Inverse and thermal quenching coexisting upconversion luminescent material and preparation method thereof

Abstract

The application discloses an up-conversion luminescent material with reverse thermal quenching and thermal quenching, belongs to the field of rare earth luminescent materials, and has a chemical formula of NaEr 0.695 F4:Yb 0.2 / Gd 0.1 / Eu 0.005 The material morphology is a micron-level hexagonal disc, and the NaEr 0.695 F4:Yb 0.2 / Gd 0.1 / Eu 0.005 The up-conversion micro-particle is used as a dual-function up-conversion luminescent temperature sensor, and can be used for a sensitized sensor and a thermal quenching sensor, and can also be used for non-contact optical temperature measurement or high-sensitivity optical temperature measurement under extreme temperature conditions. Temperature detection is realized based on thermal coupling energy levels, the distance between two emission peaks is large, and data processing errors are greatly reduced; the up-conversion luminescent intensity of the energy level is enhanced with the increase of temperature, which is called reverse thermal quenching, and the temperature sensing performance is better. The application further discloses a preparation method of the material, and the method is simple to operate, the material has good crystal phase, uniform phase, high yield and stable performance, and has good dual-function temperature response effect.

Description

Technical Field

[0001] This invention belongs to the field of rare earth luminescent materials, and specifically relates to luminescent materials that combine reverse thermal quenching and thermal quenching upconversion. Background Technology

[0002] With the current trend towards miniaturization of equipment and the urgent need for scientific research under extreme temperature conditions, fluorescence temperature sensors have attracted much attention due to their advantages such as fast response and high resolution. Among them, upconversion luminescent materials have the special ability to convert near-infrared light into visible light; and due to their advantages such as low toxicity, high signal-to-noise ratio, ability to avoid interference from sample autofluorescence to a certain extent, and resistance to photobleaching, these materials can achieve ultrasensitive detection and have great application prospects in the field of temperature sensing.

[0003] However, the "thermal quenching" phenomenon, where the luminescence intensity of upconversion luminescent materials rapidly decreases with increasing temperature, is one of the key factors limiting their application in temperature detection. Scientists have now discovered a rare class of materials exhibiting "negative thermal expansion"—materials whose volume or length anomalously decreases with increasing temperature. Compared to most materials that exhibit thermal expansion and contraction, these materials possess anomalous "thermal contraction and expansion" properties. Developing negative thermal expansion materials as the matrix for upconversion luminescent materials, thus reversing the thermal quenching property of upconversion luminescence—that is, "reverse thermal quenching" upconversion luminescence—is of paramount importance for its application in extreme high-temperature environments.

[0004] In addition, most reports currently use, for example, Er 3+ of 2 H 11 / 2 and 4 S 3 / 2 Temperature detection using adjacent thermally coupled energy levels is problematic due to significant data processing errors caused by the partial overlap of the two emission peaks. Furthermore, these thermally coupled sensors utilizing green light generally suffer from low sensitivity and severe tissue absorption, severely limiting their application in the biological field. In contrast, red light (600-700 nm), emitted from the "optical window" of biological tissue, exhibits significantly reduced tissue absorption and autofluorescence. Therefore, obtaining upconversion optical thermometric materials with efficient simultaneous emission of red and green light, and developing optical thermometers based on FIR (540 / 654) thermally coupled energy level technology, is of great significance for their application in the biological field. Summary of the Invention

[0005] To address the shortcomings of the prior art, this invention discloses a luminescent material that combines reverse thermal quenching and thermal quenching upconversion, thereby solving at least one of the above problems.

[0006] To achieve the above-mentioned objectives, the technical solution disclosed in this invention is as follows: A luminescent material exhibiting both reverse thermal quenching and thermal quenching upconversion luminescence, with the molecular formula NaEr 0.695 F4:Yb 0.2 / Gd 0.1 / Eu 0.005 .

[0007] Furthermore, the material exhibits an emission spectrum in the visible light region of 500–700 nm when excited by 980 nm infrared light.

[0008] Preferably, NaErF4 is used as the matrix and Eu is utilized. 3+ By regulating energy transfer, upconversion fluorescence with output of only 652 nm red light and 520 nm and 538 nm green light was obtained.

[0009] Preferably, under infrared light excitation, Er 3+ Fluorescence emission peak intensities at 652 nm and 538 nm (I 652 I 538 (Far stronger than Er) 3+ The fluorescence emission peak intensity at 520 nm (I 520 Within a wide temperature range of 298–498 K, green (I) 520 Upconversion light output is enhanced; while green (I) 538 (and red upconversion luminescence have a stronger thermal quenching effect.)

