Fluorophosphate-based red fluorescent materials, their preparation methods and applications

Abstract

This invention discloses a fluorophosphate-based red fluorescent material, its preparation method, and its application. The fluorophosphate-based red fluorescent material has the chemical composition shown in formula (1): K 2+2x Ca 1‑y‑ x Eu y PO4F(1), where 2+2x represents the mole fraction of K, y represents the mole fraction of Eu, 1-y-x represents the mole fraction of Ca, 0≤x≤0.2, 0.005≤y≤0.02. This fluorophosphate-based red fluorescent material emits red fluorescence with a strongest emission peak at a wavelength of 660nm when excited by light in the 300–470nm wavelength range.

Description

Technical Field

[0001] This invention relates to a fluorophosphate-based red fluorescent material, its preparation method, and its application. Background Technology

[0002] Inorganic rare earth light-converting materials have been widely used in various fields such as white LED lighting, liquid crystal displays, laser projection, plant lighting, and light-converting agricultural greenhouse films due to their unique electronic energy level structure, excellent luminescence performance, and good chemical stability.

[0003] Among them, Eu has 4f-5d transition characteristics 2+ A series of red phosphors allow for controllable adjustment of their luminescent properties by altering the matrix composition. Currently commercially available red phosphors include (Ba,Ca,Sr)₂Si₅N₈:Eu 2+ and (Ca,Sr)AlSiN3:Eu 2+ The series of phosphors all exhibit excellent luminous efficiency and chemical stability, playing a crucial role in improving the color rendering index and optimizing the color temperature of white LEDs. However, due to the limited availability of commercially available yellow aluminate phosphors (YAG:Ce... 3+ The emission spectrum (specifically 500–750 nm) of the nitride red phosphor (CASN: Eu) is similar to that of the nitride red phosphor. 2+ The excitation spectra of these two phosphors (specifically 350–650 nm) overlap significantly. When these two phosphors are co-encapsulated into a white LED, a severe reabsorption effect occurs between them, which leads to a decrease in the luminous efficacy of the LED.

[0004] CN106544029A discloses a fluorinated phosphate red phosphor and its preparation method. The fluorinated phosphate red phosphor has the following chemical formula: Na2EuPO4F2. The phosphor emits red light at about 614nm when excited by near-ultraviolet light at about 398nm and blue light at about 467nm, and is used for white LEDs.

[0005] CN103289702B discloses a fluorophosphate-based red phosphor, its preparation method, and its application. The chemical formula of the phosphor is Ca3La. 1-x Eu x F6PO4, 0.001≤x≤0.5; containing Ca 2+ La 2+ Eu 3+ F - P 5+ The compound was used as a raw material and prepared by high-temperature solid-state reaction or chemical solution method. The fluorophosphate-based red phosphor exhibits an emission peak around 613 nm under ultraviolet light excitation of 250–350 nm.

[0006] The emission peak wavelengths of the two fluorophosphate-based red phosphors mentioned above are within 615 nm, which is still close to orange-red light.

[0007] Therefore, it is necessary to develop red phosphors with large Stokes shifts and optimize Eu. 2+ Improving the excitation and luminescence properties of white LEDs and reducing the reabsorption effect with commercial phosphors is of great significance for solving the problem of reduced luminous efficacy of white LEDs.

[0008] Furthermore, only a portion of the blue and red light components of the solar spectrum can be absorbed by photosynthetic pigments in plant chloroplasts, and ultraviolet light has minimal impact on plant photosynthesis. Therefore, developing ultraviolet-excited red rare-earth phosphors can be applied to agricultural greenhouse films. Utilizing the light-conversion function of rare-earth phosphors, unwanted ultraviolet light can be converted into the red light needed by plants, further improving the utilization rate of sunlight and thus optimizing the plant growth cycle. This plays a significant role in increasing the yield and quantity of agricultural products. Summary of the Invention

[0009] In view of this, one object of the present invention is to provide a fluorophosphate-based red fluorescent material. Another object of the present invention is to provide a method for preparing a fluorophosphate-based red fluorescent material. Yet another object of the present invention is to provide applications of the fluorophosphate-based red fluorescent material as described above.

[0010] On the one hand, the present invention provides a fluorophosphate-based red fluorescent material having a chemical composition as shown in formula (1):

[0011] K 2+2x Ca 1-y-x Eu y PO4F(1),

[0012] Where 2+2x represents the mole fraction of K, y represents the mole fraction of Eu, 1-yx represents the mole fraction of Ca, 0≤x≤0.2, and 0.005≤y≤0.02.

