Narrow-band green fluorescent powder preparation method based on composite nucleation and LED package

Abstract

The invention relates to the field of LED luminescent materials, solves the problems of harsh synthesis conditions and high production cost of narrow-band green fluorescent powder in the prior art, and provides a narrow-band green fluorescent powder preparation method based on composite nucleation and an LED package. The method comprises the following steps: weighing raw materials according to a first preset ratio; preparing a nucleating agent according to a second preset ratio; uniformly mixing the pretreated raw materials with the nucleating agent to obtain a mixture; putting the mixture into a double-layer crucible; a reaction atmosphere is established in the reaction furnace, and the pressure in the reaction furnace is controlled to reach the target pressure; applying a microwave field in the reaction furnace according to a preset microwave frequency range to sinter the mixture, heating to a first target temperature interval, and preserving heat to obtain a sintered material; and quickly cooling the sintered material to obtain the narrow-band green nitrogen oxide fluorescent powder. The preparation difficulty and production cost of beta-Sialon: Eu are reduced, and the method is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of LED light-emitting materials, and in particular to a method for preparing narrowband green phosphor based on composite nucleation and LED packaging. Background Technology

[0002] β-Sialon:Eu narrowband green oxynitride phosphor is a typical narrowband green oxynitride phosphor with excellent spectral characteristics, including an emission wavelength of approximately 535 nm and a full width at half maximum (FWHM) of 50–55 nm. Due to its high color purity and good thermal stability, it is widely used in high color rendering index (CRI) LEDs and laser lighting. However, the existing preparation process for β-Sialon:Eu still faces several technical bottlenecks.

[0003] However, the synthesis conditions for this type of phosphor are extremely demanding. The high Si–N bond energy in the β-Sialon crystal structure necessitates overcoming a significant reaction energy barrier to form the crystalline phase. The raw materials are mostly refractory powders with extremely low diffusion coefficients at medium to low temperatures, making solid-state reactions difficult to proceed. Meanwhile, Eu, as the luminescent center... 2+ Eu needs to be used in the reaction process 3+ This valence state transformation requires a strong reducing atmosphere and high temperature conditions to achieve and maintain stability. Furthermore, nitrogen easily escapes under high temperatures; without sufficient nitrogen partial pressure, the product will decompose or form impurity phases. Therefore, traditional processes typically rely on high temperature and high pressure conditions to ensure the formation of the β-Sialon crystal phase and Eu... 2+ Stable doping.

[0004] Furthermore, nitrogen is prone to escape under high-temperature sintering conditions. If the nitrogen partial pressure is insufficient, the product will decompose, the crystal lattice will be nitrogen-deficient, or impurity phases such as α-Sialon and LaAlO3 will form, which will seriously affect the luminescence performance and crystal phase purity. To suppress nitrogen escape, traditional processes usually require a high-pressure nitrogen environment or even the addition of an inert protective medium. This not only increases the complexity of the equipment and energy consumption, but also limits the scale of production.

[0005] For example, patent CN104479673B discloses a method for preparing oxynitride phosphors, which uses high-temperature and high-pressure sintering conditions of 1800–2200℃ and 1–200 MPa to obtain the target product. Although a stable β-Sialon crystal phase can be formed, this method, while achieving the β-Sialon structure, requires temperatures and pressures far exceeding the tolerance of conventional laboratory or industrial equipment. It necessitates the use of specialized high-pressure, sealed reaction equipment, resulting in a long process cycle and extremely high energy consumption. For instance, maintaining sintering at 2000℃ typically requires a constant-temperature process of several hours, with energy consumption exceeding 1000 kWh / kg per unit yield. Such processes are not only costly but also involve complex equipment maintenance and poor repeatability, limiting the large-scale production and promotion of oxynitride phosphors.

[0006] In summary, existing techniques for preparing β-Sialon:Eu narrowband green oxynitride phosphors suffer from stringent synthesis conditions, necessitating a new method that can achieve the synthesis of high-performance phosphors under milder process conditions. Summary of the Invention

[0007] In view of this, embodiments of the present invention provide a method for preparing narrowband green phosphor based on composite nucleation and LED packaging, in order to solve the problems of harsh synthesis conditions and high production costs of narrowband green phosphor in the prior art.

[0008] In a first aspect, embodiments of the present invention provide a method for preparing a narrowband green phosphor based on composite nucleation, wherein the narrowband green phosphor is β-Sialon:Eu, and the method includes: The raw materials are weighed according to the first preset ratio, and the weighed raw materials are pre-treated. According to the second preset ratio, a nucleating agent is prepared, wherein the nucleating agent includes LaN and MgO; The pretreated raw materials and the nucleating agent are mixed evenly to obtain a mixture; The mixture is loaded into a double-layered crucible, and the double-layered crucible is placed inside the reaction furnace; A reaction atmosphere is established in the reactor, and the pressure inside the reactor is controlled to reach the target pressure, wherein the target pressure is within a preset micro-positive pressure range of 0.3~0.8MPa; Under the reaction atmosphere, a microwave field is applied in the reaction furnace according to a preset microwave frequency range to sinter the mixture, heat it to a first target temperature range and hold it at that temperature to obtain sintered material. The preset microwave frequency range is 2.33~2.37 GHz, and the first target temperature range is below 1850℃. The sintered material is rapidly cooled according to a preset cooling rate to obtain narrow-band green nitrogen oxide phosphor.

[0009] Preferably, the double-layer crucible includes an inner layer and an outer layer, the inner layer being coated with a Y2O3 coating of a first preset thickness, and the outer layer being coated with a ZrO2 coating of a second preset thickness, wherein the first preset thickness is less than the second preset thickness.

[0010] Preferably, the first preset thickness is 50 μm and the second preset thickness is 100 μm.

[0011] Preferably, the step of weighing the raw materials according to the first preset ratio and pre-treating the weighed raw materials includes: The raw materials are weighed according to the first preset ratio, wherein the raw materials include nano Si3N4, aluminum nitride and Eu2O3, and the particle size of the nano Si3N4 is between 50 and 100 nm. The weighed raw materials were placed in an inert atmosphere for low-temperature vacuum dehumidification. The aluminum nitride is coated with 0.2 to 0.8 wt% magnesium powder by vacuum evaporation or mechanical ball milling to form a magnesium coating layer for oxygen barrier. The magnesium coating layer is uniformly distributed on the surface of aluminum nitride particles by planetary ball milling, while the nano-silicon nitride and europium oxide are pre-dispersed. The coated and pre-dispersed raw materials are vacuum dried and sieved to obtain pre-treated raw materials with uniform particle size distribution.

[0012] Preferably, the step of configuring the nucleating agent according to the second preset ratio includes: LaN and MgO are weighed according to a second preset ratio, wherein the second preset ratio is LaN:MgO = 1:(0.2~0.5), and LaN accounts for 0.5~2.0 wt% of the total mass of the raw materials, and MgO accounts for 0.1~0.8 wt% of the total mass of the raw materials. The weighed lanthanum nitride and magnesium oxide were dried at low temperature in an inert atmosphere. The dried lanthanum nitride and magnesium oxide were mechanically mixed and homogenized so that magnesium oxide was evenly distributed on the surface of the lanthanum nitride particles. The mixture is refined by planetary ball milling or high-energy mixing milling to obtain a composite nucleating agent mixed powder with uniform particle size distribution; The mixed powder after grinding was vacuum dried and sieved to obtain a nucleating agent with uniform particle size.

[0013] Preferably, the reaction atmosphere is nitrogen, and the step of applying a microwave field within the reactor according to a preset microwave frequency range to sinter the mixture under the reaction atmosphere to obtain a sintered material includes: The microwave source is activated according to the initial microwave power and the preset microwave frequency range to apply a microwave field within the reactor. According to a preset power boost rate, the microwave source is controlled to boost from the initial microwave power to the target microwave power, wherein the preset power boost rate is 200W / min and the target microwave power is 1500W; When the temperature inside the reactor reaches the first target temperature range, the current temperature is maintained according to the first preset holding time in order to complete the reduction and sintering reaction of the β-Sialon crystal phase; After the first preset heat preservation time ends, microwave heating is terminated to obtain sintered material. The first target temperature range is 1630~1670℃, the initial microwave power is 800W, the preset power boost rate is 200W / min, and the target microwave power is 1500W.

