An upconversion circularly polarized fluorescence device of perovskite quantum dots and a preparation method thereof

Abstract

The application discloses an up-conversion circular polarization fluorescent device of perovskite quantum dots, which comprises, from bottom to top, a light-transmitting glass substrate, a parallel orientation layer, a reflection layer, a transparent separation layer and a composite nanomaterial layer; the reflection layer is a polymer cholesteric liquid crystal layer; the transparent separation layer is made of one of polymethyl methacrylate and polyvinyl alcohol; the composite nanocrystal material layer is composed of perovskite quantum dots / up-conversion nanocrystal composite nanomaterial; the perovskite quantum dots / up-conversion nanocrystal composite nanomaterial is prepared by an in-situ synthesis method. The device has the properties of circular polarization luminescence and up-conversion circular polarization luminescence, and has excellent performances such as high stability, high energy transfer efficiency, high radiation intensity and good repeatability.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of circularly polarized luminescence, in particular to a perovskite quantum dot upconversion circularly polarized luminescence device and a preparation method thereof. BACKGROUND

[0002] Circularly polarized light is light with a rotating electric vector endpoint tracing a circular trajectory, which is a special form of elliptically polarized light. Circularly polarized light is divided into left-handed or right-handed circularly polarized light. Circularly polarized light has high-level visual perception and excellent sensitivity, and is widely concerned in many fields, such as information encryption, biological imaging and sensing, 3D display and the like. As a key indicator for quantifying the performance of circularly polarized luminescence, the luminescence asymmetry factor g lum can be expressed as glum = 2*(IL-IR) / (IL+IR), wherein IL and IR represent the left-handed circularly polarized light intensity and the right-handed circularly polarized light intensity respectively, and the maximum value of g lum is 2. The upconversion process is a process of generating high-energy photons from low-energy photons, so as to realize low-energy excitation to generate high-energy emission. It is also of great significance to study the circularly polarized luminescence characteristics in the upconversion process.

[0003] There are many methods for obtaining circularly polarized light, and using cholesteric liquid crystal (CLC) with optical rotation effect is a way to obtain circularly polarized light with high polarization. As a one-dimensional photonic crystal, cholesteric liquid crystal has the characteristics of Bragg reflection and can selectively reflect light of a specific wavelength. Since the CLC molecules can self-assemble into a structure with a certain periodicity, the molecular director rotates 360° along a normal direction, and the distance between two directors with the same direction is called the pitch (P value) of the cholesteric liquid crystal. When the wavelength of the incident light is equal to the P value, the matching photons will be selectively reflected, and circularly polarized reflected light with the same chirality as the CLC is generated, which is the photonic bandgap effect of CLC. The circularly polarized luminescence device prepared according to this principle has a series of advantages such as high stability, large adjustment range and high polarization degree.

[0004] Perovskite quantum dots have excellent optoelectronic properties. Pure inorganic CsPbX3 materials (X is halogen) have strong resistance to water and oxygen, are easy to prepare by all-solution method, are cheap, and are easy to adjust optical band gap and have high fluorescence quantum yield. The circularly polarized luminescence produced by combining perovskite quantum dots with cholesteric liquid crystals has wide optical information and excellent sensitivity. The principle is that the CLC is used as a reflective layer, and the perovskite quantum dots are used as a light-emitting layer, and the circularly polarized light with high polarization degree is successfully emitted. Zhu et al. coated the perovskite material with a high-molecular-weight polymer, polyacrylonitrile, and combined it with the CLC in a liquid crystal cell filling manner after making a thin film, obtaining a temperature-responsive circularly polarized fluorescence device with an asymmetry factor as high as 1.9. The circularly polarized luminescence of perovskite quantum dots excited by ultraviolet light has been widely reported in the literature, while the upconversion circularly polarized luminescence of perovskite quantum dots triggered by near-infrared (NIR) light is rarely reported. This is because low-cost continuous wave diode lasers cannot trigger photon upconversion based on multi-photon absorption in pure perovskite quantum dots, so perovskite quantum dots will not produce fluorescence under the excitation of 980 nm laser. The low penetration depth of ultraviolet light in biological tissues limits the application of the above-mentioned circularly polarized light device of perovskite quantum dots in medicine, biological imaging, etc. Moreover, compared with ultraviolet excitation, the upconversion circularly polarized luminescence triggered by near-infrared light is more friendly to organic molecules in CLC, and is more conducive to improving the stability of the circularly polarized light device.

