Phosphor Mixture for White LED Color Stability
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Solution Overview
Problem
White LED lighting units suffer from significant color shift and inadequate color rendering properties due to insufficient red and green emission components, leading to bluish white light and poor color reproducibility, especially when increased emission intensity causes temperature-related fluctuations in phosphor emission efficiency.
Innovation Solution
A phosphor mixture with a composition formula MmAaBbOoNn:Z, including elements like Ca, Al, Si, and Eu, with a garnet crystal structure and emission spectrum peaking between 500 nm to 630 nm, is developed to maintain consistent emission intensity across a temperature range of 25°C to 200°C, minimizing color shift and enhancing color rendering properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the emission intensity of white LED lighting unit is increased, then the luminance is improved, but the color shift occurs due to temperature-related fluctuations in phosphor emission efficiency
Solution Approach 1:
The patent applies parameter changes by selecting phosphors with specific characteristics (emission peaks, temperature coefficients) and adjusting their mixing ratios to achieve stable color output. The second phosphor is specifically selected to have an emission peak between 560-630nm and a temperature coefficient of -0.02%/°C or less, compensating for the temperature-dependent efficiency changes of the first phosphor during high-intensity operation.
Solution Approach 2:
The patent uses a composite phosphor mixture combining two different phosphor materials with complementary characteristics. The first phosphor (emitting 480-530nm) and second phosphor (emitting 560-630nm) are mixed in specific ratios to create a composite material whose overall emission characteristics remain stable under temperature variations, resolving the color shift problem during high luminance operation.
2Device complexity
If conventional phosphor combinations are used to generate white light, then the device complexity is reduced, but the color rendering properties deteriorate due to insufficient red and green emission components
Solution Approach 1:
The patent applies local quality by targeting specific wavelength regions (red and green) with the second phosphor having an emission peak between 560-630nm. This phosphor specifically supplements the insufficient red and green emission components in the spectrum, improving color rendering properties in these critical regions while maintaining the simplicity of the two-phosphor overall structure.
3Illumination intensity
If the emission intensity of phosphors is increased to improve luminance, then the brightness is improved, but the emission efficiency deteriorates at elevated temperatures
Solution Approach 1:
The patent applies the counterweight principle by using the second phosphor with a low temperature coefficient (-0.02%/°C or less) to compensate for the efficiency deterioration of the first phosphor at elevated temperatures. The second phosphor maintains stable emission intensity, effectively counterbalancing the temperature-induced efficiency loss and maintaining overall luminance without energy waste.
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 ensures minimal variation in emission intensity and chromaticity, suppressing color shift and achieving high color rendering indices, even under high temperature conditions, resulting in improved luminance and color fidelity for white LED lighting units.
Implementation Method 1
A phosphor mixture which emits a visible light under an excitation of an excitation light of ultraviolet to green color
Data Source
AI summary
To provide a phosphor mixture realizing a light emitting device having a phosphor and a light emission element, by which light emission is performed, with a small color shift due to a feeding current and having an excellent color rendering properties. CaAlSin3:Eu as a red phosphor and YAG:Ce as a yellow phosphor are manufactured, and emission spectra thereof are obtained. Meanwhile, the emission spectrum of an excitation light emitted by a light emitting part is obtained. From the emission spectra thus obtained, a relative mixing ratio of each phosphor is obtained by simulation, so that a correlated color temperature of the light emitting device becomes a target temperature. Then, based on the relative mixing ratio thus obtained, each phosphor is measured and mixed, and a phosphor mixture is thereby obtained.