Rare earth doped up-conversion nanomaterials, methods of making and using the same

Abstract

This invention relates to a rare-earth-doped upconversion nanomaterial, its preparation method, and its application, belonging to the technical field of rare-earth luminescent nanomaterials. The rare-earth-doped upconversion nanomaterial provided by this invention comprises a core layer, an inner shell layer, and an outer shell layer. The core layer is composed of LiYb. (1‑x‑y) Gd x Tm y F4, x and y satisfy: 0

Description

Technical Field

[0001] This invention relates to the field of rare earth nanoluminescence technology, and in particular to a rare earth-doped upconversion nanomaterial, its preparation method, and its application. Background Technology

[0002] Deep ultraviolet (DUV) lasers with wavelengths less than 280 nm possess higher photon energy and greater electron flux density compared to lasers in other wavelength bands, making them applicable to various fields such as precision micromachining, optical storage and communication, and laser medicine. Currently, among DUV laser output methods, multiphoton simultaneous absorption and nonlinear optical crystal frequency doubling methods both rely on coherent nonlinear optical effects, requiring expensive and bulky ultrashort pulse lasers. In contrast, converting low-energy near-infrared pump lasers into high-energy, stable DUV lasers through multiphoton upconversion schemes is a more user-friendly photon conversion strategy. Rare earth elements, due to their unique 4f... N Its electronic structure, with its abundant energy levels, long excitation lifetime, and thermal and chemical stability, makes the pump energy density required for upconversion luminescence several orders of magnitude lower than that of traditional nonlinear processes, which is more conducive to the development of low-cost, integrable micro all-solid-state lasers.

[0003] By combining rare-earth-doped upconversion nanocrystals with microresonant cavities, the absorption of pump energy can be effectively improved and energy loss reduced, which is beneficial for achieving low-power deep ultraviolet coherent light output. The most prominent example is the whispering corridor mode microcavity, which confines light within the cavity through total internal reflection to form a resonant mode. This offers advantages such as a high quality factor (Q), small mode volume, and high energy density, significantly improving light-matter interaction and reducing the complexity of the mode spectrum. This is particularly beneficial for realizing low-threshold single-mode micro / nano laser devices. These lasers can be combined with standard semiconductor fabrication processes, possessing large manufacturing tolerances, enabling the fabrication of low-cost, large-scale integrated on-chip deep ultraviolet microlasers. Furthermore, this rare-earth-doped optical functional microcavity array can be combined with flexible substrates, showing broad application prospects in flexible devices.

[0004] The main drawback of whispering-gallery mode microring resonators is their rotational symmetry, which causes the emitted laser to have isotropic characteristics. Many experimental and application requirements, such as microlasers and single-photon sources, necessitate a unidirectional output beam, and this specific condition greatly limits their development in practical applications.

[0005] Therefore, by breaking the rotational symmetry of traditional microcavities, a rare-earth ion-doped on-chip microlaser capable of directional deep ultraviolet laser emission was designed to achieve directional deep ultraviolet coherent light output. This device also possesses high Q value and low threshold characteristics, which can promote breakthroughs in the application of rare-earth inorganic materials in the optoelectronic field. Summary of the Invention

[0006] The object of the present invention is to overcome the deficiencies of the prior art and provide a rare-earth doped upconversion nanomaterial, a preparation method thereof and an application thereof. The rare-earth doped upconversion nanomaterial provided by the present invention is used in a specific laser device, can stably and directionally emit deep ultraviolet light, and promotes the application breakthrough of rare-earth nanomaterials.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] In the first aspect, the present invention provides a rare-earth doped upconversion nanomaterial, which includes a core layer, an inner shell layer and an outer shell layer. The components of the core layer include LiYb (1-x-y) Gd x Tm y F4, where x and y satisfy: 0 < x < 1, 0 < y < 1; the components of the inner shell layer include LiYbF4, and the components of the outer shell layer include LiLuF4.

