Perovskite two-dimensional nanosheet liquid crystal and preparation method and application thereof

Abstract

The invention discloses a perovskite two-dimensional nanosheet liquid crystal and a preparation method and application thereof, and belongs to the technical field of light-emitting and dimming liquid crystal materials. The perovskite two-dimensional nanosheet liquid crystal is formed by dispersing perovskite two-dimensional nanosheets in a non-polar solvent; wherein the composition of the perovskite two-dimensional nanosheet is (PEA) 2 (MnnPb1-n) (YmBr1-m) 4, Y is Cl or I, n is more than or equal to 0 and less than or equal to 0.6, and m is more than or equal to 0 and less than or equal to 1. The perovskite two-dimensional nanosheet liquid crystal can present an obvious liquid crystal phase, not only shows an adjustable light emitting color, but also has a magneto-optical effect, and has the capability of regulating and controlling the whole visible laser. Meanwhile, the perovskite two-dimensional nanosheet liquid crystal can be used for constructing a novel two-dimensional liquid crystal light modulator integrating magnetic control light emitting and dimming, and a new method and a new means are provided for light emitting polarization modulation.

Description

Technical Field

[0001] The present invention belongs to the technical field of luminescent and dimming liquid crystal materials, and in particular relates to a perovskite two-dimensional nanosheet liquid crystal and a preparation method and application thereof. Background Art

[0002] Liquid crystal is a typical soft material, which has both the fluidity of liquid and the anisotropy of crystal. It plays a pivotal role in the fields of display, sensing, energy and biotechnology. The global annual market size of electro-optical devices based on liquid crystal has exceeded one trillion yuan. Traditional liquid crystals face problems such as low external field response sensitivity and single function, and can no longer meet the needs of low-energy and multifunctional optoelectronic devices in the future low-carbon society. Luminescent liquid crystals, which have both dimming and luminescence characteristics, have attracted people's attention and have begun to be used in multifunctional optoelectronic devices, which are expected to meet the needs of future devices. Existing luminescent liquid crystals are often based only on organic liquid crystals, including liquid crystal self-luminescence, dye-doped liquid crystal hybrid luminescence, and liquid crystal modified luminescent materials. However, their external field response sensitivity is not high, such as the Croton-Mouton coefficient that measures the magnetic field response is often <10. In summary, the existing luminescent organic liquid crystal system is still a long way from truly realizing the development of low-energy dimming and luminescence integrated devices in the future low-carbon market. Therefore, it is urgent to develop a new type of dimming and luminescence integrated liquid crystal system in a unique way to provide a method to solve the problems of low external field response sensitivity and single function of traditional liquid crystals.

[0003] Halogen perovskite materials are widely used in light generation and light conversion devices, such as lasers, LEDs, and solar cells, due to their controllable dimensions, components, and easy processing properties, showing designable luminescence spectra and high-purity chromaticity. In perovskite systems of different dimensions, when perovskite two-dimensional nanosheets are extremely thin, they have a nano-quantum threshold effect on the longitudinal scale and a large geometric anisotropy ratio. The former ensures the efficient fluorescence emission of the material, while the latter is expected to ensure the external field response sensitivity. Therefore, perovskite two-dimensional nanosheets are ideal materials for realizing luminescent liquid crystals with high external field response sensitivity. However, the current research on perovskite two-dimensional nanosheets is limited to solid form, and their application is also limited to using their high electron transport, high light absorption capacity, and photoelectric conversion efficiency to use them in the fields of light generation (such as LEDs) and light conversion (such as solar cells and photoelectric detection). There are no reports on the research and application of perovskite two-dimensional nanosheets in liquid crystal state. Summary of the invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a perovskite two-dimensional nanosheet liquid crystal and a preparation method and application thereof, so as to solve the technical problems of low external field response sensitivity and single function of the existing luminescent liquid crystal.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: The first aspect of the present invention discloses a perovskite two-dimensional nanosheet liquid crystal, which is formed by dispersing perovskite nanosheets in a non-polar solvent, and the volume concentration of the perovskite two-dimensional nanosheets is 0.00065 vol%~0.01962 vol%.

[0006] Preferably, the composition of the perovskite nanosheet is (PEA)2(Mn n Pb 1-n )(Y m Br 1-m )4, Y is one of Cl or I, 0≤n≤0.6, 0≤m≤1.

[0007] Preferably, the aspect ratio of the perovskite two-dimensional nanosheet is >50.

[0008] Preferably, the polarity value of the non-polar solvent is 2.4-3.5.

