Near ultraviolet excited cyan fluorescent material and preparation method thereof

Abstract

The invention discloses a near ultraviolet excited cyan fluorescent material as well as a preparation method and application thereof, and belongs to the technical field of luminescent materials. The general chemical formula of the fluorescent material is CaLu2-xScZrAl3O12: xCe < 3 + >, x is the doping molar concentration of Ce < 3 + >, and x is larger than or equal to 0.005 and smaller than or equal to 0.12. The material is prepared by adopting a high-temperature solid-phase method, the process is simple, and the cost is low. The material has a wide excitation band in a near ultraviolet to blue light region of 320-475 nm, the peak value is 420 nm, and the wide excitation band is highly matched with the emission spectrum of a commercial near ultraviolet LED chip; under the excitation of 420 nm light, strong broadband cyan light with the central wavelength of 500 nm and the full width at half maximum of about 100 nm is emitted. When x is equal to 0.01, the luminous intensity is the maximum, and the CIE color coordinate is (0.195, 0.358), which is close to ideal cyan. The material has excellent thermal stability, the luminous intensity at 225 DEG C can still be kept at 50% at room temperature, and the thermal quenching activation energy is high. The fluorescent powder is suitable for being combined with red and green fluorescent powder and a near ultraviolet chip to construct a full-spectrum white light emitting diode with a high color rendering index, and has a wide application prospect in the field of high-end illumination and display.

Description

Technical Field

[0001] This invention relates to the field of luminescent materials technology, specifically to a cyan fluorescent material that can be efficiently excited by near-ultraviolet light, its preparation method, and its application in white light emitting diodes (WLEDs). Background Technology

[0002] White light-emitting diodes (WLEDs), as a mainstream solid-state lighting and display technology, rely on innovation in fluorescent materials for their performance. Currently, the mainstream solution for achieving high-quality white light is evolving from the traditional "blue light chip exciting a single yellow phosphor" to "near-ultraviolet (NUV) chip exciting multi-color phosphors." The latter, through precise control of the mixing of red, green, and cyan primary colors, can theoretically achieve full-spectrum, high color rendering index (CRI>90) lighting close to sunlight, while avoiding the direct emission of harmful blue light, thus better aligning with the concept of healthy lighting.

[0003] However, the commercialization of this technology faces a key bottleneck: the lack of high-performance cyan phosphors. Ideal cyan phosphors need to exhibit strong and stable emission in the 480-520 nm range to fill the spectral gap between blue and green light. Despite extensive research, existing cyan phosphor systems (such as some silicates, aluminates, and nitrides / oxides) generally suffer from the following problems: First, insufficient thermal stability, leading to severe luminous efficiency degradation (thermal quenching) at high power densities, resulting in device light decay and color drift; second, demanding synthesis conditions, such as the requirement for high-efficiency nitrides to be synthesized under high temperature and pressure nitrogen, resulting in high costs and difficulty in large-scale production; and third, poor chemical stability, being susceptible to deliquescence or reaction with encapsulation materials, affecting device lifespan.

