A preparation method of a near-infrared vertical cavity surface laser with low threshold and high gain based on weak confinement quantum dots

Abstract

The application discloses a preparation method of a near-infrared vertical cavity surface laser with low threshold and high gain based on weakly confined quantum dots, and belongs to the technical field of quantum dot lasers. A CdS shell layer is grown on the weakly confined double-tapered CdSe quantum dots, and the thickness of the CdS shell layer is controlled to be 2 layers by controlling the injection amount of dodecanethiol; the CdSe / CdS quantum dots are spin-coated on the high-reflection surface of two Bragg reflectors (DBRs); and the surfaces coated with the quantum dots are close to each other and are spliced to form a vertical cavity surface laser. The vertical cavity surface laser constructed by taking the weakly confined double-tapered hexahedral CdSe / CdS quantum dots as deep red gain material has deep red / near-infrared laser emission of 720 nm, an extremely low laser threshold of 11.23 µJ / cm 2 and an extremely wide gain bandwidth of 670-730 nm.

Description

Technical Field

[0001] This invention belongs to the field of quantum dot laser technology, specifically relating to a method for fabricating a low-threshold, high-gain near-infrared vertical-cavity surface laser based on weakly confined quantum dots. Background Technology

[0002] Quantum dot materials, as a new generation of laser gain materials, have attracted widespread attention from researchers due to their solution processability, low temperature sensitivity, and low threshold properties. To date, the application of quantum dots as optical gain media in micro / nano laser technology has made groundbreaking progress. By improving the structure of quantum dots and adjusting the design of optical microcavities, quantum dot lasers are increasingly being applied in other disciplines. Due to the improved optical quality of quantum dots, the spectrum of quantum dot lasers can cover blue to infrared light. Among them, deep red / near-infrared quantum dot lasers are a current cutting-edge hot topic in the field of semiconductor lasers. This band has proven to be suitable for biocompatibility due to its unique optical window (where biological tissue absorbs and scatters light most weakly) and deep penetration depth. They are attracting significant attention due to their enormous application potential in biomedical imaging, optical communication, display technology, and on-chip photonic integration.

[0003] However, current research on deep-red / near-infrared quantum dot lasers mainly focuses on CdSeTe quantum dots and halide perovskite quantum dots. The former's wide full width at half maximum (FWHM) and high threshold are unsuitable for next-generation deep-red quantum dot lasers, while the latter suffers from narrow gain bandwidth and poor stability due to its susceptibility to reaction with oxygen in the air. Therefore, realizing a stable, low-threshold, wide-gain deep-red / near-infrared quantum dot laser is crucial. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for fabricating a low-threshold, high-gain near-infrared vertical-cavity surface laser based on weakly confined quantum dots.

[0005] This invention addresses the problems of high threshold, narrow gain bandwidth, and insufficient research in the deep red / near-infrared bands in existing quantum dot lasers, and includes the following steps: Step 1: Preparation of weakly confined bipyramidal CdSe quantum dots using the hot injection method: In a reaction system of cadmium alkylate, stearic acid, oleic acid, and octadecyl selenide, a selenium-octadecene suspension is injected under inert gas protection, and the reaction is completed by heating. After separation and purification, strongly confined bipyramidal CdSe quantum dots are obtained. Then, strongly confined bipyramidal CdSe quantum dots are added to the reaction system of cadmium alkylate, oleic acid, erucic acid, and octadecyl selenide, and a selenium-octadecene suspension is injected under inert gas protection. The reaction is completed by heating, and weakly confined bipyramidal CdSe quantum dots are obtained by separation and purification. Step 2: A CdS shell is grown on weakly confined bipyramidal CdSe quantum dots using a hot injection method; in the reaction system of cadmium alkyl alkanoate, oleic acid, octadecyl selenide and weakly confined bipyramidal CdSe quantum dots, dodecanethiol-octadecene is injected under inert gas protection, and the thickness of the CdS shell is controlled to 2 layers by controlling the amount of dodecanethiol-octadecene injected. Step 3: Select two Bragg reflectors (DBRs) with a working range of 650-800 nm; Step 4: Spin-coat the weakly confined biconical CdSe / CdS quantum dots onto the high-reflectivity surfaces of two Bragg reflectors (DBRs); Step 5: Join two Bragg reflectors (DBRs) facing each other with optical adhesive. Place the CdSe / CdS quantum dots coated with weakly confined biconical CdSe on the inner side, bringing them close together to form a vertical-cavity laser. As a further optimization: the CdSe / CdS quantum dots in Step 1 must have a CdSe core quantum dot size >9.6 nm. At this point, the fluorescence wavelength of the quantum dots reaches 680 nm, and the optical gain spectrum reaches the deep red / near-infrared band.