[0009] Preferably, the non-polar solvent is selected from at least one of toluene, chlorobenzene, o-dichlorobenzene, chloroform, dichlorobenzene, ethyl acetate and diethyl ether.

[0010] The second aspect of the present invention discloses a method for preparing the above-mentioned perovskite two-dimensional nanosheet liquid crystal, wherein PbBr2, MnBr2, PEABr, PbY2, MnY2 and PEAY in a molar ratio of (0.1~1):(0~0.6):(0.1~2):(0~1):(0~0.6):(0~2) are dissolved in a polar solvent to obtain a precursor solution; then the obtained precursor solution is added to a non-polar solvent at 0~25°C, centrifuged, and the supernatant and perovskite two-dimensional nanosheets with an aspect ratio of ≤50 are removed to obtain perovskite two-dimensional nanosheet liquid crystals.

[0011] Preferably, the polar solvent is at least one of dimethylformamide, dimethyl sulfoxide, acetonitrile and N-methylpyrrolidone.

[0012] Preferably, after removing the supernatant and the perovskite two-dimensional nanosheets with an aspect ratio of ≤50, the remaining reactants are dissolved in a non-polar solvent to obtain the perovskite two-dimensional nanosheet liquid crystal.

[0013] More preferably, the remaining reactants are dissolved in a non-polar solvent containing a benzene ring.

[0014] More preferably, among the non-polar solvents containing a benzene ring, the non-polar solvent is at least one of toluene, chlorobenzene and o-dichlorobenzene.

[0015] The third aspect of the present invention discloses the application of the above-mentioned perovskite two-dimensional nanosheet liquid crystal in the field of liquid crystal display, polarization optics or analytical sensing.

[0016] Preferably, the magnetic field response of the perovskite two-dimensional nanosheet liquid crystal requires a magnetic field > 50 mT.

[0017] Preferably, the incident light λ range that can be modulated by the perovskite two-dimensional nanosheet liquid crystal is 450 nm<λ.

[0018] Preferably, the perovskite two-dimensional nanosheet liquid crystal can modulate a light emission wavelength λ in the range of 410 nm<λ<623 nm.

[0019] A fourth aspect of the present invention discloses the application of the above-mentioned perovskite two-dimensional nanosheet liquid crystal in a liquid crystal display device.

[0020] A fifth aspect of the present invention discloses a two-dimensional liquid crystal light modulator, comprising the above-mentioned perovskite two-dimensional nanosheet liquid crystal.

[0021] The sixth aspect of the present invention discloses an optically anisotropic functional film made of the above-mentioned perovskite two-dimensional nanosheet liquid crystal.

[0022] Compared with the prior art, the present invention has the following beneficial effects: A perovskite two-dimensional nanosheet liquid crystal provided by the present invention is characterized by a polarized optical microscope, and it is found that with the increase of the volume concentration of the perovskite two-dimensional nanosheets in a non-polar solvent, the phase state of the mixture will undergo a continuous transition from an isotropic phase-a biphase-anisotropic phase. When the volume concentration of the perovskite two-dimensional nanosheets is less than 0.00065 vol%, the mixture is an isotropic phase without liquid crystal birefringence optical properties. When the volume concentration of the perovskite two-dimensional nanosheets is 0.00065 vol%~0.01962 vol%, the mixture will exhibit obvious liquid crystal birefringence optical properties, indicating that the perovskite two-dimensional nanosheets with a volume concentration of 0.00065 vol%~0.01962 vol% are dispersed in the non-polar solvent to form an obvious liquid crystal phase. The performance of the perovskite two-dimensional nanosheet liquid crystal that presents a liquid crystal phase was further investigated. The fluorescence spectrum of the perovskite two-dimensional nanosheet liquid crystal was detected by a spectrometer, and it was found that it can modulate the emission wavelength of 410~623 nm. When the perovskite two-dimensional nanosheet liquid crystal contains only PEA, Pb and Br, it emits deep blue light, and when Mn is further doped, it will also emit red light. By taking optical photos of the liquid crystal under static and shaking conditions, it is proved that the perovskite two-dimensional nanosheet liquid crystal has flow-induced behavior. Through the magnetic control dimming property detection experiment, it was found that the perovskite two-dimensional nanosheet liquid crystal can obtain excellent dimming properties under a magnetic field of >50 mT, and the external field response sensitivity is 42 T -2 m -1, higher than traditional luminescent organic liquid crystals. Through the luminescence characteristic detection experiment, it was found that the perovskite two-dimensional nanosheet liquid crystal has polarized luminescence characteristics. Under the application of a 700 mT magnetic field, its polarization intensity will be enhanced, proving that it has the ability to modulate the luminescence polarization. In summary, the perovskite two-dimensional nanosheet liquid crystal has magneto-optical and electro-optical effects, that is, it has both luminescence ability, dimming ability, and magnetically controlled and electrically controlled dimming behavior, an increase in magnetic field response sensitivity by nearly 1 order of magnitude, and multifunctional optical modulation under low fields, which can enhance polarized luminescence. Therefore, compared with traditional perovskite two-dimensional nanosheets, this perovskite two-dimensional nanosheet liquid crystal can be applied to the luminescent liquid crystal material system for light manipulation, achieving polarization dimming and polarized luminescence, providing theoretical support for broadening the physical properties of perovskite nanosheets, providing technical support for their optoelectronic applications, and meeting the modulation needs of some multifunctional optoelectronic devices under the background of low carbon.

