Nitride Phosphor Mixture for High Thermal Stability in LED Packages
Solution Overview
Problem
Current yellow phosphors used in LEDs have low thermal stability and poor water resistance, leading to luminance deterioration and color coordinate variations, and there is a need for phosphors with high emission efficiency and excellent color rendering characteristics for white light production.
Innovation Solution
A yellow light emitting phosphor mixture comprising a first phosphor (Lu3Al5O12:Ce or SrSi2O2:Eu) emitting light in the 510-550 nm range, a second phosphor (Li-α-SiAlON:Eu) emitting light in the 560-600 nm range, and a third phosphor ((Sr, Ca)AlSiN3:Eu) with a light absorption rate of 50% or less at 550 nm, excited by near ultraviolet or blue light to produce a spectrum with a full width at half maximum of 120 nm or more.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If oxide phosphors (YAG) are used for yellow light emission, then yellow light can be emitted, but thermal stability is low causing luminance deterioration and color coordinate variation at high temperature
Solution Approach 1:
The patent uses a composite phosphor system combining multiple nitride-based phosphors (β-SiAlON:Eu for yellow-green, CaAlSiN3:Eu for red) rather than a single oxide phosphor. This composite approach leverages the high thermal stability and chemical inertness of nitride materials while achieving broad spectrum emission through the combination of different phosphors with complementary emission characteristics.
Solution Approach 2:
The patent changes the material composition parameters from oxide-based (YAG) to nitride-based (SiAlON, CaAlSiN3) phosphors. This fundamental material parameter change provides superior thermal stability and chemical resistance while maintaining or improving luminous performance through optimized emission wavelength coverage.
2Illumination intensity
If oxide phosphors and silicate-based phosphors are used, then yellow and green light can be emitted, but water resistance is poor affecting LED package reliability
Solution Approach 1:
The patent employs a composite system of nitride-based phosphors (β-SiAlON:Eu and CaAlSiN3:Eu) that inherently possess excellent chemical inertness and moisture resistance. The nitride bond strength and crystalline structure provide superior protection against water degradation compared to oxide and silicate phosphors, ensuring long-term reliability in LED packages.
Solution Approach 2:
The patent selects nitride phosphor materials that offer enhanced durability and resistance to environmental degradation (water and moisture). These materials maintain their optical and structural properties over time in humid conditions, effectively extending the operational lifespan of LED devices.
3Power
If blue LED output is increased, then luminous output improves, but wavelength shifts to shorter wavelength reducing excitation efficiency of yellow phosphors
Solution Approach 1:
The patent changes the emission wavelength parameters of the phosphors to match the shifted blue LED spectrum. By using β-SiAlON:Eu with emission extending to shorter wavelengths and CaAlSiN3:Eu with appropriate red emission, the system maintains high excitation efficiency even when blue LED wavelength shifts occur, preserving overall luminous output.
Solution Approach 2:
The composite phosphor system provides a broader absorption spectrum that can accommodate wavelength variations in the blue LED excitation source. The combination of phosphors with different emission characteristics ensures that a wider range of blue wavelengths can be effectively converted, maintaining efficiency despite spectral shifts.
4Device complexity
If single phosphor system is used, then device complexity is low, but color rendering characteristics are insufficient for high-quality white light
Solution Approach 1:
The patent uses a composite phosphor system combining β-SiAlON:Eu (yellow-green emission) and CaAlSiN3:Eu (red emission) to achieve broad spectrum coverage. This composite approach enables excellent color rendering by emitting across multiple wavelength regions, producing high-quality white light with a wide color gamut while maintaining manageable device complexity.
Solution Approach 2:
The patent segments the white light emission into multiple wavelength components by using different phosphors for different spectral regions. The β-SiAlON:Eu phosphor covers the yellow-green region while CaAlSiN3:Eu covers the red region, and when combined with blue LED excitation, this segmentation creates a complete spectrum for superior color rendering.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The phosphor mixture achieves high luminance and excellent color rendering characteristics, improving visibility and emission efficiency while minimizing light absorption, resulting in high-quality white light emission with a wide color gamut and improved reliability.
Implementation Method 1
These phosphors may usually emit yellow light, green light, and red light... a fluorescent material that absorbs at least some of said light emitted from said semiconductor light emitting element and emits a fluorescent light of a wavelength different from said light
Implementation Method 2
a phosphor emitting fluorescence of a first wavelength, having optical absorption of at most 30% at a wavelength longer than said first wavelength and in a relation of complementary color to the first wavelength
Data Source
AI summary
Disclosed are phosphors and, more particularly, yellow light emitting phosphors and light emitting device packages using the same. The yellow light emitting phosphor includes a first phosphor to emit light having a central wavelength located within a band of 510 nm to 550 nm, a second phosphor adapted to be mixed with the first phosphor to emit light having a central wavelength located within a band of 560 nm to 600 nm, and a third phosphor adapted to be mixed with the first and second phosphors to emit light having a central wavelength located within a band of 610 nm to 630 nm, the third phosphor having a light absorption rate of 50% or less at a wavelength of 550 nm.