[0006] As a further optimization: the cadmium alkylate concentration in the synthesis of strongly confined CdSe quantum dots in step 1 needs to be greater than 10%. -3 mol / L.

[0007] As a further optimization: the CdSe quantum dots grown in step 1 using cadmium alkylate ligands have a bipyramidal hexahedral structure.

[0008] As a further optimization scheme: the size of the CdSe quantum dots in step 1 is greater than 9.6 nm, the fluorescence wavelength is 680 nm, and the optical gain spectrum is in the deep red / near infrared band.

[0009] As a further optimization: the concentration of the quantum dot solution in step 4 is 500 mg / ml.

[0010] As a further optimization scheme: the pulsed source of the vertical cavity surface laser is a femtosecond source with an excitation wavelength of 400nm, a laser source frequency of 1 kHz, and an average output power of approximately 7 W.

[0011] As a further optimization: continuous laser beams achieved using a vertical-cavity surface-mount laser (VCSEL) with a threshold of 11.23 µJ / cm². 2 The laser bandwidth is 670-730 nm.

[0012] As a further optimization scheme: the solution preparation of strongly confined bipyramidal CdSe quantum dots in step 1 is as follows: Cadmium acetate dihydrate, stearic acid, oleic acid, and octadecene are added to a three-necked flask, argon gas is introduced to purge the air, then the temperature is raised to 120℃ and held to purge the water vapor, then the temperature is raised to 250℃, a selenium-octadecene suspension is injected, and the temperature is held. The injection of selenium-octadecene is repeated several times, heating is stopped, and the reaction mixture is allowed to cool to room temperature. The crude reactants are then mixed uniformly with n-hexane, centrifuged to obtain a precipitate, the precipitate is dissolved in chloroform, and after complete dissolution, acetonitrile is added. The solution is placed in a water bath for insulation, then centrifuged to obtain a precipitate, and finally the precipitate is dissolved in octadecene.

[0013] As a further optimization scheme: the preparation of the weakly confined bipyramidal CdSe quantum dot solution in step 1 is as follows: Cadmium acetate dihydrate, oleic acid, erucic acid, and octadecene are added to a three-necked flask, argon gas is introduced to purge the air, the temperature is raised to 120 ℃ and held to purge the water vapor, and then the temperature is raised to 270 ℃. Subsequently, a strongly confined bipyramidal CdSe quantum dot solution is injected into the flask, and a selenium-octadecene solution is added dropwise to the reaction flask. After 2 hours, the injection of the selenium-octadecene solution is stopped, the crude reactants are mixed evenly with n-hexane, centrifuged to obtain a precipitate, and then the precipitate is dissolved in n-hexane. After complete dissolution, ethanol is added, the mixture is stirred evenly, centrifuged to obtain a precipitate, and then the precipitate is dissolved in n-hexane.

[0014] As a further optimization scheme: Step 2 is as follows: Add cadmium acetate dihydrate, oleic acid, and octadecyl selenide to a three-necked flask, purge the air with argon gas, heat to 120 ℃ and hold to purge water vapor, then inject weakly confined bipyramidal CdSe quantum dots, and then heat to 250 ℃, inject a dodecyl mercaptan-octadecene solution into the mixed reactants, and the thickness of the CdS shell increases with the amount of dodecyl mercaptan-octadecene solution injected.

[0015] The method for fabricating a low-threshold, high-gain near-infrared vertical-cavity laser based on weakly confined quantum dots provided by this invention has the following beneficial effects: This invention is based on the traditional hot-injection synthesis scheme. By precisely controlling the size of the quantum dots and the thickness of the core and shell, the optical gain band of CdSe quantum dots is extended to the near-infrared I region band. This invention fully leverages the advantages of its size and shape to achieve optical gain performance with deep red / near-infrared light gain emission and an extremely low gain threshold.