[0004] Garnet structure (A3B2C3O) 12 Ce is considered an ideal matrix platform for solving the above problems due to its excellent physicochemical stability, high thermal conductivity, and flexible cation tunability. 3+ Due to their 4f-5d electric dipole-allowed transitions, ions possess advantages such as wide excitation, wide emission, and short decay lifetime, making them a preferred activator for obtaining efficient cyan luminescence. However, traditional yttrium aluminum garnet (YAG:Ce)... 3+ The emission spectrum of the substance is yellowish, which can be corrected by simple ion substitution (such as using Ga). 3+ Partially replaces Al 3+ While this can blue-shift the emission wavelength, it often comes at the cost of thermal stability. Recent research indicates that introducing multivalent ions (such as Sc) with specific radii and coordination tendencies at the B / C sites of garnets... 3+ Zr 4+ Mg 2+ (etc.), capable of finely controlling Ce 3+The local crystal field strength and lattice rigidity of Sc effectively enhance the thermal stability of the material while achieving the desired emission wavelength. However, regarding the application of Sc... 3+ With Zr 4+ The synergistic introduction of the Ca-Lu-Al-O garnet system and the systematic study of its performance as a near-ultraviolet excited cyan fluorescent material have not been publicly reported in patents, which provides a clear space for technological innovation in this invention. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing near-ultraviolet-excited cyan phosphors in terms of thermal stability, synthesis process, or overall performance, and to provide a novel near-ultraviolet-excited cyan phosphor material based on a Sc / Zr co-doped garnet structure. This material combines broad-spectrum excitation, efficient cyan emission, excellent thermal stability, and a simple preparation process, making it suitable for constructing high-performance full-spectrum WLEDs.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a near-ultraviolet-excited cyan fluorescent material, with the general chemical formula: CaLu 2-x ScZrAl3O 12 : xCe 3+ Where x is Ce 3+ The molar concentration of the dopant, and 0.005≤x≤0.12.

[0007] In this material, Ca²⁺ and Lu³⁺ jointly occupy dodecahedral sites, and Sc 3+ Zr 4+ Al 3+ They jointly occupy octahedral and tetrahedral lattice sites (based on the structural characteristics of garnet), forming a stable high-entropy / multi-principal-element solid solution. Sc 3+ (Larger ionic radius) and Zr 4+ The introduction of (higher charge) effectively modulates Ce. 3+ (occupying Lu) 3+ The surrounding crystal field environment of the 5d energy level shifts the center of gravity of the 5d energy level downward, thereby tuning the emission wavelength to the ideal cyan band; on the other hand, it enhances the lattice bonding strength and rigidity, which is the structural basis for its excellent thermal stability.

[0008] Furthermore, through optimization, it was found that when the doping concentration x is 0.01, the luminescence intensity of the fluorescent material reaches its maximum value, and there is no obvious concentration quenching, which is the optimal practical doping amount.

[0009] Furthermore, the fluorescent material exhibits excellent excitation characteristics. It shows strong absorption across a wide wavelength range of 320-475 nm, with a main excitation peak at approximately 420 nm. This excitation band highly overlaps with the emission spectrum of commercial 395-420 nm near-ultraviolet LED chips, ensuring efficient energy conversion.

[0010] Furthermore, under 420nm light excitation, the fluorescent material emits a strong, broadband cyan light with a center wavelength of 500nm and a full width at half maximum (FWHM) of approximately 100nm. This broad emission characteristic is beneficial for improving the color rendering of WLEDs, making the synthesized white light softer and more natural.

[0011] Furthermore, colorimetric analysis of the optimal sample (x=0.01) showed that its CIE color coordinates were (0.195, 0.358), which are very close to the ideal cyan point in the NTSC television broadcasting standard, with a color purity of approximately 85%. This makes it an ideal cyan component for achieving wide color gamut display lighting.

[0012] Furthermore, one of the most prominent advantages of the material of this invention is its excellent thermal stability. Variable-temperature fluorescence testing shows that even when the operating temperature rises to 225°C, its luminescence intensity still maintains 50% of its initial room-temperature value. Using the Arrhenius model, its thermal quenching activation energies were calculated to be ΔE1 = 0.2765 eV and ΔE2 = 0.3457 eV, significantly higher than most reported similar cyan fluorescent materials, indicating that it can better suppress non-radiative transitions at high temperatures and is suitable for high-power-density LED devices.

