Method for plasma-assisted sintering of calcium stannate short-wave infrared long afterglow powder

Abstract

The invention relates to a method for plasma-assisted sintering of calcium stannate short-wave infrared long afterglow powder, the chemical composition of the long afterglow powder is Ca2SnO4: xEr < 3 + > / Pr < 3 + > / Nd < 3 + >, and x is more than or equal to 0.1 and less than or equal to 1; the long afterglow powder takes calcium stannate as a matrix and is formed by doping and sintering rare earth capable of emitting red light. The sintering adopts a stir-frying plasma assisted low-temperature sintering method, compounds containing an erbium element, a praseodymium element and a neodymium element are doped, namely erbium trioxide, praseodymium trioxide and neodymium oxide, and H3BO3 is added as a fluxing agent to prepare a sample. The method is low in energy consumption, and the yield of the calcium stannate fluorescent powder is effectively improved; according to the invention, short-wave infrared long-afterglow luminescence of doped ions is realized, and the emission wavelength is adjustable from 800nm to 1600nm.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of luminescent materials, and particularly relates to a preparation method of short-wave infrared long-afterglow powder based on calcium stannate. BACKGROUND

[0002] Rare earth activated alkaline earth aluminates, silicates are the most studied and widely used fluorescent materials in recent years. However, the luminescence color of the fluorescent system based on aluminates and silicates is concentrated in the blue-green band (mainly in the range of 440-520 nm), and the research on red and near-infrared luminescent materials (such as CN118308106A-a hexagonal aluminate near-infrared luminescent material and a preparation method and application) is very few. On the other hand, this kind of system is not stable when meeting water. Alkaline earth metal stannate fluorescent powder is considered to be a fluorescent powder with high energy conversion efficiency, which is often used in the preparation of visible light fluorescent powder (CN108148581A). In Ca2SnO4, SnO6 octahedra are connected together in a low-dimensional form, and it is easy to inject other ions into the main crystal lattice and create traps at a suitable depth to store excitation energy and emit light when reactivated at room temperature. Moreover, Ca2SnO4 is very stable in physics and chemistry.

[0003] There are many sintering methods for calcium stannate-based fluorescent powder. For example, a samarium-zirconium co-doped calcium stannate white light fluorescent powder reported in CN111100638A is prepared by soft chemical sintering, but there are many chemical impurities. The physical preparation method such as high-temperature solid phase method uses a very high temperature (1400℃), which is not environmentally friendly. Therefore, many low-temperature and low-energy sintering methods have appeared. For example, CN106433641A reports that low-temperature calcination can be achieved using a mixed atmosphere containing CO and CO2. However, the toxicity of CO increases the safety risk of the experiment; and the preparation does not consider excluding CO2 generated by calcination decomposition, which is not conducive to the formation of stable crystal phase of rare earth ion doping. In recent years, spark plasma sintering (CN119930151A) is another sintering technology that has attracted widespread attention. This method applies high voltage to the compacted powder to break down the powder and enhance the surface activity of the powder to promote doping. However, the need for mechanical high pressure leads to powder caking, which requires regrinding, increasing the process, and the limitation of high-pressure containers limits the production efficiency. In CN102584202A, it is proposed to use plasma heating solution spraying to realize chemical reaction sintering, which can obtain nanoscale visible light three-primary color fluorescent powder, effectively improving the energy utilization rate. However, this method has problems such as incomplete reaction, impure product, and inability to prepare micron-sized powder required for high-brightness fluorescent.

[0004] In recent years, due to some special applications of short-wave infrared (900-1700 nm) in military, anti-counterfeiting and biological imaging, the demand for long afterglow luminescent materials in the short-wave infrared spectral region is increasing. As reported in CN202410916691, a Cr 3+ doped gallium germanate near-infrared long afterglow luminescent material. In order to achieve high yield of low temperature and low energy consumption sintering of short-wave infrared long afterglow fluorescent powder, this invention proposes a means of preparing calcium stannate short-wave infrared long afterglow fluorescent powder by combining rolling cavity with plasma assisted low temperature sintering. SUMMARY

[0005] In order to overcome the shortcomings of the prior art, the present invention provides a method for plasma assisted sintering of calcium stannate short-wave infrared long afterglow powder, which uses a method of plasma assisted low temperature sintering to prepare calcium stannate as a matrix, doped with Er 3+ , Pr 3+ , Nd 3 + ions, which realizes short-wave infrared long afterglow luminescence of doped ions with adjustable emission wavelength from 800 nm to 1600 nm.

