Wavelength-Shifting Phosphor for LED Chromaticity Stability
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Solution Overview
Problem
Light-emitting devices using LEDs experience significant chromaticity changes, or 'color shift,' due to variations in temperature and driving current, which affect the balance of yellow, green, and red light emissions, making it difficult to maintain desired chromaticity.
Innovation Solution
Incorporating a wavelength-shifting phosphor, such as a yellow-green/yellow phosphor with a peak wavelength between 520 nm and 660 nm, which adjusts its fluorescence peak wavelength in the same direction as the excitation light, ensuring minimal chromaticity change even when the blue LED's emission wavelength shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a blue LED chip is used as an excitation light source with phosphors to generate white light, then the light-emitting device can achieve high efficiency and long life, but the emission wavelength of the blue LED changes due to temperature variation or driving current change, causing significant chromaticity change or color shift
Solution Approach 1:
The patent applies parameter changes by selecting phosphors with specific characteristics: yellow phosphor with peak wavelength 560-580nm and full width at half maximum 80-100nm, green phosphor with peak wavelength 520-540nm and full width at half maximum 40-60nm. These parameter selections enable the phosphors to compensate for blue LED wavelength shifts, maintaining stable chromaticity despite temperature or current variations
Solution Approach 2:
The patent uses composite materials by combining multiple phosphors (yellow and green) with the blue LED chip. This composite phosphor system creates a synergistic effect where the wavelength characteristics of individual phosphors complement each other, providing robust chromaticity stability that single phosphors cannot achieve alone
2Ease of operation
If the intensity of white light is changed by changing the emission intensity of the blue LED, then light adjustment functionality is achieved, but the emission wavelength of the blue LED changes due to change in driving current, making the color shift problem remarkable
Solution Approach 1:
The patent utilizes parameter changes in the phosphor characteristics to compensate for driving current-induced wavelength shifts. The specific selection of yellow phosphor (560-580nm peak) and green phosphor (520-540nm peak) ensures that as the blue LED wavelength shifts with current changes, the phosphor emission characteristics adjust accordingly, maintaining consistent white light chromaticity across different brightness levels
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 approach effectively compensates for chromaticity changes caused by shifts in the blue LED's peak wavelength, maintaining consistent color output and reducing the problem of color shift in light-emitting devices.
Implementation Method 1
A light-emitting device using a light-emitting diode (LED) is composed principally of a combination of an LED chip as an excitation light source and a phosphor
Implementation Method 2
Incorporating a wavelength-shifting phosphor, such as a yellow-green/yellow phosphor with a peak wavelength between 520 nm and 660 nm, which adjusts its fluorescence peak wavelength in the same direction as the excitation light
Data Source
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AI summary
A light-emitting device of an embodiment includes a light-emitting element emitting blue excitation light and a first phosphor excited by the blue excitation light and emitting fluorescence. A peak wavelength of the fluorescence is not shorter than 520 nm and shorter than 660 nm and the peak wavelength of the fluorescence shifting in the same direction when a peak wavelength of the blue excitation light shifts. The first phosphor is one of a yellow phosphor emitting yellow fluorescence, a green phosphor emitting green fluorescence, a yellow-green/yellow phosphor emitting yellow-green/yellow fluorescence and a red phosphor emitting red fluorescence.