Ultralow-threshold high-order nonlinear optical response composite thin film device and preparation method thereof

Abstract

The invention discloses an ultralow-threshold high-order nonlinear optical response composite thin film device and a preparation method thereof, and belongs to the technical field of nonlinear optical and micro-nano optical devices. The invention provides a high-performance thin-film device formed by compounding a gravity-assisted dielectric microsphere rapid large-area close-packed self-assembled array in a low-density solution medium and a high-order nonlinear luminescent material, the excitation threshold of the ultrahigh-order nonlinear luminescent material is remarkably reduced through the field enhancement effect of the dielectric microsphere array, and the performance of the high-performance thin-film device is improved. And meanwhile, the excellent high-order nonlinear optical response capability is kept. The high-order nonlinear optical material breaks through the limitation of the traditional high-order nonlinear optical material, greatly expands the practical application scene of the nonlinear optical technology, and has a wide industrialization prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nonlinear optics and micro-nano optical devices, and in particular to a super-low threshold high-order nonlinear optical response composite thin film device based on a gravity-assisted dielectric microsphere self-assembled array and a nonlinear optical active layer and a preparation method thereof. BACKGROUND

[0002] Nonlinear optical materials are the cornerstone of modern photonics technology, among which high-order nonlinear optical materials, especially photonic avalanche light-emitting materials, have attracted much attention due to their unique optical properties. The photonic avalanche process is a typical high-order nonlinear optical effect, characterized by a high-order nonlinear dependence (usually > 10 orders) between the excitation light intensity and the emission light intensity, and can produce extremely strong upconversion luminescence under specific wavelength excitation. This effect has great application potential in the fields of super-resolution microscopy, high-sensitivity sensing, micro-lasers, and quantum information processing.

[0003] However, despite the promising prospects of photonic avalanche materials, their path to practical application faces a fundamental technical bottleneck: extremely high excitation threshold. The photonic avalanche process relies on complex energy migration and cross-relaxation cycles, which require extremely high local light power density (hundreds of kilowatts per square centimeter). This leads to: 1. Strict requirements for excitation sources: most current photonic avalanche research must rely on expensive and bulky laser systems, which severely limits their application in portable and integrated devices. 2. Material damage and stability issues: continuous high-power laser irradiation can easily cause irreversible degradation such as photobleaching and thermal damage, severely affecting the reliability and service life of the device. 3. Limited application scenarios: in cutting-edge fields such as high-sensitivity biological imaging, the phototoxicity of high-power lasers on living samples is an insurmountable obstacle, making it difficult to achieve in vivo high-resolution imaging based on photonic avalanche.

[0004] To reduce the threshold of photonic avalanche, existing technologies have made some attempts, such as constructing photonic crystal microcavities or noble metal plasmonic structures to enhance the local optical field. However, these methods often introduce new problems: the preparation process of photonic crystal microcavities is complex, costly, and has limited bandwidth; while noble metal plasmonic structures are accompanied by huge non-radiative ohmic losses, leading to luminescence quenching, and their own thermal stability is poor, which contradicts the high light intensity environment required by photonic avalanche.

[0005] Therefore, there is an urgent need in the art to develop a new composite structure device capable of significantly reducing the excitation threshold of photonic avalanche light emission. This structure needs to be able to provide extremely strong light field localization and enhancement capability without introducing significant loss, while having the characteristics of simple preparation process, high stability, large batch preparation, high uniformity of structure and good compatibility with existing optical systems, in order to truly release the huge potential of photonic avalanche light emission materials in practical applications. SUMMARY

[0006] Based on the above background art, the present application aims to solve the technical bottlenecks of high excitation threshold, complex preparation process and insufficient stability faced by existing high-order nonlinear optical materials. Specifically, the purposes of the present application include: 1. To provide a preparation method of an ultra-low threshold high-order nonlinear optical response composite thin film device, which is simple to operate, low in cost, can realize large-area rapid high-quality preparation of microlens film, is easy to integrate and compatible with existing micro-nano processing technology; 2. To provide an ultra-low threshold high-order nonlinear optical response composite thin film device, which can significantly reduce the excitation threshold required for generating nonlinear optical effects (such as second harmonic generation, two-photon absorption luminescence, photonic avalanche fluorescence, etc.) by at least two orders of magnitude, so that it can work efficiently under low-power, compact laser source.

