Highly transparent nanocomposite thin films for UV-blue light protection and their preparation methods

Abstract

This invention provides a highly transparent nanocomposite film for ultraviolet-blue light protection and its preparation method. The aforementioned highly transparent nanocomposite film achieves a transmittance of less than 5% in the 250–500 nm ultraviolet-blue light band by precisely controlling the core-shell structure and energy levels of ZnCdS@Cd-rich nanocrystals through differentiated ligand ratios, coupled with a low filler content design of 0 < x ≤ 5 wt%. This results in highly transparent nanocomposite films that effectively shield high-energy harmful light radiation while maintaining a transmittance of not less than 90% in the long-wavelength visible light band above 520 nm, balancing protective effect and visual clarity. This solves the shortcomings of traditional materials that either provide insufficient protection or suffer from visual distortion due to poor transmittance. Furthermore, the preparation method is simple and controllable, requires no complex equipment, and is compatible with various coating methods such as drop coating, spin coating, and blade coating, making it suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of optical functional nanomaterials technology, and in particular to a highly transparent nanocomposite thin film for ultraviolet-blue light protection and its preparation method. Background Technology

[0002] Ultraviolet-blue light (250–500 nm) is ubiquitous in both natural and artificial light environments. It is characterized by high photon energy, strong penetrability, and a high susceptibility to photochemical reactions, and its potential hazards have attracted widespread attention. This wavelength range encompasses both ultraviolet (250–400 nm) and blue-violet (400–500 nm) light, posing risks to both biological health and material stability: ultraviolet light can directly damage DNA (deoxyribonucleic acid) and proteins, inducing photoaging, inflammation, and potential carcinogenic risks in the skin; while blue-violet light, although with relatively lower energy, can penetrate deep into the retina, inducing excessive generation of reactive oxygen species, leading to phototoxic damage and visual function degeneration; simultaneously, ultraviolet-blue light can accelerate the photooxidative degradation of polymers and natural organic materials (such as wood, fabrics, and cultural relics), causing yellowing, fading, and structural deterioration, significantly shortening their lifespan. With the rapid development of LED (Light-Emitting Diode) lighting, laser light sources, and display technologies, the proportion of blue-violet light in daily life and industrial scenarios continues to increase. Its long-term and cumulative exposure effects further exacerbate the aforementioned risks. Therefore, developing optical protective materials that can achieve efficient and selective absorption in the 250–500 nm wavelength range while maintaining high transparency and stability in the long-wave visible light region has become a key research direction and urgent need in the field of optical functional materials and protective coatings.

[0003] Optical shielding films / conversion films have been widely used in construction, displays, protective coatings, photovoltaic power generation, agricultural greenhouses, and material protection. However, a significant trade-off remains between efficient UV-blue light blocking and high visible light transparency, and existing technologies all have obvious shortcomings: traditional inorganic absorbing films (such as TiO2 and ZnO) are highly stable but prone to introducing scattering and haze; organic absorber / dye films have tunable absorption and simple processes, but suffer from photobleaching and insufficient long-term stability; interference-type multilayer filters have steep cutoff characteristics, but their preparation is complex, costly, and highly angle-dependent; and nanocomposite optical films developed in recent years have shown potential in terms of transparency by introducing quantum dots such as carbon dots to achieve short-wavelength enhanced absorption, but still face challenges in spectral selectivity, durability, and large-scale preparation. Overall, how to achieve efficient and stable blocking of high-energy UV-blue light while maintaining low haze and high transparency remains a key problem that urgently needs to be solved in the field of optical shielding films.

[0004] Semiconductor colloids (colloidal nanocrystals) have advantages such as highly tunable band structure, large absorption coefficient, and strong spectral selectivity. The absorption of ultraviolet-blue light can be precisely controlled by size, composition, and core-shell structure, while maintaining high transparency in the long wavelength range. High efficiency absorption can be achieved with low filling, which helps to reduce scattering and haze. The colloidal properties make them easy to process in solution and highly compatible with polymers, making them suitable for large-area, low-cost preparation. Through interface and surface engineering, optical stability and environmental durability can be significantly improved, and multifunctional integration can be supported. They are an ideal material system for high-performance optical shielding and optical filtering films. However, current optical shielding films or optical filtering films still face many common challenges: it is difficult to balance efficient short-wavelength shielding with high long-wavelength transparency; insufficient optical and structural stability under long-term light exposure and humid and hot environments; poor compatibility between low haze, low scattering, and large-area processing; traditional materials often significantly reduce visible light transmittance while blocking ultraviolet / blue light, resulting in yellowing and poor light transmittance, making it difficult to balance effective protection and visual clarity; most efficient short-wavelength absorbing materials rely on high-concentration filling or strong scattering mechanisms, which easily introduce haze and light loss, and suffer from photoaging, migration, or failure under long-term ultraviolet irradiation or humid environments; existing semiconductor nanocrystal systems mostly adjust absorption by changing size or composition, which is insufficient for fine control of band edge states, defect states, and interface energy levels, making it difficult to achieve synergistic optimization of "strong absorption-high long-wavelength transmittance" for blue and violet light. In practical applications such as protective coatings and display filters, there are still problems such as component leakage, poor moisture resistance, and insufficient resistance to ultraviolet aging, which limit their long-term use.

[0005] Therefore, developing a novel optical shielding mechanism that can achieve "intrinsic absorption enhancement rather than simple scattering suppression" through bandgap engineering or interface modulation, while taking into account transparency, stability and processability, is considered an important research direction and technological breakthrough in this field. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a highly transparent nanocomposite film for ultraviolet-blue light protection and its preparation method, which solves the technical problem that existing light shielding films are difficult to achieve both efficient ultraviolet-blue light shielding and high transparency of long-wave visible light. The above-mentioned highly transparent nanocomposite film has a strong ultraviolet-blue light absorption capacity and takes into account transparency, stability and processability.

[0007] To solve the above-mentioned technical problems, the present invention first provides a highly transparent nanocomposite film for ultraviolet-blue light protection, including a transparent carrier and a nanocrystal-organic matrix composite layer coated on the surface of the transparent carrier. The nanocrystal-organic matrix composite layer contains an organic matrix and ZnCdS@Cd-rich nanocrystals uniformly dispersed in the organic matrix.

[0008] Among them, the mass percentage of ZnCdS@Cd-rich nanocrystals in the nanocrystal-organic matrix composite layer is x, and 0<x≤5wt%; ZnCdS@Cd-rich nanocrystals have a core-shell structure, with the core being a ZnCdS nanocrystal core with an adjustable Zn / Cd molar ratio, and the outer shell being a cadmium-rich shell with a higher cadmium mass content than the core.