[0013] In the fluorophosphate-based red fluorescent material of the present invention, preferably, 0.007 ≤ y ≤ 0.015.

[0014] The fluorophosphate-based red fluorescent material of the present invention preferably emits red fluorescence with the strongest emission peak located at a wavelength of 660 nm when excited by light in the 300-470 nm wavelength band.

[0015] The fluorophosphate-based red fluorescent material of the present invention preferably has an optimal excitation wavelength of 350 nm and a strongest emission peak at a wavelength of 660 nm.

[0016] The fluorophosphate-based red fluorescent material according to the present invention preferably has the following chemical composition:

[0017] K2Ca 0.993 Eu 0.007 PO4F;

[0018] K 2.1 Ca 0.943 Eu 0.007 PO4F;

[0019] K 2.2 Ca 0.893 Eu 0.007 PO4F;

[0020] K 2.3 Ca 0.843 Eu 0.007 PO4F;

[0021] K 2.4 Ca 0.793 Eu 0.007 PO4F.

[0022] The fluorophosphate-based red fluorescent material of the present invention is preferably prepared from potassium fluoride, potassium carbonate, calcium hydrogen phosphate, europium oxide and diammonium hydrogen phosphate as reactants; wherein the molar ratio of potassium fluoride, potassium carbonate, calcium hydrogen phosphate, europium oxide and diammonium hydrogen phosphate is 1:(0.5+x):(1-yx):0.5y:(y+x), 0≤x≤0.2, 0.005≤y≤0.02.

[0023] On the other hand, the present invention also provides a method for preparing the fluorophosphate-based red fluorescent material as described above, comprising the following steps:

[0024] Based on the composition of fluorophosphate-based red fluorescent materials, with K... + Ca 2+ Eu 3+ F - PO4 3- The compound was prepared by high-temperature solid-state reaction using the compound as a raw material.

[0025] According to the preparation method of the present invention, preferably, potassium fluoride, potassium carbonate, calcium hydrogen phosphate, europium oxide and diammonium hydrogen phosphate are mixed to obtain a mixed raw material; under a reducing atmosphere, the mixed raw material is prepared by a high-temperature solid-state reaction method to obtain a fluorophosphate-based red fluorescent material; wherein, the molar ratio of potassium fluoride, potassium carbonate, calcium hydrogen phosphate, europium oxide and diammonium hydrogen phosphate is 1:(0.5+x):(1-yx):0.5y:(y+x), 0≤x≤0.2, 0.005≤y≤0.02.

[0026] According to the preparation method of the present invention, preferably, the reaction temperature of the high-temperature solid-phase reaction method is 900-1200℃ and the reaction time is 4-6h.

[0027] In another aspect, the present invention also provides the application of the fluorophosphate-based red fluorescent material as described above in the preparation of white LED lamps or agricultural greenhouse films.

[0028] The fluorophosphate-based red fluorescent material of this invention emits red fluorescence with a strongest emission peak at a wavelength of 660 nm when excited by light in the 300–470 nm wavelength range, exhibiting a large Stokes shift. This fluorophosphate-based red fluorescent material can be effectively excited by ultraviolet light. The optimal excitation wavelength is 350 nm. The fluorophosphate-based red fluorescent material of this invention also exhibits good thermal stability.

[0029] The fluorophosphate-based red fluorescent material of the present invention does not overlap with the emission spectrum of commercial yellow phosphors, and there is basically no reabsorption effect between the two. The supplemented red light component will also have a certain effect on improving the color rendering index of white LED lamps.

[0030] Instruction manual illustrations

[0031] Figure 1 The images show the XRD patterns of the fluorophosphate-based red fluorescent materials prepared in Examples 1-5.

[0032] Figure 2 The images show the excitation spectra of the fluorophosphate-based red fluorescent materials prepared in Examples 1-5.

[0033] Figure 3 The emission spectra of the fluorophosphate-based red fluorescent materials prepared in Examples 1-5 are shown.

[0034] Figure 4 The results show the thermal stability test results of the fluorophosphate-based red fluorescent materials prepared in Examples 1-5. Detailed Implementation

[0035] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0036] <Fluorophosphate-based red fluorescent materials>

[0037] The fluorophosphate-based red fluorescent material of the present invention has the chemical composition shown in formula (1):

[0038] K 2+2x Ca 1-y-x Eu y PO4F(1),

[0039] Where 2+2x represents the mole fraction of K, 0≤x≤0.2, 1-yx represents the mole fraction of Ca, and y is the mole fraction of Eu, 0.005≤y≤0.02.

