A NIR-I excited upconversion temperature probe, its preparation method, and its application.

Abstract

This invention belongs to the field of rare-earth luminescent materials and optical sensing technology, specifically disclosing an upconversion temperature probe excited by NIR-I, its preparation method, and its application. The probe includes a matrix core material, which is a fluoride crystal; and dopant ions, specifically holmium ions (Ho) doped into the matrix core material. 3+ Ho 3+ As the sole luminescent center, it is excited by a near-infrared I light source with a wavelength of 880-920 nm to generate Ho. 3+ Characteristic green upconversion luminescence and red upconversion luminescence. This invention employs the aforementioned NIR-I excited upconversion temperature probe, its preparation method, and its application, utilizing Ho... 3+ The unique energy level competition mechanism of ions enables high-sensitivity temperature measurement over a wide temperature range, and the temperature measurement signal is unaffected by fluctuations in excitation power.

Description

Technical Field

[0001] This invention relates to the fields of rare earth luminescent materials and optical sensing technology, and in particular to an upconversion temperature probe excited by NIR-I, its preparation method, and its application. Background Technology

[0002] Temperature is a crucial physical parameter in scientific research, industrial production, and biomedical diagnostics. Traditional contact thermometers (such as thermocouples and thermistors) have limitations in applications at the microscopic scale (e.g., inside cells), on moving objects, or in corrosive environments. Luminescence intensity ratio (LIR) thermometry based on rare-earth-doped luminescent materials has become a research hotspot in recent years due to its advantages such as non-contact operation, fast response, high spatial resolution, and resistance to electromagnetic interference.

[0003] In existing technologies, the more mature upconversion thermometric materials are mainly based on Yb 3+ / Er 3+ Co-doped systems (such as NaYF4:Yb,Er) are typically excited using a 980nm laser. However, this existing technology has the following significant drawbacks: Water absorption and thermal effect: The 980nm excitation wavelength is located precisely at the strong absorption peak of water molecules. When measuring the temperature of biological tissues, the excitation light is strongly absorbed by the water in the tissue, resulting in shallow penetration depth and easily causing a significant photothermal effect ("self-heating"), heating the sample under test, leading to temperature measurement distortion and potentially damaging the biological tissue.

[0004] Excitation power dependence (poor reliability): Many non-Boltzmann upconversion luminescence mechanisms involve complex multiphoton processes, and their red-to-green light emission intensity ratio often depends heavily on the excitation light power density. In practical applications, due to light source fluctuations, optical path losses, or medium scattering (such as in human tissue), the excitation power density is difficult to keep constant, which can lead to temperature measurement signal drift and seriously affect the reliability of the measurement.

[0005] Sensitivity temperature range is limited: traditional Er 3+ Thermally coupled energy level thermometry follows a Boltzmann distribution, and its relative sensitivity increases by 1 / T with increasing temperature. 2 The decrease leads to low sensitivity in the high-temperature range.

[0006] Therefore, developing a novel temperature probe that can be excited using the biological window of the near-infrared region I (NIR-I, 800-950nm), avoids the water absorption peak, and has excitation power-independent characteristics (temperature measurement signal is independent of excitation power density) is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to provide an NIR-I excited upconversion temperature probe, its preparation method, and its applications, utilizing Ho 3+ The unique energy level competition mechanism of ions enables high-sensitivity temperature measurement over a wide temperature range, and the temperature measurement signal is unaffected by fluctuations in excitation power.

[0008] To achieve the above objectives, the present invention provides an upconversion temperature probe excited by NIR-I, comprising: The matrix core material is a fluoride crystal. The dopant ions are holmium ions (Ho) incorporated into the matrix core material. 3+ Ho 3+ As the sole luminescent center, it is excited by a near-infrared I light source with a wavelength of 880-920 nm to generate Ho. 3+ Characteristic green upconversion luminescence and red upconversion luminescence.

[0009] Preferably, the upconversion temperature probe uses the fluorescence intensity ratio (LIR) of green upconversion luminescence to red upconversion luminescence as the temperature response signal, and the temperature response signal originates from Ho. 3+ Ion excited state 5 The dynamic competition between the multiphonon relaxation (MPR) channel and the cross-relaxation (CR) channel at the F3 level downwards, and the fluorescence intensity ratio of the green upconversion emission to the red upconversion emission changes monotonically with temperature; The green upconversion luminescence includes Ho 3+ of 5 S2 / 5 F4 to 5 I8 radiative transition luminescence; the red upconversion luminescence includes Ho 3+ of 5 F5 to 5 I8 radiative transition luminescence; the rate of the multiphonon relaxation channel varies with temperature; the cross-relaxation channel is Ho. 3+ -Ho 3+ Inter-energy transfer processes, the rate of which is related to Ho 3+ It is concentration-dependent and exhibits weak temperature dependence within the operating temperature range.