[0006] The technical scheme adopted by the present invention to solve its technical problems is:

[0007] A method for plasma assisted sintering of calcium stannate short-wave infrared long afterglow powder, the chemical composition of the long afterglow powder is Ca2SnO4: xEr 3+ / Pr 3+ / Nd 3+ , wherein 0.1≤x≤1; the long afterglow powder is sintered with calcium stannate as a matrix doped with rare earth elements that can cause red luminescence.

[0008] Further, the rare earth element erbium that causes red emission is 0.1-1% of the molar mass of the matrix calcium stannate, the rare earth element praseodymium is 0.1-1% of the molar mass of the matrix calcium stannate, and the rare earth element neodymium is 0.1-1% of the molar mass of the matrix calcium stannate.

[0009] Still further, the sintering uses a method of plasma assisted low temperature sintering, and the compounds containing erbium, praseodymium and neodymium are common erbium sesquioxide, praseodymium sesquioxide and neodymium sesquioxide, and H3BO3 (about 5%) is added as a fluxing agent to prepare the sample.

[0010] Preferably, the method of plasma assisted low temperature sintering comprises the following steps:

[0011] (1) according to the general formula Ca2SnO4: xEr 3+ / Pr 3+ / Nd 3+The raw materials of calcium source, tin source, erbium source, praseodymium source and neodymium source are weighed according to the stoichiometric ratio by weight respectively;

[0012] (2) The raw materials weighed in step (1) are mixed with anhydrous ethanol, ground uniformly, and dried to obtain the precursor;

[0013] (3) After grinding, the powder is placed in a calcination box, the calcination temperature is set to 700-900 DEG C, and high-temperature sintering is carried out for 2-4 hours, and the mixture is calcined in an air atmosphere to obtain a sintered body;

[0014] (4) The pre-combustion powder is placed on the inner wall of the cylindrical powder holder, and an atmosphere with a molar ratio of N2:O2=2-5 is introduced, and the vacuum degree is maintained at 5-30 Pa;

[0015] (5) The powder is sintered at 700-900 DEG C for 1-3 hours under the assistance of 80-150 W plasma, and then naturally cooled to room temperature to form a short-wave infrared fluorescent powder.

[0016] The present application adopts a sintering method assisted by plasma bombardment to activate the powder. The method uses a cylindrical tumbling powder holder to fully bombard each part of the powder with plasma, thereby improving the yield of the fluorescent powder.

[0017] In step (1), the sources of the raw materials are as follows: the calcium source is calcium carbonate; the tin source is tin oxide; the erbium source is erbium oxide; the praseodymium source is praseodymium oxide; and the neodymium source is neodymium oxide.

[0018] In step (2), the amount of anhydrous ethanol used is 0%-100% of the total weight of the raw materials.

[0019] The raw material mixture also contains a fluxing additive, and the fluxing additive is H3BO3 (about 5%).

[0020] The vacuum chamber used is quartz glass, and there is a cylindrical powder holder in the chamber for holding the powder. The powder holder is slowly rotated by a transmission device, and is made of corundum, zirconia, etc. The inner wall of the powder holder has a height of 1-3 cm of wrinkles. The calcined raw materials in steps (3) and (5) are not used in a crucible, but are directly placed on the inner wall of the powder holder. During sintering, the cylindrical powder holder is slowly rotated at a speed of 3-6 r / min, so that the powder is continuously stirred under the bombardment of plasma.

[0021] The short-wave infrared long-persistence powder prepared by the present application can be applied to the fields of night monitoring, biomedical imaging, marking and tracing, anti-counterfeiting encryption, etc.