[0016] This invention fills a research gap in deep-red / near-infrared quantum dot lasers. It innovatively uses weakly confined bipyramidal hexahedral CdSe / CdS quantum dots as the deep-red light gain material, constructing a vertical-cavity surface-mount laser with deep-red / near-infrared laser emission (720 nm) and an extremely low laser threshold (11.23 µJ / cm²). 2With its extremely wide gain bandwidth (670-730 nm), it provides guidance for the research of next-generation quantum dot lasers. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a bipyramidal CdSe quantum dot structure.

[0018] Figure 2 The images show TEM images of CdSe / CdS quantum dots. The size of the CdSe core is 9.82 nm. The values ​​of ad represent the thickness of the CdS layers as 0, 2, 5, and 10 layers, respectively. A single layer of CdS is approximately 0.7 nm thick.

[0019] Figure 3 The PL spectra of CdSe / CdS quantum dots are shown. From bottom to top, they represent CdS thicknesses of 0, 2, 5, and 10 layers, with a single layer of CdS approximately 0.7 nm.

[0020] Figure 4 The ASE spectra of CdSe / CdS quantum dots are shown. The size of the CdSe core is 9.82 nm, and ad represents the thickness of CdS layers of 0, 2, 5, and 10 layers, respectively.

[0021] Figure 5 This is the basic structure of a vertical cavity surface laser.

[0022] Figure 6 The constructed vertical cavity surface laser is shown in its working state and beam pattern under excitation, with the gain medium CdSe / CdS quantum dot shell having a thickness of 2 layers.

[0023] Figure 7 The laser spectrum of the corresponding vertical cavity surface laser is collected as a function of pump intensity, and the laser characteristic map is obtained.

[0024] Figure 8 The excitation threshold of the laser was fitted.

[0025] Figure 9 100.6 µJ / cm 2 The luminous intensity of a vertical cavity surface laser under pump intensity. Detailed Implementation

[0026] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. After reading this invention, any modifications of the invention in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims. Example 1

[0027] Weakly confined bipyramidal CdSe quantum dots were prepared by a hot-injection method, requiring a high concentration of cadmium alkylate ligands (cadmium alkylate concentration > 10). -3 (mol / L, Cd:Se≈2:1), the cadmium precursor used in this study was cadmium acetate dihydrate (Cd(Ac)2·2H2O) with a concentration of 5*10 mol / L. -3 mol / L. The specific steps are as follows: (1) Preparation of strongly confined bipyramidal CdSe quantum dots: Add 53.2 mg (0.2 mmol) cadmium acetate dihydrate (Cd(Ac)₂·2H₂O), 1137.9 mg stearic acid (Hst), 3 mL oleic acid (OA), and 20 mL selenium octadecene (ODE) to a 50 mL three-necked flask. Purge air with argon for 30 minutes, then heat to 120 °C and hold for 30 minutes to purge water vapor. Then heat to 250 °C and quickly inject 1 mL of a selenium-octadecene suspension precursor (Se-SUS 0.1 mol / L). Hold for 5 minutes, then inject 0.1 mL of Se-SUS. Repeat this process four times, then stop heating and allow the reaction mixture to cool naturally to room temperature. Mix the crude reactants with an equal volume of n-hexane and centrifuge at 4000 r / min for 5 minutes to obtain a precipitate. Since the precipitate contains a difficult-to-remove stearic acid complex, chloroform and acetonitrile were chosen as the solvent and antisolvent, respectively, for centrifugation. The precipitate was dissolved in 5 mL of chloroform. After complete dissolution, 1 mL of acetonitrile was added. The solution was placed in a water bath at 60 °C for 5 minutes to improve the solubility of stearate. Then, the solution was centrifuged at 8000 r / min for 2 minutes to obtain the precipitate. The precipitate was then dissolved in 20 mL of ODE.

[0028] (2) Weakly confined bipyramidal CdSe quantum dots Add 53.2 mg (0.2 mmol) of cadmium acetate dihydrate (Cd(Ac)₂·2H₂O), 1.2 mL of oleic acid (OA), 236.9 mg (0.7 mmol) of erucic acid, and 10 mL of octadecene selenide (ODE) to a 50 mL three-necked flask. Purge the flask with argon gas for 30 minutes to purge air, then heat to 120 °C and hold for 30 minutes to purge water vapor, then heat to 270 °C. Next, inject 5 mL of a strongly confined CdSe-ODE solution into the flask. Add a selenium-octadecene solution (Se-ODE 0.02 mol / L) dropwise to the reaction flask using a peristaltic pump at a rate of 1.8 mL / h. The quantum dot size continuously increases with the addition of the Se precursor. After injecting Se-ODE for 2 hours, stop the injection, mix the crude reactants with an equal volume of n-hexane, and centrifuge at 4000 r / min for 5 minutes to obtain the precipitate. The precipitate was then dissolved in 5 mL of n-hexane. After complete dissolution, 1 mL of ethanol was added, and the mixture was stirred evenly. The mixture was then centrifuged at 8000 r / min for 2 minutes to obtain the precipitate, which was then dissolved in 2 mL of n-hexane.

