Ultra-low threshold high-order nonlinear optical response composite thin film device and preparation method

Abstract

The application discloses a kind of ultra-low threshold high-order nonlinear optical response composite film devices and preparation method thereof, belong to the technical field of nonlinear optics and micro-nano optical device.The application provides a kind of high-performance film device based on the fast large-area dense arrangement self-assembly array of dielectric microspheres in low-density solution medium assisted by gravity, which is compounded with high-order nonlinear luminescent material, the structure is through the field enhancement effect of dielectric microsphere array, significantly reduce the excitation threshold of ultra-high-order nonlinear luminescent material, while maintaining its excellent high-order nonlinear optical response ability.The application breaks through the limitation of traditional high-order nonlinear optical material, greatly expands the practical application scene of nonlinear optical technology, and has broad industrialization prospect.

Description

Technical Field

[0001] This invention relates to the technical field of nonlinear optics and micro / nano optical devices, specifically to an ultra-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 its fabrication method. Background Technology

[0002] Nonlinear optical materials are the cornerstone of modern photonics technology. Among them, high-order nonlinear optical materials, especially photonic avalanche luminescence materials, have attracted much attention due to their unique photophysical properties. The photonic avalanche process is a typical high-order nonlinear optical effect, characterized by a high-order nonlinear dependence (typically >10th order) between excitation and emission intensity, capable of producing extremely strong upconversion luminescence under specific wavelength excitation. This effect shows enormous application potential in fields such as super-resolution microscopy, high-sensitivity sensing, microlasers, and quantum information processing.

[0003] However, despite the promising prospects of photonic avalanche materials, their path to practical application faces a fundamental technical bottleneck: an extremely high excitation threshold. The photonic avalanche process relies on complex energy transfer and cross-relaxation cycles, the initiation and maintenance of which require extremely high local optical power densities (on the order of hundreds of kilowatts per square centimeter). This leads to: 1. Stringent requirements for the excitation source: Currently, most photonic avalanche research relies on expensive and bulky laser systems, severely limiting its application in portable, integrated devices. 2. Material damage and stability issues: Continuous high-power laser irradiation easily induces irreversible degradation such as photobleaching and thermal damage in materials, seriously affecting the reliability and lifespan of devices. 3. Limited application scenarios: In cutting-edge fields such as high-sensitivity in vivo imaging, the phototoxicity of high-power lasers to living samples is an insurmountable obstacle, making it difficult to realize technologies such as high-resolution in vivo imaging based on photonic avalanche.

[0004] To lower the threshold of photon avalanche, existing technologies have made some attempts, such as enhancing the local optical field by constructing photonic crystal microcavities or noble metal plasmonic structures. However, these methods often introduce new problems: the fabrication process of photonic crystal microcavities is complex, costly, and has limited bandwidth; while noble metal plasmonic structures are accompanied by huge nonradiative ohmic losses, leading to luminescence quenching, and they themselves have poor thermal stability at high power, which contradicts the high light intensity environment required for photon avalanche.

[0005] Therefore, there is an urgent need in this field to develop a novel composite structure device that can significantly reduce the excitation threshold of photonic avalanche luminescence. This structure needs to provide extremely strong optical field localization and enhancement capabilities without introducing significant losses, while also possessing advantages such as simple fabrication process, high stability, mass production capability, highly uniform structure, and good compatibility with existing optical systems, in order to truly unleash the enormous potential of photonic avalanche luminescence materials in practical applications. Summary of the Invention

[0006] Based on the aforementioned background technology, this invention aims to solve the technical bottlenecks faced by existing high-order nonlinear optical materials, such as excessively high excitation threshold, complex fabrication processes, and insufficient stability. Specifically, the objectives of this invention include: 1. Providing a method for fabricating an ultra-low threshold high-order nonlinear optical response composite thin film device, which is simple to operate, low in cost, and can realize large-area, rapid, and high-quality fabrication of microlens thin films, is easy to integrate, and is compatible with existing micro-nano fabrication processes; 2. Providing an ultra-low threshold high-order nonlinear optical response composite thin film device, which can significantly reduce the excitation threshold required to generate nonlinear optical effects (such as second harmonic generation, two-photon absorption emission, photon avalanche fluorescence, etc.) by at least two orders of magnitude, enabling it to operate efficiently under low-power, compact laser sources.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for fabricating an ultra-low threshold high-order nonlinear optical response composite thin film device includes the following steps:

[0009] 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.

