Upconversion luminescent material with inverse thermal quenching and thermal quenching functions and preparation method thereof

Abstract

The invention discloses an upconversion luminescent material with inverse thermal quenching and thermal quenching functions, and belongs to the field of rare earth luminescent materials, the chemical formula of the material is NaEr0. 695F4: Yb0.2 / Gd0.1 / Eu0.005, the material morphology is in a micron-scale hexagonal disc shape, and NaEr0. 695F4: Yb0.2 / Gd0.1 / Eu0.005 upconversion microparticles are used as a bifunctional upconversion luminescent temperature sensor, a sensitization sensor and a thermal quenching sensor, and can be used for detecting the temperature of a luminescent device. And the method can also be used for non-contact optical temperature measurement or high-sensitivity optical temperature measurement under an extreme temperature condition. The temperature detection is realized based on the thermal coupling energy level, the distance between two emission peaks is large, and the data processing error is greatly reduced; the up-conversion luminescence intensity of the energy level can be enhanced along with the rise of the temperature and is called inverse heat quenching, and the temperature sensing performance is better. The invention also discloses a preparation method of the material, the operation is simple, the material crystal phase is good, the phase is uniform, the yield is high, the material performance is stable, and the material has a good bifunctional temperature response effect.

Description

Technical Field

[0001] The present invention belongs to the field of rare earth luminescent materials, and particularly relates to a luminescent material having both inverse thermal quenching and thermal quenching up-conversion properties. Background Art

[0002] With the current trend toward miniaturization and the urgent need to conduct scientific research under extreme temperature conditions, fluorescence temperature sensors are attracting significant attention due to their fast response and high resolution. Upconversion luminescent materials, with their unique ability to convert near-infrared light into visible light, offer significant advantages in temperature sensing, including low toxicity, high signal-to-noise ratio, and a degree of immunity to sample autofluorescence and photobleaching. These materials enable ultrasensitive detection and hold enormous promise for application in temperature sensing.

[0003] However, the "thermal quenching" phenomenon, in which the luminescence intensity of upconversion luminescent materials decreases rapidly with increasing temperature, is one of the key factors restricting their application in the field of temperature detection. Scientists have recently discovered a rare class of materials, "negative thermal expansion materials," whose volume or length decreases abnormally with increasing temperature. Compared with the vast majority of materials that have the property of thermal expansion and contraction, these materials have the abnormal "thermal contraction and cold expansion" property. Developing negative thermal expansion materials as the matrix of upconversion luminescent materials and reversing the thermal quenching property of upconversion luminescence, that is, "reverse thermal quenching" upconversion luminescence, is extremely important for its application in extremely high temperatures.

[0004] In addition, most of the reports so far are based on the use of, for example, Er 3+ of 2 H 11 / 2 and 4 S 3 / 2 Temperature detection using two adjacent thermally coupled energy levels can lead to significant errors in data processing due to the partial overlap of the two emission peaks. Furthermore, these thermally coupled sensors using green light generally have low sensitivity and severe tissue absorption, severely limiting their application in the biological field. In comparison, red light (600-700 nanometers), emitted within the "optical window" of biological tissue, has significantly reduced tissue absorption and autofluorescence. Therefore, developing upconversion optical thermometry materials with efficient simultaneous red and green light emission and optical thermometers based on FIR (540 / 654) thermally coupled energy level technology are of great significance for their application in the biological field. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention discloses a luminescent material having both reverse thermal quenching and thermal quenching upconversion properties, so as to solve at least one of the above-mentioned problems.

[0006] In order to achieve the above-mentioned purpose of the invention, the technical solution disclosed in the present invention is specifically as follows: It has both reverse thermal quenching and thermal quenching upconversion luminescent materials, and its molecular formula is NaEr 0.695 F4:Yb 0.2 / Gd 0.1 / Eu 0.005 .

[0007] Furthermore, when excited by 980-nanometer infrared light, the material has an emission spectrum in the visible light region ranging from 500 to 700 nanometers.