[0014] Preferably, when the temperature inside the reactor reaches the first target temperature range, maintaining the current temperature for a first preset holding time to complete the reduction and sintering reaction of the β-Sialon crystal phase includes: When the temperature inside the reactor approaches the upper limit of the first target temperature range, the current temperature is maintained for a first preset holding time to perform the first reduction under the reaction atmosphere, causing Eu2O3 to be partially converted into Eu. 2+ This promotes the formation of the β-Sialon crystal phase, wherein the first preset heat preservation time is 2-4 hours; After the first reduction is completed, the temperature is controlled to drop to the second temperature range. At the same time, hydrogen is introduced into the reactor and the reaction atmosphere is adjusted to a mixture of nitrogen and hydrogen with an integral ratio of 9:1. The second temperature range is 1350~1400℃. When the temperature inside the reactor drops to the second temperature range, a second reduction reaction is carried out under the adjusted reaction atmosphere, and the current temperature is maintained according to the second preset holding time, wherein the second preset holding time is 20~40min; During the first and second reduction processes, lanthanum nitride (LaN) in the composite nucleating agent reacts in situ with magnesium oxide (MgO) to generate the LaMgON transition phase, thereby lowering the nucleation energy barrier and suppressing abnormal crystal growth along the c-axis, ensuring a nucleus density of not less than 3 × 10⁻⁶. 8 cm -3 .

[0015] Preferably, the rapid cooling treatment of the sintered material according to a preset cooling rate and a preset cooling time to obtain narrow-band green oxynitride phosphor includes: At the moment when sintering is completed, the final temperature inside the reactor is obtained; The target flow rate of the cooling gas is obtained based on the end temperature and the preset cooling rate, wherein the cooling gas is argon and the preset cooling rate is 80~100℃ / min; Cooling gas is introduced into the reactor according to the target flow rate to suppress phase separation of the sintered material, thereby obtaining narrow-band green nitrogen oxide phosphor, wherein the target flow rate is 2~5 L / min.

[0016] Preferably, after rapidly cooling the sintered material according to a preset cooling rate to obtain narrow-band green oxynitride phosphor, the method further includes: The phosphor, after being rapidly cooled, undergoes surface dehumidification and deoxygenation treatment under an inert atmosphere; Prepare a coating solution containing yttrium oxide precursor solution and adjust the pH of the solution to 6-8 to improve dispersion stability; The coating liquid is uniformly distributed on the surface of the narrow-band green nitrogen oxide phosphor by spraying or impregnation to form a continuous and dense yttrium oxide thin layer. The precursor is heat-treated at 300–600 °C in an inert atmosphere to transform it into a Y2O3 ceramic layer, forming an oxygen barrier coating layer with a thickness of 50–100 nm.

[0017] Secondly, embodiments of the present invention provide an LED package including an LED light-emitting unit, the LED light-emitting unit including an excitation chip and a phosphor assembly, the phosphor assembly including at least a narrow-band green phosphor prepared by the method described in the first aspect, the LED package being used in the fields of high color rendering index LED lighting, display and long-distance lighting.

[0018] In summary, the beneficial effects of the present invention are as follows: First, by introducing the composite nucleating agents LaN and MgO during the raw material pretreatment stage, stable nucleation centers can be provided in the early stage of the reaction, promoting uniform crystal phase formation and preventing abnormal grain growth at high temperatures, thereby improving the crystal phase purity and morphological consistency of the product. Second, loading the mixed raw materials into a double-layered crucible and reacting them in a reactor can effectively isolate external impurity gases, forming a relatively closed reaction space, stabilizing the internal reaction atmosphere, reducing the introduction of oxygen impurities, and ensuring the stability of Eu ion doping.

[0019] Furthermore, by establishing a slightly positive pressure nitrogen atmosphere in the range of 0.3 to 0.8 MPa in the reactor, a high nitrogen partial pressure can be maintained, suppressing the escape of nitrogen elements at high temperatures. At the same time, it helps to control the formation equilibrium of the β-Sialon crystal phase, making the sintering reaction more complete.

[0020] Furthermore, heating with a microwave field of 2.33–2.37 GHz allows energy to act directly on the interior of the material, improving the heating rate and temperature uniformity. This enables the formation of the β-Sialon crystal phase at temperatures below 1630–1670 degrees Celsius, reducing energy consumption and improving sintering density. Finally, rapid cooling of the sintered material according to a preset cooling rate quickly lowers the temperature after crystal phase formation, preventing crystal structure inversion or component separation at high temperatures, thus maintaining the crystal phase stability and uniform distribution of luminescent centers in the β-Sialon:Eu phosphor.

[0021] Compared to existing traditional preparation processes that employ high-temperature and high-pressure sintering (e.g., reactions at 1800–2200 °C and 1–200 MPa), this invention reduces the reaction temperature by approximately 200–400 °C by combining a slightly positive pressure atmosphere and microwave heating. The required gas pressure is only on the order of one-thousandth to one-hundredth of the original method. Simultaneously, because the microwave field enables volumetric heating and efficient energy transfer, the overall sintering energy consumption is reduced by approximately 40%–50%, and the equipment structure is further simplified. Therefore, this invention enables the preparation of high-purity, highly uniform β-Sialon:Eu narrowband green oxynitride phosphors under relatively low temperature and medium pressure conditions. The process is stable, energy-efficient, and highly reproducible, making it suitable for industrial production applications. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments of the present invention will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, and these are all within the protection scope of the present invention.

[0023] Figure 1 This is a schematic flowchart of the method for preparing narrowband green phosphor based on composite nucleation according to an embodiment of the present invention.

[0024] Figure 2 This is another schematic diagram of the process for preparing narrowband green phosphor based on composite nucleation in an embodiment of the present invention.

[0025] Figure 3 This is another schematic diagram of the preparation method of narrowband green phosphor based on composite nucleation in an embodiment of the present invention. Detailed Implementation

[0026] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only configured to explain the present invention and are not configured to limit the present invention. For those skilled in the art, the present invention can be practiced without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the present invention by illustrating examples of the invention.

[0027] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0028] Example 1 This invention provides a method for preparing narrowband green phosphor based on composite nucleation, wherein the narrowband green phosphor is β-Sialon:Eu; Specifically, β-Sialon (aluminosilicate nitride) is a type of solid solution formed by the partial substitution of Si atoms with Al and the partial substitution of N atoms with O in the Si3N4 lattice. It has a stable crystal structure and strong chemical inertness. By doping with rare-earth ions (Eu), luminescent centers can be formed in the crystal, where Eu... 2+ Ions emit strong green light when excited by blue light. This is because Eu... 2 + The 4f–5d transition is an allowed transition, characterized by high luminous intensity and fast response. The phosphor's emission peak is typically located around 530 nm, with a full width at half maximum (FWHM) of less than 55 nm, exhibiting typical narrowband green emission. This emission spectrum highly matches the green region, the area of ​​greatest sensitivity for human vision, thus significantly improving the color rendering index and luminous efficacy of white LEDs. Furthermore, β-Sialon:Eu demonstrates excellent thermal stability and resistance to light decay under high temperature and high power operating conditions, maintaining stable luminous intensity over extended periods of use.

[0029] Please see Figures 1-3The method includes: This invention provides a method for preparing a narrowband green phosphor based on composite nucleation, wherein the narrowband green phosphor is β-Sialon:Eu, and the method includes: S1. Weigh the raw materials according to the first preset ratio, and pre-treat the weighed raw materials. Specifically, the first preset ratio is a raw material ratio determined in advance based on the stoichiometric relationship of β-Sialon:Eu and the target luminescence performance. The main raw materials include nano-sized silicon nitride (Si3N4), aluminum nitride (AlN), and europium oxide (Eu2O3). Among them, the nano-sized Si3N4 has a particle size of 50-100 nm, which can significantly improve the reactivity; while the high thermal conductivity and nitrogen content of AlN help maintain the stability of the crystal lattice structure.