[0009] Specifically, the high-transparency nanocomposite film for UV-blue light protection of this invention employs a strategy of in-situ construction of a cadmium-rich shell through cation exchange to finely control the edge states of ZnCdS nanocrystals. This enables the material to achieve significantly enhanced absorption capacity in the 250–500 nm UV-blue light region, thereby effectively blocking high-energy harmful light radiation. At the same time, it maintains high transmittance and low haze in the long-wave visible light region to avoid the visual distortion problem of traditional light shielding materials. Furthermore, it avoids nanocrystal leakage and improves resistance to UV aging (optical performance is almost unaffected after UV irradiation) thanks to its excellent environmental durability. Ultimately, it achieves synergistic optimization of efficient UV-blue light protection and high transparency.

[0010] Preferably, the transparent carrier includes any one of optical glass, quartz sheet with a purity of ≥99.9%, and transparent polymer substrate, and the organic matrix includes ethyl cellulose or polymethyl methacrylate.

[0011] Specifically, the core function of the transparent carrier is to provide a flat and stable supporting substrate in the nanocrystal-organic matrix composite layer. At the same time, the transparent carrier itself has excellent high transparency, which can ensure the smooth transmission of long-wavelength visible light. It also has good compatibility with solution coating processes such as drop coating, spin coating, and blade coating, and can adapt to the film formation requirements of different scenarios. The core function of the organic matrix is ​​to serve as a dispersion medium for ZnCdS@Cd-rich nanocrystals. It can make ZnCdS@Cd-rich nanocrystals uniformly dispersed in the organic matrix, avoid agglomeration, and ensure low haze and high transparency of the film. At the same time, the organic matrix itself has excellent film-forming and adhesion properties, which can tightly bind with the transparent carrier to form a continuous and dense nanocrystal-organic matrix composite layer, thereby improving the structural stability and environmental durability of the film.

[0012] Preferably, the Zn / Cd molar ratio of the core in the ZnCdS@Cd-rich nanocrystals is m:n, 0.7≤m≤0.9, 0.1≤n≤0.3, and m+n=1.

[0013] Specifically, by limiting the specific Zn / Cd molar ratio range mentioned above, the band gap of the ZnCdS nanocrystal nucleus can be precisely controlled, so that it forms a suitable energy level structure with the outer cadmium-rich shell, thereby enhancing the selective absorption capability of the nanocrystal for 250-500nm ultraviolet-blue light and achieving a significant reduction in transmittance in this band.

[0014] Preferably, the highly transparent nanocomposite film has a transmittance of less than 5% in the 250-500nm wavelength range and a transmittance of not less than 90% in the wavelength range greater than 520nm.

[0015] Specifically, the highly transparent nanocomposite film has a transmittance of less than 5% in the 250–500 nm ultraviolet-blue light band, enabling efficient and precise shielding against high-energy harmful light radiation in this band. This significantly reduces the damage of ultraviolet light to biological DNA and proteins (such as avoiding the risk of skin photoaging and retinal damage), while effectively inhibiting the photo-oxidative degradation, yellowing, and fading of polymers and other materials induced by ultraviolet-blue light. It can also block the penetration of high-intensity ultraviolet-blue lasers, providing highly targeted and reliable protection. At the same time, the film has a transmittance of no less than 90% in the long-wave visible light band with wavelengths greater than 520 nm. Combined with the support of the highly transparent carrier, it can maximize the smooth transmission of long-wave visible light, balancing excellent protective effects with ultra-high visual clarity.

[0016] Accordingly, the present invention also provides a method for preparing the above-mentioned highly transparent nanocomposite thin film for ultraviolet-blue light protection, the method comprising the following steps: S10: ZnCdS@Cd-rich nanocrystals are dispersed in a non-polar solvent, and then an organic matrix is ​​added. After ultrasonic and heating stirring, a nanocrystal-organic matrix composite colloidal solution is obtained. S20: A highly transparent nanocomposite film is prepared by coating a nanocrystal-organic matrix composite colloidal solution onto the surface of a transparent carrier and placing it in a horizontal environment with weak air circulation. After evaporation at room temperature to remove the non-polar solvent, a highly transparent nanocomposite film is obtained.

[0017] Specifically, the core function of step S10 is to utilize the dispersing effect of ultrasound and the solubilizing effect of heating and stirring to uniformly disperse ZnCdS@Cd-rich nanocrystals in the organic matrix, effectively preventing nanocrystal aggregation and ensuring low haze and high transparency of the film after subsequent film formation. Simultaneously, it forms a stable nanocrystal-organic matrix composite colloidal solution, providing a uniform and stable precursor for the coating process. The core function of step S20 is to utilize a horizontal, low-flow environment to prevent uneven thickness of the colloidal film due to external disturbances, ensuring a smooth and dense film surface. At the same time, it employs a gentle room-temperature evaporation method to avoid the harmful effects of high temperatures on ZnCdS@Cd-rich nanocrystals. The method completely preserves the high-efficiency absorption characteristics of ZnCdS@Cd-rich nanocrystals for ultraviolet-blue light and the adhesion and stability of the organic matrix, without disrupting the core-shell structure of the nanocrystals. The preparation method is simple and controllable, requires no complex equipment, and is compatible with various coating methods such as drop coating, spin coating, and blade coating, making it suitable for large-scale production. The resulting high-transparency nanocomposite film has excellent optical properties, with a transmittance of less than 5% in the ultraviolet-blue light band and a transmittance of not less than 90% in the long-wave visible light band. It also has stable properties such as no nanocrystal leakage and resistance to ultraviolet aging, successfully achieving synergistic optimization of high-efficiency protection and high transparency.

[0018] Preferably, in step S10, the preparation method of ZnCdS@Cd-rich nanocrystals includes the following steps: Add a highly active cadmium solution precursor to the reaction vessel and heat to evaporate to dryness; After the system is cooled down, ZnCdS nanocrystal nuclei and a first mixed ligand solution containing oleylamine and oleic acid are added. The system is then evacuated and slowly heated to 110-120°C, and the vacuum state is maintained for 4-5 hours. Continue heating to 160-170℃ and hold for 0.5h, then heat to 310℃ to allow Cd elements to undergo ion exchange on the surface of ZnCdS nanocrystals, thereby forming a cadmium-rich shell. After the system was cooled to 50-60°C, ethanol was added for passivation, and ZnCdS@Cd-rich nanocrystals were obtained by centrifugation and washing.

