Lead sulfide-based inorganic-organic hybrid superlattice materials having pronounced nonlinear optical absorption and preparation thereof

Abstract

The application relates to a lead sulfide-based inorganic-organic hybrid superlattice material with significant nonlinear optical absorption and preparation of the same, a series of PbS2 / C n (n=4, 6, 8) superlattices are synthesized through a simple hydrothermal synthesis method, first principle simulation shows that the PbS2 inorganic layer and interlayer molecules form covalent bonds and van der Waals interaction. Under femtosecond laser excitation with a wavelength of 515-900 nm, the PbS2 / C n superlattices all exhibit strong nonlinear absorption, and the nonlinear absorption coefficient increases with the increase of the interlayer spacing. The application utilizes quantum confinement in the inorganic layer and the dielectric enhancement effect of the superlattice, adjusts the length of the organic molecules, increases the interlayer spacing, and prepares a new lead sulfide-based hybrid superlattice material with excellent nonlinear performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nonlinear optics, and relates to a lead sulfide-based inorganic-organic hybrid superlattice material with significant nonlinear optical absorption and a preparation method thereof. BACKGROUND

[0002] Nonlinear optical materials have attracted more and more attention due to their application prospects in optical signal processing, frequency conversion, microfabrication, biological imaging and sensing, and photodynamic therapy. It is of great significance to synthesize new materials with excellent nonlinear optical performance. Among them, lead sulfide has the advantages of wide tunable band gap, high absorption coefficient, easy solution processing, and environmental stability, and is considered to be a strong candidate for the next generation of low-cost flexible nonlinear optical materials.

[0003] In recent years, significant progress has been made in the study of nonlinear optical responses of two-dimensional layered materials such as transition metal chalcogenides, graphene and black phosphorus. Among them, transition metal chalcogenides have attracted widespread attention due to their tunable band gap (1-2.5 eV) and unique nonlinear optical response. The quantum confinement effect caused by thinning greatly enhances the nonlinear optical response of two-dimensional materials. However, the extremely small light-matter interaction length (usually less than 1 nanometer) will result in a decrease in modulation depth (usually less than 5%), which cannot meet the requirements of practical applications. In addition, the strong correlation between nonlinear characteristics and material thickness also hinders the application of single-layer / multi-layer two-dimensional materials, because this correlation requires fine control and large-scale synthesis of material thickness, which is still a great challenge. Building hybrid inorganic-organic superlattices based on lead sulfide is an effective way to solve this problem. The superlattice is essentially assembled by alternating organic spacer layers and single-layer inorganic units, showing quantum confinement and dielectric enhancement independent of material size, providing a large enough light-matter interaction length. At the same time, the preparation of superlattice often uses solution-based synthesis method, which is simple, economical and efficient, overcoming the uncontrollability of single-layer / few-layer material synthesis and the challenge of post-synthesis stacking.

[0004] At present, there is no literature report on the preparation of lead sulfide-based inorganic-organic hybrid superlattice material. SUMMARY

[0005] The purpose of the present application is to provide a lead sulfide-based inorganic-organic hybrid superlattice material with significant nonlinear optical absorption and a preparation method thereof, which exhibits excellent anti-saturation absorption and saturation absorption performance in a wide spectral range, and the corresponding nonlinear absorption coefficient increases with the increase of the length of the organic component.

[0006] The purpose of the present application can be achieved by the following technical solutions:

[0007] In one aspect, the application provides a PbS2 / C

[0008] The application synthesizes a series of PbS2 / C n (n=4, 6, 8) superlattices by a simple hydrothermal synthesis method, and first-principle simulation shows that covalent bonds and van der Waals interactions are formed between the PbS2 inorganic layers and the interlayer molecules. The application utilizes the quantum confinement in the inorganic layers and the dielectric enhancement effect of the superlattice to prepare a new PbS2-based hybrid superlattice material with excellent nonlinear performance by adjusting the length of the organic molecules and increasing the interlayer spacing.

[0009] In another aspect, the application also provides a preparation method of a PbS2 / C n superlattice material with significant nonlinear optical absorption. Lead dichloride and an alkyl dithiol organic ligand are weighed and added to a reaction solvent, mixed uniformly, transferred to a hydrothermal kettle for hydrothermal reaction, and a PbS2 / C n superlattice material is obtained.

[0010] Further, the alkyl dithiol organic ligand is selected from one of 1,4-butanedithiol, 1,6-hexanedithiol, 1,8-octanedithiol, and 1,10-decanedithiol. According to the different ligands used, the corresponding PbS2 / C n superlattice materials with n=4, 6, 8, and 10 are obtained.