[0009] The present invention provides a material with a core layer doped with Yb 3+ -Tm 3+ -Gd 3+ system, and selects inner shell layer and outer shell layer structures with specific components. By controlling the types and contents of doped ions, precise regulation of the emission wavelength of the nanomaterial is achieved. The rare-earth doped upconversion nanomaterial provided by the present invention can emit high-intensity deep ultraviolet fluorescence under the excitation of near-infrared light (980 nm), and the material can be further used in a laser device to achieve directional deep ultraviolet laser emission.

[0010] The rare-earth doped upconversion nanomaterial provided by the present invention exhibits multi-band upconversion luminescence characteristics in the red, blue and deep ultraviolet bands (Yb 3+ →Tm 3+ , Yb 3+ →Tm 3+ →Gd 3+ ), especially at 252 nm (Gd 3+ , 6 D 9 / 2 → 8 S 7 / 2 ) shows a relatively high upconversion luminescence intensity, presenting an extremely high deep ultraviolet band luminescence intensity, including 252 nm ( 6 D 9 / 2 → 8 S 7 / 2 ), 279 nm ( 6 I J → 8 S 7 / 2 ), 311 nm ( 6 P 7 / 2 [[ID= June 2023]] 8 S7 / 2 ) Belongs to Gd 3+ Characteristic transition luminescence, and attribution to Tm 3+ 288nm ( 1 I6→ 3 H6) characteristic transition luminescence.

[0011] Removing any one of the dopants fails to achieve satisfactory upconversion luminescence in the deep ultraviolet band. This invention utilizes Yb... 3+ →Tm 3+ →Gd 3+ The transitions at 252nm, 279nm, and 311nm belong to Gd. 3+ Deep ultraviolet upconversion luminescent nanomaterials with characteristic transitions, if lacking the inner Gd layer 3+ Doping prevents the construction of Tm 3+ Mediated energy transfer to gain Gd 3+ Deep ultraviolet upconversion luminescence with characteristic transitions.

[0012] Meanwhile, the present invention combines inner and outer shells of specific components to further improve energy absorption during material pumping and ensure luminescence intensity in the deep ultraviolet band; if the shell is removed, the pumping energy loss caused by surface defects and residual ligands in the material nanocrystals will result in a significant decrease in upconversion luminescence intensity at 311 nm in the ultraviolet region, and it will be unable to further support upconversion luminescence in the deep ultraviolet bands at 252 nm and 279 nm.

[0013] The rare-earth-doped upconversion nanomaterials provided by this invention can be further integrated with deformable cavities. Through micro-nano fabrication and laser reflow processes, deformable cavity arrays that can achieve unidirectional laser emission while maintaining a high Q value can be fabricated. Stable, directional deep ultraviolet laser on-chip micro-laser devices can be obtained under near-infrared pumping, further promoting breakthroughs in the application of rare-earth-based nanoluminescent materials in the field of integrated optics.

[0014] Preferably, the x and y satisfy: 0 <x<0.5、0<y<0.1。

[0015] More preferably, x and y satisfy: 0.2 <x<0.4、0<y<0.05。

[0016] As a preferred embodiment, the core layer comprises LiYb 0.69 Gd 0.3 Tm 0.01 F4.

[0017] The LiYb (1-x-y) Gd x Tm y The molar ratio of F4, LiYbF4, and LiLuF4 is: LiYb (1-x-y) Gdx Tm y F4: LiYbF4: LiLuF4=1: (0.8-1.2): (0.8-1.2).

[0018] Preferably, the rare earth-doped upconversion nanomaterial has an average particle size of 60-75 nm.

[0019] The rare earth-doped upconversion nanomaterials provided by this invention have rhombic nanocrystals, and the average particle size is the long axis dimension.

[0020] Secondly, the present invention provides a method for preparing the above-mentioned rare earth-doped upconversion nanomaterials, comprising the following steps:

[0021] (1) Yb source, Gd source and Tm source are heated and mixed with oleic acid and 1-octadecene to obtain a precursor solution, which is then cooled. Then, Li source and F source are added to the precursor solution and heated to react, thereby obtaining the core layer material.

[0022] (2) The Yb source is heated and mixed with oleic acid and 1-octadecene, cooled, and then the core layer material, Li source and F source are added in sequence and heated to react to obtain the core-shell structure material.