[0005] The introduction of upconversion nanoparticles (UCNPs) into the circularly polarized fluorescence device can realize the utilization of near-infrared light by perovskite quantum dots, so that the device can not only realize the circularly polarized luminescence excited by ultraviolet light, but also realize the upconversion circularly polarized luminescence excited by near-infrared light. Moreover, since the band gap of perovskite quantum dots can be adjusted by changing halogen ions to produce red and green light emission, and upconversion nanocrystals can produce blue light emission, the upconversion circularly polarized luminescence from near-infrared light to red, green and blue light can be further realized, which is of great significance for widening the application of perovskite quantum dots in medical and biological imaging fields.

[0006] Compared with perovskite quantum dots, upconversion nanocrystals can emit higher energy photons through continuous absorption of two or more low-energy photons through energy transfer. By combining perovskite quantum dots with upconversion nanocrystals, the upconversion nanocrystals absorb the energy of near-infrared light, and then transfer the energy of near-infrared light to the perovskite quantum dots through the energy transfer mechanism, so that the perovskite quantum dots generate characteristic emission peaks, and the emission peaks generate upconversion circularly polarized luminescence through the reflection of the CLC layer. The research group of Duan doped upconversion nanoparticles and CsPbBr3 nanocrystals into chiral nematic liquid crystals, and obtained upconversion circularly polarized fluorescence in this system through radiation energy transfer between the two (see Adv. Mater. 2020, 2000820). However, both perovskite quantum dots and upconversion nanocrystals are inorganic materials, which have poor compatibility with organic cholesteric liquid crystals. Doping them into cholesteric liquid crystals will cause serious aggregation, and the low energy transfer efficiency caused by the weak coupling between the two materials is also a problem to be solved.

[0007] In summary, it is of great significance to develop a device with high stability to realize the upconversion circularly polarized luminescence of perovskite quantum dots. SUMMARY

[0008] In view of the defects and deficiencies in the prior art, one of the purposes of the present application is to provide a perovskite quantum dot upconversion circularly polarized fluorescence device, so as to broaden the application of perovskite quantum dots in medical and biological imaging. The present application combines perovskite quantum dots with rare earth doped upconversion nanoparticles to obtain a composite material that combines the luminescent advantages of upconversion nanocrystals and quantum dots. Not only can perovskite quantum dots be excited by near-infrared light to improve the stability of the perovskite quantum dot circularly polarized luminescence device, but also can realize upconversion luminescence with adjustable visible light full-band emission spectrum, making up for the deficiency of rare earth ions that cannot be continuously regulated in the full spectrum due to discrete energy levels. In this composite material system, the upconversion process of photons is completed in the rare earth doped upconversion nanoparticles, and the perovskite quantum dots mainly play the role of light conversion. The present application simultaneously has the properties of circularly polarized luminescence and upconversion circularly polarized luminescence, and can produce circularly polarized luminescence by ultraviolet light excitation and upconversion circularly polarized luminescence by 980 nm near-infrared light excitation. At the same time, it also has excellent performance such as high stability, high energy transfer efficiency, high radiation intensity and good repeatability, and has good application prospect.

[0009] The perovskite quantum dot upconversion circularly polarized fluorescence device comprises, from bottom to top, a light-transmitting glass substrate, a parallel orientation layer, a reflective layer, a transparent separation layer, and a composite nanomaterial layer.

[0010] The reflective layer is a polymer cholesteric liquid crystal layer.

[0011] The material of the transparent separation layer is selected from one of polymethyl methacrylate (PMMA) and polyvinyl alcohol (PVA);

[0012] The composite nanocrystal material layer is composed of perovskite quantum dots / upper conversion nanocrystal composite nanomaterials;

[0013] The perovskite quantum dots / upper conversion nanocrystal composite nanomaterials are perovskite quantum dots and upper conversion nanocrystals prepared by an in-situ synthesis method.