[0010] Ho 3+ Ions are excited to 5 After the F3 energy level, it can be in the ground state with its neighboring energy level. 5 I8's Ho 3+ The energy transfer due to cross-relaxation of ions can be represented as follows: Ho 3+ ( 5 F3)+Ho 3+ (5 I8)→Ho 3+ ( 5 F5)+Ho 3+ ( 5 I7).

[0011] After cross-relaxation, donor Ho 3+ Ion cloth resides in 5 F5 energy level, and through 5 F5 → 5 The radiative transition of I8 produces red upconversion luminescence at a wavelength of approximately 650 nm; the acceptor Ho... 3+ Ions are populationd to 5 The I7 level, as an energy acceptor of cross-relaxation, participates in subsequent level population and energy migration processes.

[0012] The rate of cross-relaxation is mainly related to Ho 3+ The doping concentration (corresponding to the average distance between ions and the probability of interaction) is related; within the operating temperature range of this invention, the dependence of this cross-relaxation rate on temperature is negligible or exhibits weak temperature sensitivity.

[0013] Preferred options also include: A shell material is used to coat the outer surface of the matrix core material. The shell material is an inert fluoride crystal without rare earth ions, with a specific chemical composition of NaYF4 or NaLuF4, and a shell thickness of 1~10nm.

[0014] Preferably, the chemical formula of the upconversion temperature probe is NaREF4:x%Ho 3+ Where RE is one or more of Y, Gd, Lu or La, and x is Ho 3+ The molar percentage of doping, and 1≤x≤30.

[0015] Preferably, the fluoride crystal is hexagonal β-NaYF4, and Ho 3+ The molar percentage of doping, x, is 7~12; at this concentration, Ho 3+ The cross-relaxation and multiphonon relaxation processes between ions are in optimal competition, resulting in the best temperature sensitivity.

[0016] The fluoride crystal is a low-phonon-energy rare-earth fluoride, with a maximum lattice phonon energy not exceeding 450 cm⁻¹. -1 .

[0017] The present invention also provides a method for preparing an upconversion temperature probe excited by NIR-I, including a high-temperature solid-state method or a hot injection method; The high-temperature solid-state method specifically involves weighing rare earth fluoride raw materials and NaF according to stoichiometric ratio, thoroughly grinding and mixing them in a mortar, placing the mixture in a corundum crucible, and sintering it at 600-800℃ for 2-10 hours under a nitrogen or argon protective atmosphere. After cooling to room temperature, it is ground to obtain doped Ho. 3+ Micrometer-scale probes; The hot injection method involves introducing a sodium source and a fluorine source into an organic ligand system, and reacting them at 280~320℃ to generate doped Ho. 3+ Fluoride crystals were used to obtain nanoscale probes.

[0018] Preferably, the hot injection method specifically includes: Rare earth precursors, oleic acid, and 1-octadecene are added together to a three-necked flask and heated to 140-160°C under vacuum for 30-60 minutes to obtain a clear and homogeneous rare earth precursor reaction solution. The rare earth precursor is one or more of holmium source, rare earth chloride, rare earth acetate, rare earth nitrate, rare earth oxide, or rare earth soluble organic acid salt, and the rare earth element is selected from one or more of Y, Gd, Lu, or La. After cooling the rare earth precursor reaction solution to room temperature, an alcohol solution containing sodium and fluorine sources is added to it, and the reaction is stirred for 10-60 min. Then, under inert gas protection, the temperature is raised to 280-320℃ and held for 30-90 min to remove the alcohol solvent. The sodium source is one or both of NaOH and NaOA, and the fluorine source is one or both of NH4F and NaF. Without lowering the reaction temperature, a shell precursor solution is injected into the reaction system, and the reaction continues for 30-90 minutes to form core-shell structured nanocrystals; wherein, the shell precursor solution is obtained by injecting undoped Ho... 3+ It is obtained by mixing rare earth precursors, oleic acid and 1-octadecene and then treating them with dehydration. After the reaction was completed, the product was cooled to room temperature, and an alcohol solvent was added to precipitate it. After centrifugation, the product was washed alternately with non-polar and polar solvents to obtain a core-shell structured nanoscale temperature probe.