[0023] (3) The Lu source is heated and mixed with oleic acid and 1-octadecene, cooled, and then the core-shell structure material, Li source and F source are added in sequence and heated to react, so as to obtain the rare earth-doped upconversion nanomaterial.

[0024] This invention prepares rare-earth-doped upconversion nanomaterials via a chemical coprecipitation method. The preparation steps for the inner and outer shells are similar. During the preparation of the inner shell, core nanoparticles are used as nucleation seeds to mediate its growth. The outer shell is synthesized by using core-shell structured nanoparticles as nucleation seeds to mediate its growth. The prepared rare-earth-doped upconversion nanomaterials exhibit a tetragonal LiYbF4 single-crystal structure with a highly uniform rhombic appearance.

[0025] Preferably, in the preparation method, the Li source and F source are prepared into a solution with methanol and added dropwise at 50°C; more preferably, before the heating reaction, the system is first heated to 100°C in a vacuum environment and held for 30 min to remove methanol, and then methanol gas is purged with argon gas.

[0026] Preferably, the Yb source is Yb(CH3CO2)3, the Gd source is Gd(CH3CO2)3, the Tm source is Tm(CH3CO2)3, the Li source is LiOH, and the F source is NH4F;

[0027] And / or the heating and mixing specifically refers to heating and stirring at 130-170℃ for 20-30 minutes;

[0028] And / or the temperature of the heating reaction is 270-290℃, and the reaction time is 80-100 min.

[0029] Thirdly, the present invention provides the application of the above-mentioned rare-earth-doped upconversion nanomaterials in directional deep ultraviolet laser devices, the application comprising the following steps:

[0030] S1. The rare earth-doped upconversion nanomaterial is prepared into a solution, coated on the surface of a patterned deformable cavity, and then laser device is obtained by laser reflow.

[0031] The deformation cavity is a spiral-shaped deformation cavity, and the deformation degree of the deformation cavity is 0.42-0.44;

[0032] S2. Pump the laser device to realize the application of the rare earth-doped upconversion nanomaterial in a directional deep ultraviolet laser device;

[0033] In the pumping process, the focal point of the pump light is set at the edge of the deformable cavity in the laser device.

[0034] Preferably, the deformation degree of the deformation cavity is 0.43.

[0035] This invention breaks the rotational symmetry of the whispering corridor mode resonator by using a spiral deformable cavity, thus achieving directional coherent light emission. Based on the spiral deformable cavity formula, COMSOL is used to simulate the effect of deformation degree on the light field distribution: at the above deformation degree, it has the strongest directionality, and a high-intensity unidirectional emitted light field in a specific direction.

[0036] Furthermore, through specialized laser device design and processing techniques, combined with a specific deformable cavity and the rare-earth-doped upconversion nanomaterials of this invention as the gain medium, directional deep-ultraviolet laser emission can be achieved. Simultaneously, this rare-earth-based deformable cavity laser device maintains a high Q-value and a low threshold characteristic. Compared to existing multiphoton simultaneous absorption and nonlinear frequency doubling methods, the application provided by this invention utilizes specific rare-earth-doped upconversion nanomaterials to convert low-energy near-infrared pump lasers into high-energy deep-ultraviolet lasers; this photon conversion method is more user-friendly.

[0037] Preferably, the deformable cavity is a silicon dioxide deformable microcavity with a size of 60-80 μm; more preferably, after reflow is completed, the silicon pillars of the deformable cavity are subjected to secondary ICP etching, which can reduce the loss of light by silicon and silicon dioxide.

[0038] Preferably, the concentration of rare earth-doped upconversion nanomaterials in the solution is 0.03-0.04 mg / mL.

[0039] The concentration of the rare-earth-doped upconversion nanomaterial solution has a significant impact on the Q value of the deformable cavity. Increasing the concentration causes the Q value of the deformable cavity to decrease continuously. At the optimal concentration, both high cavity Q value and high radiation intensity can be achieved. Combined with the specific structure of the deformable cavity, the optical confinement capability of the cavity is stronger, thereby realizing low-threshold single-mode laser emission.

[0040] Preferably, the laser reflow conditions are: a CO2 laser is used for reflow, and the power of the CO2 laser is 10-15W.