[0008] As a preference, NaErF4 is used as the matrix and Eu 3+ Energy transfer is regulated to obtain upconversion fluorescence with only 652 nm red light and 520 nm and 538 nm green light output.

[0009] As a preference, under infrared light excitation, Er 3+ The fluorescence emission peak intensities at 652 nm and 538 nm (I 652 , I 538 ) is much stronger than Er 3+ The peak fluorescence emission intensity at 520 nm (I 520 ); in the wide temperature range of 298‒498 K, green (I 520 ) up-conversion luminescence output is enhanced; while the green (I 538 ) and red upconversion luminescence have stronger thermal quenching effects.

[0010] The preparation method of the luminescent material with both reverse thermal quenching and thermal quenching upconversion comprises the following steps: (1) preparing a luminescent material with both reverse thermal quenching and thermal quenching upconversion according to NaEr 0.695 F4:Yb 0.2 / Gd 0.1 / Eu 0.005 The corresponding nitrate (total feed 1 mmol) and 3 mmol anionic surfactant were added to the reaction bottle in a stoichiometric ratio of the lanthanide element, 10 mL water was added, and the mixture was stirred at room temperature for 30 minutes to obtain solution A; (2) 3 mmol fluoride salt was ultrasonically dissolved in 5 mL water to obtain solution B; (3) solution B was added to solution A and the mixture was stirred at room temperature; (4) the pH value of the solution in step (3) was adjusted with alkali; (5) the solution in step (4) was transferred to a high-pressure reactor and reacted at 200°C in an electric blast drying oven for 24 hours; (6) after the temperature was lowered to room temperature after 10 hours, the mixture was centrifuged, washed with deionized water / ethanol several times, and dried in a vacuum drying oven at 60°C for 12 hours to obtain the target upconversion luminescent material.

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

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

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

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

[0015] Preferably, the corresponding rare earth nitrate in steps (1) to (2) is 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] Application of upconversion luminescent materials with both reverse thermal quenching and thermal quenching in the field of optical temperature measurement.

[0017] The invention discloses a highly sensitive and fast-responding fluorescent temperature probe material with both reverse thermal quenching and thermal quenching upconversion. Under 980-nanometer infrared light excitation, its visible light emission spectrum ranges from 500 to 700 nanometers, and only 652-nanometer red light and 520-nanometer and 538-nanometer green light output are obtained. It is worth noting that the fluorescence emission peak intensities (I 652 , I 538 ) is much stronger than the peak fluorescence emission intensity at 520 nm (I 520 ); In the wide temperature range of 298‒498 K, the three characteristic emission peaks show regular changes with temperature, specifically green (I 520 ) up-conversion luminescence output increases regularly; while the green (I 538 ) and red upconversion luminescence have stronger thermal quenching effect. 538 / I 652 and I 520 / I 652 The absolute sensitivity is calculated to be 1.464%K as a function of temperature. −1 , 1.992%K −1 ; The relative sensitivity is 1.003%K −1 , 0.996%K −1 .

[0018] Compared with the existing technology, the present invention has the following creative features: 1. This material can be used as two ratio temperature sensors. The disclosed material was synthesized using a one-step hydrothermal method, which is environmentally friendly. The obtained material has a uniform phase, high crystallinity and high yield. 2. The thermal coupling energy level utilizes red light located in the "optical window" of biological tissue, greatly reducing the absorption of biological tissue, thereby achieving highly sensitive temperature detection; 3. The distance between the two selected fluorescence emission peaks is large, which greatly reduces the data processing error; 4. The green upconversion luminescence of the material disclosed in the invention at 520 nm exhibits the property of "reverse thermal quenching", indicating that the material is based on Er 3+ The invention of "negative thermal expansion" material has opened up a new path for optimizing the performance of upconversion luminescent materials, promoted the integration of negative thermal expansion materials and luminescent materials, and also promoted the study of the correlation between structure and luminescence. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0022] Preferably, the material has an emission spectrum in the visible region of 500-700 nanometers under 980 nanometer infrared light excitation.