[0019] Specifically, the steps of adding a highly active cadmium solution precursor to the reaction vessel and heating it to dryness can achieve sufficient enrichment of the cadmium source, avoiding shell growth defects caused by uneven cadmium source dispersion; the steps of adding ZnCdS nanocrystal nuclei and the first mixed ligand solution after cooling the system, evacuating the vacuum and heating to 110-120℃ and holding for 4-5 hours can remove moisture and oxygen from the system through vacuuming, preventing the oxidation and failure of ZnCdS nanocrystal nuclei, and can also utilize the coating and stabilizing effect of the first mixed ligand solution on the ZnCdS nanocrystal nuclei to prevent nucleus aggregation, while providing a suitable reaction environment for the directional growth of the shell; The step of gradually heating to 160–170°C, holding at that temperature for 0.5 h, and then heating to 310°C allows for precise control of the deposition rate of cadmium on the surface of ZnCdS nanocrystals. This promotes the uniform, dense, and ultrathin growth of the cadmium-rich shell, thereby finely adjusting the band structure of the nanocrystals and ensuring their efficient selective absorption of ultraviolet-blue light. The step of adding ethanol for passivation after cooling the system to 50–60°C and then centrifuging and washing not only terminates the shell growth reaction in time, preventing excessive deposition from affecting the performance of the nanocrystals, but also removes excess ligands and impurities, improving the purity of the nanocrystals. At the same time, surface passivation modification enhances its compatibility with the organic matrix.

[0020] Preferably, the highly active cadmium solution precursor is a cadmium trifluoroacetate aqueous solution precursor prepared by reflux condensation, and its preparation method includes the following steps: Weigh out CdO and place it in a two-necked flask. Add deionized water to submerge the CdO and stir at low speed until the system forms a turbid liquid. Add trifluoroacetic acid dropwise according to the molar ratio of CdO, assemble a condenser and thermometer, raise the temperature to 80-100℃, and continue stirring until the solution becomes colorless and transparent; Remove the condenser, add deionized water and evaporate to remove excess trifluoroacetic acid, repeat the above water addition-evaporation operation until the trifluoroacetic acid is completely removed; Cool to room temperature and use a metering bottle to obtain the target concentration volume of cadmium trifluoroacetate aqueous solution precursor.

[0021] Specifically, the steps of weighing CdO and placing it in a two-necked flask, submerging it in deionized water, and stirring at low speed until a turbid liquid is formed ensure that the CdO particles are fully dispersed in the aqueous system, increasing the contact area with trifluoroacetic acid and providing a homogeneous reactant substrate for the complete reaction. The steps of adding trifluoroacetic acid dropwise according to the CdO molar ratio, equipping the flask with a condenser and thermometer, and heating to 80–100°C while continuously stirring until the solution is colorless and transparent effectively prevent the high-temperature volatilization of trifluoroacetic acid, ensuring sufficient acidity in the reaction system. Precise control of the molar ratio promotes the complete conversion of CdO to cadmium trifluoroacetate, and the colorless and transparent state of the solution directly reflects the complete completion of the reaction, avoiding any omissions. The CdO residue from the reaction introduces impurities. After removing the condenser, deionized water is added and excess trifluoroacetic acid is evaporated to remove it. This process of adding water and evaporating is repeated until the trifluoroacetic acid is completely removed. This thoroughly removes excess trifluoroacetic acid from the system, preventing residual acidic substances from interfering with the ligand effect and crystal nucleus stability during the subsequent nanocrystal preparation process, and significantly improving the purity of the precursor. The step of obtaining a cadmium trifluoroacetate aqueous solution precursor of the target concentration and volume using a quantitative flask after cooling to room temperature allows for precise control of the precursor concentration and dosage, ensuring that the final ZnCdS@Cd-rich nanocrystals possess a regular core-shell structure and excellent UV-blue light selective absorption performance.

[0022] Preferably, the preparation method of ZnCdS nanocrystal nuclei includes the following steps: Prepare a second mixed ligand solution containing oleylamine and oleic acid by adding zinc acetate and cadmium chloride in different molar ratios; First, heat the system to 120-130℃ and hold for 1 hour, then evacuate and heat to 150-170℃, and hold for 1 hour. After the system forms a uniform and transparent solution, cool it to room temperature, then add S powder, heat it to 100-110℃ and keep it at that temperature for 1 hour; Then continue heating to 320-330℃, stirring vigorously and maintaining the temperature for 1 hour; After cooling to 50°C, ethanol was added, and after centrifugation and washing, the mixture was dispersed in a non-polar dispersant to obtain ZnCdS nanocrystal nuclei.

[0023] Specifically, the steps of preparing the second mixed ligand solution and adding zinc acetate and cadmium chloride in different molar ratios can utilize the complexation and dispersion effect of the second mixed ligand solution on metal ions to avoid metal salt aggregation. At the same time, by controlling the molar ratio of zinc acetate to cadmium chloride, the Zn / Cd ratio of ZnCdS nanocrystals can be precisely preset. The steps of first heating the system to 120-130℃ and holding it for 1 hour, and then evacuating and heating it to 150-170℃ and holding it for 1 hour can remove moisture and oxygen impurities from the system step by step, creating a clean reaction environment, preventing metal ion oxidation and interference of impurities on crystal growth, and ensuring the purity of the crystal nuclei. After the system forms a uniform and transparent solution, it is cooled to room temperature before adding S powder, and then heating it to 100-110℃ and holding it for 1 hour. This step allows the S powder to be uniformly dispersed and activated under mild conditions, avoiding the problems of excessively fast reaction and uneven crystal particle size caused by directly adding S powder at high temperature. The next step, heating to 320–330°C with vigorous stirring and holding for 1 hour, triggers a full sulfidation reaction between metal ions and the sulfur source through high temperature. Vigorous stirring enhances mass transfer, promoting the formation of ZnCdS nanocrystals with uniform size and high crystallinity. Holding for 1 hour ensures complete reaction and further improves the structural regularity of the crystal nuclei. The next step, cooling to 50°C, adding ethanol, centrifuging and washing, and then dispersing in a non-polar dispersant, utilizes the precipitation effect of ethanol to rapidly precipitate the nanocrystals. Centrifugation and washing remove excess ligands and unreacted raw materials, improving the purity of the crystal nuclei. Dispersing in a non-polar dispersant facilitates subsequent mixing with the highly active cadmium solution precursor and the second mixed ligand solution, ensuring the smooth progress of the cadmium-rich shell deposition reaction. The final ZnCdS nanocrystals, due to their regular structure and controllable composition, can form a suitable energy level structure with the subsequently deposited cadmium-rich shell.

[0024] Preferably, the volume ratio of oleylamine to oleic acid in the first mixed ligand solution is 6.4:6.3, and the volume ratio of oleylamine to oleic acid in the second mixed ligand solution is 3:1.