[0019] The present invention also provides an application of an NIR-I excited upconversion temperature probe in non-contact temperature range measurement of 300~773K.

[0020] The preferred application method is as follows: The upconversion temperature probe is placed in the area to be measured and excited with 880~920nm excitation light. The green upconversion luminescence intensity and the red upconversion luminescence intensity are collected, the fluorescence intensity ratio is calculated, and the temperature is determined based on the fluorescence intensity ratio as a function of temperature.

[0021] Preferably, the upconversion temperature probe is one or more of the following: nanoparticles, microparticles, and thin films. The excitation power density of the upconversion temperature probe ranges from 0.1 to 100 W·cm⁻¹. -2 ; When calculating the fluorescence intensity ratio, the integrated wavelength range of the green emission band is 520~580nm, and the integrated wavelength range of the red emission band is 620~700nm.

[0022] Preferably, the upconversion temperature probe is placed in the area to be measured, excited by 897nm excitation light, and the green upconversion luminescence intensity and red upconversion luminescence intensity are collected. The fluorescence intensity ratio is calculated, and the temperature is determined based on the fluorescence intensity ratio versus temperature curve.

[0023] Therefore, the present invention employs the above-mentioned NIR-I excited upconversion temperature probe, its preparation method, and its application, and the beneficial effects are as follows: This invention utilizes the dynamic competition mechanism between temperature-dependent multiphonon relaxation and concentration-dependent cross-relaxation to ensure that the temperature measurement signal is independent of the excitation power density within a certain range of excitation power density variation, thus solving the problem of measurement inaccuracy of traditional upconversion temperature probes under complex light intensity environments. Furthermore, by employing ~900nm excitation, it effectively avoids the water molecule absorption peak at 980nm, compared to traditional Er... 3+ The system and the blue light excitation system significantly improved the penetration depth in biological tissues and minimized the thermal effects induced by the laser.

[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the energy level transition and temperature measurement mechanism of an NIR-I excited upconversion temperature probe, its preparation method, and its application embodiments, wherein (a) is a schematic diagram of the energy level transition and (b) is a schematic diagram of the temperature measurement mechanism. Figure 2 This invention provides an NIR-I excited upconversion temperature probe and its preparation method, as well as a calibration curve of LIR versus temperature in Example 1. Figure 3 This invention provides an NIR-I excited upconversion temperature probe and its preparation method, along with the XRD pattern of Example 1. Figure 4 This invention provides an NIR-I excited upconversion temperature probe and its preparation method, as well as the emission spectrum versus temperature curve of Application Example 1. Figure 5This invention provides an NIR-I excited upconversion temperature probe and its preparation method, and compares LIR-temperature curves under different excitation power densities in Application Example 1. Figure 6 This is a photoluminescence spectrum contour plot of an NIR-I excited upconversion temperature probe and its preparation method, and an application example 2, showing the photoluminescence spectrum as a function of temperature. Detailed Implementation

[0026] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0027] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0028] In all embodiments of this invention, the upconversion temperature probes are based on fluoride crystals, doped with holmium ions, and do not contain sensitizers (such as Yb). 3+ (etc.), using a light source with a wavelength of 880-920 nm (NIR-I window) to excite and generate Ho 3+ The characteristic green and red upconversion luminescence has a temperature response not based on the Boltzmann distribution of thermally coupled energy levels, but on kinetic processes under non-thermal equilibrium conditions. For example... Figure 1 As shown, the temperature measurement mechanism of this probe is based on Ho. 3+ Ion excited state 5 Two competing relaxation pathways downward from the F3 level: (1) Multiphonon relaxation (MPR) channel: from 5 The F3 energy level nonradiatively relaxes to 5 S2 / 5 The F4 energy level then emits green light (~540 nm). The rate of this process is strongly temperature-dependent.

[0029] (2) Cross-relaxation (CR) channel: Ho 3+ ( 5 F3) + Ho 3+ ( 5 I8) → Ho 3+ ( 5 F5) + Ho 3+ ( 5 I7), then 5 The F5 level emits red light (~650 nm). The rate of this process is strongly dependent on Ho. 3+ Concentration, but not sensitive to temperature.

[0030] The fluorescence intensity ratio (LIR) of green upconversion emission I_green to red upconversion emission I_red is used as the temperature response signal, i.e., LIR=I_red / I_green. Since this temperature response signal originates from the competition between the rates of the two kinetic processes mentioned above, rather than a simple multiphoton population, the LIR value depends only on the temperature and doping concentration, and is independent of the power density of the excitation light.