[0041] Specific reflow processes can further achieve an array-like distribution of deformation cavities, resulting in clean surfaces and neat, smooth edges.

[0042] Preferably, the power density of the pump is >0.27 mJ / cm³. -2 .

[0043] The rare-earth-doped upconversion nanomaterials provided by this invention, combined with a specific deformable cavity, can achieve a low laser threshold and realize stable, high-intensity directional deep ultraviolet light output at low power density.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] This invention prepares Yb by co-precipitation method 3+ Tm 3+ Gd 3+ Co-doped LiYb (1-x-y) Gd x Tm y Upconversion nanomaterials consisting of an F4 core layer, a LiYbF4 inner shell layer, and a LiLuF4 outer shell layer have initially achieved efficient conversion from near-infrared pump light to deep ultraviolet light. Simultaneously, the design of a spiral deformable cavity breaks the rotational symmetry of traditional optical resonators, endowing the deformable cavity with directional emission characteristics, thus improving the directionality and quality of the laser. Finally, the deformable cavity is integrated with rare-earth-doped upconversion nanomaterials to fabricate a micro-laser device, resulting in a laser device capable of achieving efficient directional deep ultraviolet emission while maintaining a high Q value and a low threshold. This breakthrough overcomes the rotational symmetry of traditional microcavities and represents a significant breakthrough in the application of rare-earth nanoluminescent materials. Attached Figure Description

[0046] Figure 1 a) XRD diffraction pattern of the rare earth-doped upconversion nanomaterial of the present invention; b) TEM image and particle size distribution of the rare earth-doped upconversion nanomaterial of the present invention;

[0047] Figure 2 The following is a comparison of the fluorescence spectra of the materials in the examples and comparative examples under 980nm continuous laser pumping;

[0048] Figure 3 a) Simulated field distribution diagram; b) Far-field simulated distribution diagram when the deformation degree of the spiral deformable cavity is 0.43;

[0049] Figure 4 SEM images of a single deformable cavity and an array of deformable cavities in laser devices fabricated from rare-earth-doped upconversion nanomaterials of the present invention are shown below.

[0050] Figure 5 The transmission spectrum of the deformable cavity in the laser device prepared by the rare earth-doped upconversion nanomaterial of this invention is shown.

[0051] Figure 6 A comparison of the Q values ​​of the deformable cavities of laser devices prepared with different rare earth doping concentrations of upconversion nanomaterials according to the present invention;

[0052] Figure 7 a) Laser spectra of the laser device fabricated using the rare-earth-doped upconversion nanomaterials of this invention at different pump power densities; b) Relationship between luminescence intensity and pump power density;

[0053] Figure 8 The laser far-field emitted light intensity angular distribution diagram of the laser device prepared by the rare earth-doped upconversion nanomaterial of this invention. Detailed Implementation

[0054] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available reagents and materials.

[0055] Example 1

[0056] One embodiment of the rare-earth-doped upconversion nanomaterial of the present invention includes a core layer, an inner shell layer, and an outer shell layer, wherein the core layer is composed of LiYb. 0.69 Gd 0.3 Tm 0.01 F4, the inner shell is composed of LiYbF4, the outer shell is composed of LiLuF4, and the rare earth-doped upconversion nanomaterial in this embodiment is labeled as LiYbF4:Tm / Gd@LiYbF4@LiLuF4.

[0057] The method for preparing the rare-earth-doped upconversion nanomaterials described in this embodiment is as follows:

[0058] (1) Prepare aqueous solutions of Yb(CH3CO2)3, Gd(CH3CO2)3 and Tm(CH3CO2)3 with a concentration of 0.2M respectively. Take 1.38 mL of Yb(CH3CO2)3 solution, 0.60 mL of Gd(CH3CO2)3 solution and 0.02 mL of Tm(CH3CO2)3 solution at room temperature, mix with 5 mL of oleic acid and 5 mL of octadecene, stir at 150℃ for 40 min to form a precursor solution, and let it cool naturally.

