Low-temperature rare earth nano temperature probe with ultrahigh sensitivity as well as preparation method and application of low-temperature rare earth nano temperature probe

Abstract

The invention discloses a low-temperature rare earth nano temperature probe with ultrahigh sensitivity as well as a preparation method and application thereof. The nano temperature probe is of a core-shell-shell nano structure formed by doping specific rare earth ions into a LiYF4 main matrix, and comprises a crystal nucleus LiYF4: Ho, a middle sensitized shell layer LiYF4: Yb and an optical inert protective layer LiYF4. The core-shell-shell structure nanoparticles are prepared by adopting a coprecipitation method. According to the prepared nano temperature probe, under the 980 nm near-infrared light excitation condition, the middle sensitized shell layer LiYF4: Yb absorbs energy and transmits the energy to a crystal nucleus, and red light emission and green light emission from the crystal nucleus Ho < 3 + > can be detected at the same time. As the temperature is reduced, the red light emission intensity of the crystal nucleus Ho < 3 + > is slowly reduced, and the green light emission intensity is obviously increased, so that the luminous intensity ratio of the red light to the green light is greatly changed. Thus, in the ultra-low temperature region (lt; and the highest relative sensitivity of temperature measurement can reach 15.1% K <-1 >.

Description

Technical Field

[0001] The present invention relates to the fields of rare earth luminescent materials and temperature sensing, and particularly relates to a rare earth nano temperature probe with ultra-high sensitivity at low temperature, a preparation method thereof, and an application thereof. Background Art

[0002] High-sensitivity low-temperature real-time detection has important applications in the fields of aerospace, polar scientific research, petroleum industry, biomedicine, etc. Typical contact thermometers need to contact the object to be measured for heat exchange before reading. Traditional thermometers, including liquid (solid) expansion type or pressure type, are usually not suitable for low-temperature engineering environments and cannot meet the needs of modern science and technology. The gas acoustic thermometer is one of the most accurate methods for measuring thermodynamic temperature in the medium and low temperature regions. However, it involves multiple technical elements such as temperature measurement, constant temperature control, and volume measurement, and is mainly used for basic scientific research such as accurately measuring and defining international measurement units as a reference thermometer. The complex equipment composition and working principle and the difficulty in real-time response limit its application in the engineering field. Currently, the most widely used high-performance low-temperature sensors are metal resistance thermometers, which have been widely used in low-temperature environments such as particle accelerators, artificial satellites, and MRI systems. However, when exposed to magnetic fields or ionizing radiation for a long time, there are strict requirements for the packaging materials, device design, stability, etc. of such thermometers, and the working mode based on electrical signals is also difficult to meet the temperature measurement requirements in vivo biomedicine, etc.

[0003] In recent years, the photoluminescence temperature measurement probe based on nanomaterials, as a non-contact thermometer using the luminescence intensity ratio as the temperature measurement index, has received extensive attention due to its advantages such as small size, fast response, non-invasiveness, and immunity to electromagnetic interference. Among them, rare earth-doped upconversion nanoparticles have the characteristics of good physical and chemical stability, narrow emission band, rich emission peaks, and no background fluorescence, and have developed rapidly in the field of temperature sensing. However, the currently reported rare earth upconversion luminescence ratio thermometers are mainly used for temperature detection at room temperature and above due to design principle limitations. For example, the conventional temperature probe design is based on the Boltzmann thermal distribution law of thermally coupled energy levels, and the temperature is measured by observing the luminescence change of the thermally coupled energy levels of the luminescence center (for example, the two green light emission energy levels of Er 3+ of 2 H 11 / 2 and 4 S 3 / 2), so the sensitivity of the temperature probe is severely limited by this mechanism. And because the probability of thermally excited particle numbers is very small at low temperatures (especially ultra-low temperatures <100K), the measurement principle fails, the results are inaccurate, and the sensitivity is also very low, so the related research using the Boltzmann mechanism is more difficult to use for low-temperature probe design and application. Patent CN114574189A "A design of a nano temperature probe with high sensitivity and a material preparation method" proposes a high-sensitivity nano temperature probe for high temperatures (293-443K), indicating that core-shell rare earth nanomaterials based on non-thermal coupling energy level luminescence have a higher temperature measurement performance advantage, but this material still cannot be used for low-temperature temperature measurement. There are also few reports on related rare earth nanomaterials, and the problem of how to obtain high-sensitivity low-temperature detection performance needs to be solved urgently. Therefore, it is of great scientific significance and practical value to develop an ultra-sensitive low-temperature nano thermometer based on non-thermal coupling energy level luminescence with core-shell-shell rare earth nanomaterials as the main body. Summary of the invention

