Conversion LED Phosphor Blend for High Efficiency Warm White
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Solution Overview
Problem
Existing conversion LEDs face inefficiencies and instability at high currents, particularly with nitride or oxynitride phosphors, leading to significant conversion losses and color rendering issues, especially in warm white LEDs with low color temperatures and high efficiency requirements.
Innovation Solution
A combination of a green to green-yellow emitting garnet phosphor and a short-wave, narrow-band orange-red emitting nitridosilicate phosphor is used, which significantly reduces the blue-green gap in the white spectrum, allowing for the use of shorter wavelength LEDs while maintaining high color rendering index (CRI) and stability across a wide range of blue LED wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If nitride or oxynitride phosphors such as M2Si5N8:Eu are used to achieve high efficiency, then conversion efficiency is improved, but stability at high currents (≥250 mA) deteriorates with significant conversion losses and color location instability
Solution Approach 1:
The patent changes the chemical composition parameters of the phosphor by substituting Ba with Sr in the M2Si5N8:Eu phosphor structure. This compositional parameter change results in a phosphor that maintains high conversion efficiency while achieving superior stability at high currents, eliminating the conversion losses and color instability problems of previous formulations
Solution Approach 2:
The patent creates a composite phosphor system by combining Sr2Si5N8:Eu with specific ratios of other phosphors (Y3Al5O12:Ce and CaAlSiN3:Eu) to form a multi-component phosphor blend. This composite approach allows each phosphor component to contribute its strengths, achieving both high efficiency and stability at operating currents of 350 mA and above
2Illumination intensity
If long-wave blue LEDs (455-465 nm) are used to compensate for the blue-green gap and improve color rendering, then color reproduction is improved, but system efficiency deteriorates due to lower LED efficiency
Solution Approach 1:
The patent shifts the excitation wavelength parameter from long-wave blue (455-465 nm) to shorter wavelength blue (430-450 nm). This parameter change in excitation wavelength allows the use of more efficient short-wave blue LEDs while the modified phosphor composition (particularly the Sr2Si5N8:Eu component) is optimized to absorb this shorter wavelength and emit the necessary blue-green and red components for good color rendering
3Loss of energy
If shorter wavelength blue LEDs (430-450 nm) are used to improve efficiency, then system efficiency is improved, but color rendering deteriorates due to the blue-green gap in the spectrum
Solution Approach 1:
The patent employs a composite phosphor system where Sr2Si5N8:Eu provides strong blue-green emission when excited by short-wave blue LEDs, Y3Al5O12:Ce provides yellow emission, and CaAlSiN3:Eu provides red emission. This multi-component composite fills the blue-green spectral gap that would otherwise exist when using short-wave blue LEDs, achieving both high efficiency and excellent color rendering with Ra≥90
4Loss of energy
If phosphors with high conversion efficiency are used, then efficiency is improved, but temperature stability deteriorates with increased temperature extinction behavior
Solution Approach 1:
The patent modifies the phosphor composition parameters by using Sr2Si5N8:Eu with specific Eu doping concentrations and Sr/Ba ratios. These compositional changes result in a phosphor material that maintains its luminescence properties at elevated temperatures, reducing temperature extinction behavior while preserving high conversion efficiency
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 solution achieves improved efficiency, stability, and uniform color quality, with a CRI of over 80 and reduced dependence on blue LED wavelength, ensuring consistent performance and extended lifespan of warm white LEDs.
Implementation Method 1
A combination of a green to green-yellow emitting garnet phosphor and a short-wave, narrow-band orange-red emitting nitridosilicate phosphor is used
Data Source
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AI summary
A conversion LED for generating white light uses a phosphor mixture consisting of a first phosphor of the LuAGaG type and a second phosphor of the nitridosilicate type. This achieves very high efficiency.