[0007] In order to achieve the above purposes, the present application provides the following technical solutions:

[0008] A preparation method of an ultra-low threshold high-order nonlinear optical response composite thin film device, comprising the following steps:

[0009] 1) Disperse dielectric microspheres in a first dispersion liquid to prepare a mixture; add a second dispersion liquid to a container, place a substrate inclined below the liquid surface in the container, inject the mixture from the upper end of the inclined substrate, so that the dielectric microspheres move to the lower end of the inclined substrate under the action of gravity and form a monolayer self-assembled array on the substrate; encapsulate the self-assembled array to obtain a self-assembled layer; wherein the density of the first dispersion liquid and the second dispersion liquid is less than the density of the dielectric microspheres;

[0010] 2) Prepare a nonlinear optical active layer, which has dispersed high-order nonlinear luminescent materials therein;

[0011] 3) Combine the self-assembled layer and the nonlinear optical active layer to form an ultra-low threshold high-order nonlinear optical response composite thin film device, wherein the self-assembled array of dielectric microspheres is configured to form multiple field enhancement regions in space by local regulation of incident light field; the high-order nonlinear luminescent material is located in the field enhancement region or within the near-field range thereof.

[0012] In a preferred embodiment, the dielectric microspheres are made of one of barium titanate, silicon dioxide or polystyrene, and have a size ranging from 5 microns to 500 microns; and the dielectric microspheres have a mass ratio of 30wt%-70wt% in the mixture.

[0013] In a preferred embodiment, the substrate has an inclination angle of 5°-60° with respect to the horizontal plane.

[0014] In a preferred embodiment, the first dispersion liquid and the second dispersion liquid are independently selected from water, ethanol or a mixture of the two.

[0015] In a preferred embodiment, the step of encapsulating the self-assembled array comprises: placing the substrate carrying the self-assembled array horizontally, after drying, allowing the first polymer material to penetrate into the array gap and gradually cover the dielectric microspheres, with a thickness of 1mm or more, then curing, and after curing, peeling off from the substrate to obtain the self-assembled layer; the first polymer material comprises polydimethylsiloxane (PDMS) or polymethyl methacrylate (PMMA), which serves as an encapsulation layer to provide support and stability.

[0016] Further preferably, the curing is performed at a temperature ranging from 20-80 degrees Celsius for 1 hour or more.

[0017] In a preferred embodiment, in the nonlinear optical active layer, the high-order nonlinear luminescent material is dispersed in the second polymer material in the form of random distribution of nanocrystals or microcrystals, and the second polymer material comprises polydimethylsiloxane or polymethyl methacrylate.

[0018] Further preferably, the high-order nonlinear luminescent material is one or more of rare earth Tm 3+ , Pr 3+ , Pr 3+ / Yb 3+ , Nd 3+ , Ho 3 + and Er 3+ based rare earth upconversion luminescent nanomaterials activated individually or collectively.

[0019] In a preferred embodiment, the combination of the self-assembled layer and the nonlinear optical active layer comprises interface curing bonding through a curing adhesive, or chemical bonding after plasma treatment of the surfaces of the self-assembled layer and the nonlinear optical active layer.

[0020] Further preferably, the curing adhesive comprises a chemical UV curing adhesive or a thermal curing adhesive, and uniform pressure is applied and left for a certain period of time to achieve interface curing.

[0021] The ultra-low threshold high-order nonlinear optical response composite thin film device is prepared by the preparation method; the ultra-low threshold high-order nonlinear optical response composite thin film device comprises a stacked self-assembly layer and a nonlinear optical active layer, wherein the self-assembly layer is provided with a single-layer self-assembly array of dielectric microspheres; and the nonlinear optical active layer is provided with dispersed high-order nonlinear luminescent materials.

[0022] The self-assembly array is configured as a microlens array and is arranged to form a plurality of periodically arranged field enhancement regions in space by localizing and regulating an incident light field; the nonlinear optical active layer is located in the field enhancement region and is stably combined with the self-assembly array of the dielectric microspheres; thus, the excitation threshold required for the thin film to produce nonlinear optical response is reduced by at least two orders of magnitude compared with a pure nonlinear optical active layer without the self-assembly array of the dielectric microspheres.

[0023] In a preferred embodiment, the dielectric microspheres in the self-assembly array have a hexagonal close-packed arrangement.