[0004] The present invention proposes a design and preparation method of a low-temperature rare earth nanometer temperature probe with ultra-high sensitivity. Aiming at the shortage of ultra-high sensitivity nanometer thermometers for detecting low-temperature areas (especially ultra-low-temperature areas <100K), the design principle of non-thermal coupled energy level luminescence is adopted to convert Ho 3+ The two non-thermally coupled energy-level luminescences with different temperature-sensitive properties are integrated into a single core-shell nanoparticle. By recording the intensity and ratio of the two luminescences that change rapidly with temperature, an ultra-high-sensitivity low-temperature nano-temperature probe is obtained. When the nanomaterial is irradiated by a commercial 980nm laser, Yb 3+ The energy of the 980nm laser absorbed from the outside is transferred to the Ho 3+ , thus generating Ho 3+ When working in a low temperature environment, Yb 3+ Located alone in the middle shell of the nanoparticle, it can inhibit the 3+ with Ho 3+ The reverse energy transfer process can avoid interfering with Ho 3+ The cross relaxation process of Ho 3+ Located in the nanoparticle core, high doping concentration Ho 3+ The cross relaxation between ions is affected by temperature, so that the red light emission weakens as the temperature decreases, and the green light emission increases as the temperature decreases. The red and green light emission intensities show a strong dependence on the temperature with opposite trends. Therefore, through the relationship between the luminous intensity ratio of the two and the temperature, it is possible to achieve a temperature of not less than 4.5% K in the ultra-low temperature range of 11K-88K (except 39.9K-41.9K). -1 Ultra-high temperature measurement sensitivity, the relative sensitivity of temperature measurement in ultra-low temperature area (<100K) can reach up to 15.1%K-1 (50K).

[0005] The object of the present invention is achieved by the following technical solutions.

[0006] A low-temperature rare-earth nano temperature probe with ultra-high sensitivity, wherein the nano temperature probe is composed of core-shell-shell structure nanoparticles with different luminescence characteristics, and the core-shell-shell structure nanoparticles are composed of a cubic-phase LiYF4 host matrix and a combination of doped specific rare-earth ions.

[0007] Further, the rare-earth ion doped in the crystal nucleus part is Ho 3+ , and the rare-earth ion doped in the middle sensitizing shell layer is Yb 3+ .

[0008] Further, the core-shell-shell structure nanoparticles are, from inside to outside, the crystal nucleus LiYF4:Ho that provides red and green light emissions, the middle sensitizing shell layer LiYF4:Yb, and the optically inert protective shell layer LiYF4. The chemical expression of the core-shell-shell structure nanoparticles is LiYF4:Ho@LiYF4:Yb@LiYF4.

[0009] Among them, when the crystal nucleus LiYF4:Ho is excited by a 980 nm wavelength, red and green light emissions are generated. Among them, the intensity of the green light emission increases with the decrease of temperature, and the intensity of the red light emission decreases with the decrease of temperature; the middle sensitizing shell layer LiYF4:Yb is used to absorb the energy of the 980 nm excitation light and transfer it to the crystal nucleus to make the crystal nucleus respond to light emission; the optically inert protective layer LiYF4 is used to block the quenching effect of light on the surface of the nanoparticles.

[0010] Further, the molar concentration of the rare-earth ion Ho in the crystal nucleus LiYF4:Ho 3+ is 1-100 mol%; the molar concentration of the rare-earth ion Yb in the middle sensitizing shell layer LiYF4:Yb 3+ is 20-100 mol%.