[0010] 2) Prepare a nonlinear optical active layer, wherein the nonlinear optical active layer contains dispersed high-order nonlinear luminescent materials;

[0011] 3) Combining a self-assembled layer and a 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 locally modulating the incident light field; the high-order nonlinear luminescent material is located within the field enhancement region or its near-field range.

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

[0013] In a preferred embodiment, the base is tilted at an angle of 5° to 60° relative to the horizontal plane.

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

[0015] In a preferred embodiment, the step of encapsulating the self-assembled array includes: 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 (PDMS) or polymethyl methacrylate (PMMA), which serves as a support and stabilizing layer.

[0016] More preferably, the curing process involves placing the product at a temperature between 20 and 80 degrees Celsius for more than one hour.

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

[0018] More preferably, the higher-order nonlinear luminescent material is based on rare-earth Tm. 3+ Pr 3+ Pr 3+ / Yb 3+ 、Nd 3+ Ho 3 + And Er 3+ One or more rare-earth upconversion luminescent nanomaterials that are activated individually or in combination.

[0019] In a preferred embodiment, the self-assembled layer and the nonlinear optical active layer are bonded by 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.

[0020] More preferably, the curing adhesive comprises a chemical UV-curing adhesive or a thermosetting adhesive, which is applied under uniform pressure and left to stand for a certain period of time to achieve interface curing.

[0021] An ultra-low threshold high-order nonlinear optical response composite thin film device is prepared by the above-described preparation method; 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 contains a monolayer self-assembled array of dielectric microspheres; the nonlinear optical active layer contains dispersed high-order nonlinear luminescent materials.

[0022] The self-assembled array, acting as a microlens array, is configured to form multiple periodically arranged field-enhancing regions in space by localizing and modulating the incident light field. The nonlinear optical active layer is located within the field-enhancing regions and is stably composited with the self-assembled array of dielectric microspheres. As a result, the excitation threshold required for the thin film to generate a nonlinear optical response is reduced by at least two orders of magnitude compared to a purely nonlinear optical active layer without the self-assembled array of dielectric microspheres.

[0023] In a preferred embodiment, the dielectric microspheres in the self-assembled array are arranged in a hexagonal close-packed configuration.

[0024] In a preferred embodiment, 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.

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

[0026] 1. Achieving large-area, rapid, and high-density ordered self-assembly of microlens arrays: The gravity-assisted self-assembly method in low-density solutions greatly accelerates the self-assembly speed. At the same time, the gravity effect greatly enhances the ordered assembly capability of microlenses, avoiding the common problems of time-consuming and inability to arrange densely and orderly in conventional self-assembly methods. This enables the fabrication of large-area, rapid, and high-density ordered microlens self-assembled arrays.

[0027] 2. Breakthrough reduction in excitation threshold: Through the "photonic nanojet" effect and Mie resonance effect of the dielectric microsphere array, an extremely strong local field enhancement is formed at the focal point of the microspheres, thereby reducing the excitation threshold required for nonlinear optically active materials to generate nonlinear responses by 2-3 orders of magnitude. This makes it possible to excite nonlinear effects using low-cost, low-power continuous-wave lasers or small pulsed lasers.

[0028] 3. Comprehensive performance improvement: While achieving an ultra-low threshold, the 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 and thermal stability.

[0029] 4. Stable structure and easy integration: Stable composite of the two layers is achieved through chemical bonding or plasma bonding, avoiding interlayer separation and ensuring device reliability. At the same time, the thin film structure is compact, flexible and bendable, and can be seamlessly integrated with existing CMOS processes and flexible electronics processes.

[0030] 5. Simple fabrication 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.), the process is simple and easy to operate, and it is suitable for large-area and large-scale production, which greatly reduces the manufacturing cost.

[0031] 6. Broad application prospects: This ultra-low threshold nonlinear optical response thin film provides a key material basis for the development of next-generation ultra-sensitive biosensors, low-power all-optical switches, miniaturized lasers, high-resolution biological imaging systems, and quantum light sources, and has huge market application potential. Attached Figure Description

[0032] Figure 1 This is a cross-sectional schematic diagram of the ultra-low threshold high-order nonlinear optical response composite thin film device prepared according to an embodiment of the present invention.

[0033] Figure 2 The diagram shows a process flow diagram and a physical image of the microsphere array film for the self-assembly and encapsulation of gravity-assisted dielectric microsphere solution according to an embodiment of the present invention. The physical image of the microsphere array film is the same as that in Example 1.