[0031] The excitation power density of this upconversion temperature probe ranges from 0.1 to 100 W·cm⁻¹. -2 When calculating the fluorescence intensity ratio, the integrated wavelength range of the green emission band is 520~580nm, and the integrated wavelength range of the red emission band is 620~700nm, or the equivalent spectral range covering the corresponding emission peak.

[0032] Furthermore, the fluorescence intensity ratio of green upconversion luminescence to red upconversion luminescence changes monotonically with temperature, as shown in the calibration curve of fluorescence intensity ratio (LIR) versus temperature. Figure 2 As shown, the results highly overlap at different excitation power densities (high, medium, and low), meaning the temperature measurement results depend only on temperature and are unaffected by power losses caused by light source fluctuations or medium scattering, greatly improving the reliability for practical applications. Furthermore, the probe maintains high sensitivity across the 300K to 773K range, with the relative change in LIR at the same temperature point not exceeding ±5% even with a minimum 5-fold change in excitation power density, and a relative sensitivity Sr > 0.5%K. -1 Its wide temperature range breaks through the limitation of the Boltzmann thermometer's rapid drop in high-temperature sensitivity.

[0033] Example 1 A NIR-I excited upconversion temperature probe, specifically NaYF4:Ho 3+ Micron-sized crystal temperature probe (Ho) 3+ Ho-doped materials (with a doping molar percentage of 5%) were prepared using a high-temperature solid-state method. 3+ The preparation method of NaYF4 micron-sized crystals is as follows: According to target Ho 3+ The raw materials YF3, HoF3, and NaF were weighed out according to the stoichiometric ratio corresponding to the doping concentration, with NaF in appropriate excess to compensate for the loss of sodium through volatilization during high-temperature sintering. The raw materials were thoroughly ground and mixed in an agate mortar. The mixture was then transferred to a corundum crucible, which was placed in a tube furnace and heated to the target sintering temperature of 700℃ at a constant heating rate under an inert gas atmosphere. Sintering was then carried out at this temperature for 6 hours. After the reaction was completed, the mixture was allowed to cool naturally to room temperature. The resulting sintered block was then ground to obtain a white, micron-sized crystalline powder.

[0034] Example 2 A NIR-I excited upconversion temperature probe, specifically β-NaYF4:Ho 3+ @β-NaYF4 core-shell nanotemperature probe (Ho 3+ The doping molar percentage is 5%, and the preparation method using hot injection is as follows: (1) Synthesis of nuclear nanocrystals: According to target Ho 3+ The rare earth precursor compound (including 1 mmol YF3 and 1 mmol HoF3) was weighed according to the stoichiometric ratio corresponding to the doping concentration. It was added to the reaction vessel along with 6 mL oleic acid and 15 mL 1-octadecene. The mixture was heated to 150 °C under vacuum and held for 45 min to remove moisture and dissolved oxygen, resulting in a clear and homogeneous rare earth precursor reaction solution. After cooling the rare earth precursor solution to room temperature, an alcohol solution containing sodium and fluorine sources (in this example, the alcohol solution containing sodium and fluorine sources is a mixture of 1 mmol NaOH, 1 mmol NaF, and 10 mL alcohol) is added. The mixture is stirred and reacted for 30 minutes, then heated rapidly to 300°C under inert gas protection and held for 60 minutes to remove the alcohol solvent. This allows the rare earth precursor to undergo thermal decomposition and crystallization, generating doped Ho. 3+ β-NaYF4 core nanocrystals.

[0035] (2) Shell covering: Undoped Ho 3+ Rare earth precursors, oleic acid, and 1-octadecene were mixed in a ratio of 1 mmol: 6 mL: 15 mL and subjected to dehydration treatment to prepare a shell precursor solution. Without lowering the reaction temperature of the core nanocrystals, the shell precursor solution was introduced into the reaction system, and the reaction continued for 60 min, allowing an inert β-NaYF4 shell to epitaxially grow on the surface of the core nanocrystals, forming core-shell structured nanocrystals.

[0036] (3) Purification: After the reaction was completed, the mixture was cooled to room temperature, and an alcohol solvent was added to precipitate the product. The product was then separated by centrifugation, and washed alternately with nonpolar and polar solvents. In this example, the alcohol solvent, nonpolar solvent, and polar solvent used were ethanol, cyclohexane, and methanol, respectively, to obtain a core-shell structured NaYF4:Ho. 3+ @NaYF4 nanoscale temperature probe.

