Photonic crystal fluorescent film, preparation method and application thereof

Abstract

This invention relates to the field of optical materials technology, and more particularly to a photonic crystal fluorescent thin film, its preparation method, and its applications. The photonic crystal fluorescent thin film comprises: a substrate layer; a photonic crystal layer disposed on the surface of the substrate layer; and a quantum dot emitting layer disposed on the surface of the photonic crystal layer. The photonic crystal layer has an opal structure with three-dimensionally ordered nanospheres, and the gaps between the nanospheres are filled with a polymer matrix. Preferably, the absolute value of the difference between the central emission wavelength of the fluorescent quantum dots and the central reflection wavelength of the photonic crystal layer is ≤20 nm, and the maximum peak reflectance of the photonic crystal layer is ≥50%. By using a specific photonic crystal layer to enhance the fluorescence of the quantum dot emitting layer, and simultaneously utilizing two independent coating-curing processes to achieve integrated structural molding, a fluorescent thin film with high luminous intensity and good uniformity is obtained.

Description

Technical Field

[0001] This invention relates to the field of optical materials technology, and in particular to a photonic crystal fluorescent thin film, its preparation method, and its application. Background Technology

[0002] With the rapid development of optoelectronic functional materials, fluorescent thin films have become an important research direction in advanced optical materials due to their broad application prospects in solid-state lighting, flat panel displays, high-security anti-counterfeiting labels, and photovoltaic energy conversion. Among numerous fluorescent material systems, quantum dot-based fluorescent materials have gradually become a research and industrialization hotspot due to their unique physical properties, including continuously tunable emission wavelength with size, high intrinsic luminous efficiency, excellent color purity, and relatively good chemical stability. However, when applying quantum dot materials in thin film form to high-performance optical devices, a series of common technical bottlenecks are still faced, such as the decrease in luminous efficiency caused by solid-state aggregation-induced quenching, insufficient light extraction efficiency caused by total internal reflection at the thin film-air interface, and the difficulty in ensuring luminous uniformity when forming large-area films. These defects seriously restrict their practical application in scenarios requiring high brightness and high uniformity.

[0003] On the other hand, photonic crystals, as artificial microstructure materials with periodic dielectric constant distributions, can form photonic band gaps within specific wavelength ranges, thereby effectively controlling the propagation behavior of photons. In particular, three-dimensional ordered structures constructed from monodisperse nanospheres through self-assembly, namely opal-structured photonic crystals, have been extensively studied in fields such as structural color materials, optical filters, and sensing due to their relatively simple preparation process, easily controllable periodic structure, and significant structural color effect. For example, Chinese invention patent CN111363393B discloses a method for permanently fixing the crystallized and ordered arrangement of nanospheres by adding oligomers and monomers to a nanosphere emulsion to fill the gaps between the nanospheres and introducing a photoinitiation system to crosslink and solidify the oligomers and monomers. This technical solution has successfully achieved the industrial-scale preparation of large-area opal-structured photonic crystal films with high mechanical strength, tunable central reflection wavelength, and high peak reflectivity.

[0004] Although the aforementioned industrialized photonic crystal thin films have made significant progress in optical performance, in the current technology, these films are mainly used in visual aesthetic fields such as appearance decoration and structural color printing. There are no reports of industrialized technologies that combine them with quantum dot fluorescent light-emitting layers and utilize the photonic bandgap effect of photonic crystals to achieve enhanced fluorescence emission.

[0005] In recent years, a few basic studies have attempted to couple fluorescent materials with photonic crystal structures. However, existing photonic crystal-quantum dot composite structures generally suffer from the following shortcomings: Firstly, while pursuing high luminescence intensity, the spatial uniformity of luminescence is often significantly degraded due to inhomogeneities in the photonic crystal structure or defects at the composite interface. Secondly, most fabrication schemes rely on complex multilayer assembly, high-temperature thermal treatment, or precision etching processes, which are lengthy, costly, and unsuitable for large-scale applications. It is particularly noteworthy that existing research on the spectral coupling relationship between the photonic crystal functional layer and the quantum dot luminescent layer has largely remained at the qualitative verification level, lacking a systematic quantitative investigation of key structural parameters affecting fluorescence enhancement. This makes it difficult to establish clear control criteria to guide optimized design for practical fluorescence enhancement needs.

[0006] In summary, there is an urgent need to develop a simple photonic crystal-enhanced fluorescent thin film to overcome the technical problems of existing composite structures, such as the difficulty in achieving both luminescence intensity and uniformity, complex preparation processes, and difficulty in mass production. Summary of the Invention

[0007] To address the limitations of existing quantum dot fluorescent films, such as limited luminescence efficiency, low light extraction efficiency, and insufficient luminescence uniformity, this invention innovatively provides a photonic crystal fluorescent film, comprising a substrate layer, a photonic crystal layer disposed on the surface of the substrate layer, and a quantum dot luminescent layer disposed on the surface of the photonic crystal layer. The photonic crystal layer is an opal structure with three-dimensionally ordered nanospheres, with a polymer matrix filling the gaps between the nanospheres to fix the ordered structure. The quantum dot luminescent layer contains fluorescent quantum dots dispersed in the polymer matrix. The absolute value of the difference between the central emission wavelength of the fluorescent quantum dots and the central reflection wavelength of the photonic crystal layer is ≤20 nm, and the maximum peak reflectivity of the photonic crystal layer is ≥50%. This invention enhances the fluorescence of the quantum dot luminescent layer through a specific photonic crystal layer and achieves integrated structural molding using two independent coating-curing processes, thereby obtaining a fluorescent film with high luminescence intensity and good uniformity.

