Highly-doped crosstalk-free optical temperature sensing material based on potassium-based rare earth fluoride as well as preparation method and application of highly-doped crosstalk-free optical temperature sensing material

Abstract

The invention discloses a highly-doped crosstalk-free optical temperature sensing material based on potassium-based rare earth fluoride, the sensing material is potassium-based rare earth fluoride microparticles with surfaces modified by carbon dots and highly doped with optically active rare earth ions, the general formula of the potassium-based rare earth fluoride is KMF4, and M is an optically inert rare earth element selected from Gd or La; the optical active rare earth ions are selected from Eu < 3 + > or Tb < 3 + >, and account for 1-20 mol% of the total metal ions of the rare earth elements; the average particle size D50 of the sensing material is 5.0 [mu] m to 20.0 [mu] m. The problem of valence mismatch between rare earth ions and a matrix is solved by adopting the KMF4 matrix, high-concentration doping is allowed without quenching, and rare earth characteristic luminescence is remarkably enhanced. Meanwhile, spatial isolation of the surface carbon dots and bulk phase rare earth ions is achieved through the micron particle structure, energy transfer between the surface carbon dots and the bulk phase rare earth ions is thoroughly eliminated, and complete independence of dual-mode light emission is ensured.

Description

Technical Field

[0001] This invention belongs to the field of functional materials and optical sensing technology, specifically relating to a fluorescent composite material for non-contact, high-precision ratio temperature measurement, its preparation method, and its application. In particular, this invention relates to a highly doped, crosstalk-free optical temperature sensing material based on potassium-based rare earth fluorides, its preparation method, and its application. Background Technology

[0002] With the development of technology, non-contact optical temperature sensing technology has shown great application potential in fields such as biomedicine, microelectronics, aerospace, and industrial inspection. Among these, ratiometric thermometry based on the fluorescence intensity ratio (FIR) of two luminescent centers has become a current research hotspot due to its self-calibration characteristics, effectively overcoming systematic errors such as excitation source fluctuations and probe concentration unevenness. Carbon dots (CDs), as an emerging fluorescent nanomaterial, have advantages such as abundant raw materials, good biocompatibility, and tunable luminescence, and their fluorescence intensity typically exhibits high temperature sensitivity. Rare earth ions (Ln...) 3+ These exhibit sharp characteristic emission lines, good luminescence stability, and a rich energy level structure. Combining these two technologies, utilizing the temperature-sensitive broadband emission of carbon dots as the detection signal, and using the relatively stable sharp-line emission of rare-earth ions as the reference signal, is considered one of the ideal strategies for constructing a high-performance ratio optical thermometer.

[0003] However, existing temperature sensing material systems based on carbon dots and rare earth ions still have significant shortcomings. Taking the technical solution disclosed in authorized patent CN117070212B as an example, this patent proposes a method based on carbon dots and a fluoride matrix (general formula MXF3:xLn). 3+ An optical temperature sensing material (where M is an alkali metal and X is an alkaline earth metal / transition metal) is proposed. Although this material can be prepared by room temperature co-precipitation and exhibits certain temperature sensing capabilities, its performance is limited by the following two fundamental problems:

[0004] First, the limited doping concentration leads to insufficient luminescence intensity. In this system, the luminescence center Ln 3+ The matrix needs to be replaced by divalent alkaline earth or transition metal ions X. 2+ (e.g. Mg) 2+ Due to the mismatch between valence state and ionic radius, Ln 3+ The doping concentration is strictly limited to a low level (typically below 5%). Excessive doping not only fails to enhance luminescence but also leads to a decrease in fluorescence intensity due to concentration quenching. Therefore, in this system, Ln... 3+ The characteristic emission signal is difficult to improve further, which limits the improvement of the temperature measurement signal-to-noise ratio.

[0005] Second, the nanocomposite structure causes energy crosstalk. The material prepared in this patent is nanoparticles (with a particle size of approximately 100-1000 nm). At this scale, the uniformly dispersed carbon dots and the doped rare earth ions are spatially very close, making non-radiative energy transfer (such as...) very easy. (Resonant energy transfer). This type of energy crosstalk alters the luminescence dynamics of carbon dots (e.g., shortens their fluorescence lifetime) and may cause additional modulation of rare-earth ion luminescence from energy transfer from carbon dots. As a result, the fluorescence intensity ratio (FIR) of the two luminescent centers is affected not only by temperature but also by energy transfer efficiency that is difficult to precisely control, severely impairing the accuracy, repeatability, and reliability of temperature measurements.

