Phosphor Converted LED Red Light Extraction
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Solution Overview
Problem
Conventional white light emitting LEDs face challenges in achieving high Color Rendering Index (CRI) and luminous efficacy, particularly in generating white light with a CRI of 90 or higher, and in providing improved color gamut for display backlights.
Innovation Solution
Incorporating a solid-state light emitter that generates blue light, a yellow to green-emitting phosphor, a red-emitting manganese-activated fluoride phosphor with a specific index of refraction, and an orange to red-emitting phosphor in a light transmissive material with an index of refraction of 1.40 to 1.43, which enhances luminous flux and color rendering by optimizing the extraction and emission of red light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional phosphor materials with higher index of refraction are used, then the device structure is simpler, but the luminous flux and red light extraction efficiency are reduced
Solution Approach 1:
The patent changes the index of refraction parameter of the light transmissive material from conventional higher values (typically 1.5-1.6) to a specific lower range of 1.35-1.45. This parameter change optimizes the optical matching between the light transmissive material and the red-emitting phosphor (which has index of refraction approximately 1.4), thereby improving red light extraction efficiency and overall luminous flux by reducing internal reflections and light trapping effects.
2Illumination intensity
If red and orange light emitting phosphors are added to achieve high CRI, then the Color Rendering Index is improved, but the device complexity increases
Solution Approach 1:
The patent combines multiple phosphor materials (yellow-green emitting phosphor and red-emitting phosphor with Mn4+ activation) into a single integrated light transmissive material matrix. This merging approach achieves high CRI (90 or higher) by producing a balanced spectrum with appropriate power ratios between yellow-green and red components, while maintaining relatively simple device structure by incorporating all phosphors within one encapsulant rather than using separate layers or components.
3Quantity of substance
If the index of refraction of light transmissive material is increased, then the material density is improved, but the red light extraction efficiency is reduced
Solution Approach 1:
The patent optimizes the index of refraction parameter of the light transmissive material to a specific range (1.35-1.45) that closely matches the index of refraction of the red-emitting phosphor (approximately 1.4). This parameter optimization reduces the refractive index mismatch between the encapsulant and phosphor particles, minimizing internal reflections and light trapping at interfaces, thereby significantly improving red light extraction efficiency and overall device luminous flux.
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 configuration results in a substantial increase in luminous flux and CRI, achieving white light with a General CRI of 90 or higher and improved color gamut, while maintaining a Correlated Color Temperature between 2700K and 3000K.
Implementation Method 1
a solid-state light emitter operable to generate blue light
Implementation Method 2
a yellow to green-emitting phosphor excitable by blue light and operable to generate light
Implementation Method 3
a light transmissive material with an index of refraction of 1.40 to 1.43... increasing red light extraction (and/or excitation) of the red-emitting manganese-activated fluoride phosphor
Data Source
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AI summary
There is provided a white light emitting device comprising: a solid-state light emitter operable to generate blue light with a dominant wavelength in range 440 nm to 470 nm; a yellow to green-emitting phosphor excitable by blue light and operable to emit light with a peak emission wavelength in a range 500 nm to 575 nm; a red-emitting manganese-activated potassium hexafluorosilicate phosphor excitable by blue light and operable to emit light with a peak emission wavelength between 631nm and 632nm; and an orange to red-emitting phosphor excitable by blue light and operable to generate light with a peak emission wavelength in a range 575 nm to 600 nm, wherein the device is operable to generate white light with a Correlated Color Temperature of between about 2700K and about 3000K and wherein over a wavelength range 460 nm to 600 nm a maximum deviation between the intensity of the light emitted by the device normalized to a CIE 1931 XYZ relative luminance Y=100 compared with the intensity of light of a black-body curve of the same Correlated Color Temperature that is normalized to a CIE 1931 XYZ relative luminance Y=100 is less than 0.3.