[0011] Further, the major axis diameter of the crystal nucleus LiYF4:Ho is 12-14 nm, the minor axis diameter is 9-10 nm; the thickness of the middle sensitizing shell layer LiYF4:Yb is 1.6-2.0 nm; the thickness of the optically inert protective shell layer LiYF4 is 2.4-2.8 nm.

[0012] The present invention provides a preparation method of a low-temperature rare-earth nano temperature probe with ultra-high sensitivity, which is prepared by a co-precipitation method. The specific steps are as follows:

[0013] (1) Take rare earth acetate solutions of Y(CH3COO)3 and Ho(CH3COO)3 according to molar fractions, and react them at a constant temperature of 110 - 150 °C for 50 - 70 minutes in a combined solvent of oleic acid and 1 - octadecene to form rare earth oleate complexes; when the solvent cools down to 45 - 55 °C, add a methanol solution containing NH4F and LiOH and react for 35 - 55 minutes; then continue to heat up to 100 °C and evacuate to remove residual methanol and water; continuously introduce argon and heat up to 280 - 300 °C and react for 80 - 100 minutes to obtain LiYF4:Ho crystal nucleus nanoparticles;

[0014] (2) According to the molar amount of LiYF4:Ho crystal nucleus nanoparticles in step (1), take equal - amount rare earth acetate solutions of Y(CH3COO)3 and Yb(CH3COO)3, and react them at a constant temperature of 110 - 150 °C for 50 - 70 minutes in a combined solvent of oleic acid and 1 - octadecene to form rare earth oleate complexes; after the solvent cools down to 80 - 100 °C, add a cyclohexane solution containing the LiYF4:Ho crystal nucleus nanoparticles obtained in step (1) and react at a constant temperature for 30 - 50 minutes; then cool down to 45 - 55 °C, and then add a methanol solution containing NH4F and LiOH and react for 35 - 55 minutes; then continue to heat up to 100 °C and evacuate to remove residual methanol and water; continuously introduce argon and heat up to 280 - 300 °C and react for 80 - 100 minutes to obtain LiYF4:Ho@LiYF4:Yb core - shell structure nanoparticles;

[0015] (3) Take a rare earth acetate solution of Y(CH3COO)3 according to molar fractions, and react it at a constant temperature of 110 - 150 °C for 50 - 70 minutes in a combined solvent of oleic acid and 1 - octadecene to form rare earth oleate complexes; after the solvent cools down to 80 - 100 °C, add a cyclohexane solution containing the LiYF4:Ho@LiYF4:Yb crystal nucleus nanoparticles obtained in step (2) and react at a constant temperature for 30 - 50 minutes; then cool down to 45 - 55 °C, and then add a methanol solution containing NH4F and LiOH and react for 35 - 55 minutes; then continue to heat up to 100 °C and evacuate to remove residual methanol and water; continuously introduce argon and heat up to 280 - 300 °C and react for 80 - 100 minutes; after cooling to room temperature, wash by centrifugation with cyclohexane and ethanol, and dry at 50 - 70 °C to obtain the core - shell - shell structure nanoparticles LiYF4:Ho@LiYF4:Yb@LiYF4. That is, the rare earth nano - temperature - measuring material is prepared.

[0016] Further, in the combined solvent described in steps (1), (2), and (3), the volume ratio of oleic acid to 1 - octadecene is 3 - 5 mL:5 - 7 mL.

[0017] Further, for the addition of the cyclohexane solution containing the LiYF4:Ho nanoparticles obtained in step (1) in step (2), and the addition of the cyclohexane solution containing the LiYF4:Ho@LiYF4:Yb nanoparticles obtained in step (2) in step (3), it is necessary to cool the complex to 80 - 100 °C before adding, and then keep it warm for 30 - 50 minutes.

[0018] The present invention also provides the application of the core-shell-shell structure nanoparticles LiYF4:Ho@LiYF4:Yb@LiYF4 as highly sensitive temperature probes in low-temperature detection, especially in the ultra-low temperature region (<100 K).