[0006] Therefore, developing a novel high-performance temperature sensing material capable of simultaneously achieving high-concentration rare-earth doping to enhance signals and completely isolating energy crosstalk between carbon dots and rare-earth ions is an urgent technological need with significant application value. Currently, there is an urgent need to develop a novel high-performance temperature sensing material that combines high-concentration rare-earth doping, strong characteristic luminescence, and the ability to spatially isolate carbon dots from rare-earth luminescent centers, thereby effectively avoiding energy crosstalk. Summary of the Invention

[0007] The purpose of this application is to overcome the aforementioned shortcomings of the prior art and provide a highly doped, crosstalk-free optical temperature sensing material based on potassium-based rare earth fluorides. This material allows for high-concentration doping of rare earth ions without quenching and achieves dual-mode emission that is completely independent of carbon dopant luminescence and free from energy crosstalk, thereby realizing ultra-high sensitivity and high accuracy ratiometric temperature sensing.

[0008] Another objective of this application is to provide a simple and controllable method for preparing the above-mentioned materials.

[0009] Another objective of this application is to provide the application of the above-mentioned materials in the preparation of ratio optical thermometers.

[0010] To achieve the aforementioned objectives, this application provides a highly doped, crosstalk-free optical temperature sensing material based on potassium-based rare earth fluorides. The sensing material is potassium-based rare earth fluoride micron-sized particles with surface carbon dot modification and high doping with optically active rare earth ions. The potassium-based rare earth fluoride has the general formula KMF4, and M is an optically inert rare earth element selected from Gd or La. The optically active rare earth ions are selected from Eu. 3+ or Tb 3+ The molar percentage of rare earth metal ions is 1% to 20%; the average particle size D50 of the sensing material is 5.0 μm to 20.0 μm.

[0011] This application uses rare earth ions of the same valence (Gd). 3+ / La 3+Using Eu as both a matrix and dopant, the effective doping concentration of active rare earth ions was successfully increased to 10-20%. Experiments show that within this range, Eu... 3+ or Tb 3+ The characteristic luminescence intensity continuously increases with increasing molar percentage, reaching its highest value at a molar percentage of 20%, which significantly improves the intensity and stability of the reference signal in the ratio signal. Furthermore, to achieve complete independence of dual-mode luminescence and ensure accurate temperature measurement, this invention controls the average particle size D50 of the sensing material particles to be between 5.0 μm and 20.0 μm, successfully combining carbon dots (CDs) (surface) with rare earth ions Ln. 3+ (Physical phase) spatially isolated. Monitoring Eu 3+ The excitation spectrum of CDs (~700 nm) showed a broadband excitation spectrum, indicating that there is no energy transfer between them. Therefore, CDs and Ln 3+ The luminescence behavior of each is only affected by temperature and does not interfere with each other. Temperature measurement results based on their fluorescence intensity ratio (FIR) have extremely high accuracy and reliability.

[0012] This invention creatively proposes and verifies a method for constructing micron-sized particle composite materials with "surface carbon dot modification and high-concentration rare earth doping in the bulk phase" using potassium-based rare earth fluoride (KMF4) as the host matrix. This material can be expressed as: KMF4:yLn 3+ / CDs.

[0013] M (matrix ion): An optically inert trivalent rare earth ion, selected from Gd or La. Gd is preferred. 3+ Because it has a suitable ionic radius and can serve as a medium for energy transfer. 6 P 7 / 2 energy level.

[0014] Ln (luminescent center): an optically active trivalent rare earth ion selected from Eu or Tb. Its doping molar ratio y breaks through traditional limitations, reaching 1% ≤ y ≤ 20%. Within this high concentration range, it benefits from its interaction with the matrix ion M... 3+ Perfect valence state and radius matching, Ln 3+ The luminescence of the light does not undergo concentration quenching; on the contrary, its intensity increases significantly with the increase of y.

[0015] CDs (temperature probes): mainly blue fluorescent carbon dots with carboxyl or amino groups on the surface, which selectively attach to the surface of KMF4 micron particles through coordination.

[0016] Structural characteristics: The material consists of irregular micron-sized particles with an average particle size (D). 50 The micrometer diameter (DCM) is controlled between 5.0 μm and 20.0 μm. This size is crucial for achieving both surface CDs and bulk Ln. 3+"The key to spatial physical isolation is that CDs are confined to the particle surface, while high concentrations of Ln..." 3+ They are uniformly distributed within the bulk lattice of the particles, and the average distance between them is much greater than... The effective range of resonant energy transfer (typically <10nm) fundamentally eliminates energy crosstalk.

