A laser based on a mesoporous titanium dioxide substrate and its fabrication method

Abstract

This invention relates to the field of organic photonics and laser device technology, specifically disclosing a laser based on a mesoporous titanium dioxide substrate and its fabrication method. The laser comprises a transparent substrate, a mesoporous titanium dioxide thin film on the substrate, and an organic conjugated polymer gain medium layer on the titanium dioxide thin film. The mesoporous titanium dioxide layer is fabricated by spraying or spin coating, utilizing its disordered porous structure to provide light scattering feedback. Low-threshold random laser emission can be achieved under optical pumping without the need for a traditional precision resonant cavity. This device features a simple structure, low fabrication cost, good process compatibility, and applicability to polymer gain media with various emission wavelengths, providing a new technical path for realizing low-cost, easily integrated electrically pumped organic lasers.

Description

Technical Field

[0001] This invention belongs to the field of organic photonics and laser device technology, and particularly relates to a laser based on a mesoporous titanium dioxide substrate and its fabrication method. Background Technology

[0002] Lasers play a crucial role in modern technology. Traditional lasers rely on precisely designed optical resonators (such as Fabry-Perot cavities and distributed feedback gratings) to provide optical feedback and mode selection, leading to complex manufacturing processes and high costs. Organic semiconductor materials, especially π-conjugated polymers, are considered ideal gain media for next-generation low-cost, flexible lasers due to their advantages such as tunable emission wavelength, solution-processability, and flexibility.

[0003] Random lasing is a laser phenomenon where feedback is provided by multiple scattering in a disordered medium, eliminating the need for a traditional defined resonant cavity. This characteristic makes it highly promising for simplifying laser structures and reducing manufacturing costs. Previous research has shown that doping polymer films with scattering particles (such as TiO2 nanoparticles) can achieve random lasing. However, such hybrid systems often suffer from problems such as particle agglomeration, uneven dispersion, and poor polymer compatibility, affecting the uniformity and stability of device performance.

[0004] Mesoporous titanium dioxide (m-TiO2) is a material with high specific surface area and a regular nanopore structure, widely used in photovoltaics, catalysis, and other fields. Its thin films themselves constitute a natural disordered scattering medium. If it can be used as a substrate and combined with solution-processed organic polymer gain media, it holds promise for constructing cavity-free random lasers with simple structures and excellent performance. Currently, there are no reports of using mesoporous titanium dioxide films directly as a scattering feedback layer and combining them with specific polyfluorene-based gain media to achieve low-threshold, customizable emission wavelength random lasers. Therefore, this problem urgently needs to be solved. Summary of the Invention

[0005] To address the problems of complex and costly manufacturing of organic laser resonator cavities and poor uniformity of random laser systems in existing technologies, this invention provides a laser based on a mesoporous titanium dioxide substrate and its preparation method. The mesoporous titanium dioxide layer is prepared by spraying or spin coating, and its disordered porous structure provides light scattering feedback. Low-threshold random laser emission can be achieved under optical pumping without the need for a traditional precision resonator.

[0006] To achieve the aforementioned objective, the technical solution of the present invention is implemented as follows: a laser based on a mesoporous titanium dioxide substrate includes a transparent substrate, a mesoporous titanium dioxide thin film, and an organic conjugated polymer gain medium layer; the mesoporous titanium dioxide thin film is disposed on the transparent substrate; the organic conjugated polymer gain medium layer is disposed on the mesoporous titanium dioxide thin film, and the mesoporous titanium dioxide thin film has a disordered porous structure for providing light scattering feedback for stimulated emission in the gain medium layer.

[0007] Mesoporous titanium dioxide films not only serve as components of devices, but their inherent disordered porous structure also acts as a light scattering feedback medium, replacing the precision resonant cavity in traditional lasers.