[0008] The first aspect of the present invention provides a photonic crystal fluorescent thin film, the photonic crystal fluorescent thin film comprising: basal layer; A photonic crystal layer disposed on the surface of the substrate layer; and A quantum dot light-emitting layer disposed on the surface of the photonic crystal layer; The photonic crystal layer is an opal structure with three-dimensionally ordered nanospheres, and the gaps between the nanospheres are filled with a polymer matrix.

[0009] Optionally, the quantum dot luminescent layer comprises fluorescent quantum dots dispersed in polymer matrix II; Optionally, the absolute value of the difference between the central emission wavelength of the fluorescent quantum dot and the central reflection wavelength of the photonic crystal layer is ≤20nm.

[0010] Optionally, the maximum peak reflectivity of the photonic crystal layer is ≥50%.

[0011] Optionally, the fluorescent quantum dots include at least one of perovskite quantum dots, group II-VI compound semiconductor quantum dots, group III-V compound semiconductor quantum dots, or carbon quantum dots.

[0012] Optionally, both polymer matrix one and polymer matrix two are selected from acrylate reactants by photoinitiated polymerization under the action of a photoinitiator.

[0013] Optionally, the raw materials for preparing the polymer matrix one include acrylate reactant one and photoinitiator one; the raw materials for preparing the polymer matrix two include acrylate reactant two and photoinitiator two. Further optionally, both photoinitiator one and photoinitiator two comprise ethyl 2,4,6-trimethylbenzoylphenylphosphonate.

[0014] Optionally, based on a thin film without a photonic crystal layer, the brightness multiple of the photonic crystal fluorescent thin film is greater than 1.

[0015] A second aspect of the present invention provides a method for preparing a photonic crystal fluorescent thin film as described above, wherein the preparation steps of the photonic crystal fluorescent thin film include: The nanospheres, acrylate reactant one, and photoinitiator one are mixed to prepare a photonic crystal coating solution; The photonic crystal coating liquid is applied to the surface of a substrate and dried to obtain a photonic crystal layer; another substrate layer is then laminated onto the surface of the photonic crystal layer to obtain a composite film. The composite film is subjected to a regularization treatment to obtain a composite film with microsphere crystallization; The composite film with crystallized microspheres is subjected to photocuring to obtain a photonic crystal film; another base layer on the surface of the photonic crystal layer is peeled off. The fluorescent quantum dots, acrylate reactant II, and photoinitiator II are mixed to prepare a quantum dot coating solution; The quantum dot coating liquid is coated onto the surface of the photonic crystal layer, and after photocuring, a quantum dot luminescent layer is formed, resulting in a photonic crystal fluorescent film.

[0016] Optionally, the thickness of the photonic crystal thin film is 10 μm or more.

[0017] A third aspect of the present invention provides an application of the photonic crystal fluorescent film as described above, wherein the photonic crystal fluorescent film is applied to optical products requiring at least one of the following functions: high brightness display, backlight optical enhancement, fluorescent anti-counterfeiting identification, optical information encryption, optical signal amplification, and dual-response decoration of structural color and fluorescence.

[0018] Beneficial effects: This invention provides a photonic crystal fluorescent thin film, its preparation method, and its application, which have the following advantages: (1) This invention combines a quantum dot luminescent layer with the surface of an opal structure photonic crystal layer, and controls the absolute value of the difference between the center emission wavelength of the quantum dot and the center reflection wavelength of the photonic crystal layer to be ≤20nm and the maximum peak reflectivity of the photonic crystal layer to be ≥50%, so that the photonic bandgap of the photonic crystal and the fluorescence emission band of the quantum dot can effectively overlap, thereby achieving effective enhancement of the fluorescence emission of the quantum dot. (2) The present invention further discovers that the fluorescence enhancement factor of the photonic crystal fluorescent film is positively correlated with the maximum peak reflectance of the photonic crystal layer; when the maximum peak reflectance is ≥70%, the fluorescence enhancement brightness factor can reach more than 1.6 times, showing excellent optical enhancement effect.

[0019] (3) In this invention, the photonic crystal layer and the quantum dot light-emitting layer are formed by independent coating-photocuring process in situ curing, without the need for complex multi-step assembly or high-temperature treatment. The process is simple, has good repeatability, is suitable for roll-to-roll continuous production, and is conducive to large-scale industrial application. (4) The photonic crystal fluorescent film provided by the present invention has both the structural color characteristics of photonic crystals and the fluorescence emission characteristics of quantum dots. It exhibits a structural color appearance under natural light and fluorescence emission under excitation light, and has dual optical response functions, which can meet various application needs such as high brightness display, fluorescent anti-counterfeiting, and optical encoding. Attached Figure Description

[0020] Figure 1 Comparison of the thin films prepared in Example 1 and Comparative Example 1 under excitation light; Figure 1 The left side of the image shows Comparative Example 1, and the right side shows Example 1. Figure 2 Example 1: Reflection spectrum of a photonic crystal thin film; Figure 3 Example 1: Fluorescence emission spectrum of quantum dot emitting layer. Detailed Implementation

[0021] The first aspect of the present invention provides a photonic crystal fluorescent thin film, the photonic crystal fluorescent thin film comprising: basal layer; A photonic crystal layer disposed on the surface of the substrate layer; and A quantum dot light-emitting layer disposed on the surface of the photonic crystal layer.