[0017] Preferably, the carbon dots are blue fluorescent carbon dots with a surface rich in carboxyl or amino groups, selectively attached to the surface of KMF4 micron-sized particles through coordination interactions; there is no effective non-radiative energy transfer between the luminescence of the carbon dots and the luminescence of the optically active rare earth ions. Blue fluorescent carbon dots typically have a high temperature sensitivity coefficient, and their luminescence intensity varies significantly with temperature. By utilizing the coordination interaction between carboxyl / amino groups and metal sites on the surface of micron-sized particles, carbon dots can be stably and selectively fixed on the outer surface of micron-sized particles, thereby achieving effective spatial isolation between the carbon dots and the rare earth ions doped inside the particles. This surface-anchored composite method can significantly reduce non-radiative energy transfer between the two (e.g., Resonant energy transfer avoids fluorescence intensity ratio (FIR) distortion caused by energy crosstalk, thus improving the reliability and accuracy of temperature measurement signals.

[0018] Preferably, the sensing material, when excited by ultraviolet light with a wavelength of 320 nm to 380 nm, generates independent dual-mode luminescence, including: a broadband blue light emission originating from carbon dots with a peak value near 450 nm; and one or more characteristic sharp-line emissions originating from optically active rare-earth ions in the wavelength range of 500 nm to 750 nm; when the optically active rare-earth ion is Eu... 3+ When the characteristic emission peak is located at 612 nm and / or 700 nm; when the optically active rare earth ion is Tb 3+ At that time, its characteristic emission peak is located at 542 and / or 621 nm. By selecting rare earth ions with the above characteristic emission and combining them with surface-modified blue fluorescent carbon dots (whose emission peak is usually in the range of 400-500 nm), it is possible to achieve effective spectral separation (avoid crosstalk), provide a stable reference signal, and construct a highly sensitive ratio pair.

[0019] Preferably, the blue fluorescent carbon dot aqueous solution is prepared by hydrothermal reaction of citric acid and ethylenediamine. More preferably, the mass ratio of citric acid to ethylenediamine is 1:1 to 1.3, the reaction temperature is 150 to 180°C, and the reaction time is 3 to 4 hours. After the reaction is complete, the supernatant is collected by centrifugation and diluted to obtain the blue fluorescent carbon dot aqueous solution. Using citric acid and ethylenediamine as precursors, a blue fluorescent carbon dot aqueous solution rich in carboxyl and amino groups on its surface is prepared by hydrothermal reaction. This method has the advantages of simple operation, mild conditions, good water solubility of the product, and stable luminescence performance.

[0020] In some embodiments of the present invention, the centrifugation speed is 8000 rpm to 12000 rpm.

[0021] In some embodiments of the present invention, dilution is performed by diluting with deionized water 10-15 times.

[0022] Preferably, the average particle size D50 of the sensing material is 10 μm to 20.0 μm, wherein more than 90% of the particles have a particle size greater than 3 μm. With this structural size, CDs are confined to the particle surface, while high concentrations of Ln... 3+ Uniformly distributed within the bulk lattice of the particles, it can increase spatial physical isolation.

[0023] This invention also provides a method for preparing the highly doped, crosstalk-free optical temperature sensing material based on potassium-based rare earth fluorides, comprising the following steps:

[0024] S1. Provide an aqueous solution of carbon dots;

[0025] S2. Containing M 3+ Ions and Ln 3+ A soluble salt of an ion dissolves in a solvent to obtain a first mixed solution; wherein M 3+ For Gd 3+ Or La 3+ Ln 3+ For Eu 3+ or Tb 3+ And Ln 3+ The molar percentage of rare earth metal ions is 1% to 20% of the total rare earth metal ions;

[0026] S3. Add the carbon dot aqueous solution obtained in step S1 to the first mixed solution obtained in step S2, stir and mix to obtain a mixed solution containing carbon dots;

[0027] S4. Provide an aqueous solution of potassium fluoride with a concentration of 5.5 mol / L to 7.5 mol / L;

[0028] S5. The potassium fluoride aqueous solution obtained in step S4 is added dropwise to the mixed solution containing carbon dots obtained in step S3 at a rate of 0.8 mL / min to 1.5 mL / min. The mixture is stirred at 20℃ to 30℃ to carry out a co-precipitation reaction. After the reaction is completed, the product is subjected to solid-liquid separation, washing and drying to obtain the optical temperature sensing material.