[0040] This invention discovers that by substituting a specific amount of Eu for Ca, the resulting fluorophosphate-based red fluorescent material exhibits a large Stokes shift. Simultaneously, the non-equivalent substitution of Ca with K effectively repairs cation vacancy defects in the crystal, thereby significantly improving the luminescence performance of the fluorescent material. The luminescent center of this fluorophosphate-based red fluorescent material is Eu. 2+ (Trivalent europium in the raw material is reduced), the excitation spectrum ranges from 300 to 470 nm, the optimal excitation wavelength is 350 nm, and the strongest emission peak is located at 660 nm. 660 nm is pure red light. The excitation spectrum (300–470 nm) of this fluorophosphate-based red fluorescent material does not overlap with the emission spectrum (500–750 nm) of commercially available yellow phosphors, and there is no reabsorption effect between them. The added red light component also has a certain effect on improving the color rendering index of white LED lamps. Furthermore, this fluorophosphate-based red fluorescent material can be effectively excited by ultraviolet light, converting unwanted ultraviolet light into beneficial red light for plants.

[0041] In this invention, 0 ≤ x ≤ 0.2, preferably 0.01 ≤ x ≤ 0.15, and more preferably 0.05 ≤ x ≤ 0.15. According to a specific embodiment of the invention, x = 0.1.

[0042] In this invention, 0.005 ≤ y ≤ 0.02, preferably 0.006 ≤ y ≤ 0.015, even more preferably 0.007 ≤ y ≤ 0.015, and even more preferably 0.007 ≤ y ≤ 0.008. According to a specific embodiment of the invention, y = 0.007.

[0043] The fluorophosphate-based red fluorescent material of the present invention has the following chemical composition:

[0044] K2Ca 0.993 Eu 0.007 PO4F;

[0045] K 2.1 Ca 0.943 Eu 0.007 PO4F;

[0046] K 2.2 Ca 0.893 Eu 0.007 PO4F;

[0047] K 2.3 Ca 0.843Eu 0.007 PO4F;

[0048] K 2.4 Ca 0.793 Eu 0.007 PO4F.

[0049] The emission spectrum of the fluorophosphate-based red fluorescent material of the present invention is in the range of 500–850 nm, with the strongest emission peak located at a wavelength of 660 nm.

[0050] The fluorophosphate-based red fluorescent material of the present invention has good thermal stability. When the temperature rises to 200°C, its luminescence intensity can still be maintained at more than 60% of the initial luminescence intensity.

[0051] In some embodiments, the fluorophosphate-based red fluorescent material of the present invention is prepared from potassium fluoride, potassium carbonate, calcium hydrogen phosphate, europium oxide and diammonium hydrogen phosphate as reactants; wherein the molar ratio of potassium fluoride, potassium carbonate, calcium hydrogen phosphate, europium oxide and diammonium hydrogen phosphate is 1:(0.5+x):(1-yx):0.5y:(y+x), 0≤x≤0.2, 0.005≤y≤0.02.

[0052] <Preparation Method>

[0053] The preparation method of the fluorophosphate-based red fluorescent material of the present invention includes the following steps: a high-temperature solid-phase reaction experimental step. Optionally, it further includes: a raw material grinding step, and a product grinding and sieving step. A detailed description follows.

[0054] Raw material grinding steps

[0055] Based on the chemical composition of the fluorophosphate-based red fluorescent material, weigh out the corresponding amount containing K. + Ca 2+ Eu 3+ F - PO4 3- The compound is used as a raw material for grinding, which can be done in an agate mortar to obtain the ground raw material.

[0056] The mixed raw materials can be dry-milled or wet-milled by adding anhydrous ethanol. This is beneficial for obtaining fluorophosphate-based red fluorescent materials with good luminescence properties and large Stokes shift.

[0057] In some specific implementation schemes, the raw materials contain K + The compounds are potassium fluoride and potassium carbonate, containing Ca. 2 + The compound is calcium hydrogen phosphate, containing Eu. 3+ The compound is europium oxide, containing PO4. 3-The compounds are calcium hydrogen phosphate and diammonium hydrogen phosphate, containing F. - The compound is potassium fluoride.

[0058] According to one embodiment of the present invention, the molar ratio of potassium fluoride, potassium carbonate, calcium hydrogen phosphate, europium oxide and diammonium hydrogen phosphate is 1:(0.5+x):(1-yx):0.5y:(y+x), 0≤x≤0.2, 0.005≤y≤0.02.

