Multi-Layer Phosphor Wavelength Conversion for High NTSC Ratio
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Solution Overview
Problem
Current white light-emitting devices using semiconductor light-emitting elements and phosphors suffer from poor color reproducibility and luminous efficiency, particularly in the red spectrum, making them unsuitable for high-quality illumination applications like large LCD TVs, where they fail to achieve the desired NTSC ratio and spectral purity for red, green, and blue colors.
Innovation Solution
A light-emitting device with a wavelength conversion unit comprising multiple phosphors with distinct absorption characteristics, where at least one phosphor can absorb secondary light emitted by another, arranged in a stacked configuration to minimize emission loss and enhance luminance, using specific phosphor compositions like divalent europium-activated halophosphates, aluminate, and silicate phosphors for blue, green, and red light emission, optimized for a gallium nitride-based semiconductor light-emitting element with a peak wavelength between 380 nm to 450 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single phosphor layer is used for wavelength conversion, then the device structure is simple, but the color reproducibility and luminous efficiency are poor
Solution Approach 1:
The single phosphor layer is segmented into multiple phosphor layers, each containing different phosphor materials with specific emission characteristics. This segmentation allows each layer to be optimized for specific color wavelengths (red, green, blue), thereby improving overall color reproducibility and luminous efficiency while maintaining manageable structural complexity
Solution Approach 2:
Each phosphor layer is assigned specific local quality characteristics by selecting phosphor materials with tailored emission spectra and absorption characteristics. The first phosphor layer emits red light with specific wavelength range, the second emits green light, and the third emits blue light, creating localized optimization for different color regions to achieve superior overall color reproduction
2Manufacturing precision
If multiple phosphor layers are used to improve color reproducibility, then the NTSC ratio improves, but the device complexity increases
Solution Approach 1:
The wavelength conversion unit is segmented into three distinct phosphor layers, each optimized for specific color emission (red, green, blue). This segmentation enables independent optimization of each layer's phosphor composition and thickness to maximize NTSC ratio while keeping the overall device complexity manageable through modular architecture
Solution Approach 2:
The patent transitions from a single-layer to a multi-layer vertical structure, adding the dimension of layer stacking. This dimensional change allows simultaneous optimization of multiple color wavelengths in different spatial layers, achieving high NTSC ratio while organizing complexity in a structured vertical arrangement rather than horizontal dispersion
3Power
If phosphors with broad emission spectra are used, then the luminous output is high, but the spectral purity and color fidelity deteriorate
Solution Approach 1:
Each phosphor layer is designed with local quality optimization by selecting phosphor materials with narrow emission spectra tailored to specific color wavelengths. The red phosphor layer emits in a narrow red wavelength range, green phosphor in a narrow green range, and blue phosphor in a narrow blue range, ensuring high spectral purity for each color while maintaining sufficient luminous output through optimized phosphor concentration and layer thickness
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 solution achieves high luminance and improved color reproducibility (NTSC ratio) by efficiently extracting and emitting light with narrow spectral widths for red, green, and blue, producing natural white light akin to blackbody radiation, suitable for high-quality illumination and improved brightness and color fidelity.
Implementation Method 1
a first phosphor layer containing a first phosphor which emits red light in response to absorption of the primary light; a second phosphor layer containing a second phosphor which emits green light in response to absorption of the primary light
Implementation Method 2
wherein the first phosphor layer is arranged closer to the light-emitting element than the second phosphor layer, and the second phosphor can absorb the red light emitted by the first phosphor
Data Source
AI summary
A light-emitting device includes a light-emitting element for emitting primary light, and a wavelength conversion unit for absorbing part of the primary light and emitting secondary light having a wavelength longer than that of the primary light, wherein the wavelength conversion unit includes plural kinds of phosphors having light absorption characteristics different from each other, and then at least one kind of phosphor among the plural kinds of phosphors has an absorption characteristic that can absorb the secondary light emitted from at least another kind of phosphor among the plural kinds of phosphors.