[0029] The core of the preparation method for the above materials lies in guiding the formation of micron-sized particles by controlling the kinetics of the coprecipitation reaction. The combination of high concentration of KF and slow dropwise addition provides a continuous and mild supersaturation, inhibiting explosive nucleation and promoting the reaction to be dominated by "crystal growth," thereby forming large micron-sized particles. Carbon dots are adsorbed and confined to the surface of the growing grains in the early stages of the reaction.

[0030] In some embodiments of the present invention, the solid-liquid separation is performed by centrifugation at a speed of 6000 rpm to 10000 rpm.

[0031] In some embodiments of the present invention, the washing is performed using ethanol.

[0032] In some embodiments of the present invention, the washing is performed 3 to 5 times.

[0033] Preferably, in step S2, the M 3+ The ion source is gadolinium nitrate or lanthanum nitrate, wherein Ln 3+ The ion source is europium nitrate or terbium nitrate; the solvent is a mixed solvent of water and ethanol in a volume ratio of 2:1. The selected nitrate precursor has high purity, good water solubility and thermal decomposition characteristics, which is beneficial for synthesizing micron-sized particle matrices with high crystallinity and excellent luminescence performance through co-precipitation method, providing a chemical basis for achieving high-concentration, quench-free rare earth doping.

[0034] Preferably, in step S5, the molar ratio of fluoride ions in the potassium fluoride aqueous solution to the total rare earth metal ions in step S2 is (4.5-7.5):1; and / or, the co-precipitation reaction continues with gentle stirring and aging for 0.5-1.5 hours after the addition is completed; the drying is performed under vacuum at 50℃-70℃ for 10-14 hours. The gentle stirring and aging, along with the drying temperature and time, maintain the micron-sized morphology of the particles.

[0035] In this invention, the fluorescence intensity ratio (FIR) of the dual-mode luminescence follows a functional relationship with temperature (T) in the range of 300K to 400K: FIR = Aexp(-T / B) + C, where A, B, and C are fitting parameters, and the absolute sensitivity (Sa) of the material at 300K is not less than 11.0%K. -1 .

[0036] This application also protects the application of the aforementioned potassium-based rare earth fluoride-based highly doped crosstalk-free optical temperature sensing material in ratio optical thermometers or temperature sensing devices.

[0037] Compared with the prior art, this application has the following technical effects:

[0038] 1. A significant leap in temperature sensing sensitivity: Benefiting from a stronger reference signal and a pure, independent temperature-sensitive signal, the material of this invention exhibits superior temperature sensing performance. At 300K, based on I(CDs@450nm) / I(Eu) 3+ The absolute sensitivity (Sa) at 700nm is as high as 12.3% K. -1Compared to the highest value reported in comparative patent CN117070212B (7.7% K), -1 This represents an improvement of approximately 60%. This improvement is crucial in fields requiring high precision, such as physiological temperature sensing.

[0039] 2. Significantly improved thermal cycling stability: Micron-sized large particles have a lower specific surface area and a more complete crystal structure, reducing performance degradation caused by surface defects and thermal stress. After 10 thermal cycling tests at 300K-340K, the FIR value of the material of this invention fluctuated by less than ±1.5%.

[0040] 3. The preparation process is simple, green, and controllable: While maintaining the advantages of room temperature coprecipitation method, such as simplicity, low cost, and environmental friendliness, this invention can achieve precise control of product size and structure by introducing two simple and controllable process parameters: "high concentration of KF" and "slow drop addition". It has good repeatability and is easy to scale up for production. Attached Figure Description

[0041] Figure 1 KGdF4:20% Eu prepared in Example 1 3+ X-ray diffraction patterns of / CDs material and standard cubic phase NaGdF4.

[0042] Figure 2 KGdF4:20% Eu prepared in Example 1 3+ Scanning electron microscope image of / CDs material.

[0043] Figure 3 KGdF4:20% Eu prepared in Example 1 3+ Excitation spectrum (monitoring emission at 450 nm and 700 nm) and emission spectrum (excitation wavelength at 365 nm) of / CDs materials at room temperature.

[0044] Figure 4 KGdF4:20% Eu prepared in Example 1 3+ / CDs optical temperature sensing material emission spectrum as a function of temperature (K).

