Phosphor Dopant Grading for Stable Wavelength-Converted Light
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Solution Overview
Problem
Phosphors used in wavelength converted light emitting devices experience efficiency drops (droop) at high excitation densities, leading to undesirable color shifts and reduced light output, particularly when generating warm white light with multiple phosphors.
Innovation Solution
The use of phosphors with a graded or varying dopant concentration, where the second dopant concentration is less than the first, arranged to reduce excitation density in the more highly doped regions, and the inclusion of a screening structure to further manage excitation intensity, thereby minimizing efficiency drops and color shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a phosphor with high dopant concentration is used to maintain conversion efficiency, then light output is improved, but efficiency drops (droop) and color shifts occur at high excitation densities
Solution Approach 1:
The phosphor is designed with non-uniform dopant distribution, where different regions have different dopant concentrations. The first region has a first dopant concentration and the second region has a second dopant concentration that is less than the first dopant concentration. This local variation in dopant concentration allows different regions to handle different excitation densities, maintaining overall conversion efficiency stability while enabling high light output.
2Stability of the object's composition
If multiple phosphors are used to generate warm white light, then color temperature is improved, but efficiency drops and color shifts worsen due to cumulative saturation effects
Solution Approach 1:
Each phosphor in the multi-phosphor system is designed with non-uniform dopant distribution, creating regions with different dopant concentrations. This allows each phosphor to operate within its optimal efficiency range even when multiple phosphors are combined, preventing cumulative saturation effects and maintaining stable conversion efficiency across the entire warm white light generation system.
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 maintains consistent conversion efficiency across increasing excitation densities, reducing droop and color shifts, ensuring stable light output and color consistency, especially in warm white light generation.
Implementation Method 1
The phosphor absorbs light emitted by the light source and emits light having a second peak wavelength
Data Source
AI summary
In a method according to embodiments of the invention, for a predetermined amount of light produced by a light emitting diode and converted by a phosphor layer comprising a host material and a dopant, and for a predetermined maximum reduction in efficiency of the phosphor at increasing excitation density, a maximum dopant concentration of the phosphor layer is selected.