[0024] In a preferred embodiment, the self-assembly array is located in a surface layer on one side of the self-assembly layer, and the side surface layer is close to the nonlinear optical active layer.

[0025] Compared with the prior art, the technical effects and advantages of the present application are as follows:

[0026] 1. Large-area, rapid and high-density ordered self-assembly of microlens arrays is achieved: the self-assembly speed is greatly accelerated by means of gravity in a low-density solution, and the ordered assembly ability of the microlenses is greatly improved by means of gravity, avoiding the common problems of time-consuming and inability to densely and orderly arrange in conventional self-assembly methods, and realizing the preparation of a large-area, rapid and high-density ordered microlens self-assembly array.

[0027] 2. Threshold breakthrough: the "photon nano jet" effect and Mie resonance effect of the dielectric microsphere array form a very strong local field enhancement at the focal point of the microspheres, thereby reducing the excitation threshold required for the nonlinear optical active material to produce nonlinear response by 2-3 orders of magnitude. This makes it possible to use low-cost, low-power continuous wave lasers or small pulse lasers to excite nonlinear effects.

[0028] 3. Comprehensive performance improvement: while achieving ultra-low threshold, the thin film maintains extremely high nonlinear conversion efficiency and signal-to-noise ratio due to the extremely low loss of the dielectric material itself, and has excellent optical stability and thermal stability.

[0029] 4. Stable structure and easy integration: The stable combination of two layers is achieved by chemical bonding or plasma bonding, avoiding layer separation and ensuring device reliability. At the same time, the thin film structure is compact and flexible, and can be seamlessly integrated with existing CMOS technology and flexible electronic technology.

[0030] 5. Simple preparation process and low cost: The self-assembly method used does not require complex and expensive micro-nano processing equipment (such as electron beam lithography, ion etching, etc.), and the process is simple and convenient to operate, suitable for large-area and large-scale production, greatly reducing the manufacturing cost.

[0031] 6. Wide application prospect: The ultra-low threshold nonlinear optical response thin film provides a key material basis for developing a new generation of ultra-sensitive biosensors, low-power all-optical switches, miniaturized lasers, high-resolution biological imaging systems, and quantum light sources, etc., and has great market application potential. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 A cross-sectional schematic diagram of the ultra-low threshold high-order nonlinear optical response composite thin film device prepared in the embodiment of the present application.

[0033] Figure 2 A process flow diagram of gravity-assisted dielectric microsphere solution self-assembly and packaging and a microsphere array film physical diagram of the embodiment of the present application, wherein the microsphere array film physical diagram is the physical diagram of Example 1.

[0034] Figure 3 A photonic avalanche nanomaterial morphology schematic diagram (a) and an energy level diagram (b) of the embodiment of the present application.

[0035] Figure 4 A test system schematic diagram of the ultra-low threshold high-order nonlinear optical response composite thin film device of the embodiment of the present application.

[0036] Figure 5 A double logarithmic curve diagram of the optical test results of Example 1 and Comparative Example 1 of the present application, wherein the curve of the left composite thin film is the test result of Example 1.

[0037] Figure 6 A double logarithmic curve diagram of the optical test results of Example 2 and Comparative Example 1 of the present application, wherein the curve of the left composite thin film is the test result of Example 2.

[0038] Figure 7 A double logarithmic curve diagram of the optical test results of Example 3 and Comparative Example 1 of the present application, wherein the curve of the left composite thin film is the test result of Example 3. DETAILED DESCRIPTION

[0039] The technical solutions of the present application will be further described in detail below in combination with the drawings and specific embodiments. It should be understood that the following embodiments are only used to explain the present application and do not constitute a limitation on the protection scope of the present application.

[0040] Reference Figure 1 The ultralow threshold high-order nonlinear optical response composite thin film device of the embodiment includes a stacked self-assembled layer A and a nonlinear optical active layer B, wherein the self-assembled layer A includes a first polymer material 1 and a monolayer self-assembled array 2 of dielectric microspheres, the first polymer material 1 is used to encapsulate the dielectric microspheres to form a protective layer; the nonlinear optical active layer B includes a second polymer material 3 as a polymer matrix, and the second polymer material 3 is provided with dispersed high-order nonlinear luminescent materials 4. The self-assembled array 2 is located at a surface layer on one side of the self-assembled layer A, and the surface layer on this side is close to the nonlinear optical active layer B. The self-assembled array 2 forms a dielectric microlens layer. An excitation light source 5 is arranged on one side of the self-assembled layer A, the self-assembled array 2 is configured as a microlens array and is arranged to form a plurality of field enhancement regions arranged periodically in space by localizing and regulating an incident light field; the nonlinear optical active layer B is located in the field enhancement region. Thus, the excitation threshold required for the thin film to generate nonlinear optical response can be significantly reduced.