[0023] The present invention provides a method for preparing a perovskite two-dimensional nanosheet liquid crystal, which comprises dissolving PbBr2, MnBr2, PEABr, PbY2, MnY2 and PEAY in a specific mass ratio in a polar solvent, dispersing the dissolved PbBr2, MnBr2, PEABr, PbY2, MnY2 and PEAY in a non-polar solvent under low temperature conditions, and removing the supernatant and the perovskite two-dimensional nanosheets with an aspect ratio of ≤50 to form perovskite two-dimensional nanosheet liquid crystals. The method has low cost, is simple and easy to operate, and can provide a new preparation process for luminescent liquid crystals.

[0024] The present invention provides a two-dimensional liquid crystal light modulator, which utilizes the luminescence ability, dimming ability, magnetically controlled electrically controlled dimming behavior and enhanced polarized luminescence ability of perovskite two-dimensional nanosheet liquid crystal, uses it as an active material, and combines it with a spectrometer and a polarizer to perform polarization dimming and luminescence modulation. The entire two-dimensional liquid crystal light modulator has a compact structure, is highly integrated, and can achieve precise control of light. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The liquid crystal phase diagrams of (PEA)2PbBr4 nanosheet liquid crystals prepared in Comparative Examples 1 to 3 and Examples 1 to 9 are shown; wherein, from left to right, they are the continuous transitions of isotropic phases-biphases-anisotropic phases, the control group corresponds to the liquid crystal phase diagrams of Comparative Examples 1 to Comparative Examples 3, and the implementation group corresponds to the liquid crystal phase diagrams of Examples 2, 3, 1, 4 to 9, respectively; Figure 2 Atomic force image of (PEA)2PbBr4 nanosheet liquid crystal droplets prepared in Example 1 on a silicon wafer; Figure 3 This is the fluorescence spectrum of the (PEA)2PbBr4 nanosheet liquid crystal prepared in Example 1; Figure 4 (PEA)2(Mn 0.5 Pb 0.5) Fluorescence spectrum of Br4 nanosheet liquid crystal; the solution illustrations are optical photographs of colloidal solutions without and with 365 nm laser irradiation; Figure 5 This is a flow-induced liquid crystal diagram of the (PEA)2PbBr4 nanosheet liquid crystal prepared in Example 1; the left side is a static state, and the right side is a shaking state; Figure 6 (PEA)2(Mn 0.5 Pb 0.5 ) Optical detection results of Br4 nanosheet liquid crystal shaking under a polarizer; Figure 7 Schematic diagram of magnetically controlled dimming using (PEA)2PbBr4 nanosheet liquid crystal; Figure 8 The (PEA)2PbBr4 nanosheet liquid crystal prepared in Example 1 regulates the intensity of 450 nm laser under different magnetic field intensities; Fig. 9 This is a schematic diagram of the application of liquid crystal magnetic control modulation of incident light of the (PEA)2PbBr4 nanosheet liquid crystal prepared in Example 1; wherein A is a condition without magnetic field application, and B is a condition with magnetic field application; Fig.10 (PEA)2(Mn 0.5 Pb 0.5 ) Modulation spectrum of Br4 nanosheet liquid crystal to 450nm laser in 800 mT magnetic field; Fig.11 This is a graph showing the polarized luminescence results of the (PEA)2PbBr4 nanosheet liquid crystal prepared in Example 1 under a magnetic field; Among them, 1-light source, 2-polarizer I, 3-colorimetric dish, 4-polarizer II, 5-spectrometer. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0027] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0028] In this article, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible sub-ranges and individual values ​​within the range (including integers and fractions).