[0014] Further, the perovskite quantum dots are CsPbX3.

[0015] X is selected from one of Cl, Cl m Br 3-m , Br, Br m I 3-m , I, and the value range of m is 0≤m≤3.

[0016] Further, the upper conversion nanocrystals are rare earth doped upper conversion nanoparticles; the preferred upper conversion nanoparticles of the present application are hexagonal phases synthesized by a high temperature co-precipitation method which is currently widely used, and the composition is NaYF4:Yb,Tm.

[0017] Further, the doping amounts of Yb 3+ and Tm 3+ are 30wt% and 0.5wt%, respectively.

[0018] Further, the molar ratio of the perovskite quantum dots and the upper conversion nanocrystals is 1:1-2.

[0019] Further, the upper conversion circular polarization fluorescence device of the perovskite quantum dots further comprises a pump source for providing pump energy to the fluorescence device body.

[0020] One of the purposes of the present application is to provide a preparation method of the upper conversion circular polarization fluorescence device of the perovskite quantum dots, comprising the following steps:

[0021] S1, preparing perovskite quantum dots / upper conversion nanocrystal composite nanomaterials: heating and reacting PbX2, oleic acid, oleylamine and octadecene, adding upper conversion nanocrystals, heating and keeping warm in an inert environment, adding cesium oleate precursor and reacting in an ice water bath to obtain a suspension; centrifuging the suspension and post-treating to obtain perovskite quantum dots / upper conversion nanocrystal composite nanomaterials;

[0022] S2, preparing the perovskite quantum dot up-conversion circular polarization fluorescence device: on the parallel orientation layer coated with a liquid crystal mixture, auxiliary liquid crystal orientation, ultraviolet curing, forming a reflective layer; the polyvinyl alcohol aqueous solution is coated on the surface of the reflective layer, annealing, forming a transparent separation layer; the perovskite quantum dot / up-conversion nanocrystal composite nanomaterial is coated on the surface of the transparent separation layer, annealing and curing;

[0023] In step S1, X of PbX2 is selected from one of halogen elements.

[0024] Further, the cesium oleate precursor is prepared by reaction of cesium carbonate, oleic acid and octadecene.

[0025] Further, in step S2, the components of the liquid crystal mixture include liquid crystal monomer, chiral dopant, surfactant and photoinitiator.

[0026] In the application, the liquid crystal monomer can be HCM-009, HCM-008, HCM-006 or 5CB; the chiral dopant can be RM257, S81, R811, S5011 or R5011; the photoinitiator can be Irg651; and the surfactant can be 2-methyl acrylate. The liquid crystal monomer and the chiral dopant form cholesteric phase liquid crystal with chirality, and the photoinitiator initiates polymerization of the liquid crystal monomer to form a polymer network under ultraviolet irradiation, thereby forming a polymer cholesteric phase liquid crystal. Since the polymer cholesteric phase liquid crystal layer has chirality, the up-conversion fluorescence emitted from the composite material layer also has chirality after being reflected by the polymer cholesteric phase liquid crystal layer.

[0027] One of the purposes of the application is to prepare an optical device by using the perovskite quantum dot up-conversion circular polarization fluorescence device, and the optical device can be applied in anti-counterfeiting encryption, 3D display, optical storage information, circular polarization light detector and biological medicine.

[0028] The application has at least the following beneficial effects:

[0029] 1、The upconversion nanocrystal and the perovskite quantum dot are coupled together by the in-situ synthesis method in the application, the absorption spectrum of the selected perovskite quantum dot is well matched with the emission spectrum of the upconversion nanocrystal, so that the upconversion nanocrystal can transfer the energy of the absorbed near-infrared light to the perovskite quantum dot to make it produce fluorescence through the two energy transfer mechanisms of radiative photon reabsorption (PR) and non-radiative fluorescence resonance energy transfer (FRET). However, if the perovskite quantum dot and the upconversion nanocrystal are simply combined together by the traditional physical blending method, a highly uneven material will be obtained, which reduces the optical performance and stability of the device, and is not suitable for the distance-dependent non-radiative fluorescence resonance energy transfer process. The donor (upconversion nanocrystal) and the acceptor (perovskite quantum dot) are tightly coupled by the in-situ composite method used in the application, the distance between the two luminescent centers is greatly reduced, which is more conducive to the distance-dependent non-radiative fluorescence resonance energy transfer process, and is conducive to the improvement of the energy transfer efficiency, thereby improving the overall optical performance of the device.