[0022] Optionally, the photonic crystal layer is an opal structure with three-dimensionally ordered nanospheres, and the gaps between the nanospheres are filled with a polymer matrix to fix the ordered structure.

[0023] Optionally, the average particle size of the nanospheres is 100-400nm, and can be listed as 100nm, 200nm, 210nm, 220nm, 230nm, 240nm, 250nm, 260nm, 270nm, 280nm, 290nm, 300nm, 400nm, etc.

[0024] Optionally, the polydispersity index (PDI) of the nanospheres is less than 0.15, and can be listed as 0.1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.05, etc.

[0025] Optionally, the nanospheres are selected from one or more combinations of organic polymer microspheres, inorganic microspheres, and organic polymer-inorganic composite microspheres.

[0026] Optionally, the organic polymer microspheres include one or more combinations of polystyrene (PS) microspheres, polybutyl acrylate (PBA) microspheres, polymethyl methacrylate (PMMA) microspheres, polylactic acid (PLA) microspheres, polyethylene (PE) microspheres, polypropylene (PP) microspheres, polycarbonate (PC) microspheres, polyurethane (PU) microspheres, polypyrrole microspheres, and polyaniline microspheres.

[0027] Optionally, the inorganic microspheres include one or more of the following: silicon dioxide, titanium dioxide, iron tetroxide, ferric oxide, zinc sulfide, zinc oxide, aluminum oxide, and calcium carbonate.

[0028] Optionally, the inorganic microspheres include at least one of silicon dioxide, titanium dioxide, iron tetroxide, and zinc sulfide.

[0029] Further optionally, the organic polymer microspheres include polystyrene-polymethyl methacrylate (PS-PBA) composite microspheres with a core-shell structure.

[0030] Optionally, the quantum dot luminescent layer comprises fluorescent quantum dots dispersed in a polymer matrix.

[0031] Optionally, the absolute value of the difference between the central emission wavelength of the fluorescent quantum dot and the central reflection wavelength of the photonic crystal layer is ≤20nm; more preferably, it is ≤10nm.

[0032] Optionally, the maximum peak reflectivity of the photonic crystal layer is ≥50%; more preferably, it is ≥60%.

[0033] For photonic crystals that serve as the core functional layer, the relative position of the central reflection wavelength and the quantum dot emission peak, as well as the magnitude of the maximum peak reflectivity, are key parameters that determine the fluorescence enhancement effect. However, most existing research on optical materials remains at the level of qualitative verification, lacking a systematic and quantitative investigation of the critical influence of the above two parameters, making it difficult to guide the optimized design for actual fluorescence enhancement needs.

[0034] To address the limitations of existing quantum dot fluorescent films, such as limited luminescence efficiency, low light extraction efficiency, and insufficient luminescence uniformity, this invention provides a photonic crystal fluorescent film, comprising a substrate layer, a photonic crystal layer disposed on the surface of the substrate layer, and a quantum dot luminescent layer disposed on the surface of the photonic crystal layer. The photonic crystal layer has an opal structure with three-dimensionally ordered nanospheres, and the gaps between the nanospheres are filled with a polymer matrix to fix the ordered structure. The quantum dot luminescent layer contains fluorescent quantum dots dispersed in the polymer matrix. Based on this structure, this invention can utilize the photonic bandgap effect of the photonic crystal to regulate and enhance the fluorescence emission of the quantum dots. Simultaneously, it achieves integrated molding of the structure through two independent coating-curing processes, resulting in a fluorescent film with high luminescence intensity and good uniformity. The reason for this is presumably that the photonic crystal layer has a periodic dielectric constant distribution. By controlling the high degree of matching between its central reflection wavelength and the central emission wavelength of the fluorescent quantum dots, the photonic bandgap of the photonic crystal and the fluorescence emission band of the quantum dots achieve efficient spectral overlap. In this specific coupling state, fluorescent photons radiated from the quantum dot emitting layer towards the photonic crystal layer are effectively modulated and reflected and redirected by the highly selective photonic bandgap of the photonic crystal, significantly increasing the fluorescence emission probability propagating along the film normal. Simultaneously, this structure can suppress and redirect large-angle fluorescence deviating from the normal direction through total internal reflection, effectively reducing total internal reflection losses within the film and thus significantly improving the overall light extraction efficiency. Furthermore, the polymer matrix filling the gaps between the nanospheres permanently fixes the three-dimensional ordered opal structure, ensuring the long-term stability and spatial uniformity of the entire film's photonic bandgap, thereby guaranteeing high uniformity and reproducibility of the fluorescence enhancement effect in the manufacturing process.