[0041] Embodiment 1: Based on 50 mm barium titanate microspheres and Tm 3+ Ultralow threshold nonlinear optical response thin film of activated photonic avalanche nanomaterial

[0042] In embodiment 1, barium titanate dielectric microspheres (hereinafter referred to as barium titanate microspheres) are used as dielectric microspheres to form a self-assembled array, NaYF4:15% Tm 3+ The photonic avalanche nanocrystals are used as high-order nonlinear luminescent materials, and the first polymer material and the second polymer material are both PDMS.

[0043] 1. Preparation of self-assembled layer

[0044] Cleaning and pretreatment: monodisperse barium titanate microspheres with a diameter of 50 mm are used, and the barium titanate microspheres are immersed in a mixed solution of concentrated sulfuric acid and hydrogen peroxide (volume ratio 7:3) for 30 minutes to remove organic impurities and make the surface hydrophilic. Then repeatedly centrifugal washing with deionized water until the supernatant is neutral.

[0045] Preparation of ethanol mixture: the cleaned barium titanate microspheres are dispersed in anhydrous ethanol to prepare a mixture with a concentration of 50wt%.

[0046] Low-density solvent gravity-assisted self-assembly into film: refer to Figure 2, the container 6 is a petri dish, the second dispersion 8 is anhydrous ethanol, the glass substrate 7 is a clean glass slide, and the glass substrate 7 is placed at an angle (30 degrees from horizontal) below the surface of the liquid, with the lower end of the glass substrate 7 resting on the bottom of the petri dish and the upper end resting on the side wall of the petri dish, forming a stable state. The barium titanate microsphere / ethanol mixture 9 is pipetted into the upper end of the glass substrate 7, and the barium titanate microspheres slide to the bottom of the glass substrate 7 under the assistance of gravity and realize rapid and orderly self-assembly. Further remove the excess ethanol solution with a pipette, and let stand for 1 h until the microsphere self-assembly array is completely dried. Place the glass substrate 7 horizontally with the barium titanate microspheres facing upwards, and slowly infiltrate 10 mL of PDMS 10 into the array gap, and continue to inject until the thickness reaches more than 3 mm. Place the PDMS-encapsulated microsphere self-assembly array in a 50-degree Celsius oven for 6 hours until the PDMS is completely cured. After curing, remove the PDMS-encapsulated self-assembly layer A, and the single-layer, hexagonal close-packed structure of the large-area uniform barium titanate microsphere self-assembly array is finally formed on the surface layer.

[0047] 2. Preparation of a nonlinear-optically active layer

[0048] Synthesis: NaYF4: 15% Tm was synthesized using high-temperature co-precipitation 3+ Upconversion nanocrystals. The specific steps are as follows: 1 mmol of YCl3:6H2O and TmCl3:6H2O with different molar ratios are mixed with 6.0 mL of oleic acid and 15.0 mL of 1-octadecene. The mixture is heated to 130 °C and kept under vacuum for 60 minutes to form a lanthanide-oleate complex. After cooling to 50 °C, a 10 mL methanol solution containing NH4F (0.148 g) and NaOH (0.1 g) is added, followed by stirring for one hour. Then the solution is heated to 110 °C and volatile impurities are removed under vacuum. Finally, the remaining mixture is heated to 310 °C under a nitrogen atmosphere and kept at this temperature for 90 minutes. After cooling to room temperature, the nanocrystals are collected by centrifugation, washed with ethanol, and dispersed in 10.0 mL of cyclohexane.

[0049] Morphology characterization: A small amount of the above nanocrystal dispersion is taken and dropped onto a copper grid for observation by transmission electron microscopy. The TEM image (a) shows that the synthesized nanocrystals are hexagonal phase, uniform in morphology, and about 25 nm in size. Figure 3

[0050] The above NaYF4: 15% Tm 3+ ​A cyclohexane dispersion of nanocrystals was mixed with PDMS prepolymer at a volume ratio of 1:10, with 0.5 wt% dispersant added. The mixture was then sonicated for 30 minutes to form a uniform nanocrystal / PDMS hybrid precursor. This was then spin-coated at 500 rpm for 1 minute and thermo-cured at 80°C for 2 hours to fully crosslink the PDMS, yielding a nonlinear optical active layer B.