[0059] Experimental Procedure of High Temperature Solid-Phase Reaction Method

[0060] Based on the chemical composition of fluorophosphate-based red fluorescent materials, with K... + Ca 2+ Eu 3+ F - PO4 3- The compound was used as a raw material and prepared by a high-temperature solid-state reaction method. This facilitates the preparation of the fluorophosphate-based red fluorescent material of the present invention.

[0061] In some specific implementations, the corresponding ground raw materials are placed in a crucible, and then the crucible is placed in a tube furnace for a high-temperature solid-phase reaction.

[0062] Before the high-temperature solid-phase reaction, a mixture of nitrogen and hydrogen (e.g., 5% H2 + 95% N2) can be introduced for 20 to 40 minutes to purge the air from inside the furnace.

[0063] During the heating process, the heating rate can be 3.5 to 7.5 °C / min, preferably 4.5 to 6.5 °C / min, and more preferably 5 to 6 °C / min.

[0064] In this invention, the reaction temperature of the high-temperature solid-state reaction method can be 900–1200°C, preferably 950–1100°C, and more preferably 950–1000°C. The reaction time can be 4–6 h, preferably 4–5.5 h, and more preferably 4–5 h.

[0065] Product grinding and sieving steps

[0066] After the high-temperature solid-phase reaction is completed, the furnace is cooled down, and then the reaction product is ground and sieved to obtain a fluorophosphate-based red fluorescent material.

[0067] Grinding can be done using an agate mortar. When sieving, the mesh size of the sieve used can be 300 mesh or higher, preferably 400 mesh or higher.

[0068] <Application>

[0069] This invention relates to the application of the fluorophosphate-based red fluorescent material described above in the preparation of white LED lamps or agricultural greenhouse films. The excitation spectrum of this fluorophosphate-based red fluorescent material does not overlap with the emission spectrum of commercially available yellow phosphors, and there is no reabsorption effect between them. Furthermore, the added red light component also improves the color rendering index of white LED lamps. This fluorophosphate-based red fluorescent material can be effectively excited by ultraviolet light, converting unwanted ultraviolet light into beneficial red light for plants. It also has application value in rare-earth light-converting agricultural greenhouse films.

[0070] The testing method is described below:

[0071] XRD testing: Tests were performed using an X`Pert PRO X-ray diffractometer.

[0072] Excitation and emission spectra: Tested using an Edinburgh (FL1000) fluorescence spectrometer.

[0073] Thermal stability test: The test was conducted using an Edinburgh (FL1000) fluorescence spectrometer.

[0074] In the following examples, the raw materials used are: potassium fluoride with a purity of 99.9%, potassium carbonate with a purity of 99.997%, dicalcium phosphate with a purity of ≥98.0%, europium oxide with a purity of 99.99%, and diammonium hydrogen phosphate with a purity of 99.99%.

[0075] Examples 1-5

[0076] Prepare raw materials according to the chemical composition shown in Table 1.

[0077] The weighed raw material is thoroughly ground in an agate mortar for 30 minutes to obtain the ground raw material.

[0078] The ground raw materials are transferred to a crucible and mixed evenly. The crucible is then placed in a tube furnace, and a mixture of nitrogen and hydrogen (5% H2 + 95% N2) is introduced for 30 minutes to purge the air from the furnace.

[0079] The mixed raw materials were sintered at high temperature in a reducing atmosphere. The reaction heating rate was 5℃ / min, the sintering temperature was 950℃, and the sintering time was 4h. After the reaction, the sample was cooled with the furnace. The sintered product was ground in an agate mortar and then sieved through a 400-mesh sieve to obtain a fluorophosphate-based red fluorescent material.

[0080] Table 1

[0081]

[0082] XRD testing: The fluorophosphate-based red fluorescent materials prepared in Examples 1-5 were characterized by XRD crystal structure. The results are as follows: Figure 1 As shown, the XRD diffraction peaks of the prepared fluorophosphate-based red fluorescent materials are consistent with the diffraction peaks of monoclinic K2CaPO4F crystals reported in the literature, indicating that the fluorophosphate-based red fluorescent materials prepared in Examples 1-5 have good crystallinity.

[0083] Excitation and emission spectra were measured: The prepared fluorophosphate-based red fluorescent material was subjected to spectroscopic measurements. The excitation spectrum results are shown below. Figure 2 The emission spectrum results are shown in Figure 3 .

[0084] Depend on Figure 2 It can be seen that the excitation spectrum is located in the ultraviolet and blue light bands of 300-470 nm, with the optimal excitation peak located at 350 nm.