[0025] Specifically, the second mixed ligand solution uses a volume ratio of 3:1 because oleylamine has a higher proportion at this ratio. As a long-chain amine ligand, oleylamine has a stronger ability to complex and disperse zinc acetate and cadmium chloride metal ions, which can effectively inhibit the aggregation of metal ions and provide a stable coordination environment for the uniform nucleation and growth of ZnCdS nanocrystals. At the same time, it can control the size and morphology of the crystal nuclei, ensuring that the obtained ZnCdS nanocrystals have a regular structure and a controllable Zn / Cd molar ratio. The first mixed ligand solution uses a near-equal volume ratio of 6.4:6.3 because oleylamine and oleic acid can play a synergistic coordination role at this ratio. The carboxyl functional groups of oleic acid can be more accurately adsorbed on the surface of ZnCdS nanocrystals, guiding cadmium elements to be deposited directionally and uniformly on the surface of the crystal nuclei, avoiding the growth of cadmium-rich shells that are too thick or have defects. At the same time, oleylamine can help stabilize the shell structure, thereby finely controlling the band gap of the nanocrystals.

[0026] Preferably, in step S10, the ultrasonic time is 3 to 5 hours and the heating temperature is 40 to 60°C; the mass percentage of ZnCdS@Cd-rich nanocrystals in the nanocrystal-organic matrix composite layer is x, and 0 < x ≤ 5 wt%.

[0027] Specifically, the aforementioned ultrasonic time setting ensures that ZnCdS@Cd-rich nanocrystals are uniformly dispersed in the organic matrix through sufficient ultrasonic vibration, completely avoiding the problem of increased film haze caused by nanocrystal agglomeration, while also avoiding damage to the core-shell structure of nanocrystals caused by excessively long ultrasonic waves. The heating temperature is set in a mild range of 40–60°C, which can effectively promote the dissolution and swelling of the organic matrix, enhance the interfacial compatibility between the matrix and the nanocrystals, and at the same time avoid degradation of the organic matrix or deterioration of the optical properties of the nanocrystals caused by high temperatures. The mass percentage of ZnCdS@Cd-rich nanocrystals in the nanocrystal-organic matrix composite layer is limited to 0 < x ≤ 5 wt%. On the one hand, the low filling amount ensures that the nanocrystals are uniformly dispersed in the matrix, preventing long-wavelength visible light scattering due to particle density. On the other hand, this mass percentage is sufficient to allow the nanocrystals to form a continuous light absorption network in the matrix, achieving a highly efficient shielding effect with a transmittance of less than 5% in the 250–500 nm ultraviolet-blue light band.

[0028] The beneficial effects of this invention are as follows: Unlike existing technologies, this invention provides a highly transparent nanocomposite film for ultraviolet-blue light protection and its preparation method. This highly transparent nanocomposite film achieves a transmittance of less than 5% in the 250–500 nm ultraviolet-blue light band by precisely controlling the core-shell structure and energy levels of ZnCdS@Cd-rich nanocrystals through differentiated ligand ratios. Combined with a low filler content design of 0 < x ≤ 5 wt%, the film achieves a transmittance of less than 5% in the 250–500 nm ultraviolet-blue light band, effectively shielding high-energy harmful light radiation. Simultaneously, it maintains a transmittance of not less than 90% in the long-wave visible light band above 520 nm, balancing protective effect and visual clarity. This solves the defects of traditional materials, which either provide insufficient protection or suffer from visual distortion due to poor transmittance. Furthermore, the preparation method is simple and controllable, requires no complex equipment, and is compatible with various coating methods such as drop coating, spin coating, and blade coating, making it suitable for large-scale production. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the synthesis of ZnCdS@Cd-rich nanocrystals prepared in Example 1; Figure 2 This is a schematic diagram of the ultraviolet laser transmission comparison experiment and optical transmittance spectrum of ZnCdS and ZnCdS@Cd-rich nanocrystals prepared in Example 1. Figure 3a The Zn prepared in Example 1 of this invention 0.7 Cd0.3 The left side of S is a TEM (Transmission Electron Microscopy) image, and the right side is an EDX (Energy Dispersive X-ray Spectroscopy) elemental mapping image. Figure 3b The Zn prepared in Example 1 of this invention 0.7 Cd 0.3 Left TEM image and right EDX elemental mapping of S@Cd-rich nanocrystals; Figure 4 The shielding effects of ZnCdS and ZnCdS@Cd-rich nanocrystalline colloidal solutions prepared in Example 1 under different laser irradiations are shown. Figure 5 Comparison images of the highly transparent nanocomposite films with different mass percentages of ZnCdS@Cd-rich nanocrystals provided in Embodiment 1 of the present invention, blank optical glass, and optical glass with only an ethyl cellulose film coated on the surface; Figure 6 Comparison of UV-Vis transmittance spectrum curves of ZnCdS@Cd-rich nanocrystals and ethyl cellulose films with different mass percentages provided in Example 1; Figure 7 This is a photograph of the shielding effect of the ZnCdS@Cd-rich nanocrystalline-ethyl cellulose film against blue light and ultraviolet light shown in Example 1. Figure 8a Figure 1 shows the water contact angle test results for optical glass, pure ethyl cellulose film, and ZnCdS@Cd-rich nanocrystalline-ethyl cellulose film provided in Example 1. Figure 8b The image shows the results of the dithizone colorimetric assay for the aqueous immersion solution of the ZnCdS@Cd-rich nanocrystalline-ethyl cellulose film provided in Example 1. Figure 9 The UV-Vis transmittance spectra of the ZnCdS@Cd-rich nanocrystalline-ethyl cellulose film provided in Example 1 after continuous irradiation with a 365 nm UV lamp for 0 h, 24 h, 48 h, 72 h, 96 h and 120 h. Figure 10 This is a physical verification image of the UV aging protection capability of the ZnCdS@Cd-rich nanocrystalline-ethyl cellulose film for wood in Example 1 of the present invention. Detailed Implementation

[0030] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] To address the shortcomings of existing optical shielding materials, such as difficulty in achieving both high-efficiency protection against ultraviolet-blue light and high transparency against long-wave visible light, insufficient environmental stability, and poor adaptability to large-scale processing, this invention provides a highly transparent nanocomposite film for ultraviolet-blue light protection and its preparation method. The highly transparent nanocomposite film uses ethyl cellulose, polymethyl methacrylate, and other organic matrices as the base, supplemented with nanocrystals uniformly dispersed within the organic matrix as the core functional component. It not only possesses a strong absorption and shielding capability against 250–500 nm ultraviolet-blue light, but also achieves a synergistic balance between high-efficiency protection and high light transmittance. Furthermore, it exhibits excellent environmental durability and good processing adaptability, effectively overcoming the application limitations of traditional materials.