[0013] This invention also provides a method for preparing the above-mentioned fluorescent material. The method is simple, reproducible, and suitable for industrial production. Specifically, it includes the following steps: (1) Weighing raw materials: according to the chemical formula CaLu 2-x ScZrAl3O 12 : xCe 3+The stoichiometric ratio is used to accurately weigh the high-purity (≥99.99%) raw materials: CaO (or CaCO3), Lu2O3, Sc2O3, ZrO2, Al2O3 and CeO2. (2) Mixing and grinding: Place the weighed raw materials in an agate mortar or ball mill jar, add anhydrous ethanol or deionized water as a dispersion medium, grind thoroughly for 30-120 minutes to ensure uniform mixing, and then dry to obtain precursor powder. (3) High-temperature calcination: Put the precursor powder into a high-temperature resistant crucible (such as an alumina crucible), place it in a box-type muffle furnace, and sinter it in an air atmosphere. The recommended sintering procedure is as follows: First, heat the sample to 500-700℃ (preferably 600℃) at a rate of 2-5℃ / min and pre-calcine for 2-6 hours (preferably 4 hours) to decompose carbonates or remove volatile impurities; then continue heating to 1350-1450℃ (preferably 1400℃) and hold at this temperature for 4-8 hours (preferably 6 hours) to ensure complete solid-phase reaction and form a well-crystallized pure-phase garnet structure; finally, stop heating and allow the sample to cool naturally to room temperature with the furnace. (4) Post-treatment: Grind the cooled sintered block into fine powder and sieve it according to the application requirements (e.g., 300 mesh sieve) to obtain the target phosphor product.

[0014] This invention also claims protection for the application of the near-ultraviolet-excited cyan fluorescent material, specifically its application in the fabrication of white light-emitting diodes (WLEDs). The application involves mixing the cyan phosphor with a suitable red phosphor (such as CaAlSiN3:Eu). 2 + K2SiF6:Mn 4+ (etc.) and green phosphors (such as β-SiAlON:Eu) 2+ Lu3Al5O 12 :Ce 3+ Mix (etc.) in a certain proportion, and then combine with near-ultraviolet LED chips with emission wavelengths in the range of 380-420nm to generate white light with high color rendering through light conversion.

[0015] Based on this, the present invention further provides a white light-emitting diode, the core feature of which is that it includes the above-mentioned near-ultraviolet or blue light LED chip and the near-ultraviolet excited blue light fluorescent material provided by the present invention.

[0016] The beneficial effects of this invention are: (1) Balanced and excellent performance: It successfully solves the common contradiction that it is difficult to balance the "emission wavelength", "luminescence efficiency" and "thermal stability" of cyan fluorescent materials. The material of this invention achieves high-efficiency cyan luminescence (λ) em(2) High excitation matching: The broad excitation spectrum (peak 420nm) perfectly matches the emission spectrum of mainstream near-ultraviolet LED chips, which is conducive to improving the light conversion efficiency and light output of the device. (3) Superior color quality: The emission color coordinates are close to the ideal cyan, with high color purity. When combined with red and green phosphors, it can achieve a wider color gamut coverage and a higher color rendering index, meeting the needs of high-end lighting and display. (4) Friendly preparation process: It adopts the conventional high-temperature solid-state reaction method, without the need for complex equipment or harsh atmosphere (such as high-pressure nitrogen). The raw material cost is controllable, the process is simple and stable, and it has great potential for large-scale production. (5) Broad application prospects: This material is not only suitable for general high-quality white light lighting, but also has important application value in wide color gamut backlight display, special lighting (such as museum lighting, medical lighting) and other fields. Attached Figure Description

[0017] Figure 1 The CaLu prepared in the embodiments of this invention 1.99 ScZrAl3O 12 0.01Ce 3+ X-ray diffraction (XRD) pattern of phosphor and standard Lu3Al5O 12 A comparison diagram of the garnet card (PDF#97-018-2354) demonstrates the phase purity and crystal structure.

[0018] Figure 2 It is CaLu 1.99 ScZrAl3O 12 0.01Ce 3+ The excitation spectrum (PLE, monitoring emission at 500 nm) and emission spectrum (PL, excitation at 420 nm) of the phosphor demonstrate its excitation and emission characteristics.