[0085] Depend on Figure 3 It is known that the emission spectrum is mainly located in the red light band of 500–850 nm, with the strongest emission peak at 660 nm. The spectral characteristics of the fluorophosphate-based red fluorescent material of this invention show a large Stokes shift. Meanwhile, with the increase of the K substitution content for Ca, the luminescence intensity of the fluorescent material shows a trend of first increasing and then decreasing, and the luminescence intensity is highest when the molar fraction of K is 2.2, meaning that the fluorophosphate-based red fluorescent material obtained in Example 3 has the best luminescence performance. These results indicate that the non-equivalent substitution of Ca with K can effectively repair cation vacancy defects in the crystal, thereby significantly improving the luminescence performance of the fluorescent material.

[0086] Thermal stability testing: To verify the thermal stability of the materials, variable-temperature spectroscopy was performed on the fluorophosphate-based red fluorescent materials prepared in Examples 1-5, and the change in fluorescence intensity at the maximum emission wavelength with temperature was monitored. Results are shown below. Figure 4 ( Figure 4 (a), (b), (c), (d), (e)). Figure 4 It can be seen that as the test temperature gradually increases from room temperature (25℃) to 200℃, the luminescence intensity of the fluorophosphate-based red fluorescent materials prepared in Examples 1-5 shows a gradual decreasing trend at 660nm, which may be related to the thermal activation cross-relaxation of excited-state electrons. Nevertheless, when the temperature rises to 200℃, the luminescence intensity of the prepared fluorophosphate-based red fluorescent materials can be maintained at more than 60% of the initial luminescence intensity, exhibiting excellent thermal stability.

[0087] In summary, the fluorophosphate-based red fluorescent material prepared by this invention possesses a large Stokes shift, excellent luminescence performance, and good thermal stability, showing great application potential in the fields of white LED lighting and agricultural greenhouse films for converting plants into light.

[0088] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A fluorophosphate-based red fluorescent material, characterized in that, It has the chemical composition shown in formula (1): K 2+2x That 1-y-x I y PO4F (1), Where 2+2x represents the mole fraction of K, y is the mole fraction of Eu, 1-yx represents the mole fraction of Ca, 0.05≤x≤0.15, and y is 0.007; The excitation spectrum of the fluorophosphate-based red fluorescent material is in the range of 300–470 nm; when excited by light in the 300–470 nm wavelength range, it emits red fluorescence with the strongest emission peak located at a wavelength of 660 nm.

2. The fluorophosphate-based red fluorescent material according to claim 1, characterized in that, Its optimal excitation wavelength is 350 nm.

3. The fluorophosphate-based red fluorescent material according to claim 1, characterized in that, Its chemical composition is shown below: K 2.1 That 0.943 I 0.007 PO4F; K 2.2 That 0.893 I 0.007 PO4F; K 2.3 That 0.843 I 0.007 PO4F.

4. The fluorophosphate-based red fluorescent material according to claim 1, characterized in that, It is prepared from potassium fluoride, potassium carbonate, calcium hydrogen phosphate, europium oxide and diammonium hydrogen phosphate as reaction raw materials; wherein the molar ratio of potassium fluoride, potassium carbonate, calcium hydrogen phosphate, europium oxide and diammonium hydrogen phosphate is 1:(0.5+x):(1-yx):0.5y:(y+x), 0.05≤x≤0.15, and y is 0.

007.

5. A method for preparing a fluorophosphate-based red fluorescent material according to any one of claims 1 to 4, characterized in that, Includes the following steps: Based on the composition of fluorophosphate-based red fluorescent materials, with K... + Ca 2+ Eu 3+ F - PO4 3- The compound was prepared by high-temperature solid-state reaction using the compound as a raw material.

6. The preparation method according to claim 5, characterized in that, Potassium fluoride, potassium carbonate, calcium hydrogen phosphate, europium oxide, and diammonium hydrogen phosphate were mixed to obtain a mixed raw material. Under a reducing atmosphere, the mixed raw material was prepared by a high-temperature solid-state reaction method to obtain a fluorophosphate-based red fluorescent material. The molar ratio of potassium fluoride, potassium carbonate, calcium hydrogen phosphate, europium oxide, and diammonium hydrogen phosphate was 1:(0.5+x):(1-yx):0.5y:(y+x), where 0.05≤x≤0.15 and y was 0.

007.

7. The preparation method according to claim 5, characterized in that, The reaction temperature using the high-temperature solid-phase reaction method is 900–1200℃, and the reaction time is 4–6 hours.

8. The application of the fluorophosphate-based red fluorescent material according to any one of claims 1 to 4 in the preparation of white LED lamps or agricultural greenhouse films.

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