[0035] The "central emission wavelength" involved in this invention refers to the wavelength corresponding to the position of the maximum fluorescence peak in the fluorescence emission spectrum of the quantum dot luminescent layer; the fluorescence emission spectrum is measured by a fluorescence spectrophotometer in accordance with GB / T 36081-2018 "Nanotechnology Cadmium Selenide Quantum Dot Nanocrystal Characterization Fluorescence Emission Spectroscopy".

[0036] The "central reflection wavelength" involved in this invention refers to the wavelength corresponding to the position of the maximum reflection peak in the reflection spectrum of the photonic crystal layer; it can be controlled by the ratio of nanospheres and acrylate reactants. The reflection spectrum is measured according to the method in T / CITS 301-2025 "Photonic Crystal Thin Films Based on Opal Structure".

[0037] The "maximum peak reflectance" involved in this invention refers to the reflectance value corresponding to the position of the maximum reflection peak in the reflection spectrum of the photonic crystal layer; it can be controlled by the thickness of the photonic crystal thin film. The reflectance is measured according to the method in T / CITS 301-2025 "Photonic Crystal Thin Films Based on Opal Structure".

[0038] Optionally, the fluorescent quantum dots include at least one of perovskite quantum dots, group II-VI compound semiconductor quantum dots, group III-V compound semiconductor quantum dots, or carbon quantum dots.

[0039] Examples of group II-VI compound semiconductor quantum dots include CdSe, CdTe, CdS, ZnS, ZnO, and their core-shell structure quantum dots such as CdSe / ZnS, CdSe / CdS, CdSe / CdS / ZnS, etc.

[0040] Examples of group III-V compound semiconductor quantum dots include InP, InAs, InSb, GaAs, GaP, and their core-shell structure quantum dots such as InP / ZnSe / ZnS, InP / ZnS, etc.

[0041] Examples of perovskite quantum dots include CsPbX3 (X = Cl, Br, I), MAPbX3, FAPbX3, and mixed halogen or mixed cation perovskite quantum dots such as CsPbBr. 1.5 I 1.5 Cs 0.25 FA 0.75 PbI3; Examples of carbon quantum dots (generally defined carbon-based luminescent nanomaterials) include carbon quantum dots (CQDs), graphene quantum dots (GQDs), and carbonized polymer dots (CPDs).

[0042] Optionally, both polymer matrix one and polymer matrix two are formed by photoinitiated polymerization of acrylate reactants under the action of a photoinitiator.

[0043] In some embodiments, the acrylate reactants may include one or a mixture of several of acrylate monomers, methacrylate monomers, or oligomers thereof.

[0044] The acrylate reactants include, but are not limited to, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, neopentyl methacrylate, tert-pentyl methacrylate, n-hexyl methacrylate, 2-ethylbutyl methacrylate, cyclohexyl methacrylate, n-heptyl methacrylate, n-octyl methacrylate, and methacrylate. 2-Ethylhexyl acrylate, Nonyl methacrylate, Decyl methacrylate, Dodecyl methacrylate, Tridecyl methacrylate, Tetradecyl methacrylate, Hexadecyl methacrylate, Octadecyl methacrylate, Docosyl methacrylate, Norborneol acrylate, Norborneol methyl methacrylate, Isoborneol acrylate, Borneol acrylate, Menthyl methacrylate, Octahydroindene methacrylate, Adamantyl methacrylate, Dimethyl methacrylate Arandyl ester, phenyl methacrylate, 2-ethylphenyl methacrylate, indole methacrylate, toluene methacrylate and benzyl methacrylate, acryloylmorpholine, N-hydroxyethylacrylamide, dimethacrylamide, diethylacrylamide, isopropylacrylamide, N-vinylcaprolactam, ethoxyphenol acrylate, benzyl acrylate, tetrahydrofurfuryl acrylate, cyclotrimethylolpropane formal acrylate, 4-tert-butylcyclohexyl acrylate, ethoxyethoxyethyl acrylate, diethoxyphenol acrylate, 1,6-hexanediol dipropylene glycol Acrylates, dipropylene glycol diacrylate, dipropylene glycol diacrylate, diethylene glycol diacrylate, dipropoxyneopentyl glycol diacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, triethoxytrimethylolpropane triacrylate, hexaethoxytrimethylolpropane triacrylate, nonethoxytrimethylolpropane triacrylate, pentadecylethoxytrimethylolpropane triacrylate, tripropoxytrimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, or oligomers thereof.

[0045] Optionally, the photoinitiator is preferably a free radical photoinitiator, which generates free radicals after absorbing light energy, initiating free radical polymerization of the photocurable reactants. Examples of free radical photoinitiators include one or more combinations of benzoin and its derivatives, benzoyl and its derivatives, acetophenone and its derivatives, α-hydroxy ketone derivatives, α-amino ketone derivatives, benzoylcarbamates, acylphosphine oxides, benzophenone and its derivatives, thioxanthone and its derivatives, and anthraquinone and its derivatives.

[0046] Optionally, the free radical photoinitiator includes acyl phosphorus oxides, such as ethyl 2,4,6-trimethylbenzoylphenylphosphonate, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and 2,4,6-trimethylbenzoyl-di(p-tolyl)phosphine oxide. In some embodiments, the raw materials for preparing the polymer matrix one include acrylate reactant one and photoinitiator one; the raw materials for preparing the polymer matrix two include acrylate reactant two and photoinitiator two.