[0059] Mix 1 mmol of LiOH and 1.32 mmol of NH4F in methanol, then add dropwise to the precursor solution at 50 °C and continue stirring for 30 min. Heat the solution to 100 °C in a vacuum environment and hold for 30 min. After completion, purge the methanol gas with argon gas, then heat the solution to 280 °C, hold for 90 min, and then cool to room temperature to obtain the core layer material. Disperse the core layer material in cyclohexane for later use.

[0060] (2) Take 2 mL of Yb(CH3CO2)3 solution prepared in step (1) and mix it with 5 mL of oleic acid and 5 mL of 1-octadecene. Heat and stir at 150°C for 40 min, then cool to 90°C and add the core layer material from step (1) and keep for 30 min to remove cyclohexane.

[0061] After cooling to 50°C, 1 mmol of LiOH and 1.32 mmol of NH4F were added, and the mixture was heated and stirred for 30 min. The mixture was then placed in a vacuum environment and heated to 100°C for 30 min to remove methanol. After purging the methanol gas with argon, the mixture was heated to 280°C and held for 90 min before being cooled to room temperature to obtain the core-shell structured material. The core-shell structured material was then dispersed in cyclohexane for later use.

[0062] (3) Prepare a 0.2M Lu(CH3CO2)3 aqueous solution, take 2mL of Lu(CH3CO2)3 solution and mix it with 5mL of oleic acid and 5mL of 1-octadecene, heat and stir at 150℃ for 40min, then cool to 90℃, add the core-shell structure material from step (2) and keep for 30min to remove cyclohexane;

[0063] After cooling to 50°C, 1 mmol of LiOH and 1.32 mmol of NH4F were added, and the mixture was heated and stirred for 30 min. The mixture was then placed in a vacuum environment and heated to 100°C for 30 min to remove methanol. After purging the methanol gas with argon, the mixture was heated to 280°C and held for 90 min before being cooled to room temperature to obtain the rare earth-doped upconversion nanomaterial LiYbF4:Tm / Gd@LiYbF4@LiLuF4.

[0064] The XRD diffraction pattern and TEM image of the rare earth-doped upconversion nanomaterial in this embodiment are as follows: Figure 1 In the figure, a) is the XRD diffraction pattern and b) is the TEM particle size distribution. It can be seen that the prepared rare earth-doped upconversion nanomaterial exhibits a tetragonal LiYbF4 (PDF#71-1211) single crystal structure, and the TEM structure shows a highly uniform rhombic structure with an average particle size (long axis) of 61.5 nm.

[0065] Comparative Example 1

[0066] The rare-earth-doped nanomaterial in Comparative Example 1 consists of a core layer and a shell layer, wherein the core layer is composed of LiYb. 0.69 Gd 0.3 Tm 0.01 F4, the shell composition is LiYbF4.

[0067] The difference between its preparation method and that of Example 1 is that step (3) is not performed, and only the core-shell structure material is obtained, labeled as LiYbF4:Tm / Gd@LiYbF4.

[0068] Comparative Example 2

[0069] The rare-earth-doped nanomaterial in Comparative Example 2 comprises a core layer, an inner shell layer, and an outer shell layer, wherein the core layer is composed of LiYb. 0.99 Tm 0.01 F4, the inner shell is composed of LiYbF4, and the outer shell is composed of LiLuF4.

[0070] The preparation method differs from that in Example 1 in that Gd(CH3CO2)3 solution is not added in step (1), and the amount of Yb(CH3CO2)3 solution is increased to 1.98 mL. The prepared material is labeled as LiYbF4:Tm@LiYbF4@LiLuF4.

[0071] Example of effect

[0072] To investigate the luminescence properties of the rare-earth-doped upconversion nanomaterials provided by this invention, the materials in the examples and comparative examples were pumped using a continuous laser with a wavelength of 980 nm. The obtained fluorescence spectra were compared with those of the examples. Figure 2 .