[0029] In this document, unless otherwise specified, “includes,” “including,” “contains,” “has,” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0030] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0031] In this article, unless otherwise specified, the full English name of "PEA" in the liquid crystal component of perovskite two-dimensional nanosheets is "2-Phenylethylammonium", and the full Chinese name is "phenylethylammonium".

[0032] The present invention provides a perovskite two-dimensional nanosheet liquid crystal, which is formed by dispersing perovskite nanosheets with a volume concentration of 0.00065 vol% to 0.01962 vol% and an aspect ratio of >50 in a non-polar solvent, wherein the composition of the perovskite nanosheets is (PEA)2(Mn n Pb 1-n )(Y m Br 1-m )4, Y is one of Cl or I, 0≤n≤0.6, 0≤m≤1. The perovskite two-dimensional nanosheet liquid crystal can be used as a luminescent liquid crystal material to achieve sensitive control properties of incident light and emitted light under an external field. The external field includes fluid field, magnetic field and electric field. The magnetic field required for magnetic field response only needs to be >50 mT. The incident light λ range that can be modulated is 450 nm<λ, and the luminescent wavelength λ range that can be modulated is 410 nm<λ<623 nm.

[0033] The present invention provides a method for preparing the above-mentioned perovskite two-dimensional nanosheet liquid crystal, comprising the following steps: 1. Dissolve PbBr2, MnBr2, PEABr, PbY2, MnY2 and PEAY in a polar solvent at a molar ratio of (0.1-1): (0-0.6): (0.1-2): (0-1): (0-0.6): (0-2) to obtain a precursor solution; Wherein, Y is one of Cl or I; the polar solvent is at least one of dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetonitrile and N-methylpyrrolidone (NMP); 2. The precursor solution prepared in step 1 is quickly added with a non-polar solvent at a low temperature of 0-25°C and stirred to form a gel solution; the gel solution is centrifuged at a speed of 3500-4500 r for 3-6 min, the supernatant is removed, and the small-sized perovskite two-dimensional nanosheets with an aspect ratio of ≤50 are removed, and the perovskite two-dimensional nanosheets with an aspect ratio of>50 are retained; The polarity value of the non-polar solvent is 2.4-3.5, and the non-polar solvent is selected from at least one of toluene, chlorobenzene, o-dichlorobenzene, chloroform, dichlorobenzene, ethyl acetate and ether, preferably o-dichlorobenzene; 3. Dissolving the reaction product of step 2 in a non-polar solvent containing a benzene ring to obtain a perovskite two-dimensional nanosheet liquid crystal; Among them, in the perovskite two-dimensional nanosheet liquid crystal, the volume concentration of the perovskite two-dimensional nanosheet is 0.00065 vol%~0.01962 vol%, preferably, the volume concentration is 0.001962 vol%; in the non-polar solvent containing a benzene ring, the non-polar solvent is at least one of toluene, chlorobenzene, and o-dichlorobenzene.

[0034] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0035] The following examples use conventional instruments and equipment in the art. The experimental methods in the following examples where specific conditions are not specified are usually carried out under conventional conditions or under conditions recommended by the manufacturer. The various raw materials used in the following examples, unless otherwise specified, are conventional commercial products, and their specifications are conventional specifications in the art, or can be obtained by existing known methods.

[0036] 1. Preparation of perovskite two-dimensional nanosheet liquid crystal Example 1 The preparation method of (PEA)2PbBr4 nanosheet liquid crystal comprises the following steps: 1. Weigh PbBr2 and phenylethylamine bromide (PEABr) powders in a molar ratio of 1:1, dissolve in 1 mL of dimethylformamide (DMF), and stir until transparent to obtain a precursor solution; Among them, in the precursor solution, the concentration of PbBr2 is 0.5 mmol / L; 2. At 5°C, take 30 μL of the precursor solution obtained in step 1 and quickly add it dropwise into 10 mL of o-dichlorobenzene. Stir for 2 min to obtain a gel solution.

[0037] 3. Centrifuge the gel obtained in step 2 at 3500 r for 3 min, remove the supernatant and the perovskite two-dimensional nanosheets with an aspect ratio of ≤50, and disperse the remaining reactants in 10 mL of o-dichlorobenzene to obtain (PEA)2PbBr4 nanosheet liquid crystals. The volume concentration of the perovskite two-dimensional nanosheets in the (PEA)2PbBr4 nanosheet liquid crystal is 0.001962 vol%.

