (HP) ^s L(PH) ^s The structure of the film is a symmetrical structure taking L as a center, wherein H represents a high-refractive-index dielectric layer, P represents a phase-change layer, L represents a low-refractive-index dielectric layer, each group (HP) or (PH) forms an equivalent high-refractive-index unit, each group of equivalent high-refractive-index units is formed by stacking the high-refractive-index dielectric layer H and the phase-change layer P, s represents the repeated stacking times of the equivalent high-refractive-index units, and s is a positive integer.

2. The photonic crystal structural color film based on phase change material according to claim 1, wherein the high refractive index dielectric layer H is a material film layer with a refractive index of 1.55 or more in the range of 400nm to 780nm, and lanthanum titanate, amorphous silicon, indium tin oxide, titanium dioxide, tantalum pentoxide, hafnium dioxide, zirconium dioxide, zinc sulfide or silicon monoxide is used; the thickness range of the high refractive index dielectric layer H is 20-500nm.

3. The photonic crystal structural color film based on phase change material according to claim 1, wherein the phase change layer P is made of 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 nm to 30nm.

4. The photonic crystal structural color film based on phase change material as claimed in claim 1, wherein the low refractive index dielectric layer L is a material film layer with refractive index less than 1.55 in the range of 400nm to 780nm, and silicon dioxide, magnesium fluoride, cerium fluoride, lanthanum fluoride, sodium aluminum fluoride, neodymium fluoride, banknote fluoride, barium fluoride, calcium fluoride or lithium fluoride is adopted; the thickness of the low refractive index medium layer L ranges from 20nm to 600nm.

5. A photonic crystal structured color film based on phase change material according to claim 1, wherein the number s of repeated stacks of equivalent high refractive index units is in the range of 1 to 5; when the number of s is 2 to 5, (HP) ^s The s layers of high refractive index medium layers H are made of the same material or at least two layers of the same material or different materials, (HP) ^s The s phase-change layers P in the (a) are made of the same material or at least two layers of the same material or different materials.

6. The preparation method of the photonic crystal structure color film based on the phase change material is characterized by comprising the following steps of:

step 1, designing a photonic crystal structure color film based on a phase change material according to the requirement of a user, wherein the structure of the film is as follows: (HP) ^s L(PH) ^s The structure of the film is a symmetrical structure taking L as a center, wherein H represents a high-refractive-index medium layer, P represents a phase-change layer, L represents a low-refractive-index medium layer, each group (HP) or (PH) forms an equivalent high-refractive-index unit, each group of equivalent high-refractive-index units is formed by stacking the high-refractive-index medium layer H and the phase-change layer P, s represents the repeated stacking times of the equivalent high-refractive-index units, and s is a positive integer;

step 2, adjusting the thickness and the materials of each layer in the structure of the film, so that the film shows different color changes in different temperature ranges;

step 3, determining structural parameters required for preparing the film according to a design result;

step 4, taking the surface-flattened object as a substrate, and placing the substrate in a cavity of film forming equipment; when the film does not need to be subjected to demolding treatment, executing the step 5; when the film needs to be subjected to demolding treatment, executing the step 6;

step 5, growing a first layer and a second layer … … of the film on the substrate according to the structural parameters until reaching the last layer, wherein the high-refractive-index dielectric layers H and the phase-change layers P are sequentially and alternately stacked according to the number of s between the first layer and the second layer, the middle-most layer is a low-refractive-index dielectric layer L, and the middle-most layer and the last layer are symmetrically grown by taking L as a center; completing the preparation of the film;

Step 6, growing a layer of release agent on the substrate; growing a first layer, a second layer … … of the film on a release agent according to the structural parameter until a final layer; the high refractive index medium layers H and the phase change layers P are sequentially and alternately stacked according to the number of s between the first layer and the second layer, the middle-most layer is a low refractive index medium layer L, and the middle-most layer and the last layer symmetrically grow by taking L as a center; and dissolving the release agent by using a solvent corresponding to the release agent, so that the film is separated from the release agent, and the film is obtained independently, thereby completing the preparation of the film.

7. The method for preparing a photonic crystal structure color film based on phase change materials as claimed in claim 6, wherein the step 2 specifically comprises:

step 21, designing the thickness and the material of each layer in the structure of the film;

step 22, according to (HP) ^s The materials adopted by the s-layer phase-change layers P in the step (2) determine different temperature thresholds, if the s-layer phase-change layers P are GSST materials, the temperature threshold is determined to be T1, and the step (23) is carried out; if the s layers of phase change layers P are all GST materials, determining that the temperature threshold values are T2 and T3, and entering a step 24; if the phase change layer P of the s layers has GSST material and GST material at the same time, determining that the temperature threshold values are T2, T1 and T3, and entering a step 25;

Step 23, recording a first color represented by the film in a temperature range smaller than T1, then carrying out phase change treatment on the film so that the temperature of the film is increased to a temperature range not smaller than T1, recording a second color represented by the film at the moment again, comparing color changes before and after phase change, and if the color difference changes are large, indicating that the thickness and the material of each layer in the designed film structure are reasonable; if the color difference change is small, step 21 is carried out to readjust the thickness and the material of each layer in the structure of the film;

step 24, recording a first color represented by the film in a temperature range smaller than T2, then carrying out phase change treatment on the film so that the temperature of the film is increased to a temperature range not smaller than T2 and smaller than T3, recording a second color represented by the film again, then carrying out phase change treatment on the film so that the temperature of the film is increased to a temperature range not smaller than T3, recording a third color represented by the film again, comparing the color change in the phase change process, and if the color difference change is large, indicating that the thickness and the material of each layer in the designed film structure are reasonable; if the color difference change is small, step 21 is carried out to readjust the thickness and the material of each layer in the structure of the film;

Step 25, recording a first color represented by the film in a temperature range smaller than T2, then performing phase change treatment on the film to enable the temperature of the film to rise to a temperature range not smaller than T2 and smaller than T1, recording a second color represented by the film at the moment again, then performing phase change treatment on the film to enable the temperature of the film to rise to a temperature range not smaller than T1 and smaller than T3, recording a third color represented by the film at the moment again, and then performing phase change treatment on the film to enable the temperature of the film to rise to a temperature range not smaller than T3, and recording a fourth color represented by the film at the moment again; comparing the color change in the phase change process, if the color difference change is large, indicating that the thickness and the material of each layer in the designed film structure are reasonable; if the color difference variation is small, step 21 is entered to readjust the thickness and material of each layer in the structure of the film.

8. The method for preparing a photonic crystal structure color film based on a phase change material according to claim 6, wherein the phase change process of the phase change layer P is performed by a high temperature annealing process, electric heating or laser pulse phase change.

9. The method for preparing a photonic crystal structural color film based on phase change materials according to claim 6, wherein the structural parameters include total number of layers, materials adopted by each layer, thickness of each layer and distribution among layers; the temperature threshold T1 is 310 degrees, the temperature threshold T2 is 220 degrees, and the temperature threshold T3 is 400 degrees.

10. The method for preparing a photonic crystal structural color film based on phase change material according to claim 6, wherein the substrate is made of polished glass, polished stainless steel, polished mirror aluminum, polyethylene terephthalate, cellulose triacetate, polymethyl methacrylate, polycarbonate/polymethyl methacrylate composite, polyimide, polypropylene, polyvinyl chloride, polyvinyl butyral, ethylene vinyl acetate copolymer, polyurethane elastomer, polytetrafluoroethylene, fluoroethyl propylene or polydifluoroethylene; the release agent is made of fluoride, chloride or organic material which is easy to dissolve in water.

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