[0011] Further, the molar ratio of the lead dichloride and the alkyl dithiol organic ligand is 1:1-1:3. Specifically, it can be selected as 1:1, 1:2, or 1:3, etc.

[0012] Further, before the hydrothermal reaction, the concentration of the lead dichloride in the reaction system is 0.03-0.2 mol / L. Specifically, it can be selected as 0.05 mol / L, 0.03 mol / L, 0.1 mol / L, or 0.2 mol / L, etc.

[0013] Further, the reaction solvent is one of N,N-dimethylformamide, tetrahydrofuran, and isopropyl alcohol.

[0014] Further, the temperature of the hydrothermal reaction is 80-150℃, specifically, it can be 80℃, 120℃, or 150℃, etc., and the time is 4-40h, specifically, it can be 4h, 20h, or 40h, etc.

[0015] Further, the PbS2 / C n superlattice film material is prepared by a pull-up plating film method.

[0016] Further, the PbS2 / C n The process of the superlattice thin film material is as follows:

[0017] The PbS2 / C n The superlattice material is dispersed in isopropyl alcohol and ultrasonically pulverized to obtain PbS2 / C n The dispersion liquid;

[0018] Polyvinylpyrrolidone is added into the obtained PbS2 / C n dispersion liquid to obtain a pulling plating solution;

[0019] The FTO substrate is immersed in the pulling plating solution, then taken out and dried, and the process is repeated for several times to obtain PbS2 / C n superlattice thin film material.

[0020] More preferably, the PbS2 / C n The concentration of the dispersion liquid is 5-7 mg / mL;

[0021] The concentration of the polyvinylpyrrolidone in the pulling plating solution is 1-1.4 mg / mL;

[0022] The time for each immersion is 30-50 s.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] 1. By adjusting the length of the organic molecules, the distance between the inorganic layers of PbS2 is increased, and a series of excellent nonlinear optical new materials are designed by using the quantum confinement and dielectric enhancement effect. The materials exhibit excellent reverse saturation absorption and saturation absorption performance in a wide spectral range, and the corresponding nonlinear absorption coefficient increases with the increase of the length of the organic component.

[0025] 2. The process flow of the present application is simple, easy to operate and low in cost, and can be expected to be mass-produced.

[0026] In summary, the PbS2-based hybrid superlattice material can be successfully prepared by a simple and efficient hydrothermal synthesis method, and the nonlinear optical new material with excellent reverse saturation absorption performance is obtained. By adjusting the length of the organic molecules to increase the interlayer distance, the nonlinear absorption performance of the PbS2-based hybrid superlattice is significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1-1 The powder X-ray diffraction pattern (PXRD), sample d n (n=4, 6, 8) of the PbS2 / C (100) of the organic ligand carbon chain length, powder X-ray diffraction refinement pattern.

[0028] Figure 1-2 High-resolution transmission electron microscopy (HRTEM) images of PbS2 / C n (n = 4, 6, 8) powders.

[0029] Figure 2 High-resolution transmission electron microscopy (HRTEM) images of PbS2 / C n Schematic diagrams of first-principle simulation results of PbS2 / C

[0030] Figure 3 High-resolution transmission electron microscopy (HRTEM) images of PbS2 / C n (n = 4, 6, 8) powders.

[0031] Figure 4 High-resolution transmission electron microscopy (HRTEM) images of PbS2 / C n (n = 4, 6, 8) powders. NL (n = 4, 6, 8) powders. (100) (n = 4, 6, 8) powders. DETAILED DESCRIPTION

[0032] The present application will be described in detail below with reference to the drawings and specific embodiments. The present embodiments are implemented on the basis of the technical solutions of the present application, and detailed implementation methods and specific operation processes are given, but the protection scope of the present application is not limited to the following embodiments.

[0033] In the following embodiments, if no special materials or processing techniques are specified, it means that they are all conventional commercially available materials or conventional processing techniques in the art.

[0034] In some specific embodiments, the present application provides a method for preparing a lead sulfide-based inorganic-organic hybrid superlattice material with significant nonlinear optical absorption, including PbS2 / C n powder preparation, and PbS2 / C n film preparation in two steps:

[0035] First, PbS2 / C nPowder preparation:

[0036] Into 6 mL of N,N-dimethylformamide, 0.30 mmol of PbCl2and 0.60 mmol of alkyl dithiol were added. The solution was added into a 150 ml Teflon-lined stainless steel autoclave and kept at 120 °C for 20 hours. The as-synthesized product was centrifuged and washed with absolute ethanol for five times to obtain PbS2 / C n powder.