[0030] 2、The application uses a polymer cholesteric liquid crystal layer to make a reflective layer, uses a perovskite quantum dot / upconversion nanocrystal composite nanomaterial to make a composite nanomaterial layer, and uses a transparent separation layer to separate the reflective layer and the composite nanomaterial layer. The composite nanomaterial layer belongs to an inorganic light-emitting layer, and the reflective layer is an organic layer, and the compatibility of the two layers of materials is poor, and the use of a transparent separation layer can greatly improve the stability of the device structure and the upconversion circularly polarized fluorescence performance. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 It is a transmission electron microscope image of the perovskite quantum dot / upconversion nanocrystal composite nanomaterial of embodiment 1.

[0032] Figure 2 It is a fluorescence emission spectrum of the perovskite quantum dot / upconversion nanocrystal composite nanomaterial of embodiment 1 under the excitation of a 980 nm continuous wave laser.

[0033] Figure 3 It is a structure schematic diagram of the upconversion circularly polarized fluorescence device of the perovskite quantum dot prepared in embodiment 1.

[0034] Figure 4 It is a schematic diagram of stimulated radiation of the upconversion circularly polarized fluorescence device of the perovskite quantum dot of embodiment 1 under the excitation of a pump source laser; the reference signs are as follows: a light-transmitting glass substrate 100, a parallel orientation layer 110, a reflective layer 200, a transparent separation layer 210, and a composite nanomaterial layer 300.

[0035] Figure 5The upconversion circularly polarized photoluminescence spectrum of the upconversion circularly polarized photoluminescence device of the perovskite quantum dots of Example 1 under the excitation of a 980 nm continuous wave laser.

[0036] Figure 6 The fluorescence emission spectrum of the perovskite quantum dots / upconversion nanocrystal physical mixture material of Comparative Example 1 under the excitation of a 980 nm continuous wave laser.

[0037] Figure 7 The upconversion circularly polarized photoluminescence spectrum of the upconversion circularly polarized photoluminescence device of the perovskite quantum dots of Comparative Example 2 under the excitation of a 980 nm continuous wave laser. DETAILED DESCRIPTION

[0038] The concept and technical effects of the present application will be described below in combination with examples to fully understand the purpose, features and effects of the present application. Obviously, the described examples are only a part of the examples of the present application, but not all the examples. Based on the examples of the present application, other examples obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0039] The high-temperature co-precipitation method for preparing hexagonal phase NaYF4 double-doped Yb 3+ 、Tm 3+ upconversion nanocrystals, wherein the NaYF4 is in a hexagonal phase and is in a stable state in thermodynamics, and has 3 cation lattice point positions in its crystal lattice, wherein rare earth cations (Y 3+ 、Yb 3+ 、Tm 3+ ) occupy one position, sodium ions and rare earth cations occupy one position, and the remaining position is occupied by sodium ions alone. The rare earth ions Yb 3+ 、Tm 3+ enter the crystal structure of NaYF4 after doping, and partially replace Y 3+ ions, wherein the doping amounts of Yb 3+ and Tm 3+ are 30wt% and 0.5wt% respectively (hereinafter, the upconversion nanocrystals are abbreviated as NaYF4:Yb,Tm). The synthesis method is referred to from the literature (Nature Protocols, 2014, 9, 1634).

[0040] The preparation method of the cesium oleate precursor in the specific embodiment of the present application is as follows: 2.5 mmol of cesium carbonate, 2.5 ml of oleic acid, and 40 ml of octadecene are reacted at 150°C under a nitrogen environment for 1 h to form the cesium oleate precursor.

