A rare earth frequency conversion material for broadband mid-infrared detection and its preparation method

Abstract

The present invention belongs to the field of mid-infrared sensing technology, and discloses a rare-earth frequency conversion material for broadband mid-infrared detection and a preparation method thereof. The material is based on Ce 3+ and Nd 3+ doped rare-earth frequency conversion material NaGdF4:Nd 3+ @NaGdF4:Ce 3+ , and the material is prepared by a thermal co-precipitation method. Under ultraviolet light excitation, emission peaks with wavelengths located at 806 nm and 866 nm are generated, which originate from the Ce 3+ →Nd 3+ energy transfer transition in the rare-earth frequency conversion material. In the absence of mid-infrared light-emitting diode irradiation, the luminescence intensity of the rare-earth frequency conversion material at 806 nm under ultraviolet excitation is very weak. After ultraviolet excitation and radiation of the mid-infrared light-emitting diode, the luminescence intensity of the rare-earth frequency conversion material at 806 nm is greatly enhanced. Therefore, broadband mid-infrared detection at room temperature can be realized by using the change in the ratio of the luminescence intensities at 806 nm and 866 nm.

Description

Technical Field

[0001] The present invention belongs to the technical field of mid-infrared sensing, and particularly relates to a rare-earth frequency conversion material for broadband mid-infrared detection and a preparation method thereof. Background Art

[0002] Mid-infrared spectroscopy has extensive applications in multiple fields, including life science, remote sensing, security, industrial imaging, and environmental detection. Currently, there is still great room for improvement in the development of simplified, low-cost, and low-noise systems for room-temperature mid-infrared detection and imaging systems. An alternative method is to convert mid-infrared radiation into the visible and near-infrared regions that can be detected and imaged using silicon photodetectors, because silicon photodetectors have the characteristics of high sensitivity, economy, and easy integration. However, large nonlinear crystals are usually required to achieve spectral conversion, which requires fine polarization control, phase matching, and high-power pump lasers.

[0003] Rare-earth sensitized frequency conversion nanophosphors exhibit unique optical properties, including rich energy level structures, long luminescence lifetimes, tunable emission bands, and high photostability, and have found applications in fields such as super-resolution imaging, lasers, and optogenetics. Therefore, the rich energy level structures of rare-earth ions can be utilized, and mid-infrared spectral detection can be achieved by designing novel rare-earth sensitized frequency conversion nanophosphors. This new material provides an effective way to improve mid-infrared detection methods. Summary of the Invention

[0004] In a first aspect, the present invention provides a rare-earth frequency conversion material for broadband mid-infrared detection, which can convert mid-infrared radiation into the near-infrared region. The material is doped with Ce 4 @NaGdF 4 ions and Nd 3+ ions in a NaGdF 3+ matrix. The core layer is NaGdF 4 :Nd 3+ , and the shell layer is NaGdF 4 :Ce 3+ . The chemical formula of the material is: NaGdF 4 :Nd 3+ @NaGdF 4 :Ce 3+ .

[0005] In the core layer NaGdF 4 :Nd 3+ , the molar ratio of Gd:Nd is 1:(0.05 - 0.15);

[0006] In the shell layer NaGdF 4 :Ce 3+Among them, the molar ratio of Gd:Ce is 1:0.15.

[0007] NaGdF 4 :Nd 3+ @NaGdF 4 :Ce 3+ Among them, the molar ratio of Gd:Nd in the core layer to Gd:Ce in the shell layer is 1:(0.05 - 0.15):1:0.15.

[0008] In a second aspect, the present invention also provides the rare earth frequency conversion material NaGdF 4 :Nd 3 + @NaGdF 4 :Ce 3+ for the above broadband mid-infrared detection, and a preparation method thereof, which adopts a thermal co-precipitation method and includes the following steps:

[0009] (1) According to the molar ratio of Gd:Nd:Na:F in the core layer NaGdF 4 :Nd 3+ being 1:(0.05 - 0.15):1:4; respectively weigh Gd(CH 3 CO 2 ) 3 , Nd(CH 3 CO 2 ) 3 , NH 4 F and NaOH;