[0045] Figure 5 KGdF4:20% Eu prepared in Example 1 3+ / CDs optical temperature sensing materials are based on fluorescence intensity ratio (FIR) plots.

[0046] Figure 6 The absolute sensitivity (S) of the material in Example 1 within the temperature range of 300-340K. a Comparison of curves showing changes with temperature. Detailed Implementation

[0047] To enable those skilled in the art to better understand the present invention, the present invention will now be further described in conjunction with specific embodiments.

[0048] In the following description, the embodiments of this application are for illustrative purposes and not for limiting purposes, so as to provide a thorough understanding of the embodiments. However, those skilled in the art will understand that the embodiments of this application can also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known preparation methods have been omitted so as not to obscure the description of the embodiments of this application with unnecessary details. Unless otherwise specified, the raw materials used in the following embodiments and comparative examples are all commercially available.

[0049] It should also be understood that the term "and / or" as used in the specification of embodiments of this application and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. The terms "comprising," "including," "having," and variations thereof all mean "including but not limited to," unless otherwise specifically emphasized. "A plurality" means two or more.

[0050] This section only introduces content related to the inventive points; other details can be obtained from relevant technologies and will not be described in detail here. The following embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

[0051] Example 1:

[0052] This embodiment prepares an optical temperature sensing material, and the specific process is as follows:

[0053] S1: Preparation of carbon dots: Weigh 1.26 g of citric acid and 1.2 mL of ethylenediamine, dissolve them in 30 mL of deionized water, stir to dissolve, and then transfer to a 50 mL high-pressure reactor lined with polytetrafluoroethylene. React in an oven at 160 °C for 4 hours. After naturally cooling to room temperature, centrifuge the resulting reaction solution at 10,000 rpm for 10 minutes, collect the supernatant, and dilute it 10 times with deionized water to obtain a blue fluorescent CDs stock solution for later use.

[0054] S2: Weigh out Gd(NO3)3·6H2O and Eu(NO3)3·6H2O, and control the Eu... 3+ The molar amount of Gd ions accounts for the total amount of metal ions (Gd ions). 3+ +Eu 3+The total metal ion content was 10 mmol, which was 20% of the total metal ion content. The two were placed in a 100 mL beaker, and 10 mL of deionized water and 5 mL of anhydrous ethanol were added. The mixture was stirred on a magnetic stirrer until completely dissolved, yielding a clear solution.

[0055] S3: Add 1.5 mL of the CDs dilution solution prepared in step S1 to the solution in step S2, and continue stirring for 30 minutes to allow the CDs to be fully pre-combined with rare earth ions.

[0056] S4: In another beaker, dissolve 60 mmol KF·H2O (i.e., the molar ratio of fluoride ions to rare earth metal ions is 6:1) in 10 mL of deionized water to prepare a KF solution of about 6.0 mol / L.

[0057] S5: At room temperature (approximately 25°C) and with continuous magnetic stirring, the KF solution from step S4 is slowly added dropwise to the mixed solution from step S3 at a rate of 1.0 mL / min using a constant flow pump.

[0058] S6: After the addition is complete, continue to age the mixture gently with stirring at room temperature for 1 hour. Then transfer the resulting white suspension to a 50 mL centrifuge tube, centrifuge at 8000 rpm for 5 minutes, and discard the supernatant. Wash the precipitate three times with anhydrous ethanol.

[0059] S7: Place the washed white precipitate in a vacuum drying oven and dry at 60°C for 12 hours. After grinding, the white KGdF4:20%Eu is obtained. 3+ / CDs optical temperature sensing material powder.

[0060] Example 2:

[0061] In this embodiment, KGdF4: 15% Tb 3+ Preparation of / CDs micron-sized particles

[0062] The preparation steps are basically the same as in Example 1, except that in step S2, Eu(NO3)3·6H2O is replaced with Tb(NO3)3·6H2O, and Tb is controlled. 3+ The doping molar ratio was 15%. The final result was KGdF4:15%Tb. 3+ / CDs material.

[0063] Example 3:

[0064] In this embodiment, KGdF4: 15% Eu 3+ Preparation of / CDs micron-sized particles

[0065] S1: Preparation of carbon dots: Weigh 1.26 g of citric acid and 1.2 mL of ethylenediamine, dissolve them in 30 mL of deionized water, stir to dissolve, and then transfer to a 50 mL high-pressure reactor lined with polytetrafluoroethylene. React in an oven at 170 °C for 3.5 hours. After naturally cooling to room temperature, centrifuge the resulting reaction solution at 10,000 rpm for 10 minutes, collect the supernatant, and dilute it 10 times with deionized water to obtain a blue fluorescent CDs stock solution for later use.