[0037] Second step, PbS2 / C n Thin film preparation:

[0038] PbS2 / C n powder was dispersed in isopropanol and a nanosheet dispersion (6 mg / mL) was prepared after 30 minutes of sonication. Polyvinylpyrrolidone powder was added to the dispersion while stirring to prepare a spin-coating solution (1.2 mg / mL). The FTO substrate was immersed into the dispersion for 40 seconds and then taken out and dried in air for 180 seconds. This process was repeated ten times to obtain a uniform PbS2 / C n thin film.

[0039] The above embodiments will be described in more detail with further examples.

[0040] Example 1

[0041] This example used 1,4-butanedithiol to prepare PbS2 / C4nanosheets by a hydrothermal synthesis method, and then used a spin-coating method to prepare a PbS2 / C4thin film. Nonlinear response tests were performed on it under a single-beam nonlinear transmittance setup.

[0042] The results of evaluating the nonlinear response of the PbS2 / C4thin film in an open-aperture Z-scan system (Z-scan) under a single-beam nonlinear transmittance showed that under 515 nm femtosecond laser excitation, its third-order nonlinear absorption coefficient β eff was -1466 ± 38 cm GW -1 , and the modulation depth was 27.5%; under 800 nm femtosecond laser excitation, its third-order nonlinear absorption coefficient β eff was 1549 ± 111 cm GW -1 , and the modulation depth was 13.9%; under 900 nm femtosecond laser excitation, its fifth-order nonlinear absorption coefficient γ eff was 952 ± 20 cm 3 GW -2 , and the modulation depth was 39.1%.

[0043] Example 2:

[0044] In this embodiment, PbS2 / C6 nanosheets were prepared by hydrothermal synthesis using 1,6-hexanedithiol, followed by PbS2 / C6 thin films prepared by Czochralski deposition. Nonlinear response tests were then performed under a single-beam nonlinear transmittance setting.

[0045] The results of single-beam nonlinear transmittance evaluation of PbS2 / C6 thin films using an open-aperture Z-scan system show that, under 515 nm femtosecond laser excitation, its third-order nonlinear absorption coefficient β eff -1490±115cm GW -1 The modulation depth is 35.0%; under 800 nm femtosecond laser excitation, its third-order nonlinear absorption coefficient β eff 2619±77cmGW -1 The modulation depth is 25.7%; under 900 nm femtosecond laser excitation, its fifth-order nonlinear absorption coefficient γ eff 1772±278cm 3 GW -2 The modulation depth is 56.1%.

[0046] Example 3:

[0047] In this embodiment, PbS2 / C8 nanosheets were prepared by hydrothermal synthesis using 1,8-octanedithiol, followed by PbS2 / C8 thin films prepared by Czochralski deposition. Nonlinear response tests were then performed under a single-beam nonlinear transmittance setting.

[0048] The results of single-beam nonlinear transmittance evaluation of PbS2 / C8 thin films using an open-aperture Z-scan system show that, under 515 nm femtosecond laser excitation, its third-order nonlinear absorption coefficient β eff -4932±818cm GW -1 The modulation depth is 48.1%; under 800 nm femtosecond laser excitation, its third-order nonlinear absorption coefficient β eff 10449±609cm GW -1 The modulation depth is 39.1%; under 900 nm femtosecond laser excitation, its fifth-order nonlinear absorption coefficient γ eff It is 6465±68cm 3 GW -2 The modulation depth is 88.1%.

[0049] Figure 1-1 and Figure 1-2 In Figure a, the powder X-ray diffraction (PXRD) pattern shows diffraction peaks at small angles, confirming the layered structure of the material. Figure b shows that the extension of carbon chains in the organic ligands leads to the superlattice diffraction peaks increasing from 7.6°. gradually shifted to 6.4° and 5.5° The gradual increase in the interlayer distance is illustrated. The above diffraction peaks can be accurately matched with the (100) crystal plane of the material, which is PbS2 / C n The superlattice nature of the nanosheets is clearly evidenced. Figures c-e are the Pawley refinement results of the powder X-ray diffraction data in Figure a, all samples belong to the P21 / c monoclinic space group, where the parameter a varies with the carbon chain length, while the rest of the parameters remain essentially constant. This indicates that the three samples have similar inorganic layer arrangement, and the longer carbon chain helps to increase the interlayer distance of adjacent inorganic layers. High-resolution transmission electron microscopy (HRTEM) images show the presence of distinguishable continuous lattice fringes, confirming the crystalline nature of the material. The lattice fringes in Figure f correspond to a lattice spacing of 1.22 nanometers, which is consistent with the d (100) value of PbS2 / C4. Among them, the bright inorganic layer fringes are composed of nearly vertical lattice fringes with a lattice spacing of 0.405 nanometers, corresponding to the (010) crystal plane of PbS2 / C4. These shorter fringes can be attributed to the connection of the organic ligand to the inorganic layer, providing strong evidence for the superlattice layered structure. The lattice spacing of 0.341 nanometers measured in Figure g corresponds to the (21-2) plane of PbS2 / C6, while the lattice spacing of 0.336 nanometers measured in Figure h corresponds to the (012) plane of PbS2 / C8, which is consistent with the powder X-ray diffraction results.

