A broadband near-infrared fluorescent ceramic and its preparation method and application

Abstract

The present invention provides a broadband near-infrared fluorescent ceramic, a preparation method thereof, and an application thereof, relating to the technical field of luminescent materials. The chemical composition of this broadband near-infrared fluorescent ceramic is MgAl x Si y O z : m Cr 3+ , and the preparation method includes: fully mixing raw materials to obtain a uniform mixture, first pressing the uniform mixture into a green body, then pressing it into a blank and performing a solid-phase reaction under vacuum conditions, and obtaining the broadband near-infrared fluorescent ceramic after cooling. Compared with the prior art, the broadband near-infrared fluorescent ceramic prepared by the present invention can withstand the irradiation of high-power LED / LD excitation light because its thermal conductivity (~10 W / m / K) is much higher than that of organic resin (~0.2 W / m / K). The luminescent device prepared therefrom effectively solves the problem that the organic solidifying glue in the traditional powder packaging device is prone to aging during the long-term high-temperature operation of the LED chip, resulting in a decrease in luminescent performance.

Description

Technical Field

[0001] The present invention relates to the technical field of luminescent materials, and in particular, to a broadband near-infrared fluorescent ceramic, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, broadband near-infrared light sources have broad application prospects in the fields of face recognition, night vision monitoring, deep biomedical imaging, phototherapy, petrochemical industry, polymers, pharmaceuticals, clinical medicine, environmental science, textile industry, and food detection. However, currently commercial broadband near-infrared light sources generally have problems such as low output power and complex device structures, and it is difficult to match emerging high-tech fields. Although the phosphor-converted LED (pc-LED) prepared based on a blue LED chip and an organic-inorganic composite (phosphor + organic resin) near-infrared fluorescence converter is considered to be the best solution to the above problems because of its adjustable spectrum, simple preparation, and low cost. However, the high temperature (>150 °C) during the operation of high-power excitation light sources such as LEDs and laser diodes (LDs) easily causes the aging of organic materials with poor physical and chemical stability and low thermal conductivity, thus hindering the further improvement of the output power of the light source device.

[0003] All-inorganic fluorescence converters such as fluorescent glass, fluorescent glass ceramics, and fluorescent ceramics have been proven to be able to withstand the irradiation of high-power excitation light sources, but the short emission wavelength and narrow spectral bandwidth also limit their wider applications. For example, the patent document CN112266788A discloses a fluorescent glass with a chemical formula of: BaO·aMgO·bAl 2 O 3 ·cCr 2 O 3 whose emission peak is only located at about 710 nm; the patent document CN112646576A discloses a broadband near-infrared fluorescent ceramic with a composition of (Sr 1-y Ba y ) 3 Sc 4-x Cr x O 9 and a preparation method and device thereof. The main peak of the emission spectrum is between 830 and 900 nm under visible light excitation, but the full width at half maximum of the emission spectrum is only 180 nm.

[0004] Currently, new and efficient fluorescent ceramics with longer emission wavelengths and wider spectral coverage are still very lacking. Therefore, the development of related near-infrared fluorescent ceramics, preparation methods, and devices is of great significance for the application of near-infrared light sources. Summary of the Invention

[0005] To overcome the deficiencies of the above prior art, the present invention provides a broadband near-infrared fluorescent ceramic, a preparation method thereof, and an application thereof. The fluorescent ceramic can be prepared by a powder sintering process. Under the excitation of visible light with a wavelength range of 400 - 700 nm, it emits broadband near-infrared light with an emission wavelength range between 600 - 1200 nm, an emission spectrum main peak between 800 - 930 nm, and a full width at half maximum of the emission spectrum greater than 200 nm.

[0006] The present invention provides a preparation method of a broadband near-infrared fluorescent ceramic. The preparation method specifically includes the following steps:

[0007] S1. According to the chemical composition and stoichiometric ratio of the broadband near-infrared fluorescent ceramic, weigh the raw materials, and then fully mix the raw materials to obtain a homogeneous mixture. Among them, the chemical composition of the broadband near-infrared fluorescent ceramic is MgAl x Si y O z : m Cr 3+ , and the parameters x 、 y 、 z 、 m satisfy the following conditions:

[0008] 2.0 ≤ x≤ 4.0, 0.1 < y < 0.4, 4.0 < z < 20.0, 0.01 < m < 0.20;

[0009] S2: Press the homogeneous mixture obtained in S1 into a green body first, and then press it into a blank and carry out a solid-phase reaction under vacuum conditions. After cooling, a broadband near-infrared fluorescent ceramic is obtained. The parameters of the solid-phase reaction are as follows: the vacuum degree is 10 -3 Pa, the temperature is 1400 - 1600 °C, and the time is 4 - 10 h.