[0038] Embodiment 2 to Embodiment 9 The preparation method is the same as that of Example 1, except that in the (PEA)2PbBr4 nanosheet liquid crystal, the volume concentrations of the perovskite two-dimensional nanosheets are 0.00065 vol%, 0.0013 vol%, 0.00392 vol%, 0.00589 vol%, 0.00785 vol%, 0.01177 vol%, 0.0157 vol% and 0.01962 vol%, respectively.

[0039] Example 10 (PEA)2(Mn 0.5 Pb 0.5 ) A method for preparing Br4 nanosheet liquid crystal, comprising the following steps: 1. Weigh PbBr2, MnBr2 and PEABr powders at a molar ratio of 0.5:0.5:2, dissolve in 1 mL of dimethylformamide (DMF), and stir the solution until transparent to obtain a precursor solution; Among them, in the precursor solution, the concentration of PbBr2 is 0.5 mmol / L; 2. At 25°C, add 30 μL of the precursor solution obtained in step 1 into 10 mL of o-dichlorobenzene and stir for 2 min to obtain a gel solution.

[0040] 3. Centrifuge the gel obtained in step 2 at 3500 r for 3 min, remove the supernatant and the perovskite two-dimensional nanosheets with an aspect ratio of ≤50, and disperse the remaining reactants in 10 mL of o-dichlorobenzene to obtain (PEA)2(Mn 0.5 Pb 0.5 ) Br4 nanosheet liquid crystal. (PEA)2(Mn 0.5 Pb 0.5 ) In the Br4 nanosheet liquid crystal, the volume concentration of perovskite two-dimensional nanosheets is 0.006 vol%.

[0041] Embodiment 11 (PEA)2(Mn 0.5 Pb0.5 )(Cl 0.5 Br 0.5 ) A method for preparing a nanosheet liquid crystal, comprising the following steps: 1. Weigh PbBr2, MnBr2, PEABr and PbCl2 powders in a molar ratio of 0.25:0.5:2:0.25, dissolve in 1 mL of dimethylformamide (DMF), and stir the solution until it becomes transparent to obtain a precursor solution; Among them, in the precursor solution, the concentration of PbBr2 is 0.5 mmol / L; 2. At 25°C, add 30 μL of the precursor solution obtained in step 1 into 10 mL of o-dichlorobenzene and stir for 2 min to obtain a gel solution.

[0042] 3. Centrifuge the gel obtained in step 2 at 3500 r for 3 min, remove the supernatant and the perovskite two-dimensional nanosheets with an aspect ratio of ≤50, and disperse the remaining reactants in 10 mL of o-dichlorobenzene to obtain (PEA)2(Mn 0.5 Pb 0.5 )(Cl 0.5 Br 0.5 )4 nanosheet liquid crystal. (PEA)2(Mn 0.5 Pb 0.5 )(Cl 0.5 Br 0.5 ) In the 4-nanosheet liquid crystal, the volume concentration of perovskite two-dimensional nanosheets is 0.01962 vol%.

[0043] Example 12 (PEA)2(Mn 0.4 Pb 0.6 )(I 0.5 Br 0.5 ) A method for preparing a nanosheet liquid crystal, comprising the following steps: 1. PbBr2, MnBr2, PEABr, PbI2, MnI2 and PEAI powders were weighed in a molar ratio of 0.6:0.4:2:0.6:0.4:2, dissolved in 1 mL of dimethylformamide (DMF), and stirred until the solution was transparent to obtain a precursor solution; Among them, in the precursor solution, the concentration of PbBr2 is 0.5 mmol / L; 2. At 25°C, add 30 μL of the precursor solution obtained in step 1 into 10 mL of o-dichlorobenzene and stir for 2 min to obtain a gel solution.

[0044] 3. Centrifuge the gel obtained in step 2 at 3500 r for 3 min, remove the supernatant and the perovskite two-dimensional nanosheets with an aspect ratio of ≤50, and disperse the remaining reactants in 10 mL of o-dichlorobenzene to obtain (PEA)2(Mn 0.4 Pb 0.6 )(I 0.5 Br 0.5 )4 nanosheet liquid crystal. (PEA)2(Mn 0.4 Pb 0.6 )(I 0.5 Br 0.5 ) In the 4-nanosheet liquid crystal, the volume concentration of perovskite two-dimensional nanosheets is 0.008 vol%.

[0045] Comparative Example 1~Comparative Example 3 The preparation method is the same as that of Example 1, except that in the (PEA)2PbBr4 nanosheet liquid crystal, the volume concentrations of the perovskite two-dimensional nanosheets are 0.000013 vol%, 0.000065 vol% and 0.00013 vol%, respectively.