[0032] The technical solution of the present invention will now be further described with reference to specific embodiments.

[0033] Example 1 first provides a highly transparent nanocomposite film for ultraviolet-blue light protection, including a transparent carrier and a nanocrystal-organic matrix composite layer coated on the surface of the transparent carrier. The nanocrystal-organic matrix composite layer contains an organic matrix and ZnCdS@Cd-rich nanocrystals uniformly dispersed in the organic matrix. Among them, the mass percentage of ZnCdS@Cd-rich nanocrystals in the nanocrystal-organic matrix composite layer is x, and 0<x≤5wt%; ZnCdS@Cd-rich nanocrystals have a core-shell structure, with the core being a ZnCdS nanocrystal core with an adjustable Zn / Cd molar ratio, and the outer shell being a cadmium-rich shell with a higher cadmium mass content than the core.

[0034] In Example 1, the transparent carrier of the highly transparent nanocomposite film is optical glass, and the organic matrix is ​​ethyl cellulose; the Zn / Cd molar ratio of the core in the ZnCdS@Cd-rich nanocrystal is m:n, 0.7≤m≤0.9, 0.1≤n≤0.3, and m+n=1.

[0035] Accordingly, Example 1 also provides a method for preparing a highly transparent nanocomposite film for ultraviolet-blue light protection, the method comprising the following steps: S10, take 2.5 mL of ZnCdS@Cd-rich nanocrystalline toluene dispersion with a concentration of about 3.2 mg / mL, add 0.2 g of ethyl cellulose to it, and treat the mixture by sonication and heating and stirring at 60 °C for 4 h to obtain a uniform and transparent nanocrystalline-organic matrix composite colloidal solution (containing 3.75 wt% nanocrystalline ethyl cellulose film and toluene). S20: A nanocrystalline-organic matrix composite colloidal solution is coated onto the surface of optical glass by drop coating, spin coating or blade coating. The glass is placed in a horizontal environment with little air flow. After evaporation at room temperature to remove toluene, a highly transparent nanocomposite film (optical glass + 3.75wt% nanocrystalline ethyl cellulose film) is obtained.

[0036] Specifically, when preparing 2.5wt% nanocrystalline ethyl cellulose films, 4.375wt% nanocrystalline ethyl cellulose films, and 5wt% nanocrystalline ethyl cellulose films, it is only necessary to adjust the amount of ZnCdS@Cd-rich nanocrystalline toluene dispersion in step S10, while keeping the amount of ethyl cellulose added and the volume of the final colloidal solution unchanged.

[0037] In step S10, the preparation method of ZnCdS@Cd-rich nanocrystals is as follows: Figure 1 As shown: Step (1) Preparation of ZnCdS nanocrystals with different Zn / Cd ratios: In a mixed ligand system containing oleylamine and oleic acid (volume ratio 3:1), zinc acetate and cadmium chloride in different molar ratios were added. The aqueous solution was evaporated at 130℃ and oxygen was removed by vacuum heating to 160℃ for 1 h each. After a uniform, clear, and transparent solution was formed, the temperature was lowered to room temperature, sulfur powder was added, oxygen and water vapor were removed at 110℃ for 1 h, the temperature was raised to 320℃ and the reaction was stirred vigorously for 1 h, and the temperature was lowered to 50℃. Ethanol was added for passivation, centrifugation, washing and dispersing in a non-polar dispersant such as cyclohexane to obtain ZnCdS nanocrystals (including Zn) with different Zn / Cd ratios. 0.9 Cd 0.1 S nanocrystal nuclei, Zn 0.8 Cd 0.2 S nanocrystals and Zn 0.7 Cd 0.3 S-nanocrystalline nuclei).

[0038] Step (2) Preparation of ZnCdS@Cd-rich nanocrystals: 8 mmol of highly active cadmium solution precursor was added to a flask and evaporated to dryness under heating conditions; after cooling, 4 mmol of ZnCdS nanocrystal nuclei were added, along with a mixed ligand of oleylamine and oleic acid (volume ratio 6.4:6.3). The mixture was evacuated to vacuum and slowly heated to 120°C, maintaining the vacuum state for 5 hours; then the temperature was raised to 170°C, and after half an hour, it was raised to 310°C to promote cadmium enrichment on the surface under heating conditions, forming a cadmium-rich shell. After cooling to 60°C, ethanol was added for passivation, and the mixture was centrifuged and washed to obtain ZnCdS@Cd-rich nanocrystals.

[0039] In step (2), the highly active cadmium solution precursor is a cadmium trifluoroacetate aqueous solution precursor prepared by reflux condensation, and its preparation method includes the following steps: Weigh an appropriate amount of metal oxide (such as CdO) into a two-necked flask, then add deionized water to cover the sample. Add a rotor and stir slowly until homogeneous. After a turbid liquid forms, add trifluoroacetic acid dropwise according to the molar amount of metal oxide added. Immediately install a condenser and thermometer, and slowly raise the temperature to 90°C while increasing the stirring speed until the solution is very clear, transparent, and colorless. Remove the condenser, add deionized water, and evaporate excess trifluoroacetic acid. Repeat this process several times until all the trifluoroacetic acid has evaporated. Cool to room temperature and use a quantitative flask to obtain the target concentration and volume of the cadmium trifluoroacetate aqueous solution precursor.

[0040] Please see Figure 2 It can be seen that the ZnCdS@Cd-rich nanocrystal sample exhibits a stronger absorption and shielding effect against ultraviolet lasers compared to the pure ZnCdS sample. The former can significantly block the penetration of ultraviolet lasers, while the latter has a weaker shielding ability against ultraviolet lasers.

[0041] The transmittance spectrum curve on the right further demonstrates that ZnCdS@Cd-rich nanocrystals exhibit extremely low transmittance in the ultraviolet-blue light band (short wavelength region) and high transmittance in the long-wave visible light band. This directly verifies that the core-shell nanocrystals possess excellent optical properties of "efficiently shielding ultraviolet-blue light and highly transmitting long-wave visible light," providing direct experimental evidence for their use as a functional material for ultraviolet-blue light protection.

[0042] Please see Figure 3a and Figure 3b As can be seen from the TEM image, Zn 0.7 Cd 0.3 S and Zn 0.7 Cd 0.3 The S@Cd-rich nanocrystals were almost uniformly dispersed. The size of the nanocrystals (NCs) after Cd-rich engineering did not increase significantly, only slightly, indicating the deposition of cadmium species on the surface. This also suggests the rapid release of Cd. 2+Only in Zn 0.7 Cd 0.3 A uniform thin shell forms on the surface of the S nanocrystal core. EDS mapping shows that the composition of the nanocrystals changes significantly after the formation of the Cd-rich shell, with a significant decrease in the Zn signal, reflecting the shielding effect of the Cd-rich shell on the Zn signal. Conversely, the Cd signal on the particle surface is significantly enhanced, indicating the formation of a Cd-rich shell. The S signal remains almost unchanged because S exists simultaneously in both the core and shell of the ZnCdS@Cd-rich nanocrystals.