[0023] Preferably, NaErF4 is used as the matrix and Eu 3+ Energy transfer is regulated to obtain upconversion fluorescence with only green and red light output.

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

[0025] A method for preparing a luminescent material having both reverse thermal quenching and thermal quenching upconversion properties comprises the following steps: (1) According to NaEr 0.695 F4:Yb 0.2 / Gd 0.1 / Eu 0.005 The corresponding nitrate and 3 mmol of anionic surfactant were added to the reaction bottle in the stoichiometric ratio of the lanthanide element. The total amount of nitrate was 1 mmol. 10 mL of water was added and stirred at room temperature for 30 minutes to obtain solution A. (2) Dissolve 3 mmol of fluoride salt 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) adjusting the pH value of the solution in step (3) with an alkali; (5) The solution in step (3) was transferred to a high-pressure reactor and reacted at 200° C. in an electric blast drying oven for 24 hours; (6) After the temperature dropped to room temperature over 10 hours, the mixture was centrifuged, washed with deionized water / ethanol several times, and dried in a vacuum drying oven at 60°C for 12 hours to obtain the target upconversion luminescent material.

[0026] In step (1), stirring is performed for 20-40 minutes to obtain a transparent solution; in step (2), ultrasonication is performed at room temperature for 3-5 minutes; in step (3), stirring is continued 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 nitrate corresponding to steps (1) to (2) is 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 examples are as follows: As attached Figure 1 Shown is a scanning electron microscope image of the material disclosed in the present invention, which is a hexagonal crystal, high crystallinity, regular and uniform morphology and disc-shaped micron particles with a larger specific surface area.

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

[0030] As attached Figure 3 Shown is the X-ray photoelectron spectrum of the material disclosed in the present invention, which confirms the presence of large amounts of elements such as Na, Er, F, Yb, and Gd in the prepared product.

[0031] As attached Figure 4 Shown is the in-situ variable temperature X-ray powder diffraction pattern of the material disclosed in the present invention. The results show that the prepared product has a high degree of crystallinity, and the diffraction peak intensity decreases with increasing temperature, indicating that its volume or length will abnormally decrease with increasing temperature. It is a "negative thermal expansion" material with an abnormal "heat shrinkage and cold expansion" property.

[0032] Under 980 nm near-infrared light excitation, the up-conversion fluorescence emission spectra of the material disclosed in the present invention at different temperatures were measured ( Figure 5 ), the results showed that at room temperature Er 3+ The fluorescence emission peak intensities at 652 nm and 538 nm (I 652 , I 538 ) is much stronger than Er 3+ The peak fluorescence emission intensity at 520 nm (I 520 ); Green (I 538) and red upconversion luminescence have strong thermal quenching effect. 520 ) The upconversion luminescence output gradually increases with increasing temperature, reversing the thermal quenching properties of the upconversion luminescence, that is, presenting "reverse thermal quenching" upconversion luminescence.

[0033] The temperature-dependent fluorescence emission spectrum was further quantitatively analyzed to obtain a linear curve of upconversion luminescence intensity with increasing temperature ( Figure 6 ), the results showed that the 520-nanometer green upconversion luminescence output increased linearly with temperature, revealing that the material is a "negative thermal expansion" material with the anomalous "heat contraction and cold expansion" property.

[0034] As attached Figure 7 and Figure 8 As shown, the relationship between the ratio of fluorescence emission intensity and temperature, FIR (I 538 / I 652 ) changes regularly with temperature. Specifically, the thermal quenching sensor is detected in the wide temperature range of 298‒498 K. Further calculation shows that the absolute sensitivity is 1.464%K −1 ; Relative sensitivity is 1.003%K −1 ( Figure 9 ).