[0046] 2. Performance verification of perovskite two-dimensional nanosheet liquid crystal 1. Liquid crystal characteristics detection Polarized optical microscopy was used to characterize the liquid crystal phase diagrams of the (PEA)2PbBr4 nanosheet liquid crystals prepared in Comparative Example 1 to Comparative Example 3 and Example 1 to Example 9.

[0047] Test results such as Figure 1 As shown, it can be seen that the (PEA)2PbBr4 nanosheet liquid crystal has organic lyotropic liquid crystal properties and concentration-dependent phase transitions. As the volume concentration increases, it shows a continuous transition from isotropic phase to bipolar phase to anisotropic phase. When the volume concentration of the perovskite two-dimensional nanosheet is less than 0.00065 vol% (i.e., the comparative example), the prepared material is isotropic and has no liquid crystal birefringence optical properties; and when the volume concentration is greater than or equal to 0.00065 vol% (i.e., the embodiment), obvious liquid crystal birefringence optical properties are observed.

[0048] The (PEA)2PbBr4 nanosheet liquid crystal prepared in Example 1 was dropped onto a silicon wafer, and the morphology and thickness of the nanosheet liquid crystal were detected using an atomic force microscope (AFM) method.

[0049] Test results such as Figure 2 As shown, the figure shows a nanosheet with a size of about 800 nm and a thickness of 8.2 nm.

[0050] The fluorescence spectrum of (PEA)2PbBr4 nanosheet liquid crystal was detected using a spectrometer.

[0051] Test results such as Figure 3 As shown, it can be seen that under 365 nm laser excitation, an emission peak at 410 nm is exhibited.

[0052] The above results show that the (PEA)2PbBr4 nanosheet liquid crystal prepared in Example 1 is a liquid crystal that emits deep blue light and can modulate a light emission wavelength of 410 nm.

[0053] The (PEA)2(Mn 0.5 Pb 0.5 )Absorption and fluorescence spectra of Br4 nanosheet liquid crystals.

[0054] Test results such as Figure 4 As shown, it can be seen that after Mn doping, the absorption peak is located at 405 nm, and no other peaks appear, indicating that Mn doping does not affect the intrinsic band gap; under 365 nm laser excitation, the emission peaks of 410 nm and 623 nm are displayed, and the colloidal solution shows red luminescence, indicating that the liquid crystal can modulate the emission wavelength of 410~623 nm.

[0055] The above results show that the (PEA)2(Mn 0.5 Pb 0.5 ) Br4 nanosheet liquid crystal is a liquid crystal that emits both blue and red light.

[0056] 2. Liquid crystal flow behavior detection Under the illumination of a white light LED lamp and two vertically crossed polarizers, optical photographs of the (PEA)2PbBr4 nanosheet liquid crystal prepared in Example 1 were taken under static and shaking conditions to detect the flow-induced behavior of the material.

[0057] The experimental results are as follows Figure 5 As shown, it can be clearly observed that the (PEA)2PbBr4 nanosheet liquid crystal has a flow-induced blue liquid crystal phase under shaking, indicating that it has flow-induced liquid crystal behavior.

[0058] Under the illumination of a white light LED, the (PEA)2(Mn 0.5 Pb 0.5 ) Optical photograph of Br4 nanosheet liquid crystal under shaking conditions to examine the flow-induced behavior of the material.

[0059] The experimental results are as follows Figure 6 As shown, it can be clearly observed that (PEA)2(Mn 0.5 Pb 0.5) The Br4 nanosheet liquid crystal has a flow-induced blue liquid crystal phase when shaken, indicating that it has flow-induced liquid crystal behavior.

[0060] 3. Magnetic control dimming characteristics detection according to Figure 7 A two-dimensional liquid crystal light modulator is constructed as shown in the schematic diagram. The (PEA)2PbBr4 nanosheet liquid crystal prepared in Example 1 is placed in a quartz cuvette with an optical path length of 1 cm and placed at the center of the magnetic pole. Then, a light source 1, a 45-degree Glan-Laser calcite polarizer (GL10-A, Thorlabs Inc), a cuvette containing (PEA)2PbBr4 nanosheet liquid crystal, a 135-degree Glan-Laser calcite polarizer (GL10-A, Thorlabs Inc) and a spectrometer 5 are coaxially arranged in sequence to obtain a two-dimensional liquid crystal light modulator.

[0061] The obtained two-dimensional liquid crystal light modulator is used for dimming. The light source 1 emits a 450 nm laser, which is incident on the quartz cuvette carrying the (PEA)2PbBr4 nanosheet liquid crystal through a 45-degree Glan-Laser calcite polarizer, and then enters the spectrometer 5 through a 135-degree Glan-Laser calcite polarizer. By controlling the intensity of the magnetic field perpendicular to the optical path, the change of the 450 nm laser intensity is observed through the spectrometer 5.