[0043] Please see Figure 4 , Figure 4 The images show the shielding effects of ZnCdS and ZnCdS@Cd-rich nanocrystalline colloidal solutions prepared in Example 1 under different laser irradiations; from Figure 4 As can be seen, under natural light, pure ZnCdS colloidal solutions are mostly colorless or pale yellow, while ZnCdS@Cd-rich colloidal solutions modified with Cd-rich technology all exhibit a distinct yellow color, directly reflecting the deposition of cadmium species on the surface. Under irradiation with 405nm (UV-blue light) and 450nm (blue light) lasers, pure ZnCdS colloidal solutions can clearly transmit the laser, indicating their weak shielding ability against UV-blue light; while ZnCdS@Cd-rich colloidal solutions completely block laser penetration, maintaining their overall yellow appearance without any color change due to laser transmission. Even under higher power (50mW) 505nm laser irradiation, ZnCdS@Cd-rich colloidal solutions can still effectively block laser penetration, and this effect is consistently observed in a series of samples with different Zn / Cd ratios, fully verifying that the cadmium-rich modification strategy can significantly enhance the strong shielding ability of nanocrystals against UV-blue light and even high-energy visible light.

[0044] Please see Figure 5 , Figure 5 These are comparison images of highly transparent nanocomposite films with different mass percentages of ZnCdS@Cd-rich nanocrystals provided in Example 1, along with blank optical glass and optical glass with only an ethyl cellulose film coated on the surface; [The images are from...] Figure 5 It can be seen that for high-intensity lasers, highly transparent nanocomposite films loaded with different mass percentages of ZnCdS@Cd-rich nanocrystals exhibit a strong blocking effect on ultraviolet-blue light.

[0045] Please see Figure 6 , Figure 6 This is a comparison of the UV-Vis transmittance spectra of ZnCdS@Cd-rich nanocrystals and ethyl cellulose films with different mass percentages provided in Example 1; Figure 6It can be seen that nanocrystalline-ethyl cellulose films with different ZnCdS@Cd-rich nanocrystal loadings exhibit excellent selective optical shielding performance in the ultraviolet-visible band: compared with pure ethyl cellulose films with a loading of 0 wt.%, the transmittance of nanocrystalline-loaded films is significantly reduced in the ultraviolet-blue light band of 250–500 nm, especially close to 0 in the short-wavelength band, and the shielding effect is enhanced with the increase of nanocrystalline loading; at the same time, all nanocrystalline-loaded films can maintain a high transmittance of more than 90% in the long-wavelength visible light region above 500 nm.

[0046] To verify the optical shielding performance of the highly transparent nanocomposite film prepared in Example 1, ultraviolet-visible transmission spectra were compared between blank optical glass, pure ethyl cellulose film (with optical glass as the substrate), and highly transparent nanocomposite films loaded with different mass percentages of ZnCdS@Cd-rich nanocrystals. The test results showed that the nanocrystal composite film can achieve precise band-selective shielding—in the 250–500 nm ultraviolet-blue light range, the transmittance decreases significantly, with the transmittance at 500 nm being less than 5%, effectively blocking ultraviolet-blue light; in the long-wavelength visible light region above 520 nm, the transmittance remains above 90%, ensuring good light transmission and visual clarity. Furthermore, with the increase in nanocrystal loading, the film's ability to block blue-violet light is further enhanced; even under high-energy ultraviolet laser irradiation, the composite film can still effectively block laser penetration without affecting normal visual perception.

[0047] Please see Figure 7 , Figure 7 This is a photograph of the shielding effect of the ZnCdS@Cd-rich nanocrystalline-ethyl cellulose film against blue light and ultraviolet light shown in Example 1. Figure 7 Blue light and ultraviolet light test cards were used, with optical glass and ZnCdS@Cd-rich nanocrystalline ethyl cellulose films respectively covering them. Color changes were observed under 365nm and 450nm LED irradiation and ambient light. The results showed that under irradiation, the test card area covered by optical glass exhibited a significant characteristic color change (the sensor card turned purple), while the area covered by the ZnCdS@Cd-rich nanocrystalline ethyl cellulose film showed no color change, directly proving that the film can completely block the penetration of ultraviolet and blue light. Under ambient light, all test card areas showed only the base color, further indicating that the film maintains high transparency under normal visible light and does not affect visual observation. These results directly verify that the ZnCdS@Cd-rich nanocrystalline ethyl cellulose film possesses both excellent ultraviolet-blue light shielding capability and high visible light transmittance.

[0048] Given the practical application requirements of optical shielding films, a systematic evaluation of their overall stability is necessary. Specific tests are as follows: (1) Water contact angle test: Water contact angle tests were performed on blank optical glass, pure ethyl cellulose film and ZnCdS@Cd-rich nanocrystal-ethyl cellulose composite film provided in Example 1 to evaluate the hydrophilicity and hydrophobicity of the film surface; (2) Verification of nanocrystal leakage: The nanocrystal retention stability of ZnCdS@Cd-rich nanocrystal-ethyl cellulose composite film was verified by water damage test combined with dithizone colorimetry. After the composite film was immersed in water for 2 days, the extract was subjected to dithizone colorimetric test. The results showed that the color of the extract was consistent with the blank control group without cadmium, indicating that there was no leakage of nanocrystal particles in the water environment. (3) UV aging test: The ZnCdS@Cd-rich nanocrystalline-ethyl cellulose composite film was continuously irradiated under ultraviolet light for 5 days, and the UV-Vis transmittance spectra before and after irradiation were compared. The test results showed that the UV-vis transmittance spectrum curves of the film before and after irradiation almost overlapped, indicating that the composite film has excellent UV aging resistance and can maintain a stable light shielding effect for a long time.

[0049] Please see Figure 8a , Figure 8a The water contact angle test results are shown for optical glass, pure ethyl cellulose film, and the ZnCdS@Cd-rich nanocrystalline-ethyl cellulose film provided in Example 1; Figure 8a It can be seen that the contact angle of the optical glass is 31.7°, that of the pure ethyl cellulose film is increased to 69.3°, and that of the ZnCdS@Cd-rich nanocrystal-ethyl cellulose film is further increased to 88.9°. This indicates that the introduction of ZnCdS@Cd-rich nanocrystals significantly improves the wettability of the film surface and greatly enhances its hydrophobicity and resistance to liquid penetration.