[0010] The preparation method of the upconversion luminescent material that combines reverse thermal quenching and thermal quenching includes the following steps: (1) According to NaEr 0.695 F4:Yb 0.2 / Gd 0.1 / Eu 0.005 (1) Add the corresponding nitrate (total feed 1 mmol) and 3 mmol anionic surfactant to the reaction flask according to the stoichiometric ratio of the lanthanide elements, add 10 mL of water, and stir at room temperature for 30 minutes to obtain solution A; (2) Dissolve 3 mmol of fluoride in 5 mL of water by ultrasonication to obtain solution B; (3) Add solution B to solution A and continue stirring at room temperature; (4) Adjust the pH value of the solution in step (3) with alkali; (5) Transfer the solution in step (4) to a high-pressure reactor and react at 200℃ for 24 hours in an electric heating drying oven; (6) After the temperature drops to room temperature after 10 hours, centrifuge, wash several times with deionized water / ethanol, and dry in a vacuum drying oven at 60℃ for 12 hours to obtain the target upconversion luminescent material.

[0011] Preferably, in step (1), stirring for 20-40 minutes yields a transparent solution A.

[0012] Preferably, in step (2), room temperature ultrasound is performed for 3-5 minutes.

[0013] Preferably, in step (3), stirring is continued at room temperature for 10–30 minutes.

[0014] Preferably, the pH of the solution is adjusted to 8.0 in step (4).

[0015] Preferably, the corresponding rare earth nitrates in steps (1) to (2) are Er(NO3)3, Yb(NO3)3, Gd(NO3)3 or Eu(NO3)3, the anionic surfactant is sodium citrate, the fluoride salt is NH4F, and the base is triethylamine.

[0016] Applications of upconversion luminescent materials that combine reverse thermal quenching and thermal quenching in the field of optical temperature measurement.

[0017] A highly sensitive and rapidly responding upconversion fluorescence temperature probe material employing the technical solution of this invention, possessing both reverse thermal quenching and thermal quenching properties, exhibits an emission spectrum in the visible light region of 500–700 nm under 980 nm infrared excitation, producing upconversion fluorescence with output only at 652 nm red light and 520 nm and 538 nm green light. Notably, the fluorescence emission peak intensities (IL) at 652 nm and 538 nm are achieved at room temperature. 652 I 538 The intensity is much stronger than the fluorescence emission peak intensity located at 520 nm (I). 520 Within a wide temperature range of 298–498 K, the three characteristic emission peaks all exhibit regular changes with temperature, specifically green (I). 520 The upconversion luminous output increases regularly; while at the same time, the green (I) 538 Red upconversion luminescence exhibits a stronger thermal quenching effect. An I... 538 / I 652 and I 520 / I 652 Based on the relationship with temperature, the absolute sensitivity was calculated to be 1.464% K. −1 1.992%K −1 The relative sensitivities were 1.003% K. −1 0.996%K −1 .

[0018] Compared with existing technologies, the present invention has the following inventiveness. 1. This material can be used as two ratio temperature sensors. The disclosed material was synthesized using a one-step hydrothermal method, which is green and environmentally friendly. The obtained material has a uniform phase, high crystallinity, and high yield. 2. The thermally coupled energy levels all utilize red light located in the "optical window" of biological tissue, which greatly reduces the absorption of biological tissue, thereby achieving highly sensitive temperature detection; 3. The large spacing between the two selected fluorescence emission peaks significantly reduces data processing errors; 4. The material disclosed in this invention exhibits "reverse thermal quenching" properties in its green upconversion luminescence at 520 nm, indicating that the material is based on Er 3+ The invention of the "negative thermal expansion" material opens up a new path for optimizing the performance of upconversion luminescent materials, promotes the integration of negative thermal expansion materials and luminescent materials, and also promotes the study of the correlation between structure and luminescence. Attached Figure Description

[0019] Figure 1 Here is a SEM (scanning electron microscope) image of the material disclosed in this invention; Figure 2 The image shows the EDX (energy-dispersive X-ray spectrum) of the material disclosed in this invention. Figure 3 The above is the XPS (X-ray photoelectron spectroscopy) spectrum of the material disclosed in this invention; Figure 4 The in-situ temperature-varying XRD (X-ray powder diffraction) pattern of the material disclosed in this invention; Figure 5 The present invention discloses the temperature-dependent fluorescence emission spectrum of the material under 980 nm laser excitation; Figure 6 This is a graph showing the change in upconversion fluorescence intensity of the material disclosed in this invention under 980 nm laser excitation as a function of temperature. Figure 7 The fluorescence emission intensity ratio (FIR) of the material disclosed in this invention is... 538 / I 652 Calculation results of temperature variation; Figure 8 Ln(I) of the material disclosed in this invention 538 / I 652 Calculation results of temperature variation; Figure 9 The present invention discloses the calculation results of the relative and absolute sensitivity of the optical thermometer based on FIR (538 / 652) thermal coupling energy level technology.