[0073] Depend on Figure 2 It can be known that:

[0074] In Example 1, the fluorescence spectrum of the rare-earth-doped upconversion nanomaterial provided by the present invention under 980 nm continuous laser pumping shows multi-band upconversion luminescence characteristics in the red, blue, and deep ultraviolet bands (Yb). 3+ →Tm 3+ Yb3 + →Tm 3+ →Gd 3+ Its most notable feature is its extremely high luminescence intensity in the deep ultraviolet band, including 252nm ( 6 D 9 / 2 → 8 S 7 / 2 ), 279nm ( 6 I J → 8 S 7 / 2 ), 311nm ( 6 P 7 / 2 → 8 S 7 / 2 ) Belongs to Gd 3+ Feature transition luminescence and attribution to Tm 3+ 288nm ( 1 I6→ 3 H6) characteristic transition luminescence.

[0075] In contrast, the material LiYbF4:Tm@LiYbF4@LiLuF4 in Comparative Example 2 lacks the inner Gd layer. 3+ Doping prevents the construction of Tm 3+ Mediated energy transfer cannot be achieved through Yb 3+ →Tm 3+ →Gd 3+ The transitions at 252, 279, and 311 nm belong to Gd 3+ The characteristic transition of deep ultraviolet radiation; on the other hand, the material LiYbF4:Tm / Gd@LiYbF4 in Comparative Example 1 lacks the LiLuF4 shell structure. Due to pump energy loss caused by surface defects and ligand residues, the upconversion luminescence intensity at 311nm will be greatly reduced, and it will not be able to further support upconversion luminescence in the 252 and 279nm deep ultraviolet bands.

[0076] Application examples

[0077] To explore the application of the rare-earth-doped upconversion nanomaterials of this invention in directional deep-ultraviolet laser devices, a directional deep-ultraviolet laser device was fabricated by designing a spiral deformable cavity and combining it with the rare-earth-doped upconversion nanomaterials of this invention, and its luminescence performance was investigated, as follows:

[0078] 1. Design of the spiral-shaped deformation cavity

[0079] Based on the formula for a spiral deformable cavity, r(φ) = r0(1 + εcosφ), COMSOL was used to simulate the effect of the deformation degree (ε) on the optical field distribution. The strongest directionality was observed when the deformation degree was 0.43, as shown in the simulated field distribution diagram. Figure 3As shown in -a), the light field within the cavity satisfies the emission conditions and enters the leakage region, forming directional emitted light. The far-field simulation distribution with a deformation of 0.43 is obtained through calculations, as shown in the diagram. Figure 3 As shown in -b), it can be seen that there is high-intensity unidirectional emission in the 330° direction.

[0080] 2. Fabrication of laser devices

[0081] S1. Based on the above design, taking a deformable cavity with a deformation degree of 0.43 as the object: After ultrasonically cleaning the silicon oxide wafer sequentially with acetone, isopropanol, and deionized water, photoresist (AZ2020, Microchem) is spin-coated onto the wafer, and microstructure molding is performed on the inside of the photoresist using standard photolithography technology (pre-baking 110℃, 60s; post-baking 110℃, 60s; contact exposure, energy density 10μw / cm²). -2 (Exposure time 25s).

[0082] Inductively coupled ion etching (ICE) was employed. First, C4F8 was used as the anisotropic etching gas to transfer the microstructure pattern onto the silicon dioxide layer (gas flow rate 20 sccm, temperature 70℃, power 1300W, RF power 20W, etching time 7 min). Then, SF6 was used as the isotropic etching gas to etch the silicon layer beneath the silicon dioxide (gas flow rate 20 sccm, temperature 40℃, power 1200W, RF power 0W, etching time 20 min). The photoresist was removed by immersion, resulting in a suspended silicon dioxide deformable microcavity.

[0083] S2. The rare earth-doped upconversion nanomaterial from Example 1 was prepared into a 0.0033M cyclohexane solution. The solution was spin-coated onto the deformation cavity. Initially, the spin-coating speed was 500 rpm for 5 seconds, and then the spin-coating speed was increased to 4000 rpm for 6 seconds. A CO2 laser (10.6 μm wavelength, 11.4 W power) was used for reflow. Subsequently, a second ICP etching was performed on the silicon pillar to obtain the laser device.

[0084] SEM top view of the deformation cavity after reflow is shown below Figure 4 As shown, the deformation cavities can be distributed in an array, and the surface of each deformation cavity is clean with neat and smooth edges.