[0050] Please see Figure 8b , Figure 8b This is a graph showing the dithizone colorimetric verification results of the aqueous immersion solution of the ZnCdS@Cd-rich nanocrystalline-ethyl cellulose film provided in Example 1, where different concentrations of Cd are used. 2+ Aqueous solutions were used as color controls; by Figure 8b It can be seen that the extract of ZnCdS@Cd-rich nanocrystalline-ethyl cellulose film after 2 days of water immersion has a color similar to that of Cd-free extract. 2+ Blank aqueous solution (0M Cd) 2+ Highly consistent with high concentrations of Cd 2+ Aqueous solutions (e.g., 4×10) -5 M Cd 2+The distinct red color contrasts sharply with the film, proving that the film is free of Cd in an aqueous environment. 2+ Despite leakage, the ZnCdS@Cd-rich nanocrystals are stably bonded to the ethyl cellulose matrix, exhibiting excellent structural stability and resistance to water leaching.

[0051] Please see Figure 9 , Figure 9 The UV-Vis transmittance spectra of the ZnCdS@Cd-rich nanocrystalline-ethyl cellulose film provided in Example 1 after continuous irradiation with a 365 nm UV lamp for 0 h, 24 h, 48 h, 72 h, 96 h, and 120 h are shown. Figure 9 It can be seen that in the ultraviolet-blue light band of 250–500 nm, the transmittance of all curves remains stably at a low level; in the long-wavelength visible light region above 520 nm, the transmittance remains above 90% and does not fluctuate significantly with the extension of irradiation time. This result indicates that the ZnCdS@Cd-rich nanocrystalline-ethyl cellulose film can maintain stable ultraviolet-blue light shielding performance and high visible light transmittance under long-term ultraviolet irradiation, and has excellent resistance to ultraviolet aging stability, which can meet the application requirements of long-term outdoor or strong ultraviolet environments.

[0052] To verify the application potential of the ZnCdS@Cd-rich nanocrystalline-ethyl cellulose composite film provided in Example 1 in the fields of organic substrates and UV-induced aging protection of cultural relics, a linden wood block was used as a simulated substrate to conduct UV-induced aging protection tests. The experimental design is as follows: The same linden wood block was selected and divided into different test areas. Some areas were directly exposed (blank control), while other areas were covered with ZnCdS@Cd-rich nanocrystalline-ethyl cellulose composite films, blank optical glass, and pure ethyl cellulose films with different nanocrystalline loadings (control group). The entire linden wood block was placed under a 365nm, 15W UV lamp for 120 hours and the color changes in each area were compared. The results showed that both the bare areas and the areas covered with blank optical glass and pure ethyl cellulose film exhibited obvious darkening and aging phenomena. However, the aging phenomenon was significantly reduced in the areas covered with ZnCdS@Cd-rich nanocrystal-ethyl cellulose composite film. Furthermore, the UV protection effect of the film on the linden wood block gradually increased with the increase of nanocrystal loading, which fully demonstrates that the composite film can effectively inhibit UV-induced substrate aging and has good photoprotection application value.

[0053] Please see Figure 10This figure shows a physical verification of the UV aging protection capability of the ZnCdS@Cd-rich nanocrystalline-ethyl cellulose film on wood in Example 1 of this invention. In the experiment, linden wood blocks were selected as the simulated substrate and divided into multiple test areas. These areas were covered with blank optical glass, pure ethyl cellulose film (0 wt.%), and ZnCdS@Cd-rich nanocrystalline-ethyl cellulose films with loadings of 2.5 wt.%, 4.375 wt.%, and 5 wt.%, respectively. The areas were then continuously irradiated under a 365 nm UV lamp for 5 days, and the color changes of each area before and after irradiation were compared.

[0054] from Figure 10 As can be seen, in the initial state of 0 days of UV irradiation, all covered areas retained the original light beige color of the wood. After 5 days of UV irradiation, the areas covered with blank optical glass and pure ethyl cellulose film (0 wt.%) showed almost the same color as the uncovered areas, exhibiting obvious yellowing, darkening, and aging phenomena. This indicates that pure ethyl cellulose film and optical glass cannot effectively block UV damage to wood. However, the areas covered with ZnCdS@Cd-rich nanocrystalline-ethyl cellulose film retained their initial light beige color, and the protective effect was positively correlated with the nanocrystalline loading: the higher the loading (e.g., 5 wt.%), the closer the wood color was to the initial state. This indicates that high-loading nanocrystalline films can more efficiently absorb high-energy UV light, reducing UV irradiation on the wood surface and thus preventing the color deepening and mechanical property decline caused by UV-induced degradation of lignin. This result directly verifies the practical value of ZnCdS@Cd-rich nanocrystalline-ethyl cellulose film in the field of UV protection for wood, providing an effective solution for UV protection of organic substrates, cultural relics, etc.

[0055] Compared with existing technologies, the highly transparent nanocomposite thin film for ultraviolet-blue light protection and its preparation method provided by this invention have the following advantages: (1) This invention pioneered a synthesis strategy for in-situ construction of shells through cation exchange. Taking cadmium-rich shell-modified ZnCdS core / shell nanocrystals (ZnCdS@Cd-rich) as a typical example, it can finely control the band-edge electronic states of semiconductor nanocrystals, thereby fundamentally enhancing the material's characteristic absorption capacity in the 250-500nm ultraviolet-blue light region, ensuring efficient blocking of high-energy harmful light radiation in this band, and laying a core foundation for subsequent precise band shielding.

[0056] (2) Based on the composite film constructed by ZnCdS@Cd-rich nanocrystals and ethyl cellulose, the present invention achieves the synergistic unity of "high efficiency shielding of ultraviolet-blue light" and "high transmittance of long-wave visible light" - it can achieve strong shielding with transmittance of less than 5% in the harmful wavelength range of 250-500nm, while maintaining transmittance of more than 90% in the long-wave visible light region above 520nm. Moreover, the film has low haze and excellent transparency, effectively avoiding the key defects such as poor selectivity that are common in traditional light shielding materials.

[0057] (3) When the highly transparent nanocomposite film of the present invention is applied to the surface of organic substrates such as wood, it can significantly slow down the photo-oxidative degradation process of components such as lignin by efficiently absorbing ultraviolet-blue light and reducing the irradiation of high-energy light on the substrate surface, thus avoiding aging phenomena such as darkening of color, cracking, and decline in mechanical properties of the substrate. Combined with its highly transparent characteristics, it has shown clear practical value in the fields of material protection, building decoration (such as glass film) and cultural relic protection (such as paper / wood cultural relic protection), and has broad application prospects.