[0047] Optionally, the acrylate reactant includes 1,6-hexanediol diacrylate (HDDA).

[0048] Optionally, the acrylate reactant II includes isobornyl acrylate (IBOA).

[0049] Optionally, both photoinitiator one and photoinitiator two include ethyl 2,4,6-trimethylbenzoylphenylphosphonate (TPO-L).

[0050] Optionally, the mass ratio of the nanospheres, acrylate reactant one, and photoinitiator one is (40-60):(15-35):1; most preferably, it is 50:25:1.

[0051] In some embodiments, the fluorescent quantum dots are provided by a quantum dot dispersion. Optionally, the content of fluorescent quantum dots in the quantum dot dispersion is 5-15%; more preferably, it is 10%.

[0052] Optionally, the mass ratio of the quantum dot dispersion, acrylate reactant II, and photoinitiator II is (1-5):(10-30):1; most preferably, it is 2:17:1.

[0053] Optionally, the material of the substrate layer is selected from one or more combinations of polyethylene terephthalate (PET), polyethylene terephthalate-1,4-cyclohexanediol (PETG), polymethacrylate, polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polynaphthalene dicarboxylate, polycarbonate, polyurethane, acrylonitrile-butadiene-styrene copolymer, polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), ethylene-vinyl acetate copolymer, and polyolefins.

[0054] Examples of polyurethane include thermoplastic polyurethane elastomers.

[0055] Examples of polyolefins include polyethylene (PE) and polypropylene (PP).

[0056] Optionally, the thickness of the substrate layer is 50-500 μm; examples include 50 μm, 80 μm, 100 μm, 120 μm, 150 μm, 200 μm, 300 μm, 400 μm, 500 μm, etc.

[0057] Optionally, based on a thin film without a photonic crystal layer, the brightness multiple of the photonic crystal fluorescent thin film is greater than 1; examples include 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, etc.; further, it can be greater than 1.5.

[0058] A second aspect of the present invention provides a method for preparing a photonic crystal fluorescent thin film, wherein the preparation steps of the photonic crystal fluorescent thin film include: S1. Mix the nanospheres, acrylate reactant one, and photoinitiator one to prepare a photonic crystal coating solution; S2. The photonic crystal coating liquid is coated on the surface of the substrate layer and dried to obtain a photonic crystal layer; another substrate layer is laminated on the surface of the photonic crystal layer to obtain a composite film; S3. The composite film is subjected to a regularization treatment to obtain a composite film with microsphere crystallization. S4. Perform photocuring treatment on the composite film with crystallized microspheres to obtain a photonic crystal film; peel off another base layer from the surface of the photonic crystal layer; S5. Mix the fluorescent quantum dots, acrylate reactant II, and photoinitiator II to prepare a quantum dot coating solution; S6. The quantum dot coating liquid is coated on the surface of the photonic crystal layer, and after photocuring, a quantum dot luminescent layer is formed to obtain a photonic crystal fluorescent film.

[0059] In some embodiments, the central reflection wavelength and maximum peak reflectivity of the photonic crystal layer involved in this invention refer to the central reflection wavelength and maximum peak reflectivity of the photonic crystal film obtained after regularization and photocuring of the photonic crystal layer.

[0060] In this invention, the photonic crystal layer and the quantum dot luminescent layer are formed through independent coating-curing processes. Specifically, polymer matrix one is generated in situ from a coating solution containing nanospheres and a first acrylate reactant through coating, self-assembly, and photocuring, filling the gaps between the nanospheres to permanently fix their three-dimensional ordered arrangement. Polymer matrix two is generated in situ from a coating solution containing quantum dots and a second acrylate reactant through coating and photocuring, dispersing and fixing the quantum dots on the surface of the photonic crystal layer. The polymer matrices of the two functional layers are each independently formed from the acrylate reactants in their respective coating solutions through photocuring; their compositions may be the same or different.

[0061] In this invention, polymer matrix one is prepared simultaneously during the preparation of the photonic crystal layer, and polymer matrix two is prepared simultaneously during the preparation of the quantum dot luminescent layer.

[0062] Optionally, the thickness of the photonic crystal film is 10 μm or more; more preferably, it is 10-20 μm.

[0063] Optionally, the cumulative light energy of the photocuring process in step S4 is 800-1500 mJ / cm². 2 It can be listed as 800mJ / cm 2 1000mJ / cm 2 1200mJ / cm 2 1500mJ / cm 2 wait.

[0064] Optionally, the cumulative light energy of the photocuring process in step S6 is 1200-3000 mJ / cm². 2 It can be listed as 1200mJ / cm 2 1500mJ / cm 2 2000mJ / cm 2 2500mJ / cm 2 3000mJ / cm 2 wait.

[0065] The present invention does not impose any particular limitation on the device for photocuring, as long as it can achieve the purpose of photocuring; for example, using an LED light source.

[0066] The third aspect of the present invention provides an application of a photonic crystal fluorescent film, wherein the photonic crystal fluorescent film is applied to an optical product that requires at least one of the following functions: high brightness display, backlight optical enhancement, fluorescent anti-counterfeiting identification, optical information encryption, optical signal amplification, and dual-response decoration of structural color and fluorescence.

[0067] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0068] The following are some of the raw material information used in the examples and comparative examples.