[0085] 3. Investigate the effect of different rare-earth doped upconversion nanomaterial concentrations on the Q-value of laser devices.

[0086] (A) The Q value of the laser device prepared above was measured under 1550nm tunable laser pumping by coupling it to the active micro-ring cavity via a tapered optical fiber:

[0087]

[0088] The transmission spectrum of the 75μm deformable cavity is shown below. Figure 5 The transmission characteristics at 1534 nm in the figure were evaluated, confirming that the laser device can achieve a transmission density as high as 2.2 × 10⁻⁶ nm. 6 High-quality factors.

[0089] (B) Repeat the operation in step 2, except that in S2, rare earth-doped upconversion nanomaterial solutions with concentrations of 0M, 0.0033M (2.52 mg / mL), 0.0067M (5.12 mg / mL), and 0.0125M (9.56 mg / mL) are diluted and prepared. The Q value of the deformable cavity of the laser device is tested at different rare earth-doped upconversion nanomaterial coating concentrations. The results are as follows: Figure 6 .

[0090] As can be seen, coating the gain medium increases the scattering loss of the deformable cavity. Figure 6 As the concentration of the rare-earth-doped upconversion nanomaterials increases, the Q value decreases exponentially. A clean, impurity-free surface is essential for a high-Q deformable cavity. To balance high fluorescence intensity and a high Q value, a 30-fold dilution (i.e., a concentration of 2.52 mg / mL) of rare-earth-doped upconversion nanomaterials was preferred as the gain medium. Deformable cavity laser device samples were then prepared for subsequent application performance verification.

[0091] 4. Verification of the application effect of directional deep ultraviolet laser devices

[0092] (C) An Nd:YAG nanosecond laser was used as the pump source for the unidirectional test, with an output frequency of 10 Hz and an output wavelength of 980 nm. Different power densities (0.221, 0.236, 0.259, 0.278, 0.297, 0.311, 0.365, and 0.454 mJ / cm²) were applied. -2 The deep ultraviolet (DUV) laser performance of the laser device sample was tested. The emission spectrum of the DUV light emitted by the sample as a function of pump power density is shown below. Figure 7 .

[0093] Depend on Figure 7 -a) It can be seen that as the pump power increases, the intensity of deep ultraviolet light gradually increases; from Figure 7 -b) As can be seen, the pump power-luminescence intensity curve shows a clear inflection point (i.e., the laser threshold P). th =0.27mJ / cm -2 As the pump energy continues to increase, the emitted light intensity shows a sharp upward trend, as indicated by the formula Δλ = λ. 2 0 / n eff D(Δλ is the periodic mode spacing, λ0 is the center wavelength, n)eff The effective refractive index of the microring cavity (where D is the diameter of the microring cavity) is calculated to be approximately 0.1 nm. This demonstrates that the laser device prepared by the rare-earth-doped upconversion nanomaterial of this invention supports deep ultraviolet laser output in pseudo-whispering-gallery mode.

[0094] (D) By maintaining the output power and rotating the sample stage, the deep ultraviolet laser directionality of the laser device sample was further tested. The intensity angular distribution of the far-field emitted laser light from the laser device sample is shown in the figure. Figure 8 As shown:

[0095] As can be seen, the emitted light intensity exhibits strong fluctuations with changing angles. The emitted light intensity is significantly higher in the 330° direction than in other directions, proving that the deformable cavity has a highly unidirectional emission characteristic along the 330° direction. Furthermore, it was found that this unidirectional radiation has an emission angle of less than 30°. This is basically consistent with the simulation results in step 1.

[0096] Furthermore, during the testing process, it was found that when the entire deformable cavity was pumped, directional emission could not be achieved due to the diffraction phenomenon of light; only when the pumping laser focus was placed at the edge of the deformable cavity did the measured light intensity show directional emission.