[0022] The beneficial effects of the present application mainly include:

[0023] 1. Low energy consumption. The method is a sintering method mainly using resistance heating sintering and assisted by plasma bombardment to activate the powder. Compared with the power consumption of 5 kW of the traditional high-temperature solid-phase method, the power consumption of the method is only 2.5 kW.

[0024] 2. High brightness. The brightness of the prepared fluorescent powder is increased by 20% compared with the product of the high-temperature solid-phase method. Since the rolling cavity is used to make each part of the powder fully subjected to the bombardment of the plasma, the method can effectively improve the yield of calcium stannate fluorescent powder, protect the calcium stannate powder matrix from decomposition, has low requirements for production equipment and no pollution, and is expected to produce huge social and economic benefits, and is suitable for industrialization. 3+ , Pr 3+ and Er 3+ Three Ln 3+ ion strong short-wave infrared long afterglow luminescence, and the emission wavelength is adjustable from ~800 nm to ~1600 nm. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a diagram of a plasma-assisted sintering device.

[0026] Figure 2 is a diagram of a cylindrical powder holder device.

[0027] Figure 3 is a calcium stannate doped with erbium fluorescent powder morphology diagram.

[0028] Figure 4 is a calcium stannate doped with praseodymium fluorescent powder morphology diagram.

[0029] Figure 5 is a calcium stannate doped with neodymium fluorescent powder morphology diagram.

[0030] Figure 6 is a calcium stannate doped with erbium fluorescent spectrum.

[0031] Figure 7 is a calcium stannate doped with praseodymium fluorescent spectrum.

[0032] Figure 8 is a calcium stannate doped with neodymium fluorescent spectrum. DETAILED DESCRIPTION

[0033] The application will be further described below with reference to the drawings.

[0034] Referring to Figures 1-8 , a method for plasma-assisted sintering of calcium stannate short-wave infrared long afterglow powder, the chemical composition of the long afterglow powder is Ca2SnO4:xEr 3+ / Pr 3+ / Nd 3+ , wherein 0.1≤x≤1; the long afterglow powder is a calcium stannate matrix sintered by rare earth doping which can cause red luminescence.

[0035] Further, the rare earth element erbium is 0.1-1% of the molar mass of the base calcium stannate, the rare earth element praseodymium is 0.1-1% of the molar mass of the base calcium stannate, and the rare earth element neodymium is 0.1-1% of the molar mass of the base calcium stannate.

[0036] Still further, the sintering uses a plasma-assisted low-temperature sintering method, and the compound containing the erbium element, the praseodymium element, and the neodymium element is commonly used as erbium oxide, praseodymium oxide, and neodymium oxide. H3BO3 (about 5%) is added as a fluxing agent to prepare the sample.

[0037] The process of the plasma-assisted low-temperature sintering method is as follows: calcium stannate powder is sintered by using plasma-assisted low-temperature sintering, and the rare earth raw materials to be doped, erbium oxide, praseodymium oxide, and neodymium oxide are mixed with calcium carbonate and tin dioxide powder in a proportion required in a garnet mortar to form a uniform mixture. Anhydrous ethanol is added as a grinding aid, and the mixture is fully ground and uniformly mixed. After drying, the precursor is obtained. The mixed powder is pre-combusted, and is kept at 900°C for 2 hours in air. The pre-combusted powder is ground into fine powder again, and is directly dispersed on the inner wall of a cylindrical powder holder 2 in a vacuum chamber 1 as shown in Figure 1 The vacuum degree of the chamber is 5-30 Pa, a mixed gas 3 with a nitrogen-oxygen molar ratio of 2-5 is introduced, and the gas is generally nitrogen or argon. Then, a plasma generator 4 with a power of 80-150 W is used to generate plasma to fill the vacuum chamber, and a heater 5 is used to heat the chamber to 900°C for sintering for 3 hours. In order to allow the plasma to fully bombard the powder, the vacuum chamber is made of quartz glass, and a transmission device 6 is used to rotate the powder holder at a speed of 3-6 r / min. As shown in Figure 2 The cylindrical powder holder 1 is made of corundum or zirconia. The powder holder is in a cylindrical shape, and the inner wall has a wrinkle protrusion 2 with a height of 1-3 cm. The wrinkle protrusion can be a regular horizontal strip or an irregular hilly protrusion. Regardless of the type, the purpose is to make the powder fall into the recesses on the inner wall, so that the powder is as dispersed as possible in the sintering process to increase the specific surface area, so that the powder is more fully bombarded by the plasma in the chamber. When the cylindrical powder holder is rotated by the transmission arm 3 in the chamber, the powder is brought to a high position by the wrinkle and then falls down, so that the powder is continuously stirred under the bombardment of the plasma, and the uniformity of the rare earth doping is increased. After the sintering is completed, the chamber is naturally cooled to room temperature to form short-wave infrared long-afterglow fluorescent powder. The final product has a fluorescent powder density of 3-4 g / cm3, a particle size distribution of 1-100 um, an excitation wavelength of 250-460 nm, and a luminescence wavelength of 800-1600 nm.