[0020] Figure 10 The fluorescence emission intensity ratio (FIR) of the material disclosed in this invention is... 520 / I 652 Calculation results of temperature variation; Figure 11 Ln(I) of the material disclosed in this invention 520 / I 652 Calculation results of temperature variation; Figure 12The present invention discloses the calculation results of the relative and absolute sensitivity of the optical thermometer based on FIR (520 / 652) thermal coupling energy level technology. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to the accompanying drawings: A material exhibiting both reverse thermal quenching and thermal quenching upconversion luminescence, with the chemical formula NaEr 0.695 F4:Yb 0.2 / Gd 0.1 / Eu 0.005 The material has a morphology of regular hexagonal disk-shaped micron-sized particles.

[0022] Preferably, the material has an emission spectrum in the visible region of 500–700 nm when excited by 980 nm infrared light.

[0023] Preferably, NaErF4 is used as the matrix and Eu is utilized. 3+ By regulating energy transfer, upconversion fluorescence with only green and red light output can be obtained.

[0024] Preferably, Er 3+ The fluorescence emission peaks at 652 nm and 538 nm are stronger than those at Er. 3+ The fluorescence emission peak intensity is located at 520 nm; the green upconversion luminescence output is enhanced in a wide temperature range of 298–498 K; at the same time, the green and red upconversion luminescence exhibit thermal quenching effects.

[0025] A method for preparing upconversion luminescent materials that combine reverse thermal quenching and thermal quenching includes the following steps: (1) According to NaEr 0.695 F4:Yb 0.2 / Gd 0.1 / Eu 0.005 The stoichiometric ratio of the lanthanides was used to add the corresponding nitrate and 3 mmol of anionic surfactant to the reaction flask. The total amount of nitrate added was 1 mmol. 10 mL of water was added, and the mixture was stirred at room temperature for 30 minutes to obtain solution A. (2) Dissolve 3 mmol of fluoride salt in 5 mL of water by sonication to obtain solution B; (3) Add solution B to solution A and continue stirring at room temperature; (4) Adjust the pH of the solution in step (3) with alkali; (5) Transfer the solution from step (3) to a high-pressure reactor and react it at 200°C for 24 hours in an electric heating drying oven; (6) After the temperature drops to room temperature after 10 hours, centrifuge the material, wash it several times with deionized water / ethanol, and then dry it in a vacuum drying oven at 60°C for 12 hours to obtain the target upconversion luminescent material.

[0026] In step (1), the solution is stirred for 20-40 minutes to obtain a transparent solution; in step (2), the solution is sonicated at room temperature for 3-5 minutes; in step (3), the solution is stirred at room temperature for 10-30 minutes; in step (3), the pH value of the solution is 6.5; in step (4), the pH value of the solution is adjusted to 8.0.

[0027] Preferably, the rare earth nitrates in steps (1) to (2) are one of Er(NO3)3, Yb(NO3)3, Gd(NO3)3 or Eu(NO3)3, the anionic surfactant is sodium citrate, the fluoride salt is NH4F, and the base is triethylamine.

[0028] The following is an example: As attached Figure 1 The image shown is a scanning electron microscope image of the material disclosed in this invention. It is a hexagonal, highly crystallized, regularly shaped, and larger specific surface area disc-shaped micron-sized particle.

[0029] As attached Figure 2 The image shows the energy-dispersive X-ray spectrum of the material disclosed in this invention. The results show that the prepared product contains Na, Er, F, Yb, Gd, and Eu elements, confirming the presence of co-doped elements.

[0030] As attached Figure 3 The image shown is an X-ray photoelectron spectrum of the material disclosed in this invention, confirming the presence of a large number of elements such as Na, Er, F, Yb, and Gd in the prepared product.

[0031] As attached Figure 4 The image shows the in-situ temperature-variable X-ray powder diffraction pattern of the material disclosed in this invention. The results show that the prepared product has high crystallinity and the intensity of the diffraction peak decreases with increasing temperature, indicating that its volume or length will abnormally decrease with increasing temperature. It is a "negative thermal expansion" material with anomalous "thermal contraction and cold expansion" properties.

[0032] The upconversion fluorescence emission spectra of the material disclosed in this invention were measured at different temperatures under 980 nm near-infrared light excitation. Figure 5 The results showed that Er at room temperature 3+ Fluorescence emission peak intensities at 652 nm and 538 nm (I 652 I 538 (Far stronger than Er) 3+ The fluorescence emission peak intensity at 520 nm (I 520 Green (I) within a wide temperature range of 298–498 K 538Red upconversion luminescence exhibits a strong thermal quenching effect. Green (I) and red upconversion luminescence, on the other hand, possess strong thermal quenching effects. 520 The output of upconversion luminescence gradually increases with increasing temperature, reversing the thermal quenching property of upconversion luminescence, thus exhibiting "reverse thermal quenching" upconversion luminescence.