[0030] The purpose of this step is to ensure that each reactive component is evenly distributed and has high reactivity during subsequent sintering through precise proportioning and pretreatment, thereby providing stable physical and chemical conditions for crystal nucleation.

[0031] Pretreatment refers to the purification and activation of raw materials before the reaction to improve the reactivity of the powder and reduce oxygen impurities. This can be achieved in various ways, for example rather than exclusively: vacuum drying can be used to remove adsorbed water, or heat treatment at 650°C under a nitrogen atmosphere can be used to decompose the surface oxide layer; plasma cleaning or hydrogen reduction pretreatment can also be introduced to further improve purity. In addition, trace amounts of carbon sources (such as carbon black or carbon nitride) can be pre-doped during the ball milling stage to create a weakly reducing environment to protect the valence state of Eu ions. These diverse pretreatment processes can be flexibly selected according to equipment conditions. By controlling the oxygen content, specific surface area, and surface chemical state of the powder, the risk of oxidation side reactions in subsequent reaction processes can be significantly reduced, ensuring the stable formation of the β-Sialon matrix structure.

[0032] The technical effect of this step is to significantly reduce the oxygen content of the system and inhibit Eu. 3+ The oxidation and formation of Al2O3 impurity phases make the reaction more uniform during subsequent sintering, ultimately improving the purity of the β-Sialon phase and Eu. 2+ The distribution of active sites is consistent.

[0033] S2. According to the second preset ratio, prepare the nucleating agent, wherein the nucleating agent includes LaN and MgO; Nucleating agents are additives that can lower the nucleation energy barrier of crystals and induce uniform nucleation during high-temperature sintering. The composite nucleating agent consists of lanthanum nitride (LaN) and magnesium oxide (MgO) in a mass ratio of 1:(0.2–0.5). LaN decomposes at low temperatures upon heating to form La... 3+ and N 3-The ions, particularly MgO, possess a high oxygen affinity and can capture residual oxygen in the system. The LaN–MgO synergistic effect forms the LaMgON transition phase, thereby providing uniform nucleation centers at the microscale, suppressing abnormal crystal growth along the c-axis, and increasing the nucleus density.

[0034] In this process, the LaN / MgO mass ratio has a significant impact on crystal growth behavior. When the LaN / MgO ratio is less than 0.2, the MgO content is insufficient, the oxygen content in the system is too high, making it difficult to form a complete LaMgON phase, resulting in insufficient diffusion hindrance, reduced nucleation density, and uneven grain size distribution; while when the LaN / MgO ratio is greater than 0.5, La... 3+ Excessive LaN / MgO content readily reacts with Al in the system to form the LaAlO3 impurity phase. XRD analysis shows that the peak intensity of this impurity phase exceeds 5%, disrupting the integrity of the β-Sialon crystal phase. Therefore, controlling the LaN / MgO ratio within the range of 0.2–0.5 balances oxygen capture and nucleation activity, achieving a synergistic balance between nucleation rate and grain growth.

[0035] First, LaN and MgO powders are weighed according to the second preset ratio and ultrasonically dispersed in anhydrous ethanol to prevent agglomeration. After drying, the resulting composite powder is mixed into the pretreated raw materials to form a composite system with a uniform particle size distribution. During subsequent sintering, LaN and MgO will undergo a solid-state reaction to generate LaMgON, which serves as a stable intermediate phase for the nucleation of β-Sialon crystals.

[0036] Through this composite nucleation method, the crystal nucleus density can be increased to 3×10⁻⁶. 8 cm -3 The above methods significantly reduce the fluctuation of the grain aspect ratio, resulting in β-Sialon crystals with uniform particle size distribution, thereby improving the luminescence uniformity and color stability of the phosphor.

[0037] S3. Mix the pretreated raw materials and the nucleating agent evenly to obtain a mixture; The purpose of this step is to ensure that the LaN–MgO composite nucleating agent and the main raw material are in full contact through highly uniform mixing, thus ensuring the uniform distribution of the nucleating agent during sintering and forming a continuous, high-density crystal nucleus network. In terms of implementation, besides the LaN and MgO system, rare earth-containing nitrides (such as CeN, YbN) can be combined with alkaline earth oxides (such as CaO, SrO) to form tunable transition phases, such as LaMgON and CeCaON. Planetary ball milling, twin-helix mixing, or high-speed stirring under nitrogen protection can be used. Zirconia balls are used as the milling media to prevent contamination, and the mixing time is controlled at 2–4 hours with a rotation speed of approximately 200 rpm. To prevent agglomeration, a small amount of anhydrous ethanol can be added as a dispersant during mixing.

[0038] The beneficial effect of this step is that it significantly improves the spatial uniformity of the system components, making the energy of each reaction interface consistent during subsequent sintering, and the LaMgON transition phase is more uniformly distributed, thereby improving the consistency between product batches and the stability of luminescence performance.

[0039] S4. The mixture is loaded into a double-layered crucible and placed inside the reaction furnace; The double-layer crucible is a sintering container with an inner and outer layer structure. The inner layer is coated with yttrium oxide (Y2O3), and the outer layer is coated with zirconium oxide (ZrO2), with thicknesses of approximately 50 μm and 100 μm, respectively. The structured crucible achieves a two-stage oxygen containment, that is, it forms a multi-layer barrier between the raw materials and the environment, preventing external oxygen from penetrating and reducing the oxygen diffusion rate at high temperatures.

[0040] The mixture was evenly spread at the bottom of the crucible and lightly pressed to ensure uniform microwave field coupling. The crucible was then placed in the center of the microwave reactor. The density of the crucible material and the chemical inertness of Y₂O₃ effectively prevented oxygen from entering the system.

[0041] This design reduces oxygen permeability to 10. -7 g·cm -2 ·s -1 The following significantly suppresses oxidation side reactions, thereby ensuring that Eu ions in the β-Sialon system remain in a divalent state, ultimately improving luminescence efficiency and long-term stability.

[0042] S5. Establish a reaction atmosphere in the reactor and control the pressure in the reactor to reach the target pressure, wherein the target pressure is within a preset micro-positive pressure range of 0.3~0.8MPa. The reaction atmosphere refers to the gaseous environment that controls the chemical equilibrium of the system. In this invention, high-purity nitrogen (purity ≥ 99.999%) is used.

[0043] The purpose of this step is to establish a stable inert environment and create a slight positive pressure to prevent the decomposition of raw material nitrides at high temperatures and to inhibit oxygen penetration.

[0044] In practice, nitrogen gas is continuously introduced into the reactor, and the furnace pressure is maintained within the range of 0.3–0.8 MPa using an automatic pressure regulating valve. Once the pressure stabilizes, the circulation system is activated to achieve uniform atmosphere distribution. At this point, the oxygen partial pressure in the furnace chamber is as low as 10⁻⁻⁶. 6 This scale ensures the formation of a pure β-Sialon phase during subsequent sintering processes.

[0045] The technical effect of this step is to improve the diffusion efficiency of nitrogen molecules, promote the uniform embedding of nitrogen in the crystal lattice, thereby stabilizing the β-Sialon crystal phase structure and creating a reliable inert basis for the subsequent two-step reduction.

[0046] S6. Under the reaction atmosphere, a microwave field is applied in the reaction furnace according to a preset microwave frequency range to sinter the mixture, heat it to a first target temperature range and hold it at that temperature to obtain sintered material, wherein the preset microwave frequency range is 2.33~2.37 GHz and the first target temperature range is below 1850℃. Microwave field sintering is a process in which microwaves of a specific frequency are applied directly to a material to generate uniform internal heating. The purpose of this step is to achieve rapid densification at low temperatures by utilizing the bulk heating effect and selective coupling characteristics of microwave energy, and to complete two-step reduction and LaMgON phase formation during the holding stage.

[0047] S7. The sintered material is rapidly cooled according to a preset cooling rate to obtain narrow-band green oxynitride phosphor.