[0038] Example 1

[0039] The process of the plasma-assisted sintering of the white calcium stannate infrared fluorescent powder doped with erbium is as follows:

[0040] Ca2SnO4:Er 3+ short-wave infrared long afterglow phosphor. Stoichiometric CaCO3 and SnO2 powders and 0.8 mol% Er2O3 powder are mixed and ground in a marquise mortar to form a uniform mixture. The purity of calcium carbonate and tin dioxide is required to be AR, and the purity of erbium oxide is required to be 4N. The mixed powder is pre-combusted, and is kept at 900°C for 2h in air. The pre-combusted powder is placed on the inner wall of a cylindrical powder holder, and a gas atmosphere with a molar ratio of N2:O2=2 is introduced. The vacuum degree is 10 Pa, and the powder is sintered at 900°C for 3h under plasma assistance of 100W, and then naturally cooled to room temperature to form a short-wave infrared phosphor with emission wavelengths of 978 nm and 1518 nm.

[0041] Example 2

[0042] Plasma-assisted sintering of praseodymium-doped white calcium stannate infrared phosphor, the process is:

[0043] Ca2SnO4:Pr 3+ short-wave infrared long afterglow phosphor. Stoichiometric CaCO3 and SnO2 powders and 0.2% mol% Pr2O3 powder are mixed and ground in a marquise mortar to form a uniform mixture. The purity of calcium carbonate and tin dioxide is required to be AR, and the purity of erbium oxide is required to be 4N. The mixed powder is pre-combusted, and is kept at 900°C for 2h in air. The pre-combusted powder is placed on the inner wall of a cylindrical powder holder, and a gas atmosphere with a molar ratio of N2:O2=3 is introduced. The vacuum degree is 15 Pa, and the powder is sintered at 900°C for 3h under plasma assistance of 120W, and then naturally cooled to room temperature to form a short-wave infrared phosphor with an emission wavelength of 904 nm.

[0044] Example 3

[0045] Plasma-assisted sintering of praseodymium-doped white calcium stannate infrared phosphor, the process is:

[0046] Ca2SnO4:Nd 3+ short-wave infrared long afterglow phosphor. Stoichiometric CaCO3 and SnO2 powders and 0.1% mol% Nd2O3 powder are mixed and ground in a marquise mortar to form a uniform mixture. The purity of calcium carbonate and tin dioxide is required to be AR, and the purity of erbium oxide is required to be 4N. The mixed powder is pre-combusted, and is kept at 900°C for 2h in air. The pre-combusted powder is placed on the inner wall of a cylindrical powder holder, and a gas atmosphere with a molar ratio of N2:O2=4 is introduced. The vacuum degree is 15 Pa, and the powder is sintered at 900°C for 3h under plasma assistance of 130W, and then naturally cooled to room temperature to form a short-wave infrared phosphor with emission wavelengths of 892 nm and 1076 nm.