[0019] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0020] (1) The LiYF4:Ho@LiYF4:Yb@LiYF4 core-shell-shell structure nanoparticles provided by the present invention integrate red and green light emissions in a single particle, realizing temperature detection based on the luminescence intensity ratio at the nanoscale, avoiding the microscopic inhomogeneity caused by the mixed use of two single-color light materials, and ensuring the feasibility of using it as a temperature probe at the micro-nano scale.

[0021] (2) By doping Ho at a high concentration in a single nanoparticle 3+ , the red and green light emissions caused by cross-relaxation between ions show different temperature response characteristics, which can significantly increase the luminescence intensity ratio in the low-temperature region; Yb in the intermediate sensitizing shell 3+ provides energy for Ho in the crystal nucleus 3+ , and is separated from Ho in space through the core-shell structure 3+ , reducing the reverse energy transfer process between the two ions, and realizing the change of the emission color from red light emission at room temperature to green light emission at low temperature. Using the luminescence intensity ratio of the two emissions as a temperature measurement parameter, an ultra-high temperature measurement sensitivity of up to 15.1% K -1 can be achieved (at 50 K), which is suitable for ultra-high sensitivity temperature detection in the low-temperature region of 11 K - 300 K, especially in the range below 88 K.

[0022] (3) The low-temperature rare-earth nano temperature probe of the present invention has low preparation cost and good optical stability; it has higher low-temperature temperature measurement sensitivity compared with fluorescence thermometers with non-thermally coupled energy level luminescence intensity ratios; the nano size is convenient for device design and packaging, and the working method is simple, which helps to achieve efficient and high-sensitivity low-temperature temperature detection. Description of the Drawings

[0023] Figure 1 It is a schematic diagram of the design and luminescence principle of a low-temperature rare-earth nano temperature probe with ultra-high sensitivity of the present invention.

[0024] Figure 2 Powder XRD diffraction pattern of the LiYF4:Ho(40 mol%)@LiYF4:Yb(60 mol%)@LiYF4 core-shell-shell structure nanoparticles prepared in Example 1.

[0025] Figure 3 Transmission electron microscope images and corresponding particle size distribution diagrams of the LiYF4:Ho(40 mol%) crystal nucleus, LiYF4:Ho(40 mol%)@LiYF4:Yb(60 mol%) core-shell structure, and LiYF4:Ho(40 mol%)@LiYF4:Yb(60 mol%)@LiYF4 core-shell-shell structure nanoparticles prepared in Example 1.

[0026] Figure 4 Temperature-responsive photoluminescence diagram of the LiYF4:Ho(40 mol%)@LiYF4:Yb(60 mol%)@LiYF4 core-shell-shell structure nanoparticles prepared in Example 1.

[0027] Figure 5 Diagram of the luminescence intensity ratio and temperature sensitivity of the LiYF4:Ho(40 mol%)@LiYF4:Yb(60 mol%)@LiYF4 core-shell-shell structure nanoparticles prepared in Example 1.

[0028] Figure 6 Temperature sensitivity diagram of the LiYF4:Ho(x mol%)@LiYF4:Yb(60 mol%)@LiYF4 (x = 1, 40, 60, 100) core-shell-shell structure nanothermometers prepared in Example 2.

[0029] Figure 7 Luminescence spectra of the LiYF4:Ho(40 mol%)@LiYF4:Yb(x mol%)@LiYF4 (x = 20, 40, 60, 80, 100) core-shell-shell structure nanoparticles prepared in Example 3. Detailed implementation manners

[0030] The technical solutions of the present invention will be further described below in conjunction with specific embodiments and the accompanying drawings. However, the following embodiments are only for strengthening the description of the technical solutions of the present invention, and should not be construed as any limitation to the scope of the claimed invention.

[0031] It should be noted that unless otherwise specified, the technical terms or scientific terms used in this application should have the ordinary meaning understood by those skilled in the art to which the present invention belongs.