[0008] Preferably, the thickness of the mesoporous titanium dioxide film is 50-200 nanometers. It has a disordered porous structure with pores or particles having a characteristic size of approximately 100-150 nanometers, a scale comparable to the wavelength of visible light, which provides effective multiple scattering.

[0009] Preferably, the organic conjugated polymer gain medium layer is a polyfluorene derivative; the polyfluorene derivative is at least one of blue poly(9,9-dioctylfluorene) (PFO) and its derivatives SC010 and SC005, or green poly(9,9-dioctylfluorene-benzothiadiazole) (F8BT).

[0010] Preferably, the thickness of the organic conjugated polymer gain medium layer is 80-200 nanometers.

[0011] Preferably, a method for fabricating a laser based on a mesoporous titanium dioxide substrate includes the following steps: 1) Prepare the transparent substrate; 2) A mesoporous titanium dioxide thin film is prepared on the transparent substrate; 3) An organic conjugated polymer gain medium layer is prepared on the mesoporous titanium dioxide film.

[0012] Preferably, in step 2), the mesoporous titanium dioxide film is prepared by spray pyrolysis or spin coating. Spray coating can quickly prepare films with a large area, while spin coating can obtain a more uniform nanostructure.

[0013] Preferably, the process of the spray pyrolysis method includes: first preparing an ethanol solution containing titanium precursor, then spraying it onto the surface of a heated transparent substrate using a spray gun, and finally performing high-temperature annealing treatment.

[0014] Specifically, the process involves preparing an ethanol solution containing a titanium precursor (e.g., mixing tetraisopropyl titanate and 2,4-pentanedione in a 2:1 molar ratio to prepare a solution with a titanium atom concentration of 0.25 M), spraying it onto a transparent substrate surface preheated to 250-350°C using a spray gun at a distance of approximately 20 cm, employing intermittent operation (e.g., spraying for 1 second followed by a 20-30 second interval), repeating this process until the desired thickness is achieved, and then annealing the sample in a muffle furnace at 400-500°C (preferably 450°C) for 30 minutes. Further, the titanium precursor is a mixture of tetraisopropyl titanate and 2,4-pentanedione, and the annealing temperature is 400-500°C.

[0015] Preferably, the spin coating process includes: first preparing an ethanol solution containing titanium precursor and dilute hydrochloric acid, then spin coating it onto a transparent substrate, followed by spin coating with deionized water, and finally performing high-temperature annealing treatment.

[0016] Specifically, prepare an ethanol solution containing a titanium precursor (e.g., 210 µL tetraisopropyl titanate) and a catalyst (e.g., 20 µL dilute hydrochloric acid) (total solvent approximately 1428 µL). Spin-coat this solution onto a transparent substrate at a speed of 1500-2000 rpm (e.g., 1600 rpm), an acceleration rate of 2000 rpm / s, and a time of 60 seconds. Immediately afterward, spin-coat deionized water (e.g., 4 µL) at the same speed. Then, heat the sample in a muffle furnace to 500°C at a programmed rate of 5 °C / min and hold for 2 hours, followed by cooling at a rate of 5 °C / min.

[0017] Preferably, the titanium-containing precursor is a mixture of tetraisopropyl titanate and 2,4-pentanedione; the annealing temperature is 400-500℃.

[0018] Preferably, in step 3), the process of forming the organic conjugated polymer gain medium layer includes: dissolving the organic conjugated polymer in an organic solvent and forming a film on a mesoporous titanium dioxide film by spin coating.

[0019] Specifically, the polymer is dissolved in an organic solvent (such as toluene, at a concentration of 25 mg / mL), and a film is formed by spin coating. The spin coating speed is adjusted in the range of 1200-2000 rpm according to the required thickness (for example, 1500 rpm can be used for SC010 or SC005, and 1200 rpm can be used for F8BT). Then, the film is annealed at 80-100°C for 10-20 minutes to remove residual solvent.