[0097] In summary, the present invention optimizes the preparation of materials with Yb 3+ Tm 3+ Gd 3+ Co-doped LiYb (1-x-y) Gd x Tm y Upconversion nanomaterials consisting of an F4 core layer, a LiYbF4 inner shell layer, and a LiLuF4 outer shell layer have been used to initially achieve efficient conversion from near-infrared pump light to deep ultraviolet light. By combining this with a spiral deformable cavity design, the rotational symmetry of traditional whispering corridor mode optical resonators has been broken, and the deformable cavity has been successfully endowed with directional emission characteristics, improving the directionality and quality of the laser. Finally, the deformable cavity and rare-earth-doped upconversion nanomaterials were integrated to fabricate a laser device, achieving efficient directional deep ultraviolet emission. This rare-earth-based device has a high Q value and a low threshold characteristic, representing a breakthrough in the application of rare-earth nanoluminescent materials.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A rare-earth-doped upconversion nanomaterial, characterized in that, It includes a core layer, an inner shell layer and an outer shell layer. The components of the core layer include LiYb (1-x-y) Gd x Tm y F4, where x and y satisfy 0 < x < 1 and 0 < y < 1. The components of the inner shell layer include LiYbF4, and the components of the outer shell layer include LiLuF4.

2. The rare-earth-doped upconversion nanomaterial as described in claim 1, characterized in that, The x and y satisfy: 0 <x<0.5、0<y<0.1。 3. The rare-earth-doped upconversion nanomaterial as described in claim 1, characterized in that, The LiYb (1-x-y) Gd x Tm y The molar ratio of F4, LiYbF4, and LiLuF4 is: LiYb (1-x-y) Gd x Tm y F4: LiYbF4: LiLuF4=1: (0.8-1.2): (0.8-1.2).

4. The rare-earth-doped upconversion nanomaterial as described in claim 1, characterized in that, The rare earth-doped upconversion nanomaterials have an average particle size of 60-75 nm.

5. The method for preparing rare-earth-doped upconversion nanomaterials according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Yb source, Gd source and Tm source are heated and mixed with oleic acid and 1-octadecene to obtain a precursor solution, which is then cooled. Then, Li source and F source are added to the precursor solution and heated to react, thereby obtaining the core layer material. (2) The Yb source is heated and mixed with oleic acid and 1-octadecene, cooled, and then the core layer material, Li source and F source are added in sequence and heated to react to obtain the core-shell structure material. (3) The Lu source is heated and mixed with oleic acid and 1-octadecene, cooled, and then the core-shell structure material, Li source and F source are added in sequence and heated to react, so as to obtain the rare earth-doped upconversion nanomaterial.

6. The method for preparing rare-earth-doped upconversion nanomaterials as described in claim 5, characterized in that, The Yb source is Yb(CH3CO2)3, the Gd source is Gd(CH3CO2)3, the Tm source is Tm(CH3CO2)3, the Li source is LiOH, and the F source is NH4F; And / or the heating and mixing specifically refers to heating and stirring at 130-170℃ for 20-30 minutes; And / or the temperature of the heating reaction is 270-290℃, and the reaction time is 80-100 min.

7. The application of the rare-earth-doped upconversion nanomaterials as described in any one of claims 1-4 in directional deep ultraviolet laser devices, characterized in that, The application includes the following steps: S1. The rare earth-doped upconversion nanomaterial is prepared into a solution, coated on the surface of a patterned deformable cavity, and then laser device is obtained by laser reflow. The deformation cavity is a spiral-shaped deformation cavity, and the deformation degree of the deformation cavity is 0.42-0.44; S2. Pump the laser device to realize the application of the rare earth-doped upconversion nanomaterial in a directional deep ultraviolet laser device; In the pumping process, the focal point of the pump light is set at the edge of the deformable cavity in the laser device.

8. The application of the rare-earth-doped upconversion nanomaterial as described in claim 7 in directional deep ultraviolet laser devices, characterized in that, The concentration of rare earth-doped upconversion nanomaterials in the solution is 0.03-0.04 mg / mL.

9. The application of the rare-earth-doped upconversion nanomaterial as described in claim 7 in directional deep ultraviolet laser devices, characterized in that, The conditions for laser reflow are: a CO2 laser is used for reflow, and the power of the CO2 laser is 10-15W.

10. The application of the rare-earth-doped upconversion nanomaterial as described in claim 7 in directional deep ultraviolet laser devices, characterized in that, The power density of the pump is >0.27 mJ / cm³. -2 .

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