White LED Phosphor Composition for Stable High-CRI Emission
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Solution Overview
Problem
White LEDs using ultraviolet to violet LEDs face challenges in maintaining emission intensity over long-term continuous lighting due to differences in phosphor characteristics, particularly with europium activated alkaline earth orthosilicate phosphors being more susceptible to environmental degradation.
Innovation Solution
The use of a combination of an ultraviolet to violet LED, a cerium activated yttrium aluminum garnet (YAG) phosphor, and a blue phosphor, where the blue phosphor absorbs ultraviolet to violet light and converts it to blue light, which is then converted to green to yellow light by the YAG phosphor, resulting in a stable and efficient white light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If europium activated alkaline earth orthosilicate phosphor is used in ultraviolet to violet LED, then color rendering is improved, but emission intensity degrades faster over long-term continuous lighting
Solution Approach 1:
The patent uses a composite phosphor system combining cerium activated yttrium aluminum garnet (YAG) phosphor and blue phosphor materials. This composite approach leverages the stability of YAG phosphor excited by ultraviolet to violet LED while adding blue phosphor to convert remaining ultraviolet to violet light into blue light, achieving both good color rendering and stable emission intensity over long-term operation.
2Illumination intensity
If blue LED is used with phosphors, then white light is obtained, but blue light hazards and health problems occur due to strong blue light emission
Solution Approach 1:
The patent converts the potentially harmful strong blue light emission into a beneficial effect by using blue phosphor materials that absorb the remaining ultraviolet to violet light from the LED and convert it to blue light through photoluminescence. This process reduces the harmful direct blue light while maintaining useful blue light components for white light generation, thereby mitigating blue light hazards.
3Adaptability or versatility
If ultraviolet to violet LED with multiple phosphors is used, then wide color reproducibility is achieved, but device complexity increases
Solution Approach 1:
The patent applies local quality by assigning specific functions to different phosphor materials: cerium activated YAG phosphor primarily converts ultraviolet to violet light into yellow-green light for good color rendering, while blue phosphor materials convert remaining ultraviolet to violet light into blue light. This functional differentiation achieves wide color reproducibility while keeping the phosphor combination manageable through clear role assignment.
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
This configuration achieves high color rendering and maintains luminous flux effectively over long periods, reducing the degradation issues associated with traditional phosphors, while also minimizing blue light emission to mitigate health risks.
Implementation Method 1
a blue phosphor, wherein the blue phosphor absorbs light emitted by the light emitting diode and converts the absorbed light to blue light
Implementation Method 2
one of the phosphors being at least a cerium activated yttrium aluminum garnet based phosphor
Data Source
AI summary
According to one embodiment, a white light source includes a combination of a light emitting diode and phosphors. One of the phosphors is at least a cerium activated yttrium aluminum garnet-based phosphor. There is no light emission spectrum peak at which a ratio of a largest maximum value to a minimum value is greater than 1.9. The largest maximum value is largest among at least one maximum value present in a wavelength range of 400 nm to 500 nm in a light emission spectrum of white light emitted from the white light source. The minimum value is adjacent to the largest maximum value in a longer wavelength side of the light emission spectrum.