[0020] The beneficial effects of this invention are reflected in: (1) The present invention utilizes the disordered scattering of the mesoporous titanium dioxide film itself to provide feedback, completely eliminating the complex traditional resonant cavity structure and greatly simplifying the device configuration and fabrication process.

[0021] (2) All functional layers of the device provided by the present invention can be realized by solution methods such as spraying and spin coating, with low equipment requirements and suitable for large-scale production.

[0022] (3) The device provided by the present invention has low threshold and high performance: the embodiments show that the threshold of the random laser is as low as 8.3 µJ / cm², which is comparable to some distributed feedback (DFB) lasers, and the laser linewidth is narrow.

[0023] (4) The device gain medium provided by the present invention has strong universality: the same mesoporous titanium dioxide substrate can be applied to polyfluorene derivatives with different emission colors, demonstrating the flexibility of the platform in realizing multi-wavelength organic lasers.

[0024] (5) The method provided by this invention is compatible with optoelectronic device processes: Titanium dioxide is a commonly used electron transport material in organic optoelectronic devices. This design lays a good foundation for the future development of electrically pumped organic random lasers. Attached Figure Description

[0025] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 The image shows a scanning electron microscope (SEM) image of the mesoporous titanium dioxide film prepared by the spraying method in Example 1. Figure 2 The images show random laser and magnified spontaneous emission spectra measured simultaneously at different locations in the SC010 (140 nm) / TiO2 (100 nm) glass structure sample in Example 1. Figure 3 This is the evolution of a purely random laser spectrum measured after reducing the excitation stripe length to 3 mm in Example 1; Figure 4 This is a graph showing the relationship between the random laser threshold and output energy under different stripe lengths and slit widths in Embodiment 1 of the present invention. Figure 5 The image shows a SEM image of the mesoporous titanium dioxide film prepared by spin coating in Example 2. Figure 6 The image shows the random laser performance characterization of spin-coated titanium dioxide and SC005 polymer in Example 2. Figure 7 This is a random laser performance characterization diagram based on the same titanium dioxide substrate and F8BT polymer in Example 2. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] like Figure 1-7 As shown: This invention provides a laser based on a mesoporous titanium dioxide substrate and its fabrication method. A mesoporous titanium dioxide layer is prepared by spraying or spin coating, utilizing its disordered porous structure to provide light scattering feedback. Low-threshold random laser emission can be achieved under optical pumping without the need for a traditional precision resonant cavity.

[0028] Example 1 A random laser based on sprayed pyrolysis mesoporous titanium dioxide and multicolor polymer gain medium.

[0029] 1) Substrate cleaning: The quartz glass slide was ultrasonically cleaned in acetone, isopropanol and deionized water in sequence, dried with nitrogen, and then subjected to oxygen plasma treatment.

[0030] 2) Spraying titanium dioxide thin film: Tetraisopropyl titanate and 2,4-pentanedione were dissolved in ethanol at a molar ratio of 2:1 to prepare a 0.25M titanium precursor solution. Using a spray gun propelled by a carrier gas (nitrogen), the solution was sprayed onto a preheated quartz substrate to ~300°C, with the spray gun 20 cm away from the substrate. Intermittent spraying (1 second spray, 20-30 second pause) was used, repeated multiple times until the film thickness reached approximately 100 nm. The sample was then placed in a muffle furnace and annealed at 450°C for 30 minutes, followed by natural cooling.

[0031] The obtained film SEM morphology is as follows Figure 1 As shown, Figure 1 a and 1b are scanning electron microscope (SEM) images of the mesoporous titanium dioxide thin film prepared by the spraying method in this embodiment, showing a porous structure.

[0032] 3) Spin-coated polymer layer: The blue luminescent polymer SC010 was dissolved in toluene at a concentration of 25 mg / mL. The solution was spin-coated onto the aforementioned titanium dioxide film at 1500 rpm for 60 seconds to form a film approximately 140 nm thick. The film was then annealed at 80°C for 10 minutes to remove residual solvent.