[0010] Compared with the prior art, the broadband near-infrared fluorescent ceramic prepared by the present invention can withstand the irradiation of high-power LED / LD excitation light because its thermal conductivity (~10 W / m / K) is much higher than that of organic resin (~0.2 W / m / K). The light-emitting device prepared from it effectively solves the problem that the organic curing glue in the traditional powder packaging device is prone to aging during the long-term high-temperature operation of the LED chip, resulting in a decrease in light-emitting performance. At the same time, compared with the powder material of the same component, the highly dense near-infrared fluorescent ceramic obtained by the present invention can extend the effective propagation distance of the excitation light, increase the probability of Cr 3+ absorbing the excitation light, and thus increase the blue light absorption rate by more than twice.

[0011] In some embodiments, in step S1, the raw material composition includes compounds of Mg, Al, Si, and Cr, and the types of compounds of the above four elements are selected from one of oxides, nitrates, halides, or carbonates.

[0012] In some embodiments, in step S2, the green body is obtained by cold isostatic pressing, and the pressure of cold isostatic pressing is 12 MPa.

[0013] Compared with the prior art, the present invention prepares the green body with the above parameters mainly because: cold isostatic pressing can effectively eliminate the voids between powder particles and improve the density of the green body, which is very important for the subsequent sintering process, because a high-density green body is more likely to form a dense ceramic body during sintering. By adjusting the pressing pressure (12 MPa in this application), the density and microstructure of the green body can be optimized, thereby further improving the performance of the final product.

[0014] In some embodiments, in step S2, the blank is obtained by cold isostatic pressing, and the pressure of cold isostatic pressing is 220 MPa.

[0015] Compared with the prior art, when preparing high-performance ceramic materials, a very high density needs to be achieved to ensure excellent physical and chemical properties of the materials. Cold isostatic pressing under high-pressure conditions can ensure that the pores inside the materials are eliminated to the maximum extent, thereby increasing the density. For the preparation of broadband near-infrared fluorescent ceramics in this application, the use of high-pressure cold isostatic pressing technology at 220 MPa is necessary. It can not only ensure the high density and uniformity of the materials, but also improve the performance and quality of the final product, and is suitable for application fields with extremely high performance requirements.

[0016] Compared with the prior art, the present invention conducts high-temperature solid-phase reaction under high-vacuum conditions, which can effectively remove gas impurities in the raw materials, prevent the formation of bubbles, thereby improving the density and purity of the ceramic materials. For some materials that are prone to oxidation, high-temperature treatment under high-vacuum conditions can reduce the presence of oxygen, prevent the raw materials from being oxidized at high temperatures, and maintain the chemical purity of the materials. On this basis, high-temperature and high-vacuum conditions help to optimize the microstructure of the materials, make the grain growth more uniform, and reduce crystal defects, thereby improving the overall performance of the materials.

[0017] In some embodiments, it further includes step S3. According to the designed dimensions, the broadband near-infrared fluorescent ceramic is polished to finally obtain the broadband near-infrared fluorescent ceramic with the required dimensions.

[0018] The second object of the present invention is to provide a broadband near-infrared fluorescent ceramic prepared according to the above preparation method. When the broadband near-infrared fluorescent ceramic is excited by visible light with a wavelength range of 400 - 700 nm, it emits broadband near-infrared light with an emission wavelength range between 600 - 1200 nm, an emission spectrum main peak between 800 - 930 nm, and a full width at half maximum of the emission spectrum greater than 200 nm.

[0019] Compared with the prior art, the present invention has the following advantages: The near-infrared fluorescent ceramic of the present invention can be effectively excited by visible light between 400 - 700 nm, and can be well matched with the most efficient commercial high-power blue light chips. The emission wavelength range of the near-infrared light can cover up to 1200 nm at most, the main peak position of the emission spectrum can be tuned up to 930 nm at most, and the full width at half maximum of the emission spectrum can be up to 300 nm at most. These properties are superior to those of the vast majority of near-infrared fluorescent powders, fluorescent glasses, fluorescent glass ceramics, and fluorescent ceramics.

[0020] The third object of the present invention is to provide an application of a broadband near-infrared fluorescent ceramic in a broadband near-infrared light-emitting device.