[0066] S2: Weigh out Gd(NO3)3·6H2O and Eu(NO3)3·6H2O, and control the Eu... 3+ The molar amount of Gd ions accounts for the total amount of metal ions (Gd ions). 3+ +Eu 3+ The total metal ion content was 15% and the total metal ion content was 10 mmol. Both were placed in a 100 mL beaker, and 10 mL of deionized water and 5 mL of anhydrous ethanol were added. The mixture was stirred on a magnetic stirrer until completely dissolved, yielding a clear solution.

[0067] S3: Add 1.5 mL of the CDs dilution solution prepared in step S1 to the solution in step S2, and continue stirring for 30 minutes to allow the CDs to be fully pre-combined with rare earth ions.

[0068] S4: In another beaker, dissolve 60 mmol KF·H2O (i.e., the molar ratio of fluoride ions to rare earth metal ions is 6:1) in 10 mL of deionized water to prepare a KF solution of about 6.0 mol / L.

[0069] S5: At room temperature (approximately 25°C) and with continuous magnetic stirring, the KF solution from step S4 is slowly added dropwise to the mixed solution from step S3 at a rate of 1.2 mL / min using a constant flow pump.

[0070] S6: After the addition is complete, continue to age the mixture gently with stirring at room temperature for 1.5 hours. Then transfer the resulting white suspension to a 50 mL centrifuge tube, centrifuge at 8000 rpm for 5 minutes, and discard the supernatant. Wash the precipitate three times with anhydrous ethanol.

[0071] S7: Place the washed white precipitate in a vacuum drying oven and dry at 65°C for 11 hours. After grinding, the white KGdF4:20%Eu is obtained. 3+ / CDs optical temperature sensing material powder.

[0072] Example 4:

[0073] In this embodiment, KLaF4: 15% Tb 3+ Preparation of / CDs micron-sized particles

[0074] The preparation steps are basically the same as in Example 1, except that in step S2, Eu(NO3)3·6H2O is replaced with Tb(NO3)3·6H2O, Gd(NO3)3·6H2O is replaced with La(NO3)3·6H2O, and Tb is controlled. 3+ The doping molar ratio was 15%. The final result was KLaF4:15%Tb. 3+ / CDs material.

[0075] Example 5:

[0076] In this embodiment, KLaF4: 15% Eu 3+ Preparation of / CDs micron-sized particles

[0077] The preparation steps are basically the same as in Example 1, except that in step S2, Gd(NO3)3·6H2O is replaced with La(NO3)3·6H2O, and the Eu content is controlled. 3+ The doping molar ratio was 15%. The final result was KLaF4:15%Eu. 3+ / CDs material.

[0078] Characterization and performance testing

[0079] 1. Structural and morphological characterization

[0080] KGdF4 prepared in Example 1: 20% Eu 3+ X-ray diffraction patterns of / CDs optical temperature sensing materials and standard cubic NaGdF4 are shown below. Figure 1 As shown, from Figure 1 It can be seen that the KGdF4:20%Eu prepared in Example 1 3+ The XRD diffraction peaks of the / CDs optical temperature sensing material match those of the cubic NaGdF4 standard card (PDF#27-0697). All diffraction peaks are shifted at a small angle compared to NaGdF4, confirming the K... + The inclusion of [unclear text] and the sharp diffraction peaks indicate that the KGdF4:20%Eu obtained in this invention [unclear text]. 3+ The KGdF4 phase in the / CDs optical temperature sensing material has a high degree of crystallinity.

[0081] KGdF4 prepared in Example 1: 20% Eu 3+ / CDs optical temperature sensing material scanning electron microscope image as shown Figure 2 As shown, from Figure 2 It can be seen that the KGdF4:20%Eu prepared in Example 1 3+ The / CDs optical temperature sensing material exhibits a morphology of well-crystallized particles with a size of approximately 5-30 μm. This directly demonstrates that the method of this invention has successfully prepared micron-sized large particles.