[0069] Table 1

[0070] Example 1 This embodiment provides a photonic crystal fluorescent thin film and its preparation method, wherein the photonic crystal fluorescent thin film comprises: Substrate layer (PET substrate with a thickness of 100μm); A photonic crystal layer disposed on the surface of the substrate layer; and A quantum dot light-emitting layer disposed on the surface of the photonic crystal layer.

[0071] The photonic crystal layer is an opal structure with three-dimensional ordered arrangement of nanospheres (F220), and the gaps between the nanospheres are filled with a polymer matrix to fix the ordered structure.

[0072] The quantum dot luminescent layer comprises fluorescent quantum dots 1 dispersed in polymer matrix II (provided by green quantum dot dispersion PL525).

[0073] Both polymer matrix one and polymer matrix two are formed by photoinitiated polymerization of acrylate reactants under the action of a photoinitiator.

[0074] The raw materials for preparing the polymer matrix include acrylate reactant one (HDDA) and photoinitiator one (TPO-L); wherein the mass ratio of F220, HDDA and photoinitiator one (TPO-L) is 50:25:1.

[0075] The raw materials for preparing the polymer matrix II include acrylate reactant II (IBOA) and photoinitiator II (TPO-L); wherein the mass ratio of PL525, IBOA and photoinitiator II (TPO-L) is 2:17:1.

[0076] The preparation steps of the photonic crystal fluorescent thin film include: S1. Mix the nanospheres, acrylate reactant one, and photoinitiator one evenly to prepare a photonic crystal coating solution; S2. The photonic crystal coating solution is coated onto the surface of the substrate layer and dried to obtain a photonic crystal layer (dry film thickness 20 μm); another substrate layer is laminated onto the surface of the photonic crystal layer to obtain a composite film; S3. The composite film is subjected to a regularization treatment (refer to step (b) of Chinese patent CN103534079B) to obtain a microsphere-crystallized composite film. S4. Using a 395nm LED light source, perform photocuring treatment on the microsphere-crystallized composite film (cumulative light energy 1000mJ / cm²). 2 A photonic crystal thin film (center reflection wavelength of 525 nm, maximum peak reflectivity of 70%) was obtained; another substrate layer on the surface of the photonic crystal layer was peeled off. S5. Mix the fluorescent quantum dots, acrylate reactant II, and photoinitiator II evenly to prepare a quantum dot coating solution; S6. The quantum dot coating solution is coated onto the surface of the photonic crystal layer (dry film thickness 20 μm), and photocured using a 395 nm LED light source (cumulative light energy 2000 mJ / cm²). 2 A quantum dot luminescent layer is formed to obtain a photonic crystal fluorescent thin film.

[0077] Example 2 This embodiment provides a photonic crystal fluorescent thin film and its preparation method, which is the same as in Embodiment 1; the difference is that the nanospheres F220 are replaced with nanospheres F230, and the green quantum dot dispersion PL525 is replaced with the yellow quantum dot dispersion PL575.

[0078] Example 3 This embodiment provides a photonic crystal fluorescent thin film and its preparation method, which is the same as in Embodiment 1; the difference is that the nanospheres F220 are replaced with nanospheres F250, and the green quantum dot dispersion PL525 is replaced with the red quantum dot dispersion PL625.

[0079] Example 4 This embodiment provides a photonic crystal fluorescent thin film and its preparation method, which is the same as in Embodiment 1; the difference is that the maximum peak reflectivity of the photonic crystal thin film is reduced from 70% to 60%; the adjustment method is to control the dry film thickness of the photonic crystal layer to 15μm.

[0080] Example 5 This embodiment provides a photonic crystal fluorescent thin film and its preparation method, which is the same as in Embodiment 1; the difference is that the maximum peak reflectivity of the photonic crystal thin film is reduced from 70% to 50%; the adjustment method is to control the dry film thickness of the photonic crystal layer to 10 μm.

[0081] Example 6 This embodiment provides a photonic crystal fluorescent thin film and its preparation method, which is the same as in Embodiment 1; the difference is that the central reflection wavelength of the photonic crystal thin film is adjusted from 525nm to 515nm; the adjustment method is to adjust the mass ratio of nanospheres to acrylate reactant to 5:2, while keeping the amount of nanospheres added unchanged during operation.

[0082] Example 7 This embodiment provides a photonic crystal fluorescent thin film and its preparation method, which is the same as in Embodiment 1; the difference is that the central reflection wavelength of the photonic crystal thin film is adjusted from 525nm to 535nm; the adjustment method is to adjust the mass ratio of nanospheres to acrylate reactant to 5:3, while keeping the amount of nanospheres added unchanged during operation.

[0083] Example 8 This embodiment provides a photonic crystal fluorescent thin film and its preparation method, which is the same as in Embodiment 1; the difference is that the central reflection wavelength of the photonic crystal thin film is adjusted from 525nm to 505nm; the adjustment method is to reduce the ratio of nanospheres to acrylate reactants from 2:1 to 10:3, while keeping the amount of nanospheres added unchanged during operation.

[0084] Example 9 This embodiment provides a photonic crystal fluorescent thin film and its preparation method, which is the same as in Embodiment 1; the difference is that the central reflection wavelength of the photonic crystal thin film is adjusted from 525nm to 545nm; the adjustment method is to adjust the mass ratio of nanospheres to acrylate reactant to 5:4, while keeping the amount of nanospheres added unchanged during operation.