[0021] In some embodiments, the near-infrared light-emitting device includes an excitation light source and a luminescent material. The excitation light source includes a high-power (excitation light power density greater than 1 W / mm 2 ) LED chip or a laser diode with an emission wavelength between 400 - 700 nm. The luminescent material includes the above-mentioned broadband near-infrared fluorescent ceramic. The light-emitting device is prepared by directly covering the broadband near-infrared fluorescent ceramic on the excitation light source, and it emits broadband and long-wavelength near-infrared light under the excitation of the light source. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 XRD patterns of the samples prepared in Comparative Example 1, Example 1, Example 2, and Example 3 of the present invention;

[0023] Figure 2 Emission spectra of the samples prepared in Comparative Example 1, Example 1, Example 5, Example 6, Example 9, and Example 11 of the present invention;

[0024] Figure 3 Spectra of the LED devices encapsulated with the samples prepared in Example 1, Example 5, Example 9, and Example 11 of the present invention combined with 450 nm high-power blue LEDs; DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention is provided in conjunction with the accompanying drawings.

[0026] It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0027] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the present invention's specification, which are obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of this application are merely exemplary.

[0028] The technical effects of the present invention are described below in conjunction with specific embodiments.

[0029] Example 1

[0030] The chemical composition formula of the near-infrared fluorescent ceramic in this example is MgAl 3 Si 0.1 O 6 :0.02Cr 3+ . Weigh magnesium carbonate, aluminum oxide, germanium dioxide, and chromium oxide accurately according to the stoichiometric ratios of the respective elements in the chemical formula as raw materials. Place the uniformly mixed raw materials in the mold of a tablet press. The diameter of the mold is 10 mm. Then apply the pressure of the tablet press to 12 Mpa and hold for 3 minutes. Then demold to obtain a blank. Place the blank in a cold isostatic pressing device, apply a pressure of 220 MPa, hold for 3 minutes, and then release the pressure to obtain a green body after cold isostatic pressing. Place the green body in a titanium crucible and put it in a vacuum sintering furnace with a vacuum degree of 10 -3 Pa. After sintering at 1400 °C for 8 h, wait for the sample to cool, polish it and polish the surface. Finally, obtain a highly dense broadband near-infrared fluorescent ceramic that emits a peak at about 820 nm under excitation at 400 - 700 nm.

[0031] Figure 1 shows the XRD pattern of the sample prepared in this example. From Figure 1 it can be seen that the broadband near-infrared fluorescent ceramic prepared in this example belongs to the cubic crystal phase of the spinel structure.

[0032] Figure 2 shows the emission spectrum of the sample prepared in this example. From Figure 2It can be seen that the broadband near-infrared fluorescent ceramic prepared in this embodiment emits near-infrared light with an emission wavelength range between 600 - 1200 nm, a main peak of the emission spectrum at 820 nm, and a full width at half maximum of the emission spectrum of 300 nm under the excitation of a light source in the range of 400 - 700 nm.

[0033] Through detection, it is known that the blue light absorption efficiency of the sample prepared in this embodiment is 70%.

[0034] Figure 3 Shows the spectrum of the LED device encapsulated with the sample prepared in this embodiment combined with a 450 nm high-power blue LED. From Figure 3 It can be seen that the spectrum of the LED device encapsulated with the sample prepared in this embodiment combined with a 450 nm blue LED covers 650 - 1000 nm and can be applied to related fields such as near-infrared short-wave band detection.

[0035] Example 2

[0036] The chemical composition formula of the near-infrared fluorescent ceramic in this embodiment is MgAl 4.0 Si 0.2 O 10 :0.02Cr 3+ . Except for changing the sintering temperature to 1500 °C and holding for 10 h, other preparation steps and process conditions are the same as those in Example 1. Figure 1 Shows the XRD pattern of the sample prepared in this embodiment. From Figure 1 It can be seen that this compound has a spinel structure. Figure 2 The inset in is a physical picture of the fluorescent ceramic in this embodiment.

[0037] Example 3

[0038] The chemical composition formula of the near-infrared fluorescent ceramic in this embodiment is MgAl 3.5 Si 0.3 O 8 :0.02Cr 3+ . Except for changing the sintering temperature to 1600 °C and holding for 12 h, other preparation steps and process conditions are the same as those in Example 1. The luminescence performance is similar to that of Example 1. Figure 1 Shows the XRD pattern of the sample prepared in this embodiment. From Figure 1 It can be seen that this compound is a pure phase and has a spinel structure.