[0051] 3. Fabrication and Stabilization of Composite Thin Film Devices

[0052] A PDMS prepolymer was spin-coated onto the surface of the nonlinear optical active layer B as an adhesive layer. The microsphere self-assembled array side of the previously prepared self-assembled layer A was then tightly bonded to the PDMS prepolymer layer, and a certain vertical pressure was applied. The mixture was then thermo-cured at 80°C for 2 hours to allow complete cross-linking of the PDMS, achieving a stable composite structure, resulting in the desired product. Figure 1 The ultra-low threshold high-order nonlinear optical response composite thin film device shown is illustrated.

[0053] 4. Optical performance testing and result analysis

[0054] Test system setup: as shown in the attached document Figure 4 The test optical path is shown. A 1064 nm continuous-wave fiber laser is used as the excitation source 11. After the laser beam's power is adjusted by an adjustable attenuator assembly 12, it is reflected by a dichroic mirror 13 and focused onto the sample surface by a low-power objective lens 14. The photon avalanche upconversion emission signal generated by the sample is collected by a unified objective lens 14 and returned to the optical path, then converged by a collecting lens 15 through the dichroic mirror 13. The converged light signal is coupled into two parallel detection channels: one enters a fiber optic spectrometer 16 for spectral analysis, and the other enters a single-photon detector 17 for photon counting. The signal from the single-photon detector 17 is processed by a counter 18, and both the signal from the fiber optic spectrometer 16 and the signal from the single-photon detector 17 are transmitted to a computer host 19 for data analysis. During the measurement process, the control of the light source 11 is also controlled by the computer host 19.

[0055] Photon avalanche luminescence mechanism: NaYF4: Tm 3+ The mechanism diagram of the photon avalanche process under 1064 nm excitation shows that it involves 3 F4→ 3 Excited-state absorption of H4 3 H4 / 3 H6→ 3 F4 cross relaxation and 3 The number accumulation of particles in the H4 energy level is a typical high-order nonlinear process (see appendix). Figure 3 (b)

[0056] Comparative Example 1

[0057] Pure NaYF4:Tm microsphere array without barium titanate was prepared on the same glass substrate as in Example 1 using the same preparation method as for the nonlinear optical active layer B in Example 1. 3+ / PDMS film.

[0058] Test method: Using the thin-film devices of Example 1 and Comparative Example 1 as samples, the following methods were employed: Figure 4 The test system shown gradually increases the output power of the 1064 nm laser and records the output power at ~800 nm (Tm). 3+ of 3 H4→ 3 The luminescence intensity at the H6 transition is calculated. A double logarithmic curve (i.e., luminescence intensity-power dependence plot) is plotted with laser power on the x-axis and luminescence intensity on the y-axis. The test results are as follows: Figure 5 As shown.

[0059] Double logarithmic curve (with appendix) Figure 5 Clearly displayed:

[0060] The slope of the curve in Comparative Example 1 is approximately 41, confirming its high-order nonlinear (photon avalanche) characteristics, with a emission threshold of 1000 kW / cm². 2 .

[0061] The slope of the curve in Example 1 is also approximately 40, demonstrating that its luminescence mechanism remains unchanged. However, its luminescence threshold shifts significantly to the left, with a measured value of 10 kW / cm². 2 .

[0062] Conclusion: By combining NaYF4 with barium titanate microsphere arrays, Tm 3+ The excitation threshold of photon avalanche luminescence has been reduced by more than two orders of magnitude.

[0063] Example 2: Ultra-low threshold nonlinear optical response thin films based on plasmon interface bonding

[0064] 1. Preparation of self-assembled layers

[0065] This part is exactly the same as in Example 1. The materials, cleaning and pretreatment, gravity-assisted self-assembly of the film, and PDMS encapsulation and unpacking steps are all consistent with those in Example 1 to ensure that the prepared barium titanate microsphere self-assembled array is consistent with that in Example 1.

[0066] 2. Fabrication of Nonlinear Optical Active Layers

[0067] This part is exactly the same as Example 1 in terms of synthesis method and morphological characterization, ensuring that NaYF4:15%Tm 3+ Nanocrystalline materials exhibit consistent properties.