[0034] Figure 3 The diagram shows the morphology (a) and energy level diagram (b) of the photonic avalanche nanomaterial according to an embodiment of the present invention.

[0035] Figure 4 This is a schematic diagram of a test system for an ultra-low threshold high-order nonlinear optical response composite thin film device according to an embodiment of the present invention.

[0036] Figure 5 The graph shows the double logarithmic curves of the optical test results of Example 1 and Comparative Example 1 of the present invention. The curve of the composite thin film on the left side of the graph represents the test results of Example 1.

[0037] Figure 6 The graph shows the double logarithmic curves of the optical test results of Example 2 and Comparative Example 1 of the present invention. The curve of the composite thin film on the left side of the graph represents the test results of Example 2.

[0038] Figure 7 The graph shows the double logarithmic curves of the optical test results of Example 3 and Comparative Example 1 of the present invention. The curve of the composite film on the left side of the graph represents the test results of Example 3. Detailed Implementation

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

[0040] refer to Figure 1 The embodiment of the ultra-low threshold high-order nonlinear optical response composite thin film device includes a stacked self-assembled layer A and a nonlinear optical active layer B. The self-assembled layer A comprises a first polymer material 1 and a monolayer self-assembled array 2 of dielectric microspheres. The first polymer material 1 encapsulates the dielectric microspheres to form a protective layer. The nonlinear optical active layer B comprises a second polymer material 3 as a polymer matrix, in which dispersed high-order nonlinear luminescent material 4 is disposed. The self-assembled array 2 is located on the surface of one side of the self-assembled layer A, and this surface 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 disposed on one side of the self-assembled layer A. The self-assembled array 2, as a microlens array, is configured to form multiple periodically arranged field enhancement regions in space by localizing and modulating the incident light field; the nonlinear optical active layer B is located within the field enhancement regions. Therefore, the excitation threshold required for the thin film to generate a nonlinear optical response can be significantly reduced.

[0041] Example 1: Based on 50mm barium titanate microspheres and Tm 3+ -Ultra-low threshold nonlinear optical response thin films of activated photonic avalanche nanomaterials

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

[0043] 1. Preparation of self-assembled layers

[0044] Cleaning and pretreatment: Monodisperse barium titanate microspheres with a diameter of 50 mm were used. The barium titanate microspheres were soaked 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. They were then repeatedly centrifuged and washed with deionized water until the supernatant was neutral.

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

[0046] Gravity-assisted self-assembly of films in low-density solvents: Reference Figure 2Container 6 is a petri dish, into which anhydrous ethanol is injected as the second dispersion 8. A clean glass slide, 7, is placed at an angle (around 30 degrees to the horizontal) below the liquid surface, with its lower tilted end abutting the bottom of the petri dish and its upper end abutting the sidewall, creating a stable state. A barium titanate microsphere / ethanol mixture 9 is pipetted into the upper tilted end of the glass substrate 7. Under gravity, the barium titanate microspheres slide to the bottom of the glass substrate 7 and rapidly and orderly self-assemble. Excess ethanol solution is further removed with a pipette, and the array is allowed to stand for 1 hour to allow it to dry completely. The glass substrate 7 is then placed horizontally with the barium titanate microspheres facing upwards. 10 mL of PDMS 10 is slowly injected into the array gaps, and this process continues until the thickness reaches at least 3 mm. The PDMS-encapsulated microsphere self-assembled array is placed in a 50°C oven for 6 hours until the PDMS is completely cured. After curing, the PDMS-encapsulated self-assembled layer A is peeled off, and one side of its surface finally forms a large-area uniform barium titanate microsphere self-assembled array with a single-layer, hexagonal close-packed structure.

[0047] 2. Fabrication of Nonlinear Optical Active Layers

[0048] Synthesis: NaYF4 was synthesized by high-temperature co-precipitation method: 15% Tm 3+ Upconversion nanocrystals. The specific steps were as follows: 1 mmol of YCl3:6H2O and TmCl3:6H2O in different molar ratios were mixed with 6.0 mL of oleic acid and 15.0 mL of 1-octadecene. The mixture was heated to 130 °C and maintained 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) was added, followed by stirring for one hour. The solution was then heated to 110 °C to remove volatile impurities under vacuum. Finally, the remaining mixture was heated to 310 °C under a nitrogen atmosphere and maintained at this temperature for 90 minutes. After cooling to room temperature, the nanocrystals were collected by centrifugation, washed with ethanol, and dispersed in 10.0 mL of cyclohexane.