[0033] 4) Performance Testing: A pulsed laser with a wavelength of 355 nm and a pulse width of 10 ns was used as the pump source. The laser beam was focused by a cylindrical lens and passed through an adjustable slit to form a line approximately 4 mm long and 400 mm wide on the sample surface. Excitation fringes of μm were generated. The signal was collected at the ends of the fringes using an optical fiber and then transmitted to a spectrometer for detection.

[0034] like Figure 2 As shown, in the SC010 (140 nm) / TiO2 (100 nm) glass structure sample, the random laser and amplified spontaneous emission spectra measured simultaneously at different positions are shown. The RL peak positions are: (a)=443.4 nm, (b)=440 nm, (c)=436.7 nm. When the pump energy exceeds the threshold (about 8.3 µJ / cm²), a random laser peak with a narrow linewidth (1.6-2.9 nm) appears at about 440 nm.

[0035] like Figure 3 The image shows the evolution of the pure random laser spectrum after reducing the excitation stripe length to 3 mm in this embodiment. The spectrum gradually evolves from a relatively broad amplified spontaneous emission (ASE) to a narrow and strong random laser peak. Figure 3 a is a superimposed emission spectrum diagram of the pump energy when the excitation fringe length was reduced to 3 mm and the pump energy was increased from 8.3 µJ / cm² to 166 µJ / cm² in Example 1. Figure 3 b represents selecting different stripe lengths (3 mm) while maintaining the same stripe length. Figure 3 A spectrum measured at different pump energies is used to clearly compare the spectral changes below, near, and above the threshold. like Figure 4 As shown, Figure 4 Figure 'a' shows the minimum pump energy required to achieve random laser at different fringe lengths (e.g., 1 mm, 2 mm, 3 mm, 4 mm, etc.). As can be seen from the figure, the smaller the fringe length, the higher the threshold. Figure 4 b shows the relationship between RL output energy and excitation energy under different slit widths, indicating that the size of the excitation region has a significant impact on the random laser threshold. A narrower excitation strip may lead to higher scattering loss, thus affecting the output intensity.

[0036] Example 2 Random laser based on spin-coated mesoporous titanium dioxide and multicolor polymer gain medium.

[0037] 1) Spin-coated titanium dioxide thin film: 210 µL of tetraisopropyl titanate and 20 µL of dilute hydrochloric acid were added to 1428 µL of ethanol to obtain a precursor solution. The solution was spin-coated onto a plasma-treated quartz substrate at 1600 rpm for 60 seconds. Immediately afterwards, 4 µL of deionized water was spin-coated at the same speed. The sample was transferred to a muffle furnace and heated to 500°C at 5°C / min, held at that temperature for 2 hours, and then cooled at 5°C / min.

[0038] The obtained film SEM morphology is as follows Figure 5 As shown, Figure 5 a and 5b are SEM images of the mesoporous titanium dioxide thin film prepared by spin coating in this embodiment; the pore structure is uniform.

[0039] 2) Fabrication of a blue random laser (SC005): Polymer SC005 was dissolved in toluene at a concentration of 25 mg / mL and spin-coated (1500 rpm, 60 seconds) onto the aforementioned titanium dioxide substrate to form a thin film of approximately 100 nm. The testing method was the same as in Example 1. Figure 6 The figure shows the random laser performance characterization diagram based on spin-coated titanium dioxide and SC005 polymer; where Figure 6 'a' represents the evolution of the emission spectrum under different pump energy densities, with an excitation wavelength of 355 nm. Figure 6 b represents the variation of the full width at half maximum (FWHM) and peak position with pump energy density. Figure 6 c represents the relationship between output intensity and pump energy density at 448.8 nm; when the pump energy exceeds 28.2 µJ / cm²... 2 At that time, stable random laser emission with a linewidth of about 1 nm appeared at 448.8 nm.

