Phosphor Layer Segmentation for LED Color Stability
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Solution Overview
Problem
White LED lamps face issues with phosphor saturation and reduced efficiency due to high incident fluxes from LED chips, leading to color instability and decreased lumen output, especially in UV-LED devices where phosphors with slow decay times are prone to saturation.
Innovation Solution
Selecting and arranging phosphors such that the product of incident LED flux, excitation cross-section, and phosphor decay time is less than 0.3, with faster decaying phosphors placed closer to the LED chip and slower decaying phosphors further away to minimize saturation, or using a combination of both to achieve the desired figure of merit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If phosphors with high absorption and quantum efficiency are used to reduce bleedthrough, then UV absorption improves, but phosphor saturation occurs due to slow decay times under high incident flux
Solution Approach 1:
The phosphor layer is segmented into multiple layers with different decay time characteristics. A first phosphor layer with faster decay time is positioned closer to the LED chip to handle high incident flux, while a second phosphor layer with slower decay time is positioned farther away where incident flux is reduced, preventing saturation while maintaining high UV absorption efficiency.
Solution Approach 2:
Different regions of the phosphor coating are assigned different phosphor materials with locally optimized decay times. The region closer to the LED chip receives phosphors with faster decay times to withstand high flux, while regions farther away can use phosphors with slower decay times for higher quantum efficiency, creating a spatially varying quality distribution.
2Loss of energy
If phosphor layer thickness is increased to improve UV absorption, then quantum efficiency improves, but saturation is exacerbated due to higher incident flux exposure
Solution Approach 1:
The total phosphor layer thickness is segmented into multiple sub-layers. Each sub-layer has optimized thickness to prevent saturation while collectively providing high UV absorption. The first layer has smaller thickness to handle high flux near the chip, while subsequent layers have larger cumulative thickness where flux is attenuated.
Solution Approach 2:
Instead of increasing thickness in one dimension, the solution distributes phosphor absorption across multiple spatial dimensions by creating a multi-layer structure. This dimensional approach allows each layer to operate below saturation threshold while the cumulative effect achieves high overall absorption efficiency.
3Device complexity
If a single phosphor material is used to simplify the device structure, then manufacturing complexity reduces, but color stability varies with drive current due to saturation effects
Solution Approach 1:
The phosphor system is segmented into multiple materials with different decay time characteristics arranged in layers. This segmentation allows each material to operate in its optimal flux range, preventing saturation-induced color shifts and maintaining stable color point across varying drive currents.
Solution Approach 2:
The patent uses a composite phosphor structure combining multiple phosphor materials with complementary decay time properties. This composite approach creates a synergistic system where the faster decaying phosphor protects against saturation while the slower decaying phosphor maintains color stability, achieving performance superior to single-material systems.
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 phosphor saturation, maintains high lamp efficiency, and ensures stable color output across varying drive currents, improving the overall performance of white LED lamps.
Implementation Method 1
The phosphorescence process involves the absorption of the primary light by a photoluminescent phosphor material, which acts to excite the atoms of the phosphor material to emit the secondary light.
Data Source
AI summary
An LED lamp including an LED and one or more phosphors, wherein for each phosphor, a figure of merit (FOM) defined as the product of (incident LED flux)×(excitation cross-section of the phosphor)×(phosphor material decay time) is less than 0.3. Such an arrangement provides a light emitting device with improved lumen output and color stability over a range of drive currents.