[0032] Schematic diagram of the design and luminescence principle of a low-temperature rare-earth nanothermometer with ultra-high sensitivity of the present invention is as Figure 1As shown. The rare earth nano temperature probe is a core-shell-shell nanostructure with a LiYF4 host matrix doped with specific rare earth ions. From the inside out, it is the red and green light emitting crystal nucleus LiYF4:Ho, the middle sensitizing shell LiYF4:Yb, and the optically inert protective layer LiYF4. The chemical expression of the core-shell-shell structure nanoparticles is LiYF4:Ho@LiYF4:Yb@LiYF4. In the temperature range of 11K - 300K, when the core LiYF4:Ho of the core-shell-shell structure nanoparticles is excited by a 980nm wavelength, red and green light emissions are generated. Among them, the intensity of the green light emission increases with the decrease of temperature, and the intensity of the red light emission decays with the decrease of temperature. The middle sensitizing shell LiYF4:Yb is used to absorb the energy of the 980nm excitation light and transfer it to the crystal nucleus, enabling the crystal nucleus to respond to light emission. The optically inert protective layer LiYF4 is used to block the quenching effect of light on the surface of the nanoparticles.

[0033] Example 1

[0034] The core-shell-shell structure nanoparticles prepared in this example are composed of a cubic LiYF4 host matrix doped with specific concentrations of rare earth ions in different nano spaces (the doped ion in the crystal nucleus is Ho 3+ , and the doped ion in the middle shell is Yb 3+ ), and the specific steps are as follows:

[0035] (1) In the first step, the synthesis of LiYF4:Ho (40mol%) crystal nucleus nanoparticles. Take a total of 0.4mmol of rare earth acetate solution according to specific molar fractions, including Y(CH3COO)3 (60%) and Ho(CH3COO)3 (40%). React at a constant temperature of 150°C for 50 minutes in a combined solvent of oleic acid and 1-octadecene to form a rare earth oleate complex. When the solvent cools to 50°C, add a 6mL methanol solution containing 1.6mmol NH4F and 1.0mmol LiOH and react for 40 minutes. Then continue to heat up to 100°C and evacuate to remove residual methanol and water. Continuously introduce argon and heat up to 290°C and react at a constant temperature for 90 minutes. After the reaction is completed and cooled to room temperature, wash with cyclohexane and absolute ethanol and centrifuge to obtain LiYF4:Ho crystal nucleus nanoparticles, and disperse them in 4mL of cyclohexane.

[0036] (2) Second step, synthesis of LiYF4:Ho(40 mol%)@LiYF4:Yb(60 mol%) core-shell structured nanoparticles. Take a total of 0.2 mmol of rare earth acetate solution according to specific molar fractions, including Y(CH3COO)3 (40%) and Yb(CH3COO)3 (60%). React at a constant temperature of 150 °C for 50 minutes in a combined solvent of oleic acid and 1-octadecene to form rare earth oleate complexes; after cooling to 90 °C, add 2 mL of cyclohexane solution of the LiYF4:Ho nanocrystal particles obtained in step (1), and react at a constant temperature for 40 minutes; when the solvent cools to 50 °C, add 3 mL of methanol solution containing 0.8 mmol NH4F and 0.5 mmol LiOH and react for 40 minutes; then continue to heat up to 100 °C and evacuate to remove residual methanol and water; continuously introduce argon and heat up to 290 °C and react at a constant temperature for 90 minutes. After the reaction is completed and cooled to room temperature, wash with cyclohexane and absolute ethanol and centrifuge to obtain LiYF4:Ho@LiYF4:Yb core-shell structured nanoparticles, and disperse them in 2 mL of cyclohexane.