[0085] Comparative Example 1 This comparative example provides a quantum dot thin film and its preparation method. The quantum dot thin film includes a substrate (a PET substrate with a thickness of 100 μm) and a quantum dot light-emitting layer disposed on the surface of the substrate.

[0086] The preparation steps of the thin film include: S1. Mix quantum dot dispersion PL525, acrylate reactant IBOA, and photoinitiator TPO-L in a mass ratio of 2:17:1 to prepare quantum dot coating solution. S2. The quantum dot coating solution is coated onto the surface of the substrate (dry film thickness 20 μm), and photocured using a 395 nm LED light source (cumulative light energy 2000 mJ / cm²). 2 A quantum dot light-emitting layer is formed to obtain a quantum dot thin film.

[0087] Comparative Example 2 This comparative example provides a photonic crystal fluorescent thin film and its preparation method, with the specific implementation method being the same as in Example 1; the difference is that the maximum peak reflectivity of the photonic crystal thin film is adjusted from 70% to 40%; the adjustment method is to control the dry film thickness of the photonic crystal layer to 8μm.

[0088] Comparative Example 3 This comparative example provides a photonic crystal fluorescent thin film and its preparation method, with the specific implementation method being the same as in Example 1; the difference is that the central reflection wavelength of the photonic crystal layer is adjusted from 525nm to 500nm, and the maximum peak reflectivity is reduced from 70% to 60%; the adjustment method is to adjust the mass ratio of nanospheres to acrylate reactant one to 5:1, while keeping the amount of nanospheres added unchanged during operation; at the same time, the dry film thickness of the photonic crystal layer is controlled to be 15μm.

[0089] Comparative Example 4 This comparative example provides a photonic crystal fluorescent thin film and its preparation method, with the specific implementation method being the same as in Example 1; the difference is that the central reflection wavelength of the photonic crystal layer is adjusted from 525nm to 500nm, and the maximum peak reflectivity is reduced from 70% to 50%; the adjustment method is to adjust the mass ratio of nanospheres to acrylate reactant one to 5:1, while keeping the amount of nanospheres added constant during operation; at the same time, the dry film thickness of the photonic crystal layer is controlled to be 10μm.

[0090] Comparative Example 5 This comparative example provides a photonic crystal fluorescent thin film and its preparation method, with the specific implementation method being the same as in Example 1; the difference is that the central reflection wavelength of the photonic crystal layer is adjusted from 525nm to 550nm, and the maximum peak reflectivity is reduced from 70% to 60%; the adjustment method is to adjust the mass ratio of nanospheres to acrylate reactant one to 1:1, while keeping the amount of nanospheres added constant during operation; at the same time, the dry film thickness of the photonic crystal layer is controlled to be 15μm.

[0091] Comparative Example 6 This comparative example provides a photonic crystal fluorescent thin film and its preparation method, with the specific implementation method being the same as in Example 1; the difference is that the central reflection wavelength of the photonic crystal layer is adjusted from 525nm to 550nm, and the maximum peak reflectivity is reduced from 70% to 50%; the adjustment method is to adjust the mass ratio of nanospheres to acrylate reactant one to 1:1, while keeping the amount of nanospheres added unchanged during operation; at the same time, the dry film thickness of the photonic crystal layer is controlled to be 10μm.

[0092] Comparative Example 7 This comparative example provides a photonic crystal fluorescent thin film and its preparation method, with the specific implementation method being the same as in Example 1; the difference is that the central reflection wavelength of the photonic crystal layer is adjusted from 525nm to 550nm, and the maximum peak reflectivity is reduced from 70% to 40%; the adjustment method is to adjust the mass ratio of nanospheres to acrylate reactant one to 1:1, while keeping the amount of nanospheres added unchanged during operation; at the same time, the dry film thickness of the photonic crystal layer is controlled to be 8μm.

[0093] Comparative Example 8 This comparative example provides a photonic crystal fluorescent thin film and its preparation method, which is the same as in Example 1; the difference is that the central reflection wavelength of the photonic crystal layer is increased from 525nm to 625nm; the adjustment method is to replace the nanospheres F220 with nanospheres F250.

[0094] Performance testing The photonic crystal fluorescent films obtained in Examples 1-9 and Comparative Examples 1-8 were tested as follows, and the test results are recorded in Table 2.

[0095] 1. Center emission wavelength and maximum peak reflectivity of the photonic crystal layer The reflection spectra of the photonic crystal films prepared in step S4 of each example and comparative example were measured according to the method in T / CITS 301—2025 "Photonic Crystal Thin Films Based on Opal Structure". The central emission wavelength and maximum peak reflectance data were determined based on the reflection spectra.

[0096] 2. The central emission wavelength of the quantum dot light-emitting layer Referring to GB / T 36081-2018 "Characterization of cadmium selenide quantum dot nanocrystals by fluorescence emission spectrometry", the fluorescence emission spectra of the quantum dot emitting layers prepared in each example and comparative example were tested using a fluorescence spectrophotometer (Hitachi F-7100), and the central emission wavelength was determined based on the fluorescence emission spectra.