[0033] Further quantitative analysis of the temperature-dependent fluorescence emission spectrum yielded a linear curve showing the change in upconversion luminescence intensity with increasing temperature. Figure 6 The results showed that the green upconversion luminescence output at 520 nm increased linearly with temperature, revealing that the material is a "negative thermal expansion" material with anomalous "thermal contraction and cold expansion" properties.

[0034] As attached Figure 7 and Figure 8 As shown, the relationship between the fitted fluorescence emission intensity ratio and temperature is represented by FIR(I). 538 / I 652 The sensitivity exhibits a regular variation with temperature, specifically exhibiting thermal quenching over a wide temperature range of 298–498 K. Further calculations yielded an absolute sensitivity of 1.464% K. −1 The relative sensitivity is 1.003% K. −1 ( Figure 9 ).

[0035] As attached Figure 10 and Figure 11 As shown, the relationship between the fitted fluorescence emission intensity ratio and temperature is represented by FIR(I). 520 / I 652 It exhibits an exponential relationship with temperature. Figure 12 The graphs showing the relationship between absolute and relative sensitivity and temperature in the medium-temperature range indicate that S a The maximum value is 1.992% of K at 498 K. −1 S r The maximum value is 0.996%K −1 .

[0036] This invention opens up new avenues for optimizing the performance of upconversion luminescent materials, promotes the integration of negative thermal expansion materials and luminescent materials, and also facilitates research on the correlation between structure and luminescence.

[0037] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A luminescent material possessing both reverse thermal quenching and thermal quenching upconversion luminescence, characterized in that, Er 3+ The fluorescence emission peaks at 652 nm and 538 nm are stronger than those at Er. 3+ The fluorescence emission peak intensity is located at 520 nm; the upconversion luminescence at 652 nm and 538 nm exhibits a thermal quenching effect over a wide temperature range of 298-498 K; the green upconversion luminescence output at 520 nm gradually increases with increasing temperature, reversing the thermal quenching property of upconversion luminescence, i.e., exhibiting "reverse thermal quenching" upconversion luminescence. The chemical formula of the material is NaEr. 0.695 F4:Yb 0.2 / Gd 0.1 / Eu 0.005 The material has a morphology of regular hexagonal disk-shaped micron-sized particles.

2. The upconversion luminescent material possessing both reverse thermal quenching and thermal quenching properties according to claim 1, characterized in that, When excited by 980 nm infrared light, the material emits a visible spectrum ranging from 500 to 700 nm.

3. The upconversion luminescent material possessing both reverse thermal quenching and thermal quenching properties according to claim 1, characterized in that, Using NaErF4 as the matrix and utilizing Eu 3+ By regulating energy transfer, upconversion fluorescence with only green and red light output can be obtained.

4. The preparation method of the upconversion luminescent material possessing both reverse thermal quenching and thermal quenching according to claim 1, characterized in that, Includes the following steps: (1) According to NaEr 0.695 F4:Yb 0.2 / Gd 0.1 / Eu 0.005 The stoichiometric ratio of the lanthanides was used to add the corresponding nitrate and 3 mmol of anionic surfactant to the reaction flask. The total amount of nitrate added was 1 mmol. 10 mL of water was added and the mixture was stirred at room temperature for 30 min to obtain solution A. (2) Dissolve 3 mmol of fluoride salt in 5 mL of water by sonication to obtain solution B; (3) Add solution B to solution A and continue stirring at room temperature; (4) Adjust the pH of the solution in step (3) with alkali; (5) Transfer the solution from step (3) to a high-pressure reactor and react it at 200°C for 24 hours in an electric heating drying oven; (6) After the temperature drops to room temperature after 10 hours, centrifuge the material, wash it several times with deionized water / ethanol, and then dry it in a vacuum drying oven at 60°C for 12 hours to obtain the target upconversion luminescent material.

5. The preparation method of the upconversion luminescent material with both reverse thermal quenching and thermal quenching as described in claim 4, characterized in that, In step (2), sonicate at room temperature for 3-5 minutes.

6. The method for preparing the upconversion luminescent material with both reverse thermal quenching and thermal quenching properties according to claim 4, characterized in that, In step (3), continue stirring at room temperature for 10–30 minutes; the pH of the solution in step (3) is 6.

5.

7. The method for preparing the upconversion luminescent material with both reverse thermal quenching and thermal quenching properties according to claim 4, characterized in that, In step (4), the pH of the solution is adjusted to 8.

0.

8. The method for preparing the upconversion luminescent material with both reverse thermal quenching and thermal quenching properties according to claim 4, characterized in that: The corresponding nitrates in step (1) are Er(NO3)3, Yb(NO3)3, Gd(NO3)3 and Eu(NO3)3, and the anionic surfactant is sodium citrate; the fluoride in step (2) is NH4F; and the base in step (4) is triethylamine.

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