[0041] Example 1

[0042] The application discloses an up-conversion circular polarization fluorescence device of perovskite quantum dots, which can output green up-conversion circular polarization fluorescence, and has the structure of a light-transmitting glass substrate (1.5 mm) / a parallel orientation layer (200 nm) / a reflection layer (10 mu m) / a transparent separation layer (200 nm) / a composite nanomaterial layer (1100 nm) from bottom to top.

[0043] The specific preparation process is as follows:

[0044] S1, preparing perovskite quantum dots / up-conversion nanocrystal composite nanomaterials.

[0045] S1-1, preparing hexagonal phase NaYF4:Yb, Tm up-conversion nanocrystals by a high-temperature coprecipitation method;

[0046] S1-2, adding 0.138 g of PbBr2 into a three-necked flask, adding 1 ml of oleic acid, 1 ml of oleylamine and 10 ml of octadecene, heating to 120 DEG C, reacting for 1 h under vacuum, removing water and oxygen, injecting 0.188 mmol of the up-conversion nanocrystals (the molar ratio of the perovskite quantum dots and the up-conversion nanocrystals is 2:1), then passing nitrogen, increasing the temperature to 155 DEG C, keeping for 10 min, injecting 0.376 mmol of a cesium oleate precursor, and quenching the reaction in an ice water bath after 5 s of reaction to obtain a suspension.

[0047] S1-3, then centrifuging the obtained suspension, removing the supernatant of the perovskite quantum dots and the separated up-conversion nanocrystals with a size of about 5-8 nm, then adding 1 ml of cyclohexane, centrifuging at 4500 rpm for 5 min, removing the yellow precipitate, obtaining the perovskite quantum dots / up-conversion nanocrystal composite nanomaterials, and dispersing the perovskite quantum dots / up-conversion nanocrystal composite nanomaterials into 3 ml of cyclohexane for standby.

[0048] Figure 1 It is a transmission electron microscope image of the perovskite quantum dots / up-conversion nanocrystal composite nanomaterials of the embodiment 1 of the application.

[0049] Figure 2 It is a fluorescence emission spectrum of the perovskite quantum dots / up-conversion nanocrystal composite nanomaterials of the embodiment 1 of the application under the excitation of a 980 nm continuous wave laser.

[0050] S2, preparing an up-conversion circular polarization fluorescence device of perovskite quantum dots.

[0051] S2-1, under yellow light, dissolving 0.3842 g of a liquid crystal monomer RM257, 0.0198 g of a chiral dopant HCM-006, 0.004 g of a surfactant 2-methacrylate ethyl and 0.004 g of a photoinitiator Irg651 (benzoin dimethyl ether) into 1.1 wt% of dimethylbenzene, stirring uniformly in a brown bottle at 40 DEG C for 1 h, and preparing a liquid crystal mixture;

[0052] S2-2, take a clean transparent glass substrate, clean, ozone treatment, spin coating 5wt% polyvinyl alcohol solution, annealing at 60°C for 30min, cooling to room temperature, the transparent glass substrate coated with polyvinyl alcohol solution is rubbed with swan black flannel in one direction, forming a parallel orientation layer of transparent glass substrate;

[0053] S2-3, the liquid crystal mixture is spotted on the parallel orientation layer, and another clean glass substrate is pressed thereon and gently rubbed to assist the orientation of the liquid crystal, then the transparent glass substrate coated with the liquid crystal mixture is cured under ultraviolet light for 2min, and the upper glass substrate is removed to obtain a reflective layer;

[0054] S2-4, spin coating 5wt% polyvinyl alcohol solution on the surface of the reflective layer, annealing at 50°C for 1h to obtain a transparent separation layer; then drop coating the perovskite quantum dot / upper conversion nanocrystal composite nanomaterial prepared in step S1 on the surface of the transparent separation layer, annealing treatment on a hot stage at 45°C for 30min to form a composite nanomaterial layer, and obtaining a finished product.

[0055] Figure 3 Structure diagram of the perovskite quantum dot upper conversion circularly polarized fluorescence device prepared in example 1.