[0050] Figure 2 The simulation results of the structure of the PbS2 / C n material are shown. First, the present application simulates the structure of -(CH2) n - bridges covalently connected to sulfur atoms in adjacent PbS2 layers, and explores the effect of increasing the number of -CH2- groups on the interlayer distance of PbS2. When n is less than 8, the interlayer distance is significantly smaller than the experimental value; when n = 8, the interlayer distance is about 1.45 nanometers, close to the measured value (1.61 nanometers, Figure 1a); further increasing the length of the -(CH2) n - bridge will result in an increase in the interlayer distance, but it is difficult to match the molecules used in the experiment (i.e. n = 4, 6, 8). Therefore, another model is proposed, i.e. -(CH2) n-1 CH3molecules are covalently connected to sulfur atoms in one PbS2 layer, while -(CH2) n-1 CH3ends of the methyl groups are connected to another PbS2 layer by van der Waals forces. When n = 8, the calculated interlayer distance is 1.71 nanometers, which is slightly larger than the measured value of PbS2 / C8 (1.61 nanometers, Figure 1a). For the above two models (Model A, PbS2-(CH2) n ; Model B, PbS2-(CH2) n-1CH3), the carbon-to-lead ratio is 1 for all n, which is less than the theoretical value (e.g., 8 for n = 8) due to steric repulsion between the hydrocarbon chains in the simulation. To compensate for this difference, CH3(CH2) n-2 CH3molecules were used to fill the interlayer space until the carbon-to-lead ratio approached the measured value, and the corresponding structures are shown in Figure 2 a and 2d. In this case, the PbS2interlayers are covalently filled with -(CH2) n -bridge systems (Model A) have little variation in the interlayer spacing (~0.02 nm), while -(CH2) n-1 CH3bridges connect to another PbS2layer via van der Waals forces (Model B), the CH3(CH2) n-2 CH3molecules into the interlayer space results in an increase in the interlayer distance to 1.86 nm, which is greater than the measured value for the highest carbon-to-lead ratio material. Therefore, Figure 2 Model A shown in a can serve as a model for PbS2 / C n materials with lower carbon-to-lead ratios, while Figure 2 Model B shown in d is a viable model for PbS2 / C n materials with the highest carbon-to-lead ratios.

[0051] The formation of covalent bonds between the sulfur atoms and the -CH2- groups results in dangling bonds in the PbS2layers. These bonds cause a peak in the vicinity of the Fermi level in the corresponding total density of states (see Figure 2 b and 2e). The filling of the interlayer space with CH3(CH2)6CH3molecules can cause this peak to disappear and broaden the otherwise narrow band gap (see the region between -1 eV and 0 in Figure 2 b and 2e). To reveal the reason for the disappearance of the dangling bond-related peak, the present inventors simulated the charge density redistribution after the interlayer is filled with CH3(CH2)6CH3molecules. Figure 2 c and 2f show the visible charge transfer from the CH3(CH2)6CH3molecules to the PbS2layers. Although the above-mentioned atomic structure differences form different charge redistribution patterns in the space Figure 2 c and Figure 2 f), these transferred electrons can all saturate the dangling bonds, causing the related peak to disappear and form Figure 2 a similarity in the electronic structure shown in b and 2e. This similarity is consistent with the conclusion that the electronic structure of halide perovskite superlattices is mainly determined by the inorganic layers.

[0052] Figure 3 The ultraviolet-visible-near-infrared absorption spectrum (UV-Vis-NIR) of the PbS2 / C n nanosheets shows an absorption band edge near 405 nm, and the data after fitting can give the band gap value of the material, PbS2 / C nThe direct band gap values ​​of the samples (n=4, 6, 8) are 2.78, 2.80, and 2.85 eV, respectively. Figure b shows the PbS2 / C... n A schematic diagram of the band structure shows that PbS2 / C n The band gap of the material widens as the ligand length increases.