[0010] Heat the mixture of Gd(CH 3 CO 2 ) 3 , Nd(CH 3 CO 2 ) 3 , oleic acid and octadecene to 120 - 150 °C and react for 0.5 - 1 h to form a rare earth-oleic acid complex; then add NH 4 F and NaOH to the rare earth-oleic acid complex and stir at 25 - 50 °C for 30 minutes, and then react at 280 - 310 °C for 1.5 h. After the reaction is completed, cool to room temperature, add ethanol for centrifugal separation, and wash and dry with cyclohexane and ethanol to obtain the core layer NaGdF 4 :Nd 3+ ;

[0011] (2) According to the molar ratio of Gd:Ce:Na:F in the shell layer being NaGdF 4 :Ce 3+ being 1:0.15:1:4; respectively weigh Gd(CH 3 CO 2 ) 3 , Ce(CH3 CO 2 ) 3 ,NH 4 F and NaOH;

[0012] Heat the mixture of Gd(CH 3 CO 2 ) 3 ,Ce(CH 3 CO 2 ) 3 ,oleic acid and octadecene to 120 - 150 °C and react for 0.5 - 1 h to form a rare earth - oleic acid complex; then add the core layer NaGdF obtained in step (1) to the rare earth - oleic acid complex 4 :Nd 3+ ,then add NH 4 F and NaOH, stir at 25 - 50 °C for 30 minutes, and then react at 280 - 310 °C for 1.5 h; after the reaction is completed, cool to room temperature, add ethanol for centrifugal separation, wash and dry with cyclohexane and ethanol to obtain NaGdF 4 :Nd 3+ @NaGdF 4 :Ce 3+ .

[0013] In steps (1) and (2), the volume ratio of oleic acid to octadecene is 2:3.

[0014] Thirdly, the present invention also provides the application of the above rare earth frequency conversion material NaGdF 4 :Nd 3+ @NaGdF 4 :Ce 3+ in broadband mid - infrared detection, and detect the mid - infrared spectrum by measuring the fluorescence intensity ratio of the 806 nm and 866 nm emission peaks of this material.

[0015] The specific operation is as follows:

[0016] (1) Use ultraviolet light of 254 nm to excite NaGdF 4 :Nd 3+ @NaGdF 4 :Ce 3+ , use an Edinburgh FLS980 fluorescence steady - state transient fluorescence spectrometer to perform fluorescence spectrum testing on the NaGdF 4 :Nd 3+ @NaGdF 4 :Ce 3+ phosphor, and calculate the fluorescence intensity ratio of the 806 nm and 866 nm emission peaks to be 0.05;

[0017] (2) Use ultraviolet light of 254 nm and an external mid - infrared diode to co - excite NaGdF4 : Nd 3+ @NaGdF 4 : Ce 3+ , the fluorescence spectrum of NaGdF 4 : Nd 3+ @NaGdF 4 : Ce 3+ phosphor was tested by fluorescence spectrum, and the fluorescence intensity ratio of the emission peaks at 806 nm and 866 nm was calculated to be 1.12.

[0018] The fluorescence intensity ratio of 1.12 is significantly increased compared with the fluorescence intensity ratio of 0.05, which can verify the presence of mid-infrared. This phenomenon can be used to detect broadband mid-infrared.

[0019] The beneficial effects of the present invention are as follows:

[0020] The rare earth frequency conversion material NaGdF 4 : Nd 3+ @NaGdF 4 : Ce 3+ for broadband mid-infrared detection according to the present invention is prepared by a thermal co-precipitation method and generates emission peaks at wavelengths of 806 nm and 866 nm under ultraviolet light excitation, which originate from the 3+ of Nd 4 F 5 / 2 → 4 I 9 / 2 and 4 F 3 / 2 → 4 I 9 / 2 energy level transitions in the rare earth frequency conversion material. In the absence of mid-infrared light-emitting diode irradiation, the luminescence intensity of the rare earth frequency conversion material at 806 nm under ultraviolet excitation is very weak. This is because 4 F 5 / 2 non-radiatively relaxes to the 4 F 3 / 2 energy level, thus reducing the emission at 806 nm. After ultraviolet excitation and mid-infrared light-emitting diode radiation, the luminescence intensity of the rare earth frequency conversion material at 806 nm is greatly enhanced. This is because 4 F 3 / 2 → 4 F 5 / 2 transition is in the mid-infrared region, and mid-infrared excitation promotes the energy level transition to 4 F 5 / 2 , resulting in enhanced luminescence at 806 nm. Therefore, the change in the ratio of the luminescence intensities at 806 nm and 866 nm can be used to achieve broadband mid-infrared detection at room temperature. The present invention provides a new idea for designing broadband mid-infrared detection materials and has high research and application value. Description of the Drawings

[0021] Figure 1 XRD diffraction pattern of the rare earth frequency conversion material of Example 3 of the present invention.