[0049] Morphological characterization: A small amount of the above nanocrystalline dispersion was dropped onto a copper grid and observed using a transmission electron microscope. Figure 3 In the TEM image (a), the synthesized nanocrystals are hexagonal, uniform in morphology, and approximately 25 nm in size.

[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: The surface layer of one side of the self-assembled barium titanate microsphere array with NaYF4:Tm 3+ The surface of the PDMS nonlinear optical active layer was treated with oxygen plasma. Treatment parameters: power 100 W, treatment time 60 seconds. Plasma bombardment breaks the Si-CH3 bonds on the PDMS surface, generating silanol groups, and introduces active groups such as hydroxyl groups onto the surface of the barium titanate microspheres, changing the surface from hydrophobic to hydrophilic.

[0070] Room temperature contact bonding: Immediately (usually within minutes after treatment, to prevent surface activity degradation) align the two plasma-treated surfaces face to face. Apply gentle, even finger pressure. At room temperature, the two active surfaces will spontaneously bond together through hydrogen bonds and van der Waals forces.

[0071] Final curing: The bonded sample is 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 an ultra-low threshold high-order nonlinear optical response composite thin film device. The purpose of this step is not to achieve bonding, but to enhance the bonding strength. During the standing or slight heating process, the silanol groups at the interface will further undergo a condensation reaction to form strong 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. The test results are as follows: Figure 6 As shown.

[0073] Figure 6 Preview of the double logarithmic curve:

[0074] The slope of the curve in Example 2 is also approximately 40, proving that the luminescence mechanism does not change due to the change in recombination method.

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

[0076] Conclusion: A significant reduction in the photon avalanche emission threshold was successfully achieved through plasma bonding, demonstrating universal applicability to various interfacial recombination methods.

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

[0078] 1. Preparation of self-assembled layers

[0079] In this embodiment, monodisperse barium titanate microspheres with a diameter of 100 μm are used as dielectric microspheres.

[0080] Cleaning and pretreatment: The steps are exactly the same as in 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 film formation: The process flow is exactly the same as in Example 1. Gravity-assisted self-assembly technology is used to form a single-layer, hexagonal close-packed 100 μm barium titanate microsphere self-assembly array on the substrate.

[0083] PDMS encapsulation and transfer: The steps are exactly the same as in Example 1, and finally an independent, self-assembled layer encapsulated by PDMS is obtained.

[0084] 2. Fabrication of Nonlinear Optical Active Layers

[0085] This part is exactly the same as in Example 1.

[0086] 3. Preparation and stabilization of composite films

[0087] This part is exactly the same as in Example 1.

[0088] Using the exact same PDMS adhesive layer process as in Example 1, the self-assembled layer of the 100 μm barium titanate microsphere array was bonded to NaYF4:Tm 3+ By stably compositing the PDMS nonlinear optical active layer, an ultra-low threshold high-order nonlinear optical response composite thin film device is obtained.

[0089] The ultra-low threshold high-order nonlinear optical response composite thin film device prepared in Example 3 was tested using the same optical testing method as in Example 1, and compared with Comparative Example 1. The test results are as follows: Figure 7 As shown.

[0090] Figure 7 The double logarithmic curve clearly shows:

[0091] The emission threshold of Comparative Example 1 remains 1000 kW / cm². 2 .

[0092] The slope of the curve in Example 3 is also approximately 40, which proves that its photon avalanche luminescence mechanism remains unchanged.

[0093] However, its emission threshold underwent a dramatic leap, with the measured value significantly decreasing to ~1 kW / cm². 2It can be seen that by constructing a self-assembled array using larger-sized (100 μm) barium titanate dielectric microspheres, and with the assistance of a PDMS binder layer, and with NaYF4:15% Tm 3+ Photonic avalanche nanocrystal composites can further significantly reduce the excitation threshold of photonic avalanche luminescence, achieving ultra-low threshold operation at the sub-kW / cm² level.

[0094] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the 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) 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 gravity and form a monolayer self-assembled array on the substrate; the substrate carrying the self-assembled array is placed horizontally, dried, and then a first polymer material is allowed to penetrate into the array gaps and gradually cover the dielectric microspheres to a thickness of more than 1 mm. Then, it is cured and peeled off from the substrate 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, wherein the high-order nonlinear luminescent materials are dispersed in the second polymer material in a random distribution morphology of nanocrystals or microcrystals; 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 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: The second polymer material 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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