[0019] Figure 3 It is CaLu 1.99 ScZrAl3O 12 0.01Ce 3+ The curve of the integral luminescence intensity of the phosphor as a function of temperature demonstrates its excellent thermal stability. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings. Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0021] To prepare CaLu 1.99 ScZrAl3O 120.01Ce 3+ (x=0.01) For example: Accurately weigh the following high-purity (>99.99%) oxide raw materials according to stoichiometry: CaO 0.0563 g, Lu2O3 0.7944 g, Sc2O3 0.0771 g, ZrO2 0.1232 g, Al2O3 0.3059 g, CeO2 0.0172 g. Place all weighed raw materials into an agate mortar, add an appropriate amount of anhydrous ethanol, and grind thoroughly by hand for 40 minutes until uniformly mixed into a slurry. Place the mixture in an 80℃ oven and dry for 12 hours to obtain a dry mixed precursor powder.

[0022] The precursor powder was loaded into an alumina crucible and gently compacted. The crucible was then placed in a box-type muffle furnace and calcined in air. The program was set as follows: pre-calcination was performed by increasing the temperature to 600°C at 3°C / min and holding for 4 hours; then, the temperature was increased to 1400°C at 5°C / min and calcined at 1400°C for 6 hours. After calcination, the power was turned off, and the sample was allowed to cool naturally to room temperature with the furnace.

[0023] The cooled sintered block was gently crushed and ground in an agate mortar, then passed through a 300-mesh sieve (approximately 48 μm pore size) to obtain a light blue, uniform CaLu. 1.99 ScZrAl3O 12 0.01Ce 3+ The final product is phosphor.

[0024] Using the same method, simultaneously adjust the amounts of CeO2 and Lu2O3 (CaLu 2-x ScZrAl3O 12 :xCe 3+ Keeping the proportions of other raw materials constant, a series of comparative samples with x values ​​of 0.005, 0.008, 0.02, 0.03, 0.04, 0.05, 0.06, 0.09, and 0.12 were prepared.

Claims

1. A near-ultraviolet-excited cyan fluorescent material, characterized in that, Its general chemical formula is: CaLu 2-x ScZrAl3O 12 : xCe³⁺, where x is the molar concentration of Ce³⁺ doping, and 0.005 ≤ x ≤ 0.12; the material has a cubic garnet crystal structure with space group Ia-3d.

2. The near-ultraviolet-excited cyan fluorescent material according to claim 1, characterized in that, The value of x is 0.

01.

3. The near-ultraviolet-excited cyan fluorescent material according to claim 1 or 2, characterized in that, When excited by 420nm light, the material emits broadband cyan fluorescence with a center wavelength of 500nm and a full width at half maximum (FWHM) of 100nm.

4. The near-ultraviolet-excited cyan fluorescent material according to claim 2, characterized in that, The CIE chromaticity coordinates of this material are (0.195, 0.358).

5. The near-ultraviolet-excited cyan fluorescent material according to claim 1, characterized in that, The luminescence intensity of this material at 225°C is 50% of that at room temperature.

6. A method for preparing the near-ultraviolet-excited cyan fluorescent material as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) According to the general chemical formula CaLu 2-x ScZrAl3O 12 (1) Weigh the raw materials CaO, Lu2O3, Sc2O3, ZrO2, Al2O3 and CeO2 according to the stoichiometric ratio of xCe³⁺; (2) Mix and grind the raw materials weighed in step (1) to obtain a mixed precursor; (3) Calcine the mixed precursor obtained in step (2) at a temperature of 1350-1450℃ for 4-8 hours; (4) Grind the product after calcination in step (3) into powder to obtain the fluorescent material.

7. The preparation method according to claim 6, characterized in that, The calcination procedure in step (3) is as follows: first pre-calcin at 600℃ for 4 hours, and then calcin at 1400℃ for 6 hours.

8. A white light-emitting diode, characterized in that, It comprises a near-ultraviolet or blue LED chip and a near-ultraviolet-excited blue fluorescent material as described in any one of claims 1-5.

9. The application of the near-ultraviolet-excited cyan fluorescent material as described in any one of claims 1-5 in the preparation of white light-emitting diodes.

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