[0062] Test results such as Figure 8 As shown, it can be seen that under the magnetic field of 50 mT, the 450 nm laser intensity has been enhanced to a certain extent; then, with the gradual increase of the magnetic field, the laser intensity further increases, indicating that the (PEA)2PbBr4 nanosheet liquid crystal can obtain excellent dimming characteristics under a magnetic field of >50 mT.

[0063] In addition, Figure 7 The optical path was fine-tuned based on the experiment, and the "SIAT" pattern was attached to the front side of the quartz cuvette carrying the (PEA)2PbBr4 nanosheet liquid crystal. The magnetically controlled dimming was performed under the irradiation of three red, green and blue flat LED lights (450, 520 and 635 nm) and with the assistance of a front 45-degree Glan-Laser calcite polarizer and a rear 135-degree Glan-Laser calcite polarizer. The brightness of the displayed pattern was controlled by controlling the magnetic field strength to 0 and 0.8 T, respectively, and the magnetically controlled dimming capability of the (PEA)2PbBr4 nanosheet liquid crystal prepared in Example 1 was tested.

[0064] Test results such as Fig. 9As shown, it can be seen that for the three primary colors of red, green and blue, the pattern changes from non-display to bright display, indicating that (PEA)2PbBr4 nanosheet liquid crystal can achieve clear display of the pattern and has liquid crystal dimming characteristics for lasers >450 nm. Based on the dimming characteristics of 450 nm, the converted magneto-optical Cotton-Morton coefficient (reaction field modulation sensitivity) is 42 T - 2 m -1 , which is higher than that of traditional light-emitting organic liquid crystals, indicating that it has excellent field response sensitivity.

[0065] Likewise Figure 7 As shown, the (PEA)2PbBr4 nanosheet liquid crystal in the quartz cuvette was replaced with the (PEA)2(Mn 0.5 Pb 0.5 ) Br4 nanosheet liquid crystal, magnetically controlled dimming was performed, and the intensity of the 450 nm laser (obtained by spectrometer 5) was monitored by controlling the magnetic field strength to 0 and 0.8 T respectively, and the (PEA)2(Mn 0.5 Pb 0.5 ) Magnetically controlled dimming capability of Br4 nanosheet liquid crystals.

[0066] Test results such as Fig.10 As shown in the figure, under the 0.8 T magnetic field switch, the ratio of the 450 nm laser dimming intensity is about 12, and the converted magneto-optical Cotton-Morton coefficient is 31 T. -2 m -1 , which also shows that it has excellent field response sensitivity.

[0067] 4. Luminescence characteristics detection The (PEA)2PbBr4 nanosheet liquid crystal (without polarizer) prepared in Example 1 was excited by 365 nm laser under different magnetic field strengths (no magnetic field and 700 mT magnetic field), the angle of the polarizer was rotated, and the optical intensity at different angles was tested by a spectrometer to examine its polarization.

[0068] Test results such as Fig.11 As shown in the figure, it can be seen that the perovskite two-dimensional nanosheet liquid crystal has certain polarized luminescence characteristics regardless of the presence or absence of a magnetic field, but its polarization intensity will be enhanced to a certain extent under the application of a 700 mT magnetic field. This result demonstrates the modulation ability of the (PEA)2PbBr4 nanosheet liquid crystal to emit polarized light.

[0069] In summary, perovskite nanosheet liquid crystals have the dual functional properties of luminescence and dimming.

[0070] 3. Application of Perovskite 2D Nanosheet Liquid Crystals 1. Two-dimensional liquid crystal light modulator A two-dimensional liquid crystal light modulator capable of realizing polarization dimming.

[0071] Reference for setting up a 2D liquid crystal light modulator Figure 7 , comprising a coaxially arranged light source 1, a polarizer I 2, a cuvette 3, a polarizer II 4 and a spectrometer 5, wherein the cuvette 3 is filled with a perovskite two-dimensional nanosheet liquid crystal, and the cuvette 3 is located at the center of the magnetic pole. When in use, a 450 nm laser is provided by the light source 1, the polarization direction of the incident light is ensured by the polarizer I 2, polarization dimming is performed by the perovskite two-dimensional nanosheet liquid crystal, the polarization state of the outgoing light is analyzed by the polarizer II 4, and the change of the spectral intensity is obtained by the spectrometer.

[0072] A two-dimensional liquid crystal light modulator capable of realizing light emission modulation.