[0056] Figure 4 Schematic diagram of the stimulated radiation of the perovskite quantum dot upper conversion circularly polarized fluorescence device of example 1 under the excitation of the pump source laser. In use, the upper conversion nanocrystal in the composite nanomaterial layer receives the energy generated by the pump light of the 980nm continuous wave laser, and then transfers the energy of the absorbed near-infrared light to the perovskite quantum dot through radiative energy transfer and non-radiative fluorescence resonance energy transfer, so that the perovskite quantum dot generates upper conversion fluorescence excited by near-infrared light; then, when the wavelength of the fluorescence radiated by the perovskite quantum dot just overlaps with the reflection band of the polymer cholesteric liquid crystal layer, the matched photons will be selectively reflected, generating upper conversion circularly polarized fluorescence with the same chirality as the polymer cholesteric liquid crystal. It comprises a transparent glass substrate 100, a reflective layer 200, a parallel orientation layer 110 provided on the transparent glass substrate 100, the reflective layer 200 being a polymer cholesteric liquid crystal layer, and the reflective layer 200 being provided on the parallel orientation layer 110; a transparent separation layer 210 is provided between the composite nanomaterial layer 300 and the reflective layer 200, and is used to separate the composite nanomaterial layer 300 and the reflective layer 200.

[0057] Figure 5 Upper conversion circularly polarized spectrum of the perovskite quantum dot upper conversion circularly polarized fluorescence device of example 1 under the excitation of the 980nm continuous wave laser.

[0058] Example 2

[0059] An upconversion circularly polarized fluorescent device of perovskite quantum dots, which can output green upconversion circularly polarized fluorescence, has the structure of, from bottom to top, a light-transmitting glass substrate (1.5 mm) / a parallel orientation layer (200 nm) / a reflective layer (10 μm) / a transparent separation layer (200 nm) / a composite nanomaterial layer (1100 nm).

[0060] The specific preparation process is as follows:

[0061] S1, preparation of perovskite quantum dots / upconversion nanocrystal composite nanomaterial.

[0062] S1-1, preparation of hexagonal phase NaYF4:Yb,Tm upconversion nanocrystals by high-temperature coprecipitation;

[0063] S1-2, 0.046 g of PbBr2 and 0.1156 g of PbI2 were added to a three-necked flask, 1 ml of oleic acid, 1 ml of oleylamine and 10 ml of octadecene were added, heated to 120℃, reacted for 1 h under vacuum, and water and oxygen were removed, 0.188 mmol of upconversion nanocrystals (the molar ratio of perovskite quantum dots to upconversion nanocrystals was 2:1) were injected, then nitrogen was introduced, the temperature was raised to 170℃, and the reaction was kept for 10 min, 0.376 mmol of cesium oleate precursor was injected, the reaction was quenched by ice water bath after 5 s, and a suspension was obtained.

[0064] S1-3, then the obtained suspension was centrifuged, the supernatant of 5-8 nm perovskite quantum dots and separated upconversion nanocrystals was removed, then 1 ml of cyclohexane was added, centrifuged at 4500 rpm for 5 min, the yellow precipitate was removed, and perovskite quantum dots / upconversion nanocrystal composite nanomaterial was obtained, which was dispersed in 3 ml of cyclohexane for standby.

[0065] S2: preparation of an upconversion circularly polarized fluorescent device of perovskite quantum dots.

[0066] S2-1, under yellow light, 0.3764 g of liquid crystal monomer RM257, 0.0156 g of chiral dopant HCM-006, 0.004 g of surfactant 2-methacrylate ethyl and 0.004 g of photoinitiator Irg651 (benzoin dimethyl ether) were dissolved in 1.1 wt% of xylene, stirred uniformly in a brown bottle at 40℃ for 1 h, and a liquid crystal mixture was prepared;

[0067] S2-2, a clean light-transmitting glass substrate was washed and treated with ozone, 5 wt% of polyvinyl alcohol aqueous solution was spin-coated, annealed at 60℃ for 30 min, cooled to room temperature, and the light-transmitting glass substrate coated with polyvinyl alcohol aqueous solution was rubbed in one direction with a swan black velvet to form a light-transmitting glass substrate with a parallel orientation layer;