[0047] The embodiments of the present specification are merely illustrative of the implementation forms of the inventive concept, and are only used for the purpose of description. The protection scope of the present application should not be regarded as being limited to the specific forms described in the present embodiments, and the protection scope of the present application also encompasses equivalent technical means that can be thought of by those skilled in the art according to the inventive concept.

Claims

1. A method of plasma assisted sintering of calcium stannate short wave infrared long afterglow powder, characterized in that, The chemical composition of the long afterglow powder is Ca2Sn04: xEr 3+ / Pr 3+ / Nd 3+ wherein 0.1≤x≤1; the long afterglow powder is sintered with calcium stannate as a matrix and rare earth doping which can cause red light emission.

2. A method of plasma assisted sintering of calcium stannate short wave infrared long persistent powder as claimed in claim 1 wherein, The rare earth element erbium is 0.1-1% of the molar mass of the calcium stannate matrix, the rare earth element praseodymium is 0.1-1% of the molar mass of the calcium stannate matrix, and the rare earth element neodymium is 0.1-1% of the molar mass of the calcium stannate matrix.

3. A method of plasma assisted sintering of calcium stannate short wave infrared long persistent powder as claimed in claim 1 or 2, wherein, The sintering adopts a plasma-assisted low-temperature sintering method, The compound containing the erbium element, the praseodymium element, and the neodymium element is commonly used erbium trioxide, praseodymium trioxide, and neodymium trioxide, and H3BO3 (about 5%) is added as a fluxing agent to prepare the sample.

4. A method of plasma assisted sintering of calcium stannate short wave infrared long persistent powder as claimed in claim 3 wherein, The plasma-assisted low-temperature sintering method comprises the following steps: (1) Ca2SnO4: xEr 3+ / Pr 3+ / Nd 3+ The raw materials of calcium source, tin source, erbium source, praseodymium source and neodymium source are weighed according to the stoichiometric ratio of general formula Ca2SnO4: xEr (2) The raw materials weighed in step (1) are fully mixed with anhydrous ethanol, ground uniformly, and dried to obtain a precursor; (3) After grinding, the powder is placed in a calcination box, a calcination temperature of 700-900°C is set, high-temperature sintering is performed for 2-4 hours, the mixture is calcined in an air atmosphere, and a sintered body is obtained; (4) The pre-burning powder is placed on the inner wall of a cylindrical powder holder, an atmosphere with a molar ratio of N2:O2=2-5 is introduced, and the vacuum degree is maintained at 5-30 Pa; (5) The powder is sintered at 700-900°C for 1-3 hours under the assistance of 80-150W plasma and then naturally cooled to room temperature to form a short-wave infrared fluorescent powder.

5. A method of plasma assisted sintering of calcium stannate short wave infrared long persistent powder as claimed in claim 4 wherein, In step (1), the sources of the raw materials are as follows: the calcium source is calcium carbonate; the tin source is tin oxide; the erbium source is erbium oxide; the praseodymium source is praseodymium oxide; and the neodymium source is neodymium oxide.

6. A method of plasma assisted sintering of calcium stannate short wave infrared long persistent powder as claimed in claim 4 wherein, In step (2), the amount of anhydrous ethanol used is 0%-100% of the total weight of the raw materials.

7. A method of plasma assisted sintering of calcium stannate short wave infrared long persistent powder as claimed in claim 4 wherein, The raw material mixture also contains a fluxing additive, which is H3BO3.

8. A method of plasma assisted sintering of calcium stannate short wave infrared long persistent powder as claimed in claim 4 wherein, The vacuum chamber used is made of quartz glass, and there is a cylindrical powder holder in the chamber for holding the powder. The powder holder is slowly rotated using a transmission device, and is made of corundum, zirconia, etc. The inner wall of the powder holder has a height of 1-3 cm. In steps (3) and (5), the calcined raw materials are not placed in a crucible but directly on the inner wall of the powder holder. During sintering, the cylindrical powder holder is slowly rotated at a speed of 3-6 r / min, so that the powder is continuously stirred under the bombardment of plasma.

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