[0037] (3) Third step, synthesis of LiYF4:Ho(40 mol%)@LiYF4:Yb(60 mol%)@LiYF4 core-shell-shell structured nanoparticles. Take a total of 0.2 mmol of rare earth acetate solution according to specific molar fractions, including Y(CH3COO)3 (100%). React at a constant temperature of 150 °C for 50 minutes in a combined solvent of oleic acid and 1-octadecene to form rare earth oleate complexes; after cooling to 90 °C, add 2 mL of cyclohexane solution of the LiYF4:Ho(40 mol%)@LiYF4:Yb(60 mol%) core-shell structured nanoparticles obtained in step (2), and react at a constant temperature for 40 minutes; when the solvent cools to 50 °C, add 3 mL of methanol solution containing 0.8 mmol NH4F and 0.5 mmol LiOH and react for 40 minutes; then continue to heat up to 100 °C and evacuate to remove residual methanol and water; continuously introduce argon and heat up to 300 °C and react at a constant temperature for 90 minutes. After the reaction is completed and cooled to room temperature, wash with cyclohexane and absolute ethanol, centrifuge, and dry at 50 °C to obtain LiYF4:Ho(40 mol%)@LiYF4:Yb(60 mol%)@LiYF4 core-shell-shell structured nanoparticles.

[0038] Figure 2 Powder XRD diffraction pattern of the LiYF4:Ho(40 mol%)@LiYF4:Yb(60 mol%)@LiYF4 core-shell-shell structured nanoparticles prepared in Example 1. Its diffraction peaks are consistent with the standard card of cubic LiYF4 (JCPDS: 81-2254), indicating that the core-shell-shell structured nanoparticles prepared in Example 1 are cubic LiYF4 structure without impurity phases.

[0039] Figure 3 TEM images and corresponding particle size distribution diagrams of the LiYF4:Ho(40 mol%) crystal nuclei, LiYF4:Ho(40 mol%)@LiYF4:Yb(60 mol%) core-shell structure, and LiYF4:Ho(40 mol%)@LiYF4:Yb(60 mol%)@LiYF4 core-shell-shell structure nanoparticles prepared in Example 1; the results show that high-quality epitaxially grown core-shell nanoparticles can be achieved using the co-precipitation method, and the particle sizes are uniform. Among them, the major axis diameter of the crystal nuclei is about 13.36 nm, and the minor axis diameter is about 9.40 nm; the major axis diameter of the core-shell structure nanoparticles is about 16.46 nm, and the minor axis diameter is about 10.25 nm; the major axis diameter of the core-shell-shell structure nanoparticles is about 19.50 nm, and the minor axis diameter is about 12.05 nm. The average thickness of the intermediate sensitizing shell layer is about 1.96 nm, and the average thickness of the optically inert protective layer is about 2.52 nm.

[0040] Figure 4 The luminescence spectrum results show that when the LiYF4:Ho(40 mol%)@LiYF4:Yb(60 mol%)@LiYF4 core-shell-shell structure nanoparticles are excited by a 980 nm laser, the 550 nm green light characteristic emission and 640 nm red light characteristic emission of Ho 3+ are detected. As the temperature decreases from 300 K to 11 K, the 640 nm red light emission intensity of Ho 3+ slowly decreases, while the 550 nm green light emission intensity significantly increases, and the emission color gradually changes from red to green. Using the ratio of the two emission intensities as the temperature measurement parameter, the highest relative temperature measurement sensitivity can be obtained as 15.1% K -1 , as Figure 5 shown.

[0041] Example 2

[0042] The core-shell-shell structure nanoparticles prepared in this example are composed of a cubic LiYF4 host matrix doped with different concentrations of Ho in the crystal nucleus space 3+ , and higher sensitivity is achieved by regulating the optimal Ho 3+ doping concentration. The specific steps are as follows:

[0043] (1) The first step is the synthesis of LiYF4:Ho(x mol%) (x = 1, 40, 60, 100) core nanoparticles. Take a total of 0.4 mmol of rare earth acetate solution according to specific molar fractions, including Y(CH3COO)3 (100 - x%) and Ho(CH3COO)3 (x%). React at a constant temperature of 150 °C for 50 minutes in a combined solvent of oleic acid and 1 - octadecene to form rare earth oleate complexes; when the solvent cools to 50 °C, add a 6 mL methanol solution containing 1.6 mmol NH4F and 1.0 mmol LiOH and react for 40 minutes; then continue to heat up to 100 °C and evacuate to remove residual methanol and water; continuously introduce argon and heat up to 290 °C and react at a constant temperature for 90 minutes. After the reaction ends and cools to room temperature, wash with cyclohexane and absolute ethanol and centrifuge to obtain LiYF4:Ho core nanoparticles, and disperse them in 4 mL of cyclohexane.