[0039] Example 4

[0040] The chemical composition formula of the near-infrared fluorescent ceramic in this embodiment is MgAl 2.5 Si 0.3 O 6 :0.06Cr 3+。The preparation steps and process conditions are the same as those in Example 1. Through testing, it can be known that the main peak position of the emission spectrum of the sample prepared in this example is at 870 nm, the full width at half maximum of the emission spectrum is 240 nm. After further testing, it can be known that the blue light absorption efficiency of the sample prepared in this example is 77%.

[0041] Example 5

[0042] The chemical composition formula of the near-infrared fluorescent ceramic in this example is MgAl 4.0 Si 0.35 O 10 :0.04Cr 3+ 。Its preparation steps and process conditions are the same as those in Example 2. Figure 2 shows the emission spectrum of the sample prepared in this example. From Figure 2 it can be known that the main peak position of the emission spectrum prepared in this example is at 850 nm, the full width at half maximum of the emission spectrum is 260 nm, and after further testing, it can be known that the blue light absorption efficiency of the sample prepared in this example is 72%.

[0043] Figure 3 shows the electroluminescence spectrum of the device obtained by packaging the sample prepared in this example with a 450 nm high-power blue LED chip, which is consistent with the photoluminescence spectrum.

[0044] Example 6

[0045] The chemical composition formula of the near-infrared fluorescent ceramic in this example is MgAl 3.5 Si 0.1 O 8 :0.10Cr 3+ 。Its preparation steps and process conditions are the same as those in Example 3. Figure 2 shows the emission spectrum of the sample prepared in this example. From Figure 2 it can be known that the main peak position of the emission spectrum of the sample prepared in this example is at 930 nm, the full width at half maximum of the emission spectrum is 200 nm, and after further testing, it can be known that the blue light absorption efficiency of the sample prepared in this example is 85%.

[0046] Example 7

[0047] The chemical composition formula of the near-infrared fluorescent ceramic in this example is MgAl 2.5 Si 0.25 O 7 :0.03Cr 3+Except that the sintering temperature was changed to 1550 °C and held for 11 h, the other preparation steps and process conditions were the same as those in Example 1. Through detection, it can be known that the main peak position of the emission spectrum of the sample prepared in this example is at 830 nm, the full width at half maximum of the emission spectrum is 250 nm, and through further detection, it can be known that the blue light absorption efficiency of the sample prepared in this example is 72%.

[0048] Example 8

[0049] The chemical composition formula of the near-infrared fluorescent ceramic in this example is MgAl 3.2 Si 0.2 O 8 :0.04Cr 3+ Except that the sintering temperature was changed to 1450 °C and held for 7 h, the other preparation steps and process conditions were the same as those in Example 1. Through detection, it can be known that the main peak position of the emission spectrum of the sample prepared in this example is at 850 nm, the full width at half maximum of the emission spectrum is 260 nm, and through further detection, it can be known that the blue light absorption efficiency of the sample prepared in this example is 73%.

[0050] Example 9

[0051] The chemical composition formula of the near-infrared fluorescent ceramic in this example is MgAl 3.8 Si0.3O 15 :0.08Cr 3+ Except that the sintering temperature was changed to 1550 °C and held for 8 h, the other preparation steps and process conditions were the same as those in Example 1. Figure 2 The emission spectrum of the sample prepared in this example is shown. From Figure 2 it can be known that the main peak position of the emission spectrum of the sample prepared in this example is at 880 nm, the full width at half maximum of the emission spectrum is 210 nm, and through further detection, it can be known that the blue light absorption efficiency of the sample prepared in this example is 80%.

[0052] Figure 3 The electroluminescence spectrum of the device obtained by packaging the sample prepared in this example with a 450 nm high-power blue LED chip is shown, which is consistent with the photoluminescence spectrum.

[0053] Example 10

[0054] The chemical composition formula of the near-infrared fluorescent ceramic in this example is MgAl 3.0 Si 0.25 O 12 :0.10Cr 3+Except that the sintering temperature was changed to 1600 °C and held for 9 h, other preparation steps and process conditions were the same as those in Example 1. It was found through testing that the main peak position of the emission spectrum of the sample prepared in this example was at 930 nm, the full width at half maximum of the emission spectrum was 200 nm, and further testing showed that the blue light absorption efficiency of the sample prepared in this example was 83%.