[0097] 3. Brightness multiplier test Referring to GB / T 37664.1-2019 "Key Control Characteristics of Nanofabrication: Luminescent Nanomaterials - Part 1: Quantum Efficiency", the quantum dot film without a photonic crystal layer in Comparative Example 1 was used as a control. Under the same test conditions (excitation source: 395nm UV-LED lamp, light power density: 10mW / cm²), the fluorescence intensity of the photonic crystal fluorescent films of each example and the comparative example was measured, and the brightness multiple was calculated according to the following formula; where the peak intensity represents the vertical coordinate value corresponding to the highest point (i.e., the maximum fluorescence peak) in the fluorescence emission spectrum curve.

[0098] Brightness factor = peak intensity of sample / peak intensity of reference standard.

[0099] Table 2

[0100] Table 2 shows that, based on Comparative Example 1 without a photonic crystal layer, Examples 1-9 all achieved fluorescence enhancement (brightness multiplier ≥ 1.1 times). Examples 1-3 achieved a brightness multiplier of over 1.5 times when wavelength matching (absolute difference ≤ 10 nm) and maximum peak reflectivity ≥ 70%. However, the comparative examples all showed varying degrees of decline. Comparative Example 2, although having a wavelength difference of 0, had a maximum peak reflectivity of 40% (below 50%), resulting in a brightness multiplier of only 0.9. Comparative Examples 3-8 had wavelength differences exceeding 20 nm, causing brightness multipliers to drop below 1. These results indicate that fluorescence enhancement can only be achieved when the absolute difference between the central emission wavelength of the fluorescent quantum dot and the central reflection wavelength of the photonic crystal layer is ≤ 20 nm and the maximum peak reflectivity of the photonic crystal layer is ≥ 50%. Beyond this range, the fluorescence enhancement effect weakens or even disappears, failing to meet the requirements of high-end products.

[0101] The embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A photonic crystal fluorescent thin film, characterized in that, The photonic crystal fluorescent thin film includes: basal layer; A photonic crystal layer disposed on the surface of the substrate layer; and A quantum dot light-emitting layer disposed on the surface of the photonic crystal layer; The photonic crystal layer is an opal structure with three-dimensionally ordered nanospheres, and the gaps between the nanospheres are filled with a polymer matrix.

2. The photonic crystal fluorescent thin film according to claim 1, characterized in that, The quantum dot luminescent layer comprises fluorescent quantum dots dispersed in polymer matrix II; The absolute value of the difference between the central emission wavelength of the fluorescent quantum dot and the central reflection wavelength of the photonic crystal layer is ≤20nm.

3. The photonic crystal fluorescent thin film according to claim 1, characterized in that, The maximum peak reflectivity of the photonic crystal layer is ≥50%.

4. The photonic crystal fluorescent thin film according to claim 2, characterized in that, The fluorescent quantum dots include at least one of perovskite quantum dots, group II-VI compound semiconductor quantum dots, group III-V compound semiconductor quantum dots, or carbon quantum dots.

5. The photonic crystal fluorescent thin film according to claim 2, characterized in that, Both polymer matrix one and polymer matrix two are formed by photoinitiated polymerization of acrylate reactants under the action of a photoinitiator.

6. The photonic crystal fluorescent thin film according to claim 5, characterized in that, The raw materials for preparing polymer matrix one include acrylate reactant one and photoinitiator one; the raw materials for preparing polymer matrix two include acrylate reactant two and photoinitiator two. Both photoinitiator one and photoinitiator two comprise ethyl 2,4,6-trimethylbenzoylphenylphosphonate.

7. The photonic crystal fluorescent thin film according to claim 1, characterized in that, Based on a thin film without a photonic crystal layer, the brightness factor of the photonic crystal fluorescent thin film is greater than 1.

8. A method for preparing a photonic crystal fluorescent thin film according to claim 6, characterized in that, The preparation steps of the photonic crystal fluorescent thin film include: The nanospheres, acrylate reactant one, and photoinitiator one are mixed to prepare a photonic crystal coating solution; The photonic crystal coating solution is coated onto the surface of a substrate layer and dried to obtain a photonic crystal layer; another substrate layer is then laminated onto the surface of the photonic crystal layer to obtain a composite film. The composite film is subjected to a regularization treatment to obtain a composite film with microsphere crystallization; The composite film with crystallized microspheres is subjected to photocuring to obtain a photonic crystal film; another base layer on the surface of the photonic crystal layer is peeled off. The fluorescent quantum dots, acrylate reactant II, and photoinitiator II are mixed to prepare a quantum dot coating solution; The quantum dot coating liquid is coated onto the surface of the photonic crystal layer, and after photocuring, a quantum dot luminescent layer is formed, resulting in a photonic crystal fluorescent film.

9. The method for preparing a photonic crystal fluorescent thin film according to claim 8, characterized in that, The thickness of the photonic crystal thin film is 10 μm or more.

10. An application of a photonic crystal fluorescent thin film according to any one of claims 1-7, characterized in that, The photonic crystal fluorescent film is used in optical products that require at least one of the following functions: high brightness display, backlight optical enhancement, fluorescent anti-counterfeiting identification, optical information encryption, optical signal amplification, and dual-response decoration of structural color and fluorescence.

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