Phosphor Composite Stabilizes LED Chromaticity
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Solution Overview
Problem
Semiconductor light emitting devices with mixed color emission face challenges in maintaining consistent chromaticity due to variations in the emission wavelength of nitride semiconductor light emitting elements, which affect the excitation intensity of phosphors, leading to unwanted chromaticity variations.
Innovation Solution
Incorporating a combination of phosphors with specific excitation spectrum characteristics, such as SOSE and YAG phosphors, where the excitation intensity of one phosphor increases with wavelength while the other remains flat or decreases, ensuring a stable excitation spectrum region that compensates for variations in the semiconductor light emitting element's peak wavelength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single phosphor is used for wavelength conversion, then the device structure is simple, but chromaticity variation occurs when the semiconductor light emitting element's peak wavelength shifts
Solution Approach 1:
The patent combines multiple phosphors with different excitation spectrum characteristics into a single phosphor layer. Specifically, it merges a first phosphor whose excitation intensity increases with wavelength and a second phosphor whose excitation intensity is flat or decreases with wavelength, creating a composite phosphor system that compensates for peak wavelength shifts and stabilizes chromaticity.
Solution Approach 2:
The patent uses composite phosphor materials with complementary excitation spectrum properties. By selecting phosphors whose excitation intensity responses to wavelength changes are opposite or complementary, the composite material achieves wavelength-insensitive excitation, thereby maintaining stable chromaticity despite variations in the semiconductor light emitting element's peak wavelength.
2Manufacturing precision
If the semiconductor light emitting element's composition and thickness are precisely controlled, then emission wavelength distribution is narrow, but manufacturing difficulty increases
Solution Approach 1:
The patent converts the harmful effect of emission wavelength variation into a beneficial outcome. Instead of trying to eliminate wavelength distribution through precise manufacturing control, it selects phosphors whose excitation intensity characteristics compensate for wavelength shifts, transforming the manufacturing challenge into a design opportunity for broader wavelength tolerance.
Solution Approach 2:
The patent changes the approach from controlling the semiconductor layer parameters (composition, thickness) to selecting phosphors with appropriate excitation spectrum parameters. By shifting the control parameter from the light emitting element to the phosphor material properties, the system achieves wavelength stability without requiring extreme manufacturing precision.
3Use of energy by moving object
If phosphor excitation intensity is highly wavelength-dependent, then wavelength conversion efficiency is high at peak wavelength, but chromaticity stability decreases when peak wavelength shifts
Solution Approach 1:
The patent applies different local quality characteristics to different phosphors in the composite system. The first phosphor is selected with excitation intensity that increases with wavelength, while the second phosphor is selected with excitation intensity that is flat or decreases with wavelength. This local differentiation in excitation characteristics allows the overall system to achieve wavelength-insensitive excitation while maintaining efficient wavelength conversion.
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 reduces chromaticity variation by maintaining consistent excitation intensity across a range of wavelengths, even when the semiconductor light emitting element's peak wavelength shifts, thereby stabilizing the mixed color output.
Implementation Method 1
a first phosphor which absorbs light emitted from the semiconductor light emitting element and emits first wavelength-converted light
Implementation Method 2
a second phosphor which absorbs light emitted from the semiconductor light emitting element and emits second wavelength-converted light
Data Source
AI summary
A semiconductor light emitting device includes: a semiconductor light emitting element; a first phosphor which absorbs light emitted from the semiconductor light emitting element and emits first wavelength-converted light; and a second phosphor which absorbs light emitted from the semiconductor light emitting element and emits second wavelength-converted light. The first phosphor has a first excitation spectrum region where excitation intensity increases with increasing wavelength around a peak wavelength of the semiconductor light emitting element. The second phosphor has a second excitation spectrum region where excitation intensity is flat or decreases with respect to increasing wavelength around the peak wavelength of the semiconductor light emitting element.