[0082] 2. Optical performance characterization

[0083] KGdF4 prepared in Example 1: 20% Eu 3+ The excitation-emission spectrum of / CDs optical temperature sensing materials, such as Figure 3 As shown, from Figure 3 It can be seen that the material exhibits obvious dual-mode emission characteristics under 365nm ultraviolet light excitation: one is broadband blue light emission centered at 450nm, originating from CDs; the other is Eu... 3+ Characteristic sharp-line emission, mainly located at 577nm ( 5 D0→ 7 F0), 588nm 5 D0→ 7 F1), 612nm 5 D0→ 7 F2), 653nm 5 D0→ 7 F3) and 700nm 5 D0→ 7 F4). The emission peak intensity at 700 nm is particularly significant in the cubic KGdF4 matrix and is easily detected. Simultaneously, monitoring Eu... 3+ No broadband absorption of CDs was observed in the excitation spectrum at (~700 nm), which conclusively proves that in the micron-sized particle structure of this invention, CDs and bulk Eu... 3+ There is no energy transfer between them.

[0084] 3. Temperature sensing performance test

[0085] The KGdF4 prepared in Example 1 was mixed with 20% Eu. 3+ / CDs optical temperature sensing material was placed on a precisely temperature-controlled sample stage, and the emission spectrum (excitation wavelength 365 nm) was measured every 5 K within the range of 300 K to 340 K (physiologically relevant temperature range). The results are as follows: Figure 4 As shown, the luminescence intensity (IL) of CDs at 450 nm increases with increasing temperature. 450 The temperature sensitivity of Eu decreases sharply with increasing temperature, exhibiting extremely high temperature sensitivity; while Eu... 3+ The luminescence intensity at 700 nm (I 700 It exhibits excellent thermal stability, showing almost no change with temperature. Therefore, with I 70 0 as an internal standard, with I 450 / I 700 Using the fluorescence intensity ratio (FIR) as a temperature measurement parameter enables high-precision, self-calibrating temperature measurements. The relationship between FIR and temperature (T) follows a reciprocal decay function: FIR = 1 / (A*T + B), where A and B are fitting constants. Calculating FIR(I...)...450 / I 700 The relationship between FIR and temperature T is perfectly fitted by the formula FIR = 1 / (0.156*T - 45.85). 2 >0.999), which can be applied in the field of optical temperature sensing.

[0086] Based on this fitting function, the absolute sensitivity (S) of the material can be calculated. a =d(FIR) / dT), such as Figure 6 As shown. Absolute sensitivity (S a The absolute sensitivity exhibits a good linear relationship with temperature (K). As the temperature increases, the absolute sensitivity continuously decreases, reaching its highest value of 11.5% K at 300 K. -1 The optical temperature sensing material of this invention exhibits sensitivity far exceeding that of existing technologies and is more suitable for temperature measurement in lower temperature ranges.

[0087] Furthermore, after multiple heating-cooling cycles within the 300-340K range, the material exhibits good FIR value reproducibility, with fluctuations less than ±1.5%, demonstrating its reliability and stability as a sensor. Its emission color also shifts significantly from blue-white to red with increasing temperature, making it suitable for use in colorimetric thermometers. This invention provides the application of the described optical temperature sensing material in the fabrication of ratio optical thermometers or temperature sensing devices. This device utilizes a 365nm LED as the excitation source, simultaneously acquiring emission signals at 450nm and 700nm using a fiber optic spectrometer, calculating the FIR value, and then inferring the temperature from the calibration curve.

[0088] This invention innovatively replaces the matrix with potassium-based rare earth fluoride (KMF4) and cleverly controls the synthesis process to obtain micron-sized particles, successfully constructing a "surface CDs / bulk high-concentration Ln" structure. 3+ The invention features a spatially isolated composite structure. This design effectively solves two major problems in existing technologies: "low rare-earth doping concentration and weak luminescence" and "severe energy crosstalk in nanocomposite materials." Experimental data fully demonstrate that the material of this invention significantly surpasses the closest existing technologies in terms of rare-earth luminescence intensity, signal independence, temperature sensitivity, and thermal stability, exhibiting outstanding substantive characteristics and significant progress.

[0089] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A highly doped, crosstalk-free optical temperature sensing material based on potassium-based rare earth fluorides, characterized in that, The sensing material is a potassium-based rare earth fluoride micron-sized particle with surface carbon dot modification and high doping with optically active rare earth ions, wherein the potassium-based rare earth fluoride has the general formula KMF4, and M is an optically inert rare earth element selected from Gd or La; the optically active rare earth ions are selected from Eu. 3+ or Tb 3+ The molar percentage of rare earth metal ions is 1% to 20%; the average particle size D50 of the sensing material is 5.0 μm to 20.0 μm.