[0022] Figure 2 TEM image of the rare earth frequency conversion material of Example 3 of the present invention.

[0023] Figure 3 Emission spectrum of the rare earth frequency conversion material of Example 3 of the present invention. Detailed implementation manners

[0024] To better illustrate the objectives, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific examples.

[0025] Example 1

[0026] The rare earth frequency conversion material for broadband mid-infrared detection described in the present invention, NaGdF 4 : 5% Nd 3+ @NaGdF 4 : 15% Ce 3+ , and its preparation method includes the following steps:

[0027] (1) Weigh 0.38 mmol of Gd(CH 3 CO 2 ) 3 , 0.02 mmol of Nd(CH 3 CO 2 ) 3 , a mixture of oleic acid and octadecene and add them to a three-necked flask. Heat the solution to 150 °C and react for 1 h to form a rare earth-oleic acid complex; in the obtained rare earth-oleic acid complex, add 1.6 mmol of NH 4 F and 1 mmol of NaOH, stir at 50 °C for 30 minutes, and then react at 290 °C for 1.5 h;

[0028] After the reaction is completed, cool the three-necked flask to room temperature, add ethanol for centrifugal separation, and wash and dry with cyclohexane and ethanol to obtain the core layer NaGdF 4 :Nd 3+ .

[0029] (2) Weigh 0.38 mmol of Gd(CH 3 CO 2 ) 3 , 0.06 mmol of Ce(CH 3 CO 2 ) 3, A mixture of oleic acid and octadecene was added to a three-necked flask, and the solution was heated to 150 °C and reacted for 1 h to form a rare earth-oleic acid complex; then, the product NaGdF obtained in step (1) was added to the rare earth-oleic acid complex 4 :Nd 3+ , and then 1.6 mmol of NH 4 F and 1 mmol of NaOH were added, and the mixture was stirred at 50 °C for 30 minutes, and then reacted at 290 °C for 1.5 h.

[0030] After the reaction was completed, the three-necked flask was cooled to room temperature, ethanol was added for centrifugal separation, and the product was washed and dried with cyclohexane and ethanol to obtain NaGdF 4 :Nd 3+ @NaGdF 4 :Ce 3+ .

[0031] Example 2

[0032] A rare earth frequency conversion material NaGdF for broadband mid-infrared detection according to the present invention 4 : 10% Nd 3+ @NaGdF 4 : 15% Ce 3+ , and its preparation method includes the following steps:

[0033] (1) Weigh 0.36 mmol of Gd(CH 3 CO 2 ) 3 , 0.04 mmol of Nd(CH 3 CO 2 ) 3 , a mixture of oleic acid and octadecene was added to a three-necked flask, and the solution was heated to 150 °C and reacted for 1 h to form a rare earth-oleic acid complex; 1.6 mmol of NH 4 F and 1 mmol of NaOH were added to the obtained rare earth-oleic acid complex, and the mixture was stirred at 50 °C for 30 minutes, and then reacted at 290 °C for 1.5 h.

[0034] After the reaction was completed, the three-necked flask was cooled to room temperature, ethanol was added for centrifugal separation, and the product was washed and dried with cyclohexane and ethanol to obtain the core layer NaGdF 4 :Nd 3+ .

[0035] (2) Weigh 0.36 mmol of Gd(CH 3 CO 2 ) 3 , 0.054 mmol of Ce(CH 3 CO 2 ) 3, A mixture of oleic acid and octadecene was added to a three-necked flask, and the solution was heated to 150 °C and reacted for 1 h to form a rare earth-oleic acid complex; then, in the rare earth-oleic acid complex, the product obtained in step (1) of NaGdF 4 :Nd 3+ was added; then 1.6 mmol of NH 4 F and 1 mmol of NaOH were added, and the mixture was stirred at 50 °C for 30 minutes, and then reacted at 290 °C for 1.5 h.