[0058] (4) The high-transparency nanocomposite film of the present invention has excellent environmental stability. After being tested under harsh conditions such as water immersion and long-term ultraviolet irradiation, it can still maintain stable optical shielding performance and structural integrity, with no nanocrystal leakage and no performance degradation. It effectively overcomes the industry pain points of existing optical shielding films such as "insufficient stability and easy failure" and can be adapted to complex application environments such as outdoor and humid environments.

[0059] (5) The nanocrystal synthesis and composite film preparation process adopted in this invention has clear steps and mild and controllable reaction conditions, and does not require special high-end equipment. Moreover, the core film formation process is highly compatible with existing mature processes such as solution coating (such as blade coating, spin coating, and spray coating). It not only has good experimental repeatability, but can also be directly connected to industrial production lines, providing a reliable guarantee for the large-scale promotion of the technology.

[0060] It should be noted that all the above embodiments belong to the same inventive concept, and the descriptions of each embodiment have different focuses. Where the description in a particular embodiment is not detailed, please refer to the description in other embodiments.

[0061] The above embodiments merely illustrate implementation methods of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A highly transparent nanocomposite film for ultraviolet-blue light protection, characterized in that, The invention includes a transparent carrier and a nanocrystal-organic matrix composite layer coated on the surface of the transparent carrier. The nanocrystal-organic matrix composite layer comprises an organic matrix and ZnCdS@Cd-rich nanocrystals uniformly dispersed in the organic matrix. Wherein, the ZnCdS@Cd-rich nanocrystals in the nanocrystal-organic matrix composite layer have a mass percentage of x, and 0 < x ≤ 5 wt%; the ZnCdS@Cd-rich nanocrystals have a core-shell structure, with the core being a ZnCdS nanocrystal core with an adjustable Zn / Cd molar ratio, and the outer shell being a cadmium-rich shell with a cadmium mass content higher than that of the core.

2. The highly transparent nanocomposite film for ultraviolet-blue light protection according to claim 1, characterized in that, The transparent carrier includes any one of optical glass, quartz sheet with a purity of ≥99.9%, and transparent polymer substrate, and the organic matrix includes ethyl cellulose or polymethyl methacrylate.

3. The highly transparent nanocomposite film for ultraviolet-blue light protection according to claim 1, characterized in that, The Zn / Cd molar ratio of the core in the ZnCdS@Cd-rich nanocrystals is m:n, where 0.7≤m≤0.9, 0.1≤n≤0.3, and m+n=1.

4. The highly transparent nanocomposite film for ultraviolet-blue light protection according to claim 1, characterized in that, The highly transparent nanocomposite film has a transmittance of less than 5% in the 250-500nm wavelength range and a transmittance of not less than 90% in the wavelength range greater than 520nm.

5. A method for preparing a highly transparent nanocomposite thin film for ultraviolet-blue light protection as described in any one of claims 1 to 4, characterized in that, The method includes the following steps: S10, the ZnCdS@Cd-rich nanocrystals are dispersed in a non-polar solvent, and then the organic matrix is ​​added. After ultrasonic and heating stirring, a nanocrystal-organic matrix composite colloidal solution is obtained. S20, the nanocrystal-organic matrix composite colloidal solution is coated onto the surface of the transparent carrier and placed in a horizontal environment with weak air circulation. After evaporation at room temperature to remove the non-polar solvent, the highly transparent nanocomposite film is obtained.

6. The method for preparing the highly transparent nanocomposite thin film according to claim 5, characterized in that, In step S10, the preparation method of the ZnCdS@Cd-rich nanocrystals includes the following steps: Add a highly active cadmium solution precursor to the reaction vessel and heat to evaporate to dryness; After the system is cooled down, the ZnCdS nanocrystal nuclei and a first mixed ligand solution containing oleylamine and oleic acid are added. The system is then evacuated and slowly heated to 110-120°C, and the vacuum state is maintained for 4-5 hours. Continue heating to 160-170℃ and hold for 0.5h, then heat to 310℃ to allow Cd elements to undergo ion exchange on the surface of the ZnCdS nanocrystal nuclei to form the cadmium-rich shell. After the system was cooled to 50-60°C, ethanol was added for passivation, and the ZnCdS@Cd-rich nanocrystals were obtained by centrifugation and washing.

7. The method for preparing the highly transparent nanocomposite thin film according to claim 6, characterized in that, The highly active cadmium solution precursor is a cadmium trifluoroacetate aqueous solution precursor prepared by reflux condensation, and its preparation method includes the following steps: Weigh out CdO and place it in a two-necked flask. Add deionized water to submerge the CdO and stir at low speed until the system forms a turbid liquid. Add trifluoroacetic acid dropwise according to the molar ratio of CdO, assemble a condenser and thermometer, raise the temperature to 80-100℃, and continue stirring until the solution becomes colorless and transparent; Remove the condenser, add deionized water and evaporate to remove excess trifluoroacetic acid, and repeat the above water addition-evaporation operation until the trifluoroacetic acid is completely removed; Cool to room temperature and use a metering bottle to obtain the target concentration volume of the cadmium trifluoroacetate aqueous solution precursor.

8. The method for preparing the highly transparent nanocomposite thin film according to claim 6, characterized in that, The preparation method of the ZnCdS nanocrystal nuclei includes the following steps: Prepare a second mixed ligand solution containing oleylamine and oleic acid by adding zinc acetate and cadmium chloride in different molar ratios; First, heat the system to 120-130℃ and hold for 1 hour, then evacuate and heat to 150-170℃, and hold for 1 hour. After the system forms a uniform and transparent solution, it is cooled to room temperature. Then, S powder is added, and the temperature is raised to 100-110℃ under negative pressure and kept at that temperature for 1 hour. Then continue heating to 320-330℃, stirring vigorously and maintaining the temperature for 1 hour; After cooling to 50°C, ethanol was added, and the mixture was dispersed in a non-polar dispersant after centrifugation and washing to obtain the ZnCdS nanocrystal nuclei.

9. The method for preparing the highly transparent nanocomposite thin film according to claim 8, characterized in that, The volume ratio of oleylamine to oleic acid in the first mixed ligand solution is 6.4:6.3, and the volume ratio of oleylamine to oleic acid in the second mixed ligand solution is 3:

1.

10. The method for preparing the highly transparent nanocomposite thin film according to claim 6, characterized in that, In step S10, the ultrasonic time is 3-5 hours and the heating temperature is 40-60°C; the mass percentage of the ZnCdS@Cd-rich nanocrystals in the nanocrystal-organic matrix composite layer is x, and 0 < x ≤ 5 wt%.

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