[0037] Test 1. Structural analysis was performed on the upconversion temperature probe prepared in Example 1. The XRD pattern of the micron-sized crystal in Example 1 is shown below. Figure 3 As shown.

[0038] Depend on Figure 3This indicates that the product has a pure hexagonal β-NaYF4 structure, demonstrating that Ho 3+ Successfully doped into the NaYF4 lattice.

[0039] 2. Temperature measurement performance test NaYF4:Ho from Example 1 3+ Micron-sized crystalline powder was placed on a temperature-controlled heating and cooling stage. An upconversion emission test was performed on the sample using a semiconductor laser with a center wavelength in the near-infrared region I as the excitation source. The upconversion emission spectrum under 897nm excitation changed with temperature as follows: Figure 4 As shown.

[0040] Depend on Figure 4 It can be seen that, under near-infrared excitation, the sample exhibits characteristics originating from Ho. 3+ The ions exhibit green and red upconversion emission. As the ambient temperature increases from room temperature to the high-temperature range, the green emission intensity gradually increases relative to the red emission intensity.

[0041] This phenomenon is attributed to the increased temperature promoting Ho... 3+ Ions from excited state 5 The multiphonon relaxation process from the F3 energy level to lower energy levels modulates the relative intensity between different emission channels.

[0042] The 897nm excitation light has a significantly greater penetration depth in biological tissue than visible or ultraviolet light. Near-infrared excitation avoids photodamage to biological samples caused by visible light, and the tissue absorption coefficient at this excitation wavelength is low, greatly reducing the local thermal effect caused by laser irradiation. This demonstrates that the temperature probe in Example 1 has a significantly improved penetration depth in biological tissue, minimizing the laser-induced thermal effect.

[0043] 3. Power independence verification By adjusting the output power of the excitation source, the excitation power density on the sample surface in Example 1 was varied over multiple orders of magnitude. Under different excitation power density conditions, the fluorescence intensity ratio (LIR) of the sample was tested over a wide temperature range. The LIR-temperature curves under different excitation power densities were compared, for example... Figure 5 As shown.

[0044] Depend on Figure 5 It can be seen that the LIR-temperature curves obtained under different excitation power densities basically overlap, and the LIR deviation at each temperature point is within a small range, indicating that the temperature probe has significant excitation power independent temperature measurement characteristics under predetermined power variation conditions.

[0045] 4. The structure and thermometric performance of the nanoprobe from Example 2 were analyzed. This probe has a core-shell structure, which is used to suppress surface quenching effects and improve luminescence efficiency. The probe has a uniform particle size distribution, ranging from tens of nanometers. Figure 6 As shown, it exhibits stable upconversion luminescence characteristics under near-infrared excitation, and its thermometric behavior is similar to that of NaYF4:Ho in Example 1. 3+ Micron-sized crystal powders are consistent and also exhibit excitation power independence.

[0046] Therefore, this invention employs the aforementioned NIR-I excited upconversion temperature probe, its preparation method, and its application, utilizing Ho 3+ The unique energy level competition mechanism of ions enables high-sensitivity temperature measurement over a wide temperature range, and the temperature measurement signal is unaffected by fluctuations in excitation power.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. 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 still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. An upconversion temperature probe excited by NIR-I, characterized in that, include: The matrix core material is a fluoride crystal. The dopant ions are holmium ions (Ho) incorporated into the matrix core material. 3+ Ho 3+ As the sole luminescent center, it is excited by a near-infrared I light source with a wavelength of 880-920 nm to generate Ho. 3+ Characteristic green upconversion luminescence and red upconversion luminescence.

2. The upconversion temperature probe excited by NIR-I according to claim 1, characterized in that: The upconversion temperature probe uses the fluorescence intensity ratio of green upconversion luminescence to red upconversion luminescence as the temperature response signal, which originates from Ho. 3+ Ion excited state 5 The dynamic competition between the multiphonon relaxation channel and the cross-relaxation channel at the F3 level downwards, and the fluorescence intensity ratio of the green upconversion emission to the red upconversion emission changes monotonically with temperature. The green upconversion luminescence includes Ho 3+ of 5 S2 / 5 F4 to 5 I8 radiative transition luminescence; the red upconversion luminescence includes Ho 3+ of 5 F5 to 5 I8 radiative transition luminescence; the rate of the multiphonon relaxation channel varies with temperature; the cross-relaxation channel is Ho. 3+ -Ho 3+ Inter-energy transfer processes, the rate of which is related to Ho 3+ It is concentration-dependent and exhibits weak temperature dependence within the operating temperature range.