[0068] S2-3, the liquid crystal mixture was spotted on the parallel orientation layer, another clean glass substrate was pressed on it, and was gently rubbed to assist the liquid crystal orientation, then the transparent glass substrate coated with the liquid crystal mixture was cured under ultraviolet light for 2 min, and the upper glass substrate was removed to obtain a reflective layer;

[0069] S2-4, a 5wt% polyvinyl alcohol aqueous solution was spin-coated on the surface of the reflective layer, and after annealing at 50℃ for 1h, a transparent separation layer was obtained; then the perovskite quantum dot / upper conversion nanocrystal composite nanomaterial prepared in step S1 was drop-coated on the surface of the transparent separation layer, and annealing treatment was performed on a hot stage at 45℃ for 30 min to form a composite nanomaterial layer, thereby obtaining a finished product.

[0070] Comparative Example 1

[0071] A perovskite quantum dot up-conversion circularly polarized fluorescence device, the preparation method of Comparative Example 1, the raw materials used and the amount of the raw materials are the same as those of Example 1, and the only difference is that the step in Comparative Example 1 is different from step S1 in Example 1, that is, the perovskite quantum dots and the up-conversion nanocrystals are mixed by using a conventional physical blending method, which is as follows: first, the up-conversion nanocrystals NaYF4:Yb,Tm are prepared by a traditional high-temperature co-precipitation method; then, the CsPbBr3 perovskite quantum dots are prepared, 0.138g of PbBr2 is added to a three-necked flask, 1ml of oleic acid, 1ml of oleylamine and 10ml of octadecene are added, and the temperature is heated to 120℃, and the water and oxygen are removed under vacuum for 1h, then nitrogen is introduced, the temperature is increased to 155℃, and the temperature is kept for 10min, 0.376mmol of cesium oleate precursor is injected, and after 5s of reaction, the reaction is quenched by ice water bath, to obtain a suspension, which is centrifuged and purified and then dispersed in 3ml of cyclohexane for subsequent use; finally, the prepared 0.4mmol of cubic phase CsPbBr3 quantum dots are physically mixed with 0.2mmol of hexagonal phase NaYF4:Yb,Tm up-conversion nanocrystals, and the mixture is magnetically stirred for 1h, and then ultrasonically dispersed for 10min to obtain a physical mixture of CsPbBr3 perovskite quantum dots and NaYF4:Yb,Tm up-conversion nanocrystals.

[0072] Figure 6 The fluorescence emission spectrum of the perovskite quantum dot / upper conversion nanocrystal physical mixture of Comparative Example 1 under 980nm excitation.

[0073] Comparative Example 2

[0074] A perovskite quantum dot upconversion circularly polarized fluorescence device, the preparation method of the comparative example 1, the raw materials used and the amount of the raw materials are the same as those of the example 1, the only difference is that the transparent separation layer is not prepared in step (2) S4 of the comparative example 1, but the perovskite quantum dot / upconversion nanocrystal composite nanomaterial is directly drop-coated on the surface of the reflective layer, that is, the structure of the comparative example 2 from bottom to top is: light-transmitting glass substrate (1.5 mm) / parallel orientation layer (200 nm) / reflective layer (10 μm) / composite nanomaterial layer (1100 nm).

[0075] Figure 7 The upconversion circularly polarized spectrum of the perovskite quantum dot upconversion circularly polarized fluorescence device of the comparative example 2 under the excitation of a 980 nm continuous wave laser.

[0076] As can be seen from the above picture, the perovskite quantum dot and the upconversion nanocrystal are closely coupled together by using the in-situ compounding method, compared with the method of mixing the two together by using the traditional physical compounding method, the characteristic peak of the upconversion nanocrystal basically disappears, the energy transfer efficiency from the upconversion nanocrystal to the perovskite quantum dot is significantly improved, which shows the superiority of the in-situ compounding method used in the present application; by not setting the transparent separation layer in the device structure, the circularly polarized performance test is compared with the device structure of the present application which sets the transparent separation layer, the luminescence asymmetry factor (g lum ) of the device structure of the present application is obviously better than that of the device structure without setting the transparent separation layer, which shows that the circularly polarized performance of the device can be significantly improved by setting the transparent separation layer to separate the organic layer and the inorganic luminescent layer in the present application.