[0048] Rapid cooling refers to the process of reducing the material temperature at an extremely high rate (≥50 ℃ / s) after high-temperature sintering.

[0049] Its purpose is to prevent Eu from being exposed to high temperatures. 2+ It is oxidized again to Eu 3+ And freeze the lattice structure to maintain ideal luminescent centers and microstructure stability.

[0050] In the process, the microwave source is first turned off and high-purity argon gas is immediately introduced to create a protective environment. The crucible is then cooled by forced airflow. The cooling curve is automatically adjusted by the furnace control system to prevent thermal stress cracking. If necessary, Y2O3 sol coating can be applied after cooling to further enhance oxidation resistance.

[0051] After rapid cooling, the oxygen content of the product, as measured by an oxygen analyzer, was no higher than 200 ppm; the external quantum efficiency (EQE) of the phosphor, measured using an integrating sphere testing system (excitation wavelength of 450 nm), reached over 86%. These results demonstrate that the rapid cooling process effectively prevents crystal phase decomposition and Eu²⁺ reoxidation reactions, maintaining the high brightness and excellent thermal stability of the β-Sialon:Eu phosphor, thus providing a reliable performance foundation for its application in high-power LEDs and display light sources.

[0052] Preferably, the double-layer crucible includes an inner layer and an outer layer, the inner layer being coated with a Y2O3 coating of a first preset thickness, and the outer layer being coated with a ZrO2 coating of a second preset thickness, wherein the first preset thickness is less than the second preset thickness.

[0053] The term "double-layer crucible" refers to a crucible substrate with two oxide coatings having different functions, forming a composite protective system consisting of an inner layer of Y₂O₃ and an outer layer of ZrO₂. Y₂O₃ (yttrium oxide) has an extremely low oxygen ion diffusion coefficient and excellent chemical inertness, primarily serving as a dense oxygen barrier and preventing reaction. ZrO₂ (zirconia) has high thermal stability and strong oxygen absorption buffering capacity, acting as an outer oxygen absorption and stress buffer layer to resist the influence of external atmospheric fluctuations on the internal reaction environment.

[0054] The core purpose of setting an inner layer thickness smaller than the outer layer is to achieve functional zoning for oxygen barrier and thermal stress release. The thinner Y₂O₃ layer ensures the chemical inertness and thermal conductivity uniformity of the reaction chamber wall; the thicker ZrO₂ layer provides additional oxygen storage and mechanical support, causing the oxygen partial pressure to decrease exponentially along the crucible wall thickness. Finite element thermal diffusion simulation results show that when the outer layer thickness is 1.5 to 2 times that of the inner layer, the maximum stress inside the crucible wall decreases by about 30%, and the oxygen concentration gradient decreases by about two orders of magnitude, forming a stable "dense inside, buffered outside" synergistic barrier system.

[0055] Preferably, the first preset thickness is 50 μm and the second preset thickness is 100 μm.

[0056] This thickness combination represents the optimal ratio obtained through long-term thermal cycling and oxygen barrier experiments. The inner Y₂O₃ layer has a thickness of 50 μm, and the outer ZrO₂ layer has a thickness of 100 μm, forming a 1:2 thickness ratio. The purpose of this ratio is to provide a sufficiently thick outer buffer layer while ensuring the compactness of the inner layer, thereby balancing gas barrier, thermal conduction, and mechanical stability under high-temperature, slightly positive pressure conditions.

[0057] Isotope tracing experiments showed that after holding the double-layer crucible structure at 1800 ℃ for 8 hours, only the outer ZrO2 coating surface showed significant¹ chromatic aberration. 8 The presence of an oxygen isotope signal, while no oxygen isotope enrichment peaks were observed in the inner Y₂O₃ coating and its inner reaction chamber, indicates that oxygen diffusion was effectively blocked. Based on the isotope distribution signal intensity, the oxygen blocking efficiency can reach approximately 99.5%.

[0058] The oxygen permeability test results show that after treatment with this composite coating, the oxygen permeability coefficient of the crucible decreased from 10 in the uncoated state. -5 cm² / s decreased to approximately 10 -9The oxygen diffusion activation energy increased from approximately 120 kJ / mol to around 210 kJ / mol, while the oxygen diffusion rate was increased by cm² / s. Oxygen analysis showed that the oxygen content of the sintered product obtained under these double-layer crucible conditions was consistently below 200 ppm, indicating that the double-layer coating structure significantly inhibits oxygen infiltration during high-temperature reactions, ensuring the purity of the β-Sialon:Eu²⁺ crystal phase and the stability of the luminescent centers.

[0059] Preferably, the step of weighing the raw materials according to the first preset ratio and pre-treating the weighed raw materials includes: S11. Weigh the raw materials according to the first preset ratio, wherein the raw materials include nano Si3N4, aluminum nitride and Eu2O3, and the particle size of the nano Si3N4 is between 50 and 100 nm. In this step, the first preset ratio refers to the ratio based on β-Sialon:Eu 2+ The raw material ratios determined by the stoichiometric formula are used to ensure the chemical balance of Al, O, Si, and N elements in the target crystalline phase. Nanoscale Si3N4 possesses high specific surface area and high reactivity, which can significantly reduce the sintering temperature; controlling the particle size within the 50-100 nm range ensures sufficient reaction while avoiding agglomeration. Through strict stoichiometric control and particle size screening, the chemical reaction proceeds according to the expected ratio, ensuring that the elemental ratio in the final β-Sialon lattice is close to the theoretical value, thus providing a basis for Eu... 2+ It provides a uniform lattice site environment. The weighing process is usually carried out using a high-precision electronic balance (accuracy 0.1 mg) under a dry and inert atmosphere to prevent the raw materials from absorbing moisture or oxidizing.

[0060] By precisely metering and controlling particle size, the deviation of Si / Al / N / O in the reaction system can be less than 1%, which significantly improves the phase purity and Eu doping uniformity of subsequent reactions and avoids the formation of impurity phases such as Si2N2O.

[0061] S12. Place the weighed raw material in an inert atmosphere for low-temperature vacuum dehumidification; Low-temperature vacuum dehumidification refers to removing adsorbed water from the surface of powders by vacuum extraction and circulation of nitrogen or argon gas at a lower temperature. Since both Si3N4 and AlN are hydrophilic materials, their surfaces readily adsorb water vapor. If this moisture is not removed, it will generate oxides or ammonia gas during high-temperature reactions, disrupting the stoichiometric relationship.

[0062] The purpose of this step is to reduce the oxygen and moisture content of the raw materials to prevent bubbles, cracking, or oxidation reactions during the sintering stage. This can be achieved by dynamic vacuum dehumidification (-0.095 MPa) combined with nitrogen backflushing for 30-60 minutes.

[0063] After this treatment, the moisture content of the raw materials can be reduced to below 0.01%, and the oxygen content can be reduced by about 40%, thereby improving the purity of the system and reducing Eu. 3+ Probability of generation.

[0064] S13. By vacuum evaporation or mechanical ball milling, 0.2 to 0.8 wt% of metallic magnesium powder is coated on the surface of the aluminum nitride to form a magnesium coating layer for oxygen barrier. Coating refers to depositing a thin film of magnesium metal on the surface of AlN particles using physical or chemical methods to capture oxygen in situ during the reaction. Mg has an extremely strong affinity for oxygen and preferentially reacts with O2 to form MgO, thereby preventing oxygen from penetrating into the reaction system.

[0065] The purpose of this step is to construct the first barrier of the raw material-level oxygen dual-stage containment system, namely, to form an oxygen trapping layer at the particle scale. The Mg coating amount is controlled at 0.2–0.8 wt%. Too low a coating amount will result in insufficient oxygen barrier effect, while too high a coating amount will easily lead to the formation of Mg2Si impurity phase during sintering.

[0066] In practical implementation, the Mg coating layer can be prepared using vacuum evaporation, mechanochemical methods, or wet reduction methods. Vapor evaporation can obtain a uniform magnesium layer with a thickness of approximately 100–200 nm, ensuring that the AlN particles remain chemically inert even when exposed to air. This treatment can reduce the oxygen content of the powder to below 200 ppm and form a dense MgO isolation film during sintering, providing a protective layer for Eu. 2+ It provides a stable low-oxygen environment.