[0055] Example 11

[0056] The chemical composition formula of the near-infrared fluorescent ceramic in this example is MgAl 3.6 Si 0.25 O 13 :0.06Cr 3+ Except that the sintering temperature was changed to 1400 °C and held for 12 h, other preparation steps and process conditions were the same as those in Example 1. Figure 2 The emission spectrum of the sample prepared in this example is shown. It can be seen from Figure 2 that the main peak position of the emission spectrum of the sample prepared in this example was at 860 nm, the full width at half maximum of the emission spectrum was 230 nm, and further testing showed that the blue light absorption efficiency of the sample prepared in this example was 77%.

[0057] Figure 3 The electroluminescence spectrum of the device obtained by encapsulating the sample prepared in this example with a 450 nm high-power blue LED chip is shown, which is consistent with the photoluminescence spectrum.

[0058] Comparative Example 1

[0059] The material described in this comparative example is a near-infrared fluorescent powder material, and the chemical formula of the compound it contains is: MgAl 3 Si 0.1 O 6 :0.02Cr 3+ Magnesium oxide, aluminum oxide, silicon dioxide and chromium oxide were accurately weighed respectively according to the stoichiometric ratios of the elements in the chemical formula as raw materials. After grinding and mixing evenly, they were transferred to a corundum crucible and placed in a tubular furnace with a mixed gas of nitrogen and hydrogen, and sintered at 1550 °C for 6 h. After cooling, a broadband near-infrared fluorescent powder material could be obtained.

[0060] Figure 1 The XRD pattern of the sample prepared in this comparative example is shown. It can be seen from Figure 1 that the crystal form of the powder sample is consistent with the crystal form of the solid ceramic structure, both of which are spinel structures.

[0061] Figure 2 The emission spectrum of the sample prepared in this comparative example is shown. It can be seen from Figure 2It can be seen that since the composition of the sample in this comparative example is exactly the same as that in Example 1, the emission spectrum of the sample prepared in this comparative example is consistent with the spectrum of the sample prepared in Example 1. Under the excitation of 450 nm blue light, the peak position of the emission spectrum is at 820 nm.

[0062] However, it is known through detection that the blue light absorption efficiency of the sample prepared in this comparative example is 35%.

[0063] It can be seen from the results of Comparative Example 1 and Example 1 that the present invention can adjust the spectral range and luminescence performance through process conditions such as different element selections and ratios, different heat treatment temperatures and durations.

[0064] Although the present invention is disclosed as above, the protection scope disclosed by the present invention is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention disclosed, and these changes and modifications will all fall within the protection scope of the present invention.

Claims

1. A method for preparing a broadband near-infrared fluorescent ceramic, characterized in that: The preparation method specifically comprises the following steps: S1. According to the chemical composition and stoichiometric ratio of the broadband near-infrared fluorescent ceramic, the raw materials are weighed, and then the raw materials are fully mixed to obtain a uniform mixture, wherein the chemical composition of the broadband near-infrared fluorescent ceramic is MgAl x Si y O z :mCr 3+ , the parameters x, y, z, and m satisfy the following conditions: 2.0≤x≤4.0, 0.1<y<0.4, 4.0<z<20.0, 0.01<m<0.20; S2: The uniform mixture obtained in S1 is first pressed into a green embryo, then pressed into a blank and subjected to solid phase reaction under vacuum conditions. After cooling, a broadband near-infrared fluorescent ceramic is obtained. The parameters of the solid phase reaction are as follows: the vacuum degree is 10 -3 Pa, temperature is 1400-1600℃, time is 4-10h; In the step S2, the green embryo is obtained by cold isostatic pressing, and the pressure of the cold isostatic pressing is 12 MPa; In the step S2, the blank is obtained by cold isostatic pressing, and the pressure of the cold isostatic pressing is 220 MPa.

2. The method for preparing the broadband near-infrared fluorescent ceramic according to claim 1, characterized in that: In step S1, the composition of the raw materials includes Mg compounds, Al compounds, Si compounds and Cr compounds, and the types of the compounds of the above four elements are selected from one of oxides, nitrates, halides or carbonates.

3. The method for preparing the broadband near-infrared fluorescent ceramic according to claim 1, characterized in that: The method also includes step S3. grinding and polishing the broadband near-infrared fluorescent ceramic according to the designed size, and finally obtaining the broadband near-infrared fluorescent ceramic of the required size.

4. A broadband near-infrared fluorescent ceramic, characterized in that: Prepared according to any one of the preparation methods described in claims 1-3.

5. Use of the broadband near-infrared fluorescent ceramic according to claim 4 in a broadband near-infrared light-emitting device.

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