[0053] Figure 4 ac respectively showed PbS2 / C n (n = 4, 6, 8) T under laser excitation at 515 nm, 800 nm and 900 nm NL The -Z pattern shows PbS2 / C. n The sample exhibits a strong nonlinear optical response over a broad spectral range. Figure 4 The df data indicates that its nonlinear performance significantly improves with increasing interlayer spacing. PbS2 / C n The superlattice structure consists of alternating stacked inorganic and organic layers. The organic layers act as potential barriers to mitigate the interactions between the inorganic layers; therefore, this structure can be considered a typical quantum well. Meanwhile, Figure 3 b shows that the band gap of the material increases with increasing carbon chain length, which is direct evidence of quantum confinement, indicating the existence of quantum confinement in the inorganic layer. Both ground-state and excited-state electrons are confined within the inorganic layer, leading to an increase in carrier concentration and consequently an increase in the optical transition matrix elements in the sample, which contributes to the enhancement of the two-photon absorption coefficient. PbS2 / C n Another striking feature of superlattices is the alternating variation of dielectric constant within the sample, where the dielectric constant (ε) of the organic layers varies. o The dielectric constant (ε, 2.0–2.7) is significantly smaller than that of the inorganic layer. i For example, lead sulfide has a concentration of 17–24%. This characteristic is beneficial for incident light and PbS2 / C. n The effective interaction of nanosheets enables PbS2 / C n The reduced effective dielectric constant of the nanosheets leads to a larger local field enhancement factor, ultimately resulting in a larger effective nonlinear absorption coefficient. Therefore, PbS2 / C n The inherent quantum confinement and dielectric enhancement effects in the material's structural features can significantly improve multiphoton absorption performance. Thiols with long carbon chains can enhance these effects, thus making the sample exhibit stronger multiphoton absorption behavior.

[0054] The foregoing description of the embodiments has been presented for the purpose of illustration and description. It is not intended to be exhaustive or to limit the application to the precise form disclosed. Modifications and variations are possible in light of the above teachings or can be acquired from practice of the application. As well, the description is presented in the context of the preferred embodiments as a number of alternatives. It is not intended to limit the application to the precise form described.

Claims

1. A method for preparing a lead sulfide-based inorganic-organic hybrid superlattice material with significant nonlinear optical absorption, characterized in that, This superlattice material was prepared by hydrothermal reaction using lead dichloride and alkyl dithiol organic ligands as raw materials. The specific process of the preparation method is as follows: Lead dichloride and alkyl dithiol organic ligands were weighed and added to the reaction solvent, mixed thoroughly, and then transferred to a hydrothermal reactor for hydrothermal reaction to obtain PbS2 / C. n Superlattice material; the alkyl dithiol organic ligand is selected from one of 1,4-butanedithiol, 1,6-hexanedithiol, 1,8-octanedithiol and 1,10-decanedithiol; The PbS2 / C n In superlattice materials, n = 4, 6, 8; The reaction solvent is one of N,N-dimethylformamide, tetrahydrofuran, and isopropanol; The hydrothermal reaction temperature is 80-150℃, and the time is 4-40h.

2. The method for preparing a lead sulfide-based inorganic-organic hybrid superlattice material with significant nonlinear optical absorption according to claim 1, characterized in that, The molar ratio of lead dichloride to alkyl dithiol organic ligand is 1:1 to 1:

3.

3. The method for preparing a lead sulfide-based inorganic-organic hybrid superlattice material with significant nonlinear optical absorption according to claim 1, characterized in that, Before the hydrothermal reaction, the concentration of lead dichloride in the reaction system was 0.03-0.2 mol / L.

4. A method for preparing a lead sulfide-based inorganic-organic hybrid superlattice thin film material with significant nonlinear optical absorption, characterized in that, The PbS2 / C prepared by the preparation method as described in claim 1 n PbS2 / C superlattice materials were prepared by the Czochralski method. n Superlattice thin film materials; The specific process of the dip coating method is as follows: PbS2 / C n The superlattice material was dispersed in isopropanol and then ultrasonically pulverized to obtain PbS2 / C. n Dispersion; The obtained PbS2 / C n Polyvinylpyrrolidone was added to the dispersion to obtain the dip coating solution; The FTO substrate was immersed in the dip coating solution, then removed and dried. This process was repeated several times to obtain PbS2 / C. n Superlattice thin film materials.

5. The method for preparing a lead sulfide-based inorganic-organic hybrid superlattice thin film material with significant nonlinear optical absorption according to claim 4, characterized in that, PbS2 / C n The concentration of the dispersion is 5-7 mg / mL; The concentration of polyvinylpyrrolidone in the dip coating solution is 1-1.4 mg / mL; Each soaking time is 30-50 seconds.

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