[0067] S14. The magnesium coating layer is uniformly distributed on the surface of aluminum nitride particles by planetary ball milling, while the nano silicon nitride and europium oxide are pre-dispersed. Planetary ball milling is a high-energy mechanical mixing method that can achieve uniform dispersion and interface homogenization of powders in a short time. Its purpose is to make the magnesium coating layer more dense and uniform through mechanical shearing and impact, and to promote full contact between Si3N4 and Eu2O3 particles at the microscale.

[0068] In practice, zirconium oxide or silicon nitride balls are typically used as the grinding media under an inert atmosphere to prevent contamination; the ball-to-material ratio is 10:1, the rotation speed is approximately 200-300 rpm, and the time is 1-3 hours. A small amount of anhydrous ethanol or isopropanol can be added as a dispersion medium to reduce powder agglomeration. The mixture after ball milling has a more uniform component distribution, a continuous and dense magnesium film on the AlN surface, and consistent distribution of Si3N4 and Eu2O3, effectively improving the reaction rate and doping uniformity in the subsequent sintering stage, ensuring that the Eu ion distribution deviation σ in the crystal lattice is ≤5%.

[0069] S15. The coated and pre-dispersed raw materials are vacuum dried and sieved to obtain pre-treated raw materials with uniform particle size distribution.

[0070] Vacuum drying is used to remove dispersant or solvent residues and prevent organic impurities from carbonizing during sintering; particle size sieving is used to remove agglomerated particles and ensure uniform powder particle size. The purpose of this step is to obtain pretreated raw materials with highly consistent chemical composition and particle distribution, providing stable reaction conditions for subsequent mixing of nucleating agents and sintering. This is generally achieved by vacuum drying at 80–100 °C for 2 hours, followed by sieving using a 100–200 mesh sieve or an air classifier.

[0071] This step resulted in a concentrated particle size distribution, stable surface area, and good powder flowability in the raw material. XPS analysis of the final pretreated raw material showed a decrease in O 1s peak intensity of over 60%, indicating a significant reduction in oxygen content, resulting in β-Sialon:Eu... 2+ This lays the foundation for subsequent high-purity synthesis.

[0072] Preferably, the step of configuring the nucleating agent according to the second preset ratio includes: S21. Weigh LaN and MgO according to the second preset ratio, wherein the second preset ratio is LaN:MgO = 1:(0.2~0.5), and LaN accounts for 0.5~2.0 wt% of the total mass of the raw materials, and MgO accounts for 0.1~0.8 wt% of the total mass of the raw materials. In this step, the second preset ratio is a predetermined ratio of LaN to MgO based on the kinetic conditions of the nucleation reaction, used to control the formation rate and nucleus density of the transition phase LaMgON. LaN (lanthanum nitride) can decompose at high temperatures to release La... 3+ and N 3- Ions are the main reaction source for inducing crystal nucleation in the β-Sialon system; MgO (magnesium oxide) acts as an interface stabilizer, inhibiting abnormal grain growth along the c-axis and providing oxygen capture.

[0073] The purpose of setting the mass ratio LaN:MgO = 1:(0.2~0.5) is to ensure that LaN reacts fully to form LaMgON while preventing the formation of spinel impurity phase (MgAl2O4) from excessive MgO. When the ratio is below 0.2, the diffusion inhibition effect is insufficient, and the crystal nucleus density decreases; when it is above 0.5, obvious LaAlO3 impurity phase peaks will appear in XRD. Experiments have shown that within this range, the generated LaMgON transition phase has a particle size of approximately 80~150 nm, and the crystal nucleus density can be stabilized at 3×10⁻⁶. 8 cm -3 above.

[0074] By precisely weighing and controlling the amount of LaN and MgO added, it can be ensured that the nucleating agent reacts uniformly in the subsequent sintering and generates a stable intermediate phase, thereby significantly improving the β-Sialon grain distribution and Eu ion diffusion uniformity.

[0075] S22. The weighed lanthanum nitride and magnesium oxide were dried at low temperature in an inert atmosphere. The purpose of this step is to remove adsorbed water and carbonate impurities from the surfaces of LaN and MgO. LaN is highly sensitive to moisture and is prone to oxidation or ammoniation to form La2O3 or La(OH)3, while MgO adsorbs CO2 in the air to form basic magnesium carbonate. Therefore, drying must be carried out under low temperature and inert conditions.

[0076] Specifically, vacuum drying under nitrogen or argon protection (temperature 80~120 ℃, time 30~60 min) can be used to prevent material oxidation. This process is similar to S12.

[0077] After drying, the oxygen content on the surface of LaN powder can be reduced to below 0.1 wt%, ensuring the stability of La during the nucleation reaction. 3+ It can be effectively released without being oxidized and passivated.

[0078] S23. The dried lanthanum nitride and magnesium oxide are mechanically mixed and homogenized so that magnesium oxide is evenly distributed on the surface of the lanthanum nitride particles. The key to this step is achieving uniform contact between the two components to facilitate an in-situ interfacial reaction during high-temperature sintering to generate LaMgON. MgO needs to be uniformly attached to or coated on the surface of the LaN particles to form a three-dimensional reaction interface in the early stages of heating. Specific methods include dry mixing and wet dispersion: dry mixing can be achieved using a double-cone mixer or a V-type mixer with low-speed tumbling for 20-30 minutes; wet dispersion can be achieved by ultrasonic dispersion in anhydrous ethanol, followed by low-speed evaporation. Compared to simple physical mixing, wet dispersion effectively avoids MgO agglomeration and improves reaction uniformity. The resulting powder exhibits a "point-like adsorption—area-like adhesion" structure, ensuring that MgO forms a reaction interface before LaN decomposes during the sintering stage, providing a reaction precursor for the formation of the LaMgON phase.

[0079] S24. The mixture is refined by planetary ball milling or high-energy mixing milling to obtain a composite nucleating agent mixed powder with uniform particle size distribution; High-energy grinding is similar to the aforementioned S14 principle; it is a process that uses mechanical energy to refine and further homogenize particles. Its purpose is to increase the contact area between LaN and MgO, shorten the diffusion path, and thus promote the formation of the LaMgON transition phase.

[0080] Specifically, a planetary ball mill (ball-to-material ratio 10:1, rotation speed 200~300 rpm, time 1~2 h) or a high-energy vibratory mill can be used. Zirconia or silicon nitride can be selected as the grinding media to prevent metal contamination. If necessary, a small amount of ethanol can be added as a wet grinding media.

[0081] After grinding, the powder particle size D50 is approximately 0.5~0.8 μm, the particle size distribution range is narrowed (σ<0.2), and the contact surface between LaN and MgO is uniform and continuous. This refined structure enables faster formation of the LaMgON phase during sintering, making the crystal nucleation process more stable and controllable.

[0082] S25. The mixed powder after grinding is vacuum dried and sieved to obtain a nucleating agent with uniform particle size.

[0083] This step is used to remove dispersants or solvents introduced during wet milling and to eliminate agglomeration. The procedure is similar to S15, including drying at 80-100 °C under vacuum for 1-2 hours, followed by sieving through a 100-200 mesh sieve.

[0084] After this treatment, the composite nucleating agent exhibits uniform particle size and good flowability. SEM observation shows that MgO forms a continuous thin-layer structure on the surface of LaN particles; XRD analysis confirms the absence of La2O3 or Mg2Si impurities in the mixed powder. This nucleating agent can react in situ to generate the LaMgON transition phase during subsequent sintering, achieving a nucleus density of 3 × 10⁻⁶. 8 cm -3 The above laid the foundation for the uniform nucleation of the β-Sialon crystal phase.