[0029] The weakly confined CdSe quantum dots in Example 1 did not grow a shell, and their TEM results are as follows: Figure 2 As shown in (a), the PL spectrum is as follows Figure 3 As shown, its ASE spectrum is as follows Figure 4 (a) The quantum dot of Example 1 has a size of approximately 9.82 nm, a fluorescence wavelength of approximately 675 nm, and an ASE range of 650-710 nm. Example 2

[0030] Based on the aforementioned weakly confined CdSe quantum dots, a coating process was performed. In the study of CdSe / CdS quantum dots, the thickness of a single layer of CdS was approximately 0.7 nm.

[0031] (1) Add 53.2 mg (0.2 mmol) cadmium acetate dihydrate (Cd(Ac)2·2H2O), 1.2 mL oleic acid (OA), and 10 mL octadecyl selenide (ODE) to a 50 mL three-necked flask. Purge the air with argon gas for 30 minutes, raise the temperature to 120 °C and hold for 30 minutes to purge water vapor, then inject 2 mL of weakly confined CdSe quantum dots, followed by raising the temperature to 250 °C. Inject a dodecathiol-octadecene (DDT-ODE 0.1 mol / L) solution into the mixed reactants. The thickness of the CdS shell increases with the amount of DDT-ODE solution injected. When the amount of DDT-ODE injected is 0.5 mL, the shell thickness is approximately 2 layers. Then, stop heating after holding for 30 minutes, remove the crude reactant, and centrifuge to purify it as in Example 1. The monolayer CdS is approximately 0.7 nm thick.

[0032] The TEM of the weakly confined CdSe / CdS quantum dots in Example 2 is as follows: Figure 2 As shown in (b), the PL spectrum is as follows Figure 3 As shown, its ASE spectrum is as follows Figure 4 (b) The quantum dot size of Example 1 was calculated to be approximately 11.35 nm, the CdS shell thickness was approximately 2 layers, the fluorescence wavelength was approximately 690 nm, and the ASE range was 660-725 nm. Example 3

[0033] In Example 2, a slight modification was made to the synthesis steps of weakly confined CdSe / CdS quantum dots, and the DDT injection volume was adjusted to 1 ml.

[0034] The TEM of the weakly confined CdSe / CdS quantum dots in Example 3 is as follows: Figure 2 As shown in (c), the PL spectrum is as follows Figure 3 As shown, its ASE spectrum is as follows Figure 4 (c) The quantum dot size of Example 1 was calculated to be approximately 13.57 nm, the CdS shell thickness was approximately 5 layers, the fluorescence wavelength was approximately 690 nm, and the ASE range was 665-720 nm. The monolayer CdS was approximately 0.7 nm. Example 4

[0035] In Example 2, the synthesis steps of weakly confined CdSe / CdS quantum dots were slightly modified, and the DDT injection volume was adjusted to 1.5 ml.

[0036] The TEM of the weakly confined CdSe / CdS quantum dots in Example 4 is as follows: Figure 2 As shown in (d), the PL spectrum is as follows Figure 3 As shown, its ASE spectrum is as follows Figure 4 (d) The quantum dot size of Example 1 was calculated to be approximately 17.36 nm, the CdS shell thickness was approximately 10 layers, the fluorescence wavelength was approximately 690 nm, and the ASE range was 665-695 nm. The monolayer CdS was approximately 0.7 nm. Example 5

[0037] Construction of a vertical-cavity surface-mount laser: Two Bragg mirrors (DBRs) with an operating range of 650-800 nm are selected. Weakly confined biconical CdSe / CdS quantum dots are spin-coated onto the high-reflectivity surfaces of the two DBRs and then fixed with glue. The CdSe / CdS quantum dots coated with weakly confined biconical CdSe / CdS quantum dots are stacked close to each other on the inner side, which constitutes a simple vertical-cavity surface-mount laser.