[0044] (2) and (3) are the same as steps (2) and (3) of Example 1. Finally, LiYF4:Ho(x mol%)@LiYF4:Yb(60 mol%)@LiYF4 (x = 1, 40, 60, 100) core - shell - shell structure nanoparticles are prepared.

[0045] Figure 6 It is a comparative diagram of the temperature sensitivity of the LiYF4:Ho(x mol%)@LiYF4:Yb(60 mol%)@LiYF4 (x = 1, 40, 60, 100) core - shell - shell structure nanoparticles prepared in Example 2. The results show that Ho in the crystal nucleus of the core - shell - shell structure nanoparticles 3+ has the highest temperature sensitivity (15.1% K -1 ) when the doping concentration is 40 mol%.

[0046] Example 3

[0047] The core - shell - shell structure nanoparticles prepared in this example are composed of a cubic - phase LiYF4 host matrix doped with different concentrations of Yb in the intermediate sensitizing shell layer 3+ , and achieve the best up - conversion luminescence by regulating the optimal Yb 3+ doping concentration. The specific steps are as follows:

[0048] (1) The first step is the same as step (1) of Example 1.

[0049] (2) Second step: Synthesis of LiYF4:Ho(40 mol%)@LiYF4:Yb(x mol%) (x = 20, 40, 60, 80, 100) core-shell structured nanoparticles. Take a total of 0.2 mmol of rare earth acetate solution according to specific molar fractions, including Y(CH3COO)3 (100 - x%) and Yb(CH3COO)3 (x%). React at a constant temperature of 150 °C for 50 minutes in a combined solvent of oleic acid and 1-octadecene to form rare earth oleate complexes; after cooling to 90 °C, add 2 mL of cyclohexane solution of the LiYF4:Ho(40 mol%) crystal nucleus nanoparticles obtained in step (1), and react at a constant temperature for 40 minutes; when the solvent cools to 50 °C, add a 3 mL methanol solution containing 0.8 mmol NH4F and 0.5 mmol LiOH and react for 40 minutes; then continue to heat up to 100 °C and evacuate to remove residual methanol and water; continuously introduce argon and heat up to 300 °C and react at a constant temperature for 90 minutes. After the reaction is completed and cooled to room temperature, wash with cyclohexane and absolute ethanol and centrifuge to obtain LiYF4:Ho@LiYF4:Yb core-shell structured nanoparticles, and disperse them in 2 mL of cyclohexane.

[0050] (3) The third step is the same as step (3) of Example 1.

[0051] Figure 7 It is the luminescence spectrum diagram of the LiYF4:Ho(40 mol%)@LiYF4:Yb(x mol%)@LiYF4 (x = 20, 40, 60, 80, 100) core-shell-shell structured nanoparticles prepared in Example 3. The results show that the nanoparticles have the best upconversion emission when the doping concentration of Yb in the middle sensitization layer of the core-shell-shell structured nanoparticles is 60 mol%. 3+ The nanoparticles have the best upconversion emission when the doping concentration is 60 mol%.

Claims

1. A low-temperature rare-earth nano temperature probe with ultra-high sensitivity, characterized in that, The nano temperature probe is composed of core-shell-shell structure nanoparticles with different luminescent properties, and the core-shell-shell structure nanoparticles are composed of a cubic-phase LiYF4 host matrix and a combination of doped specific rare earth ions.

2. The low-temperature rare-earth nano temperature probe with ultra-high sensitivity according to claim 1, wherein The rare earth ion doped in the crystal nucleus of the core-shell-shell structure nanoparticles is Ho 3+ , and the rare earth ion doped in the middle sensitizing shell layer is Yb 3+ .

3. The low-temperature rare-earth nano temperature probe with ultra-high sensitivity according to claim 1, characterized in that, The core-shell-shell structure nanoparticles are, from the inside out, a red and green light-emitting crystal nucleus LiYF4:Ho, an intermediate sensitizing shell layer LiYF4:Yb, and an optically inert protective layer LiYF4. The chemical expression of the core-shell-shell structure nanoparticles is LiYF4:Ho@LiYF4:Yb@LiYF4.