[0085] Preferably, the reaction atmosphere is nitrogen, and the step of applying a microwave field within the reactor according to a preset microwave frequency range to sinter the mixture under the reaction atmosphere to obtain a sintered material includes: S51. Control the microwave source to start according to the initial microwave power and the preset microwave frequency range, so as to apply a microwave field in the reactor. Specifically, the reaction atmosphere is nitrogen. After the mixture is placed in the reactor, the microwave source is first activated according to the set microwave frequency range to establish a stable microwave field within the furnace cavity. The initial power is set to 800 W, and the microwave frequency is controlled within the range of 2.33–2.37 GHz (preferably 2.35 GHz) to ensure matching with the dielectric properties of the material. This stage is mainly used to achieve stable coupling between the microwave field and the powder, ensuring a uniform electromagnetic field distribution within the cavity and avoiding discharge or uneven sintering of the material due to localized overheating.

[0086] S52. According to the preset power boost rate, control the microwave source to boost from the initial microwave power to the target microwave power, wherein the preset power boost rate is 200W / min and the target microwave power is 1500W; Following a preset power boost program, the microwave power is gradually increased at a rate of 200 W / min until the target power of 1500 W is reached. During the power boost process, the control module monitors the temperature, reflected power, and power feedback curves in real time to ensure a uniform heating rate and a stable thermal field. In this heating phase, microwave energy directly interacts with the polar bonds and free electrons within the material, causing the powder to heat up overall and triggering the diffusion reaction of the β-Sialon precursor phase, forming a continuous solid-phase network structure.

[0087] S53. When the temperature inside the reactor reaches the first target temperature range, the current temperature is maintained according to the first preset holding time to complete the reduction and sintering reaction of the β-Sialon crystal phase. When the reactor temperature reaches the first target temperature range of 1630–1670 °C, the current temperature is maintained and the process enters the holding phase. The holding time is set according to the raw material batch and the thermal inertia of the chamber to ensure the complete formation of the β-Sialon crystal phase and the initial reduction of Eu₂O₃. During the holding process, the nitrogen atmosphere is maintained at a stable slightly positive pressure. The magnesium coating layer and the LaN–MgO component in the nucleating agent play the roles of oxygen capture and promoting crystal nucleation at high temperatures, respectively, keeping the oxygen partial pressure in the reaction system extremely low. 3+ It can be restored to Eu in situ 2+ .

[0088] S54. When the first preset heat preservation time ends, microwave heating is terminated to obtain sintered material. Once the preset holding time is reached, microwave heating is terminated. At this point, a uniform and dense β-Sialon crystal structure has formed within the sintered system, with a significantly increased nucleation density. Through this programmed power increase and holding temperature control, complete reaction can be achieved at temperatures lower than traditional sintering temperatures, reducing the diffusion activation energy (approximately 2.5 eV) and enabling Eu... 2+ The distribution is more uniform, laying a thermally stable foundation for subsequent atmosphere switching and secondary reduction processes. Specifically, the first target temperature range is 1630~1670℃, the initial microwave power is 800W, the preset power boost rate is 200W / min, and the target microwave power is 1500W.

[0089] Preferably, when the temperature inside the reactor reaches the first target temperature range, maintaining the current temperature for a first preset holding time to complete the reduction and sintering reaction of the β-Sialon crystal phase includes: S531. When the temperature inside the reactor approaches the upper limit of the first target temperature range, the current temperature is maintained for a first preset holding time to perform the first reduction under the reaction atmosphere, causing Eu2O3 to be partially converted into Eu. 2+ This promotes the formation of the β-Sialon crystal phase, wherein the first preset heat preservation time is 2-4 hours; In a preferred embodiment, when the temperature inside the reactor reaches the first target temperature range, the current temperature is maintained and a heat preservation stage is entered to complete the reduction and sintering reaction of the β-Sialon crystal phase.

[0090] First, as shown in S531, when the reactor temperature approaches the upper limit of the first target temperature range (approximately 1670°C), the first reduction reaction is carried out under a pure nitrogen atmosphere. During this stage, the temperature is kept constant for 2–4 hours to promote the partial reduction of Eu in Eu₂O₃. 3+ The ions are reduced to Eu by active nitrogen species or metallic magnesium precipitated from the nitride matrix. 2+ Simultaneously, the solid-state reaction between Si3N4 and AlN accelerates, and the β-Sialon main crystalline phase gradually forms. The first reduction not only achieves valence state adjustment but also promotes the transformation of the precursor mixture from an amorphous or metastable structure to an ordered β-Sialon lattice, creating a stable crystal framework for subsequent deep reduction.

[0091] S532. After the first reduction is completed, the temperature is controlled to drop to the second temperature range. At the same time, hydrogen is introduced into the reactor and the reaction atmosphere is adjusted to a mixture of nitrogen and hydrogen with an integral ratio of 9:1. The second temperature range is 1350~1400℃. Next, as shown in S532, after the first reduction is completed, the furnace temperature is controlled to decrease at a controlled rate to the second temperature range (1350–1400°C). Simultaneously, hydrogen is gradually introduced, and the furnace atmosphere is adjusted to a mixture of nitrogen and hydrogen in a 9:1 ratio. This atmosphere switching process can be completed within 10–20 minutes to avoid lattice thermal shock caused by a sudden temperature drop. At this time, hydrogen acts as a reducing agent, reducing the oxygen partial pressure in the system and further promoting Eu reduction. 3+ To Eu 2+ The complete transformation of the crystal and the repair of residual oxygen vacancies and defects in the lattice.

[0092] S533. When the temperature inside the reactor drops to the second temperature range, a second reduction reaction is carried out under the adjusted reaction atmosphere, and the current temperature is maintained according to the second preset holding time, wherein the second preset holding time is 20~40min. Subsequently, as shown in S533, when the reactor temperature stabilizes within the second temperature range, the current temperature is maintained for a second reduction reaction, with a holding time of 20–40 min. This stage constitutes a deep reduction and lattice defect repair process, which can significantly improve Eu... 2+ The stability of the valence state and the uniform distribution of the luminescent centers.

[0093] During the first and second reduction processes, lanthanum nitride (LaN) in the composite nucleating agent reacts in situ with magnesium oxide (MgO) to generate the LaMgON transition phase, thereby lowering the nucleation energy barrier and suppressing abnormal crystal growth along the c-axis, ensuring a nucleus density of not less than 3 × 10⁻⁶. 8 cm -3 .

[0094] In the first and second reduction processes described above, lanthanum nitride (LaN) and magnesium oxide (MgO) in the composite nucleating agent undergo an in-situ reaction at high temperature to generate the LaMgON transition phase. This transition phase possesses low interfacial energy characteristics and can serve as a nucleation template for β-Sialon, effectively reducing the nucleation energy barrier and limiting abnormal grain growth along the c-axis. Scanning electron microscopy and grain statistics show that the nucleus density can be stably maintained at 3 × 10⁻⁶. 8 cm -3 In the above, the crystal morphology tends to be equiaxed and uniform. Through this two-step reduction and nucleation synergistic mechanism, not only is the Eu crystal structure ensured... 2+ It has a complete valence state and extremely low oxygen impurity content, which significantly improves the structural integrity and luminescence performance of β-Sialon crystals.

[0095] Preferably, the rapid cooling treatment of the sintered material according to a preset cooling rate and a preset cooling time to obtain narrow-band green oxynitride phosphor includes: S71. At the moment when sintering is completed, obtain the end temperature inside the reactor. First, as shown in S71, at the moment the sintering reaction ends, the control system acquires the final temperature inside the reactor in real time. By detecting the final temperature through a thermocouple array or an infrared temperature measurement module, automatic closed-loop control of the cooling stage can be achieved, providing a basis for maintaining the linear characteristics of the cooling curve.

[0096] S72. Based on the end temperature and the preset cooling rate, obtain the target flow rate of the cooling gas, wherein the cooling gas is argon and the preset cooling rate is 80~100℃ / min; The "preset cooling rate" in this step refers to the ideal cooling rate preset based on the material's thermal properties and crystal phase stability, used to quickly pass through the phase transition sensitive region while maintaining lattice integrity. Argon, as a cooling medium, has the advantages of high chemical inertness, stable thermal conductivity, and no reaction with β-Sialon, making it an ideal gas for achieving rapid cooling.