[0035] As attached Figure 10 and Figure 11 As shown, the relationship between the ratio of fluorescence emission intensity and temperature, FIR (I 520 / I 652 ) shows an exponential relationship with temperature changes. Figure 12 The absolute sensitivity and relative sensitivity versus temperature graph shows that S a The maximum value is 1.992%K at 498 K −1 ;S r The maximum value is 0.996%K −1 .

[0036] This invention has opened up a new path for optimizing the performance of upconversion luminescent materials, promoted the integration of negative thermal expansion materials and luminescent materials, and also promoted the study of the correlation between structure and luminescence.

[0037] The above is a detailed description of an embodiment of the present invention. However, the content described is only a preferred embodiment of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A luminescent material having both reverse thermal quenching and thermal quenching upconversion, characterized in that: The chemical formula of the material is NaEr 0.695 F4:Yb 0.2 / Gd 0.1 / Eu 0.005 The material morphology is regular hexagonal disk-shaped micron particles.

2. The luminescent material having both reverse thermal quenching and thermal quenching upconversion according to claim 1, characterized in that: When excited by 980-nanometer infrared light, the material's emission spectrum in the visible region ranges from 500 to 700 nanometers.

3. The luminescent material having both reverse thermal quenching and thermal quenching upconversion according to claim 1, characterized in that: Using NaErF4 as the matrix and using Eu 3+ Energy transfer is regulated to obtain upconversion fluorescence with only green and red light output.

4. The luminescent material having both reverse thermal quenching and thermal quenching upconversion according to claim 1, characterized in that: Er 3+ The fluorescence emission peaks at 652 nm and 538 nm are stronger than those of Er 3+ The peak intensity of fluorescence emission is at 520 nanometers; within the wide temperature range of 298-498K, the green upconversion luminescence output is enhanced; at the same time, the green and red upconversion luminescence have a thermal quenching effect.

5. A method for preparing a luminescent material having both reverse thermal quenching and thermal quenching upconversion properties, characterized in that: The steps include: (1) According to NaEr 0.695 F4:Yb 0.2 / Gd 0.1 / Eu 0.005 The corresponding nitrate and 3 mmol of anionic surfactant were added to a reaction bottle in a stoichiometric ratio of the lanthanide element, with a total nitrate charge of 1 mmol. 10 mL of water was added and stirred at room temperature for 30 minutes to obtain solution A. (2) Ultrasonic dissolution of 3 mmol of fluoride salt in 5 mL of water to obtain solution B; (3) Add solution B to solution A and continue stirring at room temperature; (4) adjusting the pH value of the solution in step (3) with an alkali; (5) The solution in step (3) was transferred to a high-pressure reactor and reacted at 200° C. in an electric blast drying oven for 24 hours; (6) After the temperature dropped to room temperature over 10 hours, the mixture was centrifuged, washed with deionized water / ethanol several times, and dried in a vacuum drying oven at 60° C. for 12 hours to obtain the target upconversion luminescent material.

6. The method for preparing a luminescent material having both reverse thermal quenching and thermal quenching upconversion according to claim 5, characterized in that: In step (1), the mixture is stirred for 20-40 minutes to obtain a transparent solution A.

7. The method for preparing a luminescent material having both reverse thermal quenching and thermal quenching upconversion according to claim 5, characterized in that: In step (2), ultrasonication was performed at room temperature for 3-5 minutes.

8. The method for preparing a luminescent material having both reverse thermal quenching and thermal quenching upconversion according to claim 5, characterized in that: In step (3), stirring is continued at room temperature for 10-30 minutes; the pH value of the solution in step (3) is 6.

5.

9. The method for preparing a luminescent material having both reverse thermal quenching and thermal quenching upconversion according to claim 5, characterized in that: In step (4), the pH value of the solution is adjusted to 8.

0.

10. The method for preparing a luminescent material having both reverse thermal quenching and thermal quenching upconversion according to claim 5, characterized in that: The corresponding rare earth nitrate in steps (1) to (2) is 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.

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