[0040] 3) Fabrication of a green random laser (F8BT): The polymer F8BT was dissolved in toluene at 25 mg / mL and spin-coated (1200 rpm, 60 s) onto another titanium dioxide substrate prepared in step 1 to form a film of about 150 nm.

[0041] like Figure 7 As shown, random laser performance characterization diagrams based on the same titanium dioxide substrate and F8BT polymer are presented; where... Figure 7 a represents the evolution of the emission spectrum measured at different pump energy densities. Figure 7 b represents the relationship between the full width at half maximum (FWHM) and peak position of the random laser peaks in the emission spectrum as a function of pump energy density. Figure 7 c represents the curve of random laser output intensity at 553.8 nm as a function of pump energy density. When the pump energy increases, a narrowing of the spectrum is observed at approximately 553.8 nm, thus realizing random laser emission in the green band.

[0042] The above embodiments demonstrate that the cavity-free organic random laser based on a mesoporous titanium dioxide substrate provided by the present invention has a simple structure, an economical and convenient preparation method, and can efficiently realize low-threshold random lasers from blue to green light bands, and has important application prospects.

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A laser based on a mesoporous titanium dioxide substrate, characterized in that, The invention comprises a transparent substrate, a mesoporous titanium dioxide film, and an organic conjugated polymer gain medium layer; the mesoporous titanium dioxide film is disposed on the transparent substrate; the organic conjugated polymer gain medium layer is disposed on the mesoporous titanium dioxide film, and the mesoporous titanium dioxide film has a disordered porous structure.

2. A laser based on a mesoporous titanium dioxide substrate according to claim 1, characterized in that, The thickness of the mesoporous titanium dioxide film is 50-200 nanometers.

3. A laser based on a mesoporous titanium dioxide substrate according to claim 1, characterized in that, The organic conjugated polymer gain medium layer is a polyfluorene derivative; the polyfluorene derivative is at least one of blue poly9,9-dioctylfluorene and its derivatives SC010 and SC005, or green poly9,9-dioctylfluorene-benzothiadiazole.

4. A laser based on a mesoporous titanium dioxide substrate according to claim 1, characterized in that, The thickness of the organic conjugated polymer gain medium layer is 80-200 nanometers.

5. A method for fabricating a laser based on a mesoporous titanium dioxide substrate according to any one of claims 1-4, characterized in that, The method includes the following steps: 1) Prepare the transparent substrate; 2) A mesoporous titanium dioxide thin film is prepared on the transparent substrate; 3) An organic conjugated polymer gain medium layer is prepared on the mesoporous titanium dioxide film.

6. The method for fabricating a laser based on a mesoporous titanium dioxide substrate according to claim 5, characterized in that, In step 2), the mesoporous titanium dioxide film is prepared by spray pyrolysis or spin coating.

7. The method for fabricating a laser based on a mesoporous titanium dioxide substrate according to claim 6, characterized in that, The process of the spray pyrolysis method includes: first, preparing an ethanol solution containing titanium precursor; then, spraying the ethanol solution containing titanium precursor onto a preheated transparent substrate using an intermittent spray gun; and finally, performing high-temperature annealing treatment.

8. The method for fabricating a laser based on a mesoporous titanium dioxide substrate according to claim 6, characterized in that, The spin coating process includes: first, preparing an ethanol solution containing titanium precursor and dilute hydrochloric acid, then spin coating it onto a transparent substrate, followed by spin coating with deionized water, and finally performing high-temperature annealing.

9. The method for fabricating a laser based on a mesoporous titanium dioxide substrate according to claim 8, characterized in that, The titanium-containing precursor is a mixture of tetraisopropyl titanate and 2,4-pentanedione; the annealing temperature is 400-500℃.

10. The method for fabricating a laser based on a mesoporous titanium dioxide substrate according to claim 6, characterized in that, In step 3), the process of forming the organic conjugated polymer gain medium layer includes: dissolving the organic conjugated polymer in an organic solvent and forming a film on a mesoporous titanium dioxide film by spin coating.

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