[0036] After the reaction was completed, the three-necked flask was cooled to room temperature, ethanol was added for centrifugal separation, and it was washed and dried with cyclohexane and ethanol to obtain NaGdF 4 :Nd 3+ @NaGdF 4 :Ce 3+ .

[0037] Example 3

[0038] A rare earth frequency conversion material NaGdF 4 : 15% Nd 3+ @NaGdF 4 : 15% Ce 3+ for broadband mid-infrared detection according to the present invention, and its preparation method includes the following steps:

[0039] (1) Weigh 0.34 mmol of Gd(CH 3 CO 2 ) 3 , 0.051 mmol of Nd(CH 3 CO 2 ) 3 , a mixture of oleic acid and octadecene was added to a three-necked flask, and the solution was heated to 150 °C and reacted for 1 h to form a rare earth-oleic acid complex; in the obtained rare earth-oleic acid complex, 1.6 mmol of NH 4 F and 1 mmol of NaOH were added, and the mixture was stirred at 50 °C for 30 minutes, and then reacted at 290 °C for 1.5 h.

[0040] After the reaction was completed, the three-necked flask was cooled to room temperature, ethanol was added for centrifugal separation, and it was washed and dried with cyclohexane and ethanol to obtain the core layer NaGdF 4 :Nd 3+ .

[0041] (2) Weigh 0.34 mmol of Gd(CH 3 CO 2 ) 3 , 0.051 mmol of Ce(CH 3 CO 2 ) 3, A mixture of oleic acid and octadecene was added to a three-necked flask, and the solution was heated to 150 °C and reacted for 1 h to form a rare earth-oleic acid complex; in the obtained rare earth-oleic acid complex, it was added to the NaGdF obtained in step (1) 4 :Nd 3+ ; Then 1.6 mmol of NH 4 F and 1 mmol of NaOH were added, and the mixture was stirred at 50 °C for 30 minutes, and then reacted at 290 °C for 1.5 h.

[0042] After the reaction was completed, the three-necked flask was cooled to room temperature, ethanol was added for centrifugal separation, and it was washed and dried with cyclohexane and ethanol to obtain NaGdF 4 :Nd 3+ @NaGdF 4 :Ce 3+ .

[0043] Figure 1 This is the XRD diffraction pattern of the rare earth frequency conversion material in Example 3 of the present invention. The XRD diffraction pattern shows that the synthesized rare earth frequency conversion material is hexagonal NaGdF 4 .

[0044] Figure 2 This is the TEM pattern of the rare earth frequency conversion material in Example 3 of the present invention. The morphology of the synthesized nanocrystals is spherical, and the size is about 30 nanometers.

[0045] Figure 3 This is the emission spectrum of the rare earth frequency conversion material in Example 3 of the present invention. Under the irradiation of a mid-infrared light-emitting diode, the emission intensity of the rare earth frequency conversion material at 806 nm is very weak under 254-nm ultraviolet excitation. After 254-nm ultraviolet excitation and the radiation of a mid-infrared light-emitting diode, the emission intensity of the rare earth frequency conversion material at 806 nm has been greatly enhanced.

[0046] Example 4

[0047] An application of the rare earth frequency conversion material NaGdF 4 :Nd 3+ @NaGdF 4 :Ce 3+ for broadband mid-infrared detection according to the present invention, the specific method is: using 254-nm ultraviolet light to excite NaGdF 4 :Nd 3+ @NaGdF 4 :Ce 3+ , and using an Edinburgh FLS980 fluorescence steady-state transient fluorescence spectrometer to measure NaGdF 4 :Nd 3+ @NaGdF 4 :Ce 3+The phosphor was subjected to fluorescence spectroscopy, and the fluorescence intensity ratio of the emission peaks at 806 nm and 866 nm was calculated to be 0.05; the NaGdF was co-excited with ultraviolet light at 254 nm and an external mid-infrared diode 4 :Nd 3+ @NaGdF 4 :Ce 3+ , and the fluorescence steady-state and transient fluorescence spectroscopy of NaGdF 4 :Nd 3+ @NaGdF 4 :Ce 3+ phosphor was measured, and the fluorescence intensity ratio of the emission peaks at 806 nm and 866 nm was calculated to be 1.12.