[0097] The purpose of this step is to calculate the required argon flow rate based on the final temperature and the target cooling rate, thereby achieving precise control of the gas cooling intensity. By comprehensively considering the furnace cavity volume, heat exchange coefficient, and gas heat capacity through a mathematical model, the optimal flow parameters can be obtained. Typically, when the cooling rate is set to 80–100 ℃ / min, the required argon flow rate is approximately 2–5 L / min, which can uniformly remove residual heat from the furnace cavity in a short time.

[0098] The specific implementation method is as follows: after receiving the end temperature signal, the program automatically calculates the corresponding target flow rate and transmits the parameters to the gas control module; the valve control system adjusts the argon flow rate accordingly to achieve controlled cooling.

[0099] This step enables stable and rapid cooling without introducing sudden temperature changes, avoiding powder buoyancy or thermal stress impact caused by excessive flow rates, thereby ensuring the continuity of the crystal structure and the integrity of the material surface.

[0100] S73. Cooling gas is introduced into the reactor according to the target flow rate to suppress phase separation of the sintered material and obtain narrow-band green nitrogen oxide phosphor, wherein the target flow rate is 2~5L / min.

[0101] This step is the core process of the rapid cooling phase. High-purity argon gas is continuously injected into the reactor at a target flow rate through a precision valve control system, creating a stable forced convection environment within the furnace cavity to achieve efficient heat exchange. Its main purpose is to rapidly reduce the temperature under an inert atmosphere and prevent Eu from precipitating in the crystal lattice during the high-temperature phase. 2+ Re-oxidized to Eu 3+ This also avoids phase separation or non-equilibrium precipitation of the β-Sialon crystal phase during cooling.

[0102] In practice, argon gas is introduced from the bottom of the furnace and evenly distributed through a porous distribution port or annular nozzle, creating a circulating convection field for the cooling gas. The argon gas flow rate is controlled within the range of 2–5 L / min, which can reduce the sample temperature from approximately 1600℃ to below 800℃ within minutes. The cooling curve is automatically adjusted by the temperature control system to ensure a stable cooling rate and suppress the generation of thermal stress.

[0103] Through this step, the β-Sialon:Eu lattice structure is rapidly "frozen" in a stable state, and the luminescent center Eu... 2+The valence state remains stable. Oxygen analysis showed that the oxygen content of the powder after cooling was below 200 ppm; integrating sphere testing indicated that its external quantum efficiency reached approximately 86% at an excitation wavelength of 450 nm. Therefore, this cooling process effectively improves the luminescent performance and thermal stability of the product, providing performance assurance for subsequent packaging and applications.

[0104] Preferably, after rapidly cooling the sintered material according to a preset cooling rate to obtain narrow-band green oxynitride phosphor, the method further includes: The phosphor, after being rapidly cooled, undergoes surface dehumidification and deoxygenation treatment under an inert atmosphere; First, the phosphor, after rapid cooling, undergoes surface dehumidification and deoxygenation treatment under an inert atmosphere. The key to this step is removing moisture and oxygen molecules adsorbed on the powder surface during air exposure to prevent side reactions or the formation of a non-uniform layer in the precursor during subsequent coating. Specifically, this can be achieved by holding the powder at 120–200°C for 30–60 minutes under argon or nitrogen protection, allowing complete desorption of adsorbed H₂O and O₂. This pretreatment reduces the oxygen content on the powder's specific surface area to below 200 ppm, creating a clean interface for the formation of a dense coating layer.

[0105] Prepare a coating solution containing yttrium oxide precursor solution and adjust the pH of the solution to 6-8 to improve dispersion stability; Subsequently, a coating solution containing a yttrium oxide precursor solution is prepared. Yttrium oxide is a highly stable ceramic material with an extremely low oxygen ion diffusion coefficient, making it an ideal surface oxygen barrier layer. The coating solution can use yttrium nitrate, yttrium acetate, or organic coordinated yttrium salts as precursors, with ethanol-water or ethylene glycol-water as solvent systems. By adjusting the pH of the solution to 6–8, the precursor colloid can be kept in a stable dispersion state, avoiding hydrolysis and precipitation, and improving the uniformity and adhesion of the coating solution.

[0106] The coating liquid is uniformly distributed on the surface of the narrow-band green nitrogen oxide phosphor by spraying or impregnation to form a continuous and dense yttrium oxide thin layer. Next, spray coating or impregnation coating is used to ensure the coating solution is evenly distributed on the surface of the phosphor particles. Spray coating is suitable for continuous batch processing and can achieve nanoscale uniform film formation through ultrasonic atomization; impregnation is suitable for small batches of samples with high uniformity requirements, and negative pressure filtration or drum stirring ensures that the solution completely wets the powder surface. After drying, a continuous precursor gel layer is formed on the powder surface.

[0107] The precursor is heat-treated at 300–600 °C in an inert atmosphere to transform it into a Y2O3 ceramic layer, forming an oxygen barrier coating layer with a thickness of 50–100 nm.

[0108] Finally, heat treatment is performed in an inert atmosphere at temperatures of 300–600 °C to promote the thermal decomposition of the precursor and sintering into a stable Y₂O₃ ceramic layer. The heat treatment time is typically 30–90 min to obtain a yttrium oxide thin layer with a thickness of approximately 50–100 nm. This layer has a dense and continuous structure, forming a strong interface with the substrate through physical adsorption and chemical bonding. This interface effectively blocks oxygen diffusion without significantly affecting the excitation light transmittance.

[0109] After this surface coating treatment, the antioxidant and thermal stability of the phosphor are significantly improved. Isotope permeation experiments showed that after 4 hours of incubation at 850℃ in air, the oxygen isotope signal of the coated sample was limited to the outer Y₂O₃ film, and no oxygen permeation was detected in the bulk powder. Aging tests showed no significant redshift in the emission peak wavelength (<1 nm), and the luminescence intensity retention rate exceeded 95%. This demonstrates that the surface yttrium oxide coating can form a highly efficient oxygen barrier, further ensuring the protection of β-Sialon:Eu 2+ Valence stability and long-term luminescence performance.

[0110] Example 2 Based on the preparation method of Example 1, Example 2 of the present invention also provides an LED package, namely an LED package structure, the LED package structure including an LED light-emitting unit, the LED light-emitting unit including an excitation chip and a phosphor combination, the phosphor combination including at least a narrow-band green phosphor prepared by the method of Example 1, the LED package being used in the fields of high color rendering index LED lighting, display and long-distance lighting.

[0111] Specifically, the phosphor combination includes β-Sialon:Eu narrowband green oxynitride phosphor prepared by the method of Example 1 of this invention. This phosphor can efficiently emit narrowband green light under blue / ultraviolet excitation; and can be combined with phosphors of other wavelengths (such as red nitride phosphors and yellow YAG:Ce phosphors) to ultimately output white light with high color rendering and high stability.

[0112] The LED packaging structure uses a blue or near-ultraviolet excitation chip as the excitation source to excite the β-Sialon:Eu narrowband green oxynitride phosphor prepared in Example 1 to emit light. Because the phosphor's emission peak is concentrated around 530 nm, its full width at half maximum (FWHM) is less than 55 nm, and its emission spectrum is narrow with high color purity, it can interact with red light (such as CaAlSiN3:Eu). 2+ ) and yellow light (such as YAG:Ce) 3 + A combination of phosphors is used to obtain white light output with a high color rendering index (Ra>95).

[0113] Compared to β-Sialon:Eu phosphors prepared using traditional high-temperature and high-pressure methods, the product prepared in Example 1 exhibits lower oxygen content (≤200 ppm), lower lattice stress, and higher uniformity of luminescent centers, resulting in superior photothermal stability and anti-light decay performance in LED packaging. Integrating sphere testing shows that under blue light chip excitation (λ=450 nm), the overall external quantum efficiency (EQE) of the LED device is increased by approximately 8–12%, and the brightness retention rate exceeds 90% at an ambient temperature of 150 °C.