2. The highly doped, crosstalk-free optical temperature sensing material based on potassium-based rare earth fluorides as described in claim 1, characterized in that, The carbon dots are blue fluorescent carbon dots with a surface rich in carboxyl or amino groups, which selectively attach to the surface of KMF4 micron particles through coordination. There is no effective non-radiative energy transfer between the luminescence of the carbon dots and the luminescence of the optically active rare earth ions.

3. The highly doped, crosstalk-free optical temperature sensing material based on potassium-based rare earth fluorides as described in claim 1, characterized in that, The sensing material, when excited by ultraviolet light with wavelengths from 320 nm to 380 nm, produces independent dual-mode emission, including: a broadband blue light emission originating from carbon dots with a peak value near 450 nm; and one or more characteristic sharp-line emissions originating from optically active rare-earth ions in the wavelength range of 500 nm to 750 nm; when the optically active rare-earth ion is Eu... 3+ When the characteristic emission peak is located at 612 nm and / or 700 nm; when the optically active rare earth ion is Tb 3+ At that time, its characteristic emission peak is located at 542 and / or 621 nm.

4. The highly doped, crosstalk-free optical temperature sensing material based on potassium-based rare earth fluorides as described in claim 2, characterized in that, Blue fluorescent carbon dot aqueous solution was prepared by hydrothermal method using citric acid and ethylenediamine.

5. The highly doped, crosstalk-free optical temperature sensing material based on potassium-based rare earth fluorides as described in claim 4, characterized in that, The mass ratio of citric acid to ethylenediamine is 1:1 to 1.3, the reaction temperature is 150 to 180°C, and the reaction time is 3 to 4 hours. After the reaction is completed, the supernatant is collected by centrifugation and diluted to obtain an aqueous solution of blue fluorescent carbon dots.

6. The highly doped, crosstalk-free optical temperature sensing material based on potassium-based rare earth fluorides as described in claim 1, characterized in that, The average particle size D50 of the sensing material is 10 μm to 20.0 μm, of which more than 90% of the particles have a particle size greater than 3 μm.

7. The method for preparing the highly doped, crosstalk-free optical temperature sensing material based on potassium-based rare earth fluorides according to claim 1, characterized in that, Includes the following steps: S1. Provide an aqueous solution of carbon dots; S2. Containing M 3+ Ions and Ln 3+ A soluble salt of an ion dissolves in a solvent to obtain a first mixed solution; wherein M 3+ For Gd 3 + Or La 3+ Ln 3+ For Eu 3+ or Tb 3+ And Ln 3+ The molar percentage of ions in the total metal ions is 1% to 20%; S3. Add the carbon dot aqueous solution obtained in step S1 to the first mixed solution obtained in step S2, stir and mix to obtain a mixed solution containing carbon dots; S4. Provide an aqueous solution of potassium fluoride with a concentration of 5.5 mol / L to 7.5 mol / L; S5. The potassium fluoride aqueous solution obtained in step S4 is added dropwise to the mixed solution containing carbon dots obtained in step S3 at a rate of 0.8 mL / min to 1.5 mL / min. The mixture is stirred at 20℃ to 30℃ to carry out a co-precipitation reaction. After the reaction is completed, the product is subjected to solid-liquid separation, washing and drying to obtain the optical temperature sensing material.

8. The method for preparing a highly doped, crosstalk-free optical temperature sensing material based on potassium-based rare earth fluorides as described in claim 7, characterized in that, In step S2, the M 3+ The ion source is gadolinium nitrate or lanthanum nitrate, wherein Ln 3+ The ion source is europium nitrate or terbium nitrate; the solvent is a mixed solvent of water and ethanol in a volume ratio of 2:

1.

9. The method for preparing a highly doped, crosstalk-free optical temperature sensing material based on potassium-based rare earth fluorides as described in claim 7, characterized in that, In step S5, the molar ratio of fluoride ions in the potassium fluoride aqueous solution to the total metal ions in step S2 is (4.5-7.5):1; And / or, The coprecipitation reaction is followed by gentle stirring and aging for 0.5 to 1.5 hours after the addition is completed; the drying is carried out under vacuum at 50°C to 70°C for 10 to 14 hours.

10. The application of the highly doped, crosstalk-free optical temperature sensing material based on potassium-based rare earth fluorides as described in claim 1 in a ratio optical thermometer or temperature sensing device.

Images