[0077] It is apparent for those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and the present application can be implemented in other concrete forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered as exemplary and non-limiting, the scope of the present application is defined by the appended claims rather than the above description, and all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application.

[0078] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, the description manner of the specification is only for the sake of clarity, those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments which can be understood by those skilled in the art.

Claims

1. An upconversion circularly polarized photoluminescence device of perovskite quantum dots, characterized in that, The up-conversion circular polarization fluorescence device of the perovskite quantum dots comprises, from bottom to top, a light-transmitting glass substrate, a parallel orientation layer, a reflective layer, a transparent separation layer, and a composite nanomaterial layer. The reflective layer is a polymer cholesteric liquid crystal layer. The transparent separation layer is made of one of polymethyl methacrylate and polyvinyl alcohol. The composite nanomaterial layer is composed of perovskite quantum dots and up-conversion nanocrystals. The perovskite quantum dots and up-conversion nanocrystals are prepared by an in-situ synthesis method. The up-conversion nanocrystals are rare earth doped up-conversion nanoparticles. The molar ratio of the perovskite quantum dots to the up-conversion nanocrystals is 2:

1. The preparation method of the perovskite quantum dots and up-conversion nanocrystals comprises the following steps: heating and reacting PbX2, oleic acid, oleylamine, and octadecene, adding up-conversion nanocrystals, heating and keeping warm in an inert environment, adding a cesium oleate precursor and reacting in an ice water bath to obtain a suspension; centrifuging the suspension and post-processing to obtain the perovskite quantum dots and up-conversion nanocrystals. 2.The upconversion circularly polarized photoluminescence device of perovskite quantum dots of claim 1, wherein, The perovskite quantum dots are CsPbX3. wherein X is selected from the group consisting of Cl, Cl m Br 3-m , Br, Br m I 3-m , I, and m has a value in the range of 0 m 3. 3.The upconversion circularly polarized photoluminescence device of perovskite quantum dots of claim 1, wherein, The up-conversion circular polarization fluorescence device of the perovskite quantum dots further comprises a pump source.

4. The method of claim 1-3 for preparing the upconversion circularly polarized photoluminescence device of perovskite quantum dots, characterized in that, The method comprises the following steps: S1, preparing perovskite quantum dots and up-conversion nanocrystals: heating and reacting PbX2, oleic acid, oleylamine, and octadecene, adding up-conversion nanocrystals, heating and keeping warm in an inert environment, adding a cesium oleate precursor and reacting in an ice water bath to obtain a suspension; centrifuging the suspension and post-processing to obtain the perovskite quantum dots and up-conversion nanocrystals; S2, preparing the up-conversion circular polarization fluorescence device of the perovskite quantum dots: assisting liquid crystal orientation on the parallel orientation layer coated with a liquid crystal mixture, ultraviolet curing to form a reflective layer; coating a polyvinyl alcohol aqueous solution on the surface of the reflective layer, annealing to form a transparent separation layer; coating the perovskite quantum dots and up-conversion nanocrystals on the surface of the transparent separation layer, and annealing and curing. In step S1, X of PbX2 is selected from one of halogen elements.

5. The method for fabricating the perovskite quantum dot upconversion circular polarization fluorescent device according to claim 4, characterized in that, The cesium oleate precursor is prepared by reacting cesium carbonate, oleic acid, and octadecene.

6. The method for fabricating the perovskite quantum dot upconversion circular polarization fluorescent device according to claim 4, characterized in that, In step S2, the components of the liquid crystal mixture include liquid crystal monomers, chiral dopants, surfactants, and photoinitiators.

7. The up-conversion circular polarization fluorescence device of the perovskite quantum dots in any one of claims 1-3 is applied in anti-counterfeiting encryption, 3D display, optical storage information, circular polarization light detector, and biological medicine.

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