[0048] Finally, it should be emphasized that the above examples are only used to illustrate the technical solution of the present invention, rather than limiting the protection scope of the present invention. Although we have described the preferred embodiments in detail, those skilled in the art should understand that modifications or equivalent substitutions can be made without departing from the core and scope of the technical solution of the present invention.

Claims

1. Application of a rare earth frequency conversion material for broadband mid-infrared detection in broadband mid-infrared detection, wherein the material is doped with Ce 4 @NaGdF 4 ions and Nd 3+ ions in a NaGdF 3+ matrix, with a core layer of NaGdF 4 :Nd 3+ and a shell layer of NaGdF 4 :Ce 3 + . The chemical formula of the material is: NaGdF 4 :Nd 3+ @NaGdF 4 :Ce 3+ . It is characterized in that the mid-infrared spectrum is detected by measuring the fluorescence intensity ratio of the emission peaks at 806 nm and 866 nm of the material.

2. The application according to claim 1, it is characterized in that Nuclear layer NaGdF 4 :Nd 3+ In 4 :Nd 3+ , the molar ratio of Gd:Nd is 1:(0.05 - 0.15).

3. The application according to claim 1, it is characterized in that Shell NaGdF 4 :Ce 3+ In 4 :Ce 3+ , the molar ratio of Gd:Ce is 1:0.

15.

4. The application according to claim 2 or 3, it is characterized in that NaGdF 4 :Nd 3+ @NaGdF 4 :Ce 3+ In it, the molar ratio of Gd:Nd in the core layer to Gd:Ce in the shell layer is 1:(0.05 - 0.15):1:0.

15.

5. The application according to claim 1, it is characterized in that the preparation of the rare earth frequency conversion material comprises the following steps: (1) According to the core layer NaGdF 4 :Nd 3+ The molar ratio of Gd:Nd:Na:F in it is 1:(0.05 - 0.15):1:4; Weigh Gd(CH 3 CO 2 ) 3 , Nd(CH 3 CO 2 ) 3 , NH 4 F and NaOH respectively; React Gd(CH 3 CO 2 ) 3 , Nd(CH 3 CO 2 ) 3 , oleic acid and octadecene mixture by heating for the first reaction to form a rare earth-oleic acid complex; then add NH 4 F and NaOH to the rare earth-oleic acid complex and stir, followed by a second reaction. After the reaction is completed, cool to room temperature, add ethanol for centrifugal separation, wash and dry with cyclohexane and ethanol to obtain the core layer NaGdF 4 :Nd 3+ ; (2) According to the shell being NaGdF 4 :Ce 3+ in which the molar ratio of Gd:Ce:Na:F is 1:0.15:1:4; Weigh out Gd(CH 3 CO 2 ) 3 , Ce(CH 3 CO 2 ) 3 , NH 4 F and NaOH respectively; Heat the mixture of Gd(CH 3 CO 2 ) 3 , Ce(CH 3 CO 2 ) 3 , oleic acid and octadecene for the third reaction to form rare earth-oleic acid complexes; then add the core layer NaGdF 4 :Nd 3+ obtained in step (1) to the rare earth-oleic acid complexes, then add NH 4 F and NaOH and stir, followed by the fourth reaction; after the reaction is completed, cool to room temperature, add ethanol for centrifugal separation, wash and dry with cyclohexane and ethanol to obtain NaGdF 4 :Nd 3+ @NaGdF 4 :Ce 3+ .

6. The application according to claim 5, it is characterized in that In step (1), the temperature of the first reaction is 120 - 150 °C, and the time is 0.5 - 1 h; the stirring temperature is 25 - 50 °C, and the time is 30 minutes; the temperature of the second reaction is 280 - 310 °C, and the time is 1.5 h.

7. The application according to claim 5, it is characterized in that In step (2), the temperature of the third reaction is 120 - 150 °C, and the time is 0.5 - 1 h; the stirring temperature is 25 - 50 °C, and the time is 30 minutes; the temperature of the fourth reaction is 280 - 310 °C, and the time is 1.5 h.

8. The application according to claim 5, it is characterized in that in steps (1) and (2), the volume ratio of oleic acid to octadecene is both 2:

3.

9. The application according to claim 5, it is characterized in that NaGdF 4 :Nd 3+ @NaGdF 4 :Ce 3+ In, the molar ratio of Gd:Nd in the core layer to Gd:Ce in the shell layer is 1:(0.05 - 0.15):1:0.15.

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