[0038] A schematic diagram of the bipyramidal hexahedral CdSe quantum dot structure and its growth principle is shown below. Figure 1 As shown, high concentrations of cadmium alkylate (cadmium alkylate concentration > 10) -3mol / L) in strongly confined CdSe quantum dots <111> The introduction of twin facets alters the stacking plane of zinc sphalerite from ABC-ABC-ABC to AB-C-BA, where the C facet resembles a mirror. Subsequently, with the injection of the precursor, quantum dots epitaxially grow on the CdSe seed with twin facets. During this process, the surface energy of the (100) facet of the quantum dot growth process is significantly greater than that of other surfaces, thus the epitaxial growth of quantum dots tends to be more inclined to grow on small facets. The final morphology of the quantum dots grows into a bipyramidal hexahedron morphology composed of 6 (100) facets. As shown in the figure, in the bipyramidal hexahedron morphology, symmetrical structures such as triangles and rhombuses can be obtained by rotating the crystal orientation of the quantum dots.

[0039] like Figure 2 The morphological and dimensional changes of bipyramidal hexahedral CdSe quantum dots as they grow with CdS shells are shown. Figure 3 The changes in fluorescence luminescence of bipyramidal hexahedral CdSe quantum dots as they grow with a CdS shell are shown.

[0040] Figure 4 The ASE spectra of weakly confined CdSe / CdS quantum dots with different shell thicknesses are shown. When the CdS thickness is 2 layers, the gain range can reach 725 nm. Quantum dots with other shell thicknesses do not meet the objective requirements for constructing near-infrared lasers. Therefore, a deep red / near-infrared vertical-cavity surface laser is constructed using weakly confined CdSe / CdS quantum dots with a CdS thickness of 2 layers as the gain material.

[0041] like Figure 5 The basic structure and working principle of a vertical cavity surface laser are demonstrated. Figure 6 The laser emission and spot characteristics of the constructed deep red / near-infrared vertical-cavity surface laser were recorded during operation. Subsequently... Figure 7 The fluorescence signal of a vertical-cavity surface-mount laser was measured as a function of pump power, and the threshold of the fitted laser was calculated as follows: Figure 8 As shown, it is approximately 11.23 µJ / cm. 2 The range of deep red / near-infrared lasers is 680-720 nm.

[0042] like Figure 9 At 100.6 µJ / cm 2 At pump intensity, the laser emission almost covers the entire 670-730 nm spectrum.

Claims

1. A method for fabricating a low-threshold, high-gain near-infrared vertical-cavity surface laser based on weakly confined quantum dots, characterized in that, Includes the following steps: Step 1: Weakly confined bipyramidal CdSe quantum dots were prepared using a hot-injection method. A selenium-octadecene suspension was injected into a reaction system of cadmium alkyl alkylate, stearic acid, oleic acid, and octadecene under inert gas protection, and the reaction was completed by heating. After separation and purification, strongly confined bipyramidal CdSe quantum dots were obtained. Then, strongly confined bipyramidal CdSe quantum dots were added to the reaction system of cadmium alkyl alkylate, oleic acid, erucic acid, and octadecene, and a selenium-octadecene suspension was injected under inert gas protection. The reaction was completed by heating, and weakly confined bipyramidal CdSe quantum dots were obtained by separation and purification. Step 2: A CdS shell is grown on weakly confined bipyramidal CdSe quantum dots using the hot injection method. In the reaction system of cadmium alkyl alkanoate, oleic acid, octadecyl selenide and weakly confined bipyramidal CdSe quantum dots, dodecanethiol-octadecene is injected under inert gas protection. The thickness of the CdS shell is controlled to 2 layers by controlling the amount of dodecanethiol-octadecene injected. Step 3: Select two Bragg reflectors (DBRs) with a working range of 650-800 nm; Step 4: Spin-coat the weakly confined biconical CdSe / CdS quantum dots onto the high-reflectivity surfaces of two Bragg reflectors (DBRs); Step 5: Join two Bragg reflectors (DBRs) together with optical adhesive, and stack the inner sides of the two DBRs coated with weakly confined biconical CdSe / CdS quantum dots close to each other to form a vertical cavity laser.