4. The highly sensitive low-temperature rare-earth nano temperature probe according to claim 3, characterized in that, The rare earth ion Ho in the red and green light emitting crystal nucleus LiYF4:Ho 3+ has a molar concentration of 1-100 mol%; the rare earth ion Yb in the intermediate sensitizing shell LiYF4:Yb 3+ has a molar concentration of 20-100 mol%.

5. A method for preparing a low-temperature rare-earth nano temperature probe with ultra-high sensitivity according to any one of claims 1-4, specifically a core-shell-shell structure nanoparticle LiYF4:Ho@LiYF4:Yb@LiYF4, characterized in that, Specifically, it includes the following steps: (1) Take rare earth acetate solutions of Y(CH3COO)3 and Ho(CH3COO)3 according to molar fractions, and react them at a constant temperature in a combined solvent of oleic acid and 1-octadecene to form a complex. After the solvent is cooled to room temperature, add a methanol solution containing NH4F and LiOH to react, and then evacuate to remove residual methanol and water. Continuously introduce argon for reaction to obtain LiYF4:Ho crystal nucleus nanoparticles. (2) Take rare earth acetate solutions of Y(CH3COO)3 and Yb(CH3COO)3 according to molar fractions, and react them at a constant temperature in a combined solvent of oleic acid and 1-octadecene to form a complex. Add a cyclohexane solution containing the LiYF4:Ho crystal nucleus nanoparticles obtained in step (1) to react, and then add a methanol solution containing NH4F and LiOH to react. Subsequently, evacuate to remove residual methanol and water, and continuously introduce argon for reaction to obtain LiYF4:Ho@LiYF4:Yb core-shell structure nanoparticles. (3) Take a rare earth acetate solution of Y(CH3COO)3 according to molar fractions, and react it at a constant temperature in a combined solvent of oleic acid and 1-octadecene to form a complex. Add a cyclohexane solution containing the LiYF4:Ho@LiYF4:Yb core-shell structure nanoparticles obtained in step (2) to react, and then add a methanol solution containing NH4F and LiOH to react. Subsequently, evacuate to remove residual methanol and water, and continuously introduce argon for reaction. After cooling to room temperature, centrifuge and wash with cyclohexane and ethanol, and then dry to obtain the core-shell-shell structure nanoparticles LiYF4:Ho@LiYF4:Yb@LiYF4.

6. The preparation method of a low-temperature rare-earth nano temperature probe with ultra-high sensitivity according to claim 5, characterized in that, The temperature of the constant temperature reaction in steps (1), (2), and (3) is 110 - 150 °C, and the reaction time is 50 - 70 minutes.

7. The preparation method of a low-temperature rare-earth nano temperature probe with ultra-high sensitivity according to claim 5, characterized in that, The temperature of the reaction of adding a methanol solution containing NH4F and LiOH in steps (1), (2), and (3) is 45 - 55 °C, and the reaction time is 35 - 55 minutes.

8. The preparation method of a low-temperature rare-earth nano temperature probe with ultra-high sensitivity according to claim 5, characterized in that, The reaction temperature of introducing argon for reaction in steps (1), (2), and (3) is 280 - 300 °C, and the reaction time is 80 - 100 minutes.

9. The preparation method of a low-temperature rare-earth nano temperature probe with ultra-high sensitivity according to claim 5, characterized in that, For the addition of the cyclohexane solution containing the LiYF4:Ho nanoparticles obtained in step (1) in step (2), and the addition of the cyclohexane solution containing the LiYF4:Ho@LiYF4:Yb nanoparticles obtained in step (2) in step (3), it is necessary to cool the complex to 80 - 100 °C before adding, and then keep it warm for 30 - 50 minutes.

10. Application of the core-shell-shell structured nanoparticles LiYF4:Ho@LiYF4:Yb@LiYF4 prepared by the preparation method according to any one of claims 5-9 in low-temperature detection.

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