[0073] The two-dimensional liquid crystal light modulator includes a coaxially arranged magnetic pole I, a cuvette, a magnetic pole II, a polarizer and a spectrometer. The cuvette is filled with perovskite two-dimensional nanosheet liquid crystal. The cuvette is located at the center of the magnetic pole. A 365 nm ultraviolet light source is set just above the cuvette. When in use, the emission spectrum is collected by the spectrometer, and the polarization angle is adjusted by rotating the polarizer to obtain the luminescence spectrum and intensity. According to the spectral data at different polarization angles, the functional relationship between light intensity and polarization angle can be obtained.

[0074] It should be noted that the above-mentioned two-dimensional liquid crystal light modulator can realize polarization dimming and luminescence modulation functions separately, or can integrate polarization dimming and luminescence modulation functions at the same time.

[0075] 2. Optically anisotropic functional films First, the alignment layer material (such as polyimide, polyvinyl alcohol, silicon dioxide) is uniformly coated on the first substrate (such as glass) and dried to form an alignment layer; secondly, perovskite two-dimensional nanosheet liquid crystal is coated on the alignment layer to form a birefringent layer; thirdly, the birefringent layer is bonded to the second substrate (such as glass), and the perovskite two-dimensional nanosheet liquid crystal in the birefringent layer is oriented to make it arranged in a directional manner; finally, the birefringent layer is cured to fix the directional arrangement of the liquid crystal molecules, and the first substrate and the alignment layer are removed to obtain an optically anisotropic functional film.

[0076] It should be noted that the core functional component of the above optical anisotropic functional film is perovskite two-dimensional nanosheet liquid crystal, which is not limited to being prepared by the above liquid crystal orientation method, but can also be prepared by physical vapor deposition, sol-gel method and other methods.

[0077] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A perovskite two-dimensional nanosheet liquid crystal, characterized in that: The perovskite nanosheets are dispersed in a non-polar solvent, and the volume concentration of the perovskite two-dimensional nanosheets is 0.00065 vol% to 0.01962 vol%.

2. The perovskite two-dimensional nanosheet liquid crystal according to claim 1, characterized in that: The composition of perovskite nanosheets is (PEA)2(Mn n Pb 1-n )(Y m Br 1-m )4, Y is one of Cl or I, 0≤n≤0.6, 0≤m≤1.

3. The perovskite two-dimensional nanosheet liquid crystal according to claim 1, characterized in that: The aspect ratio of perovskite two-dimensional nanosheets is >50.

4. The method for preparing the perovskite two-dimensional nanosheet liquid crystal according to any one of claims 1 to 3, characterized in that: PbBr2, MnBr2, PEABr, PbY2, MnY2 and PEAY in a molar ratio of (0.1~1):(0~0.6):(0.1~2):(0~1):(0~0.6):(0~2) are dissolved in a polar solvent to obtain a precursor solution; the obtained precursor solution is then added to a non-polar solvent at 0~25°C, centrifuged, and the supernatant and perovskite two-dimensional nanosheets with an aspect ratio of ≤50 are removed to obtain perovskite two-dimensional nanosheet liquid crystals.

5. Application of the perovskite two-dimensional nanosheet liquid crystal according to any one of claims 1 to 3 or the perovskite two-dimensional nanosheet liquid crystal prepared by the preparation method according to claim 4 in the fields of liquid crystal display, polarization optics or analytical sensing.

6. The use according to claim 5, characterized in that: The magnetic field response of the perovskite two-dimensional nanosheet liquid crystal requires a magnetic field >50 mT.

7. The use according to claim 5, characterized in that: The perovskite two-dimensional nanosheet liquid crystal can modulate the incident light λ range of 450 nm<λ, and can modulate the emission wavelength λ range of 410 nm<λ<623 nm.

8. Use of the perovskite two-dimensional nanosheet liquid crystal according to any one of claims 1 to 3 or the perovskite two-dimensional nanosheet liquid crystal prepared by the preparation method according to claim 4 in a liquid crystal display device.

9. A two-dimensional liquid crystal light modulator, characterized in that: It comprises the perovskite two-dimensional nanosheet liquid crystal according to any one of claims 1 to 3 or the perovskite two-dimensional nanosheet liquid crystal prepared by the preparation method according to claim 4.

10. An optically anisotropic functional film, characterized in that: It is made of the perovskite two-dimensional nanosheet liquid crystal described in any one of claims 1 to 3 or the perovskite two-dimensional nanosheet liquid crystal prepared by the preparation method described in claim 4.

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