2. The method for fabricating a low-threshold, high-gain near-infrared vertical-cavity surface laser based on weakly confined quantum dots according to claim 1, characterized in that: In step 1, the concentration of cadmium alkylate in the synthesis of strongly confined CdSe quantum dots is greater than 10. -3 mol / L.

3. The method for fabricating a low-threshold, high-gain near-infrared vertical-cavity surface laser based on weakly confined quantum dots according to claim 1, characterized in that: The CdSe quantum dots grown in step 1 via cadmium alkylate ligands have a bipyramidal hexahedral structure.

4. The method for fabricating a low-threshold, high-gain near-infrared vertical-cavity surface laser based on weakly confined quantum dots according to claim 1, characterized in that: The CdSe quantum dots in step 1 have a size greater than 9.6 nm, a fluorescence wavelength of 680 nm, and an optical gain spectrum in the deep red / near-infrared band.

5. The method for fabricating a low-threshold, high-gain near-infrared vertical-cavity surface laser based on weakly confined quantum dots according to claim 1, characterized in that: The concentration of the quantum dot solution in step 4 is 500 mg / ml.

6. The method for fabricating a low-threshold, high-gain near-infrared vertical-cavity laser based on weakly confined quantum dots according to claim 1, characterized in that: The pulsed source of the vertical cavity surface laser is a femtosecond source with an excitation wavelength of 400 nm, a laser source frequency of 1 kHz, and an average output power of approximately 7 W.

7. The method for fabricating a low-threshold, high-gain deep-red / near-infrared vertical-cavity laser based on weakly confined CdSe / CdS quantum dots according to claim 1, characterized in that: Continuous laser beams achieved using a vertical-cavity surface-mount laser (VCSEL) with a threshold of 11.23 µJ / cm² 2 The laser bandwidth is 670-730 nm.

8. The method for fabricating a low-threshold, high-gain deep-red / near-infrared vertical-cavity laser based on weakly confined CdSe / CdS quantum dots according to claim 1, characterized in that: The preparation of the strongly confined bipyramidal CdSe quantum dot solution in step 1 is as follows: Cadmium acetate dihydrate, stearic acid, oleic acid, and octadecene are added to a flask. Argon gas is introduced to purge the air, and then the temperature is raised to 120°C and held to purge the water vapor. Then the temperature is raised to 250°C, and a selenium-octadecene suspension is injected and held at this temperature. This process of injecting selenium-octadecene is repeated several times. Heating is then stopped, and the reaction mixture is allowed to cool to room temperature. The crude reactants are then mixed uniformly with n-hexane, centrifuged to obtain a precipitate, and the precipitate is dissolved in chloroform. After complete dissolution, acetonitrile is added, and the solution is kept warm in a water bath. Then the precipitate is obtained by centrifugation and finally dissolved in octadecene.

9. The method for fabricating a low-threshold, high-gain deep-red / near-infrared vertical-cavity laser based on weakly confined CdSe / CdS quantum dots according to claim 1, characterized in that: The preparation of the weakly confined bipyramidal CdSe quantum dot solution in step 1 is as follows: Cadmium acetate dihydrate, oleic acid, erucic acid, and octadecene are added to a flask. Argon gas is introduced to purge the air, and the temperature is raised to 120 °C and held to purge the water vapor. Then, the temperature is raised to 270 °C. Subsequently, a strongly confined bipyramidal CdSe quantum dot solution is injected into the flask. A selenium-octadecene solution is added dropwise to the reaction flask. After 2 hours, the injection of the selenium-octadecene solution is stopped. The crude reactants are mixed uniformly with n-hexane, centrifuged to obtain a precipitate, and then the precipitate is dissolved in n-hexane. After complete dissolution, ethanol is added, the mixture is stirred uniformly, centrifuged to obtain another precipitate, and then the precipitate is dissolved in n-hexane.

10. The method for fabricating a low-threshold, high-gain deep-red / near-infrared vertical-cavity laser based on weakly confined CdSe / CdS quantum dots according to claim 1, characterized in that: Step 2 specifically involves adding cadmium acetate dihydrate, oleic acid, and octadecyl selenide to a three-necked flask, purging the air with argon gas, heating to 120 °C and holding at that temperature to purge water vapor, then injecting weakly confined bipyramidal CdSe quantum dots, followed by heating to 250 °C and injecting a dodecyl mercaptan-octadecene solution into the mixed reactants. The thickness of the CdS shell increases with the amount of dodecyl mercaptan-octadecene solution injected.

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