[0068] 3. Preparation and stabilization of composite films

[0069] Plasma surface activation: One side surface of the self-assembled array of barium titanate microspheres was treated with oxygen plasma. 3+ The other side surface of the self-assembled array of barium titanate microspheres and the PDMS nonlinear optical active layer were treated with oxygen plasma respectively. Treatment parameters: power 100 W, treatment time 60 seconds. The plasma bombardment will break the Si-CH3 bond on the surface of the PDMS, generating silanol groups, and introduce active groups such as hydroxyl groups on the surface of the barium titanate microspheres, making the surface change from hydrophobic to hydrophilic.

[0070] Room temperature contact bonding: The two surfaces treated by plasma were immediately aligned face to face (usually within a few minutes after treatment to prevent surface activity decay). A light and uniform finger pressure was applied. At room temperature, the two active surfaces will spontaneously adhere closely through hydrogen bonding and van der Waals forces.

[0071] Final curing: The bonded sample was left to stand at room temperature for 12 hours, or placed on a hot stage at 60-80°C for 1-2 hours to obtain the ultra-low threshold high-order nonlinear optical response composite thin film device. The purpose of this step is not to achieve bonding, but to strengthen the bonding strength. During the standing or slight heating process, the silanol groups between the interfaces will further undergo condensation reaction to form firm Si-O-Si or Si-O-Ti covalent bonds, thereby achieving permanent and stable chemical bonding.

[0072] The ultra-low threshold high-order nonlinear optical response composite thin film device prepared in Example 2 was tested using the same optical testing method as in Example 1, and compared with Comparative Example 1, and the test results are shown in the double logarithmic curve graph of Figure 2. Figure 6

[0073] Figure 6 The double logarithmic curve graph of Figure 2 shows that:

[0074] The curve slope of Example 2 is also about 40, proving that the light emission mechanism has not changed due to the change in the composite method.

[0075] The measured value of the light emission threshold of Example 2 is expected to be of the same order of magnitude (~10 kW / cm²) as Example 1, which is significantly lower than that of Comparative Example 1.

[0076] Conclusion: By plasma bonding method, the significant reduction of the photon avalanche light emission threshold is also successfully achieved, which is universal for various interface composite methods.

[0077] Example 3: Ultra-low threshold nonlinear optical response thin film based on 100 mm barium titanate microspheres and PDMS bonding

[0078] 1. Preparation of self-assembled layer

[0079] ​In this example, monodisperse barium titanate microspheres with a diameter of 100 μm were used as the dielectric microspheres.

[0080] Cleaning and pretreatment: The same as step 1 of example 1.

[0081] Preparation of ethanol mixture: The cleaned 100 μm barium titanate microspheres were dispersed in anhydrous ethanol to prepare a mixture with a concentration of 50 wt%.

[0082] Gravity-assisted self-assembly into a film: The process flow was the same as example 1, and a monolayer, hexagonal close-packed structure of 100 μm barium titanate microsphere self-assembly array was formed on the substrate by using gravity-assisted self-assembly technology.

[0083] PDMS encapsulation and transfer: The steps were the same as example 1, and finally an independent self-assembly layer encapsulated by PDMS was obtained.

[0084] 2. Preparation of a nonlinear optical active layer

[0085] This part is the same as example 1.

[0086] 3. Preparation and stable combination of a composite film

[0087] This part is the same as example 1.

[0088] The self-assembly layer of 100 μm barium titanate microsphere array was stably combined with the NaYF4: Tm 3+ / PDMS nonlinear optical active layer by using the same PDMS bonding layer process as example 1, and an ultra-low threshold high-order nonlinear optical response composite film device was obtained.

[0089] The ultra-low threshold high-order nonlinear optical response composite film device prepared in example 3 was tested by using the same optical test method as example 1, and was compared with comparative example 1, and the test results are shown in Figure 7 .

[0090] Figure 7 The double logarithmic curve of

[0091] The light emission threshold of comparative example 1 is still 1000 kW / cm 2 .

[0092] The curve slope of example 3 is also about 40, which proves that the photon avalanche light emission mechanism has not changed.