[0114] Furthermore, since phosphors can be synthesized in batches under moderate pressure and low energy consumption conditions, the energy consumption is reduced by about 40% and the equipment investment cost is reduced by more than 50% compared with the existing high-temperature and high-pressure solid-state reaction method. This not only simplifies the production process of LED packaging materials, but also provides a low-cost, high-performance material solution for the industrialization of LEDs for high color rendering index, long-distance lighting, automotive and display applications.

[0115] It should be clarified that the present invention is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, detailed descriptions of known methods are omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications, and additions, or change the order of steps, after understanding the spirit of the present invention.

[0116] It should also be noted that the exemplary embodiments mentioned in this invention describe methods or systems based on a series of steps or apparatus. However, this invention is not limited to the order of the steps described above; that is, the steps can be performed in the order mentioned in the embodiments, or in a different order, or several steps can be performed simultaneously.

[0117] The above description is merely a specific embodiment of the present invention. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the protection scope of the present invention.

Claims

1. A method for preparing a narrowband green phosphor based on composite nucleation, wherein the narrowband green phosphor is β-Sialon:Eu, characterized in that, The method includes: The raw materials are weighed according to the first preset ratio, and the weighed raw materials are pre-treated. According to the second preset ratio, a nucleating agent is prepared, wherein the nucleating agent includes LaN and MgO; The pretreated raw materials and the nucleating agent are mixed evenly to obtain a mixture; The mixture is loaded into a double-layered crucible, and the double-layered crucible is placed inside the reaction furnace; A reaction atmosphere is established in the reactor, and the pressure inside the reactor is controlled to reach the target pressure, wherein the target pressure is within a preset micro-positive pressure range of 0.3~0.8MPa; Under the reaction atmosphere, a microwave field is applied in the reaction furnace according to a preset microwave frequency range to sinter the mixture, heat it to a first target temperature range and hold it at that temperature to obtain sintered material. The preset microwave frequency range is 2.33~2.37 GHz and the first target temperature range is 1630~1670℃. The sintered material is rapidly cooled according to a preset cooling rate to obtain narrow-band green nitrogen oxide phosphor.

2. The method according to claim 1, characterized in that, The double-layer crucible includes an inner layer and an outer layer. The inner layer is coated with a Y2O3 coating of a first preset thickness, and the outer layer is coated with a ZrO2 coating of a second preset thickness, wherein the first preset thickness is less than the second preset thickness.

3. The method according to claim 2, characterized in that, The first preset thickness is 50 μm, and the second preset thickness is 100 μm.

4. The method according to claim 1, characterized in that, The step of weighing the raw materials according to the first preset ratio and pre-treating the weighed raw materials includes: The raw materials are weighed according to the first preset ratio, wherein the raw materials include nano Si3N4, aluminum nitride and Eu2O3, and the particle size of the nano Si3N4 is between 50 and 100 nm. The weighed raw materials were placed in an inert atmosphere for low-temperature vacuum dehumidification. The aluminum nitride is coated with 0.2 to 0.8 wt% magnesium powder by vacuum evaporation or mechanical ball milling to form a magnesium coating layer for oxygen barrier. The magnesium coating layer is uniformly distributed on the surface of aluminum nitride particles by planetary ball milling, while the nano-silicon nitride and europium oxide are pre-dispersed. The coated and pre-dispersed raw materials are vacuum dried and sieved to obtain pre-treated raw materials with uniform particle size distribution.

5. The method according to claim 4, characterized in that, The step of preparing the nucleating agent according to the second preset ratio includes: LaN and MgO are weighed according to a second preset ratio, wherein the second preset ratio is LaN:MgO = 1:(0.2~0.5), and LaN accounts for 0.5~2.0 wt% of the total mass of the raw materials, and MgO accounts for 0.1~0.8 wt% of the total mass of the raw materials. The weighed lanthanum nitride and magnesium oxide were dried at low temperature in an inert atmosphere. The dried lanthanum nitride and magnesium oxide were mechanically mixed and homogenized so that magnesium oxide was evenly distributed on the surface of the lanthanum nitride particles. The mixture is refined by planetary ball milling or high-energy mixing milling to obtain a composite nucleating agent mixed powder with uniform particle size distribution; The mixed powder after grinding was vacuum dried and sieved to obtain a nucleating agent with uniform particle size.

6. The method according to claim 5, characterized in that, The reaction atmosphere is nitrogen. Under the reaction atmosphere, a microwave field is applied in the furnace according to a preset microwave frequency range to sinter the mixture to obtain a sintered material, including: The microwave source is activated according to the initial microwave power and the preset microwave frequency range to apply a microwave field within the reactor. According to a preset power boost rate, the microwave source is controlled to boost from the initial microwave power to the target microwave power, wherein the preset power boost rate is 200W / min and the target microwave power is 1500W; When the temperature inside the reactor reaches the first target temperature range, the current temperature is maintained according to the first preset holding time in order to complete the reduction and sintering reaction of the β-Sialon crystal phase; After the first preset heat preservation time ends, microwave heating is terminated to obtain sintered material. The initial microwave power is 800W, the preset power boost rate is 200W / min, and the target microwave power is 1500W.

7. The method according to claim 6, characterized in that, When the temperature inside the reactor reaches the first target temperature range, the current temperature is maintained for a first preset holding time to complete the reduction and sintering reaction of the β-Sialon crystal phase, including: When the temperature inside the reactor approaches the upper limit of the first target temperature range, the current temperature is maintained for a first preset holding time to perform the first reduction under the reaction atmosphere, causing Eu2O3 to be partially converted into Eu. 2+ This promotes the formation of the β-Sialon crystal phase, wherein the first preset heat preservation time is 2-4 hours; After the first reduction is completed, the temperature is controlled to drop to the second temperature range. At the same time, hydrogen is introduced into the reactor and the reaction atmosphere is adjusted to a mixture of nitrogen and hydrogen with an integral ratio of 9:

1. The second temperature range is 1350~1400℃. When the temperature inside the reactor drops to the second temperature range, a second reduction reaction is carried out under the adjusted reaction atmosphere, and the current temperature is maintained according to the second preset holding time, wherein the second preset holding time is 20~40min; During the first and second reduction processes, lanthanum nitride in the composite nucleating agent reacts in situ with magnesium oxide to generate the LaMgON transition phase, thereby lowering the nucleation energy barrier and suppressing abnormal crystal growth along the c-axis, ensuring a nucleus density of not less than 3 × 10⁻⁶. 8 cm -3 .

8. The method according to any one of claims 1-7, characterized in that, The rapid cooling process of the sintered material according to a preset cooling rate and a preset cooling time to obtain narrow-band green oxynitride phosphor includes: At the moment when sintering is completed, the final temperature inside the reactor is obtained; The target flow rate of the cooling gas is obtained based on the end temperature and the preset cooling rate, wherein the cooling gas is argon and the preset cooling rate is 80~100℃ / min; Cooling gas is introduced into the reactor according to the target flow rate to suppress phase separation of the sintered material, thereby obtaining narrow-band green nitrogen oxide phosphor, wherein the target flow rate is 2~5 L / min.

9. The method according to claim 8, characterized in that, After rapidly cooling the sintered material according to a preset cooling rate to obtain narrow-band green oxynitride phosphor, the method further includes: The phosphor, after being rapidly cooled, undergoes surface dehumidification and deoxygenation treatment under an inert atmosphere; Prepare a coating solution containing yttrium oxide precursor solution and adjust the pH value to 6-8 to improve dispersion stability; The coating liquid is uniformly distributed on the surface of the narrow-band green nitrogen oxide phosphor by spraying or impregnation to form a continuous and dense yttrium oxide thin layer. The precursor is heat-treated at 300–600 °C in an inert atmosphere to transform it into a Y2O3 ceramic layer, forming an oxygen barrier coating layer with a thickness of 50–100 nm.

10. An LED package, characterized in that, The LED package includes an LED light-emitting unit, which comprises an excitation chip and a phosphor assembly, wherein the phosphor assembly comprises at least a narrow-band green phosphor prepared by any one of claims 1-9, and the LED package is used in the fields of high color rendering index LED lighting, display and long-distance lighting.

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