3. The upconversion temperature probe excited by NIR-I according to claim 1, characterized in that, Also includes: A shell material is used to coat the outer surface of the matrix core material. The shell material is an inert fluoride crystal without rare earth ions, with a specific chemical composition of NaYF4 or NaLuF4, and a shell thickness of 1~10nm.

4. The upconversion temperature probe excited by NIR-I according to claim 1, characterized in that: The chemical formula of the upconversion temperature probe is NaREF4:x%Ho 3+ Where RE is one or more of Y, Gd, Lu or La, and x is Ho 3+ The molar percentage of doping, and 1≤x≤30.

5. The upconversion temperature probe excited by NIR-I according to claim 4, characterized in that: The fluoride crystal is hexagonal β-NaYF4, and Ho 3+ The molar percentage of doping, x, is 7~12; The fluoride crystal is a low-phonon-energy rare-earth fluoride, with a maximum lattice phonon energy not exceeding 450 cm⁻¹. -1 .

6. A method for preparing an NIR-I excited upconversion temperature probe as described in any one of claims 1 to 5, characterized in that: This includes high-temperature solid-state methods or hot injection methods; The high-temperature solid-state method specifically involves weighing rare earth fluoride raw materials and NaF according to stoichiometric ratio, thoroughly grinding and mixing them in a mortar, placing the mixture in a corundum crucible, and sintering it at 600-800℃ for 2-10 hours under a nitrogen or argon protective atmosphere. After cooling to room temperature, it is ground to obtain doped Ho. 3+ Micrometer-scale probes; The hot injection method involves introducing a sodium source and a fluorine source into an organic ligand system, and reacting them at 280~320℃ to generate doped Ho. 3+ Fluoride crystals were used to obtain nanoscale probes.

7. The method for preparing an NIR-I excited upconversion temperature probe according to claim 6, characterized in that, The hot injection method specifically refers to: Rare earth precursors, oleic acid, and 1-octadecene are added together to a three-necked flask and heated to 140-160°C under vacuum for 30-60 minutes to obtain a clear and homogeneous rare earth precursor reaction solution. The rare earth precursor is one or more of holmium source, rare earth chloride, rare earth acetate, rare earth nitrate, rare earth oxide, or rare earth soluble organic acid salt, and the rare earth element is selected from one or more of Y, Gd, Lu, or La. After cooling the rare earth precursor reaction solution to room temperature, an alcohol solution containing sodium and fluorine sources is added to it, and the reaction is stirred for 10-60 minutes. Then, under inert gas protection, the temperature is raised to 280-320℃ and held for 30-90 minutes. The sodium source is one or both of NaOH and NaOA, and the fluorine source is one or both of NH4F and NaF. Without lowering the reaction temperature, a shell precursor solution is injected into the reaction system, and the reaction continues for 30-90 minutes to form core-shell structured nanocrystals; wherein, the shell precursor solution is obtained by injecting undoped Ho... 3+ It is obtained by mixing rare earth precursors, oleic acid and 1-octadecene and then treating them with dehydration. After the reaction was completed, the product was cooled to room temperature, and an alcohol solvent was added to precipitate it. After centrifugation, the product was washed alternately with non-polar and polar solvents to obtain a core-shell structured nanoscale temperature probe.

8. The application of an upconversion temperature probe prepared by the method of preparing an NIR-I excited upconversion temperature probe as described in any one of claims 1 to 5 or an NIR-I excited upconversion temperature probe as described in any one of claims 6 to 7 in non-contact temperature range measurement of 300 to 773 K.

9. The application according to claim 8, characterized in that, The application method is as follows: The upconversion temperature probe is placed in the area to be measured and excited with 880~920nm excitation light. The green upconversion luminescence intensity and the red upconversion luminescence intensity are collected, the fluorescence intensity ratio is calculated, and the temperature is determined based on the fluorescence intensity ratio as a function of temperature.

10. The application according to claim 9, characterized in that: The upconversion temperature probe is one or more of the following: nanoparticles, microparticles, and thin films. The excitation power density of the upconversion temperature probe ranges from 0.1 to 100 W·cm⁻¹. -2 ; When calculating the fluorescence intensity ratio, the integrated wavelength range of the green emission band is 520~580nm, and the integrated wavelength range of the red emission band is 620~700nm.

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