[0093] However, its light emission threshold has jumped by an order of magnitude, and the measured value is significantly reduced to ~1 kW / cm 2It can be seen that by using larger size (100 μm) barium titanate dielectric microspheres to construct a self-assembled array, and with the aid of a PDMS adhesive layer, the NaYF4:15% Tm 3+ The photon avalanche nanocrystal complex can further significantly reduce the excitation threshold of the photon avalanche luminescence, and realize ultra-low threshold operation in the order of sub-kW / cm2.

[0094] The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited to this. Any change or replacement within the technical range disclosed by the present application can be easily thought by any person skilled in the art, and should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for fabricating an ultra-low threshold high-order nonlinear optical response composite thin-film device, characterized in that, Includes the following steps: 1) The dielectric microspheres are dispersed in a first dispersion to form a mixture; a second dispersion is added to a container, and the substrate is placed at an angle below the liquid surface in the container. The mixture is injected from the upper end of the tilted substrate, causing the dielectric microspheres to move towards the lower end of the tilted substrate under the action of gravity and form a monolayer self-assembled array on the substrate; the self-assembled array is encapsulated to obtain a self-assembled layer; wherein the density of the first dispersion and the second dispersion is less than the density of the dielectric microspheres. 2) Prepare a nonlinear optical active layer, wherein the nonlinear optical active layer contains dispersed high-order nonlinear luminescent materials; 3) Combining the self-assembled layer and the nonlinear optical active layer to form an ultra-low threshold high-order nonlinear optical response composite thin film device, wherein the self-assembled array of the dielectric microspheres is configured to form multiple field enhancement regions in space by locally modulating the incident light field; The higher-order nonlinear luminescent material is located within the field enhancement region or its near-field range.

2. The method for fabricating an ultra-low threshold high-order nonlinear optical response composite thin-film device according to claim 1, characterized in that: The dielectric microspheres are made of barium titanate, silicon dioxide, or polystyrene, and their size ranges from 5 micrometers to 500 micrometers; the mass ratio of the dielectric microspheres in the mixture is 30wt%-70wt%.

3. The method for fabricating an ultra-low threshold high-order nonlinear optical response composite thin-film device according to claim 1, characterized in that: The base is tilted at an angle of 5° to 60° relative to the horizontal plane.

4. The method for fabricating an ultra-low threshold high-order nonlinear optical response composite thin-film device according to claim 1, characterized in that: The first dispersion and the second dispersion are each independently selected from water, ethanol, or a mixture of both.

5. The method for fabricating an ultra-low threshold high-order nonlinear optical response composite thin-film device according to claim 1, characterized in that, The steps of encapsulating the self-assembled array include: placing the substrate carrying the self-assembled array horizontally, drying it, allowing a first polymer material to penetrate into the array gaps and gradually cover the dielectric microspheres to a thickness of more than 1 mm, then curing it, and peeling it off from the substrate after curing to obtain the self-assembled layer; the first polymer material includes polydimethylsiloxane or polymethyl methacrylate.

6. The method for fabricating an ultra-low threshold high-order nonlinear optical response composite thin-film device according to claim 1, characterized in that, In the nonlinear optical active layer, the higher-order nonlinear luminescent material is dispersed in a random distribution of nanocrystals or microcrystals in the second polymer material, which includes polydimethylsiloxane or polymethyl methacrylate.

7. The method for fabricating an ultra-low threshold high-order nonlinear optical response composite thin-film device according to claim 1, characterized in that: The self-assembled layer and the nonlinear optical active layer are bonded by means of interfacial curing with a curing adhesive, or by chemical bonding after plasma treatment of the surfaces of the self-assembled layer and the nonlinear optical active layer.

8. A composite thin-film device with ultra-low threshold high-order nonlinear optical response, characterized in that: The device is prepared by the preparation method according to any one of claims 1 to 7; the ultra-low threshold high-order nonlinear optical response composite thin film device includes a stacked self-assembled layer and a nonlinear optical active layer, wherein the self-assembled layer is provided with a single-layer self-assembled array of dielectric microspheres; the nonlinear optical active layer is provided with dispersed high-order nonlinear light-emitting material.

9. The ultra-low threshold high-order nonlinear optical response composite thin film device according to claim 8, characterized in that: In the self-assembled array, the dielectric microspheres are arranged in a hexagonal close-packed pattern.

10. The ultra-low threshold high-order nonlinear optical response composite thin film device according to claim 8, characterized in that: The self-assembled array is located on the surface layer of one side of the self-assembled layer, which is close to the nonlinear optical active layer.

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