Indirectly Pumped Red Phosphor for High CRI White Laser
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Solution Overview
Problem
Current laser-based lighting devices with high color rendering index (CRI) struggle to produce a wide range of color temperatures due to limitations in red spectral emission, which is sensitive to temperature and photo saturation, and often result in high CCT light sources with low CRI.
Innovation Solution
A lighting device comprising a laser light source, a first luminescent material for green/yellow emission, and a second luminescent material for orange/red emission, where the second material is indirectly pumped by the first material to reduce thermal and photo-saturation loads, and a thermally conductive element is used to manage heat.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If red phosphor is used to improve color rendering index (CRI), then CRI is improved, but the red phosphor becomes sensitive to temperature and photo saturation
Solution Approach 1:
The patent introduces a yellow phosphor as an intermediary between the blue laser and the red phosphor. The blue laser first excites the yellow phosphor, which then emits light that excites the red phosphor. This indirect excitation path reduces the thermal and photo-saturation load on the red phosphor, allowing it to maintain high CRI performance without suffering from direct blue laser damage or excessive heating.
2Illumination intensity
If direct pumping of red phosphor by blue laser is used to achieve high brightness, then brightness is improved, but thermal quenching and photo saturation occur
Solution Approach 1:
The yellow phosphor serves as a mediator that converts blue laser light into yellow light, which then pumps the red phosphor. This two-stage conversion process distributes the energy load, preventing direct thermal quenching and photo saturation of the red phosphor while maintaining high brightness output through the combined emission of yellow and red phosphors.
Solution Approach 2:
The patent changes the excitation parameter for the red phosphor from direct blue laser wavelengths to yellow wavelengths emitted by the yellow phosphor. This parameter change in the excitation spectrum allows the red phosphor to operate at lower temperatures and reduced photo-saturation levels while maintaining efficient light conversion and high brightness.
3Power
If high power blue laser is used to pump phosphors, then light output is improved, but thermal management becomes difficult
Solution Approach 1:
The patent segments the phosphor conversion process into two separate stages: yellow phosphor conversion first, then red phosphor conversion. This segmentation allows each phosphor to be optimized for its specific excitation wavelength and operated at lower individual power levels, reducing the cumulative thermal load and simplifying thermal management compared to direct high-power blue laser pumping of both phosphors simultaneously.
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 enables the generation of high-quality white light with a CRI >90 and CCT in the range of 2700-4000K, while minimizing thermal and photo-saturation issues in red phosphors, achieving higher brightness compared to existing LED sources.
Implementation Method 1
a first converter material, comprising a first luminescent material, configured to convert at least part of the first light source light into first luminescent material light
Implementation Method 2
a second converter material, comprising a second luminescent material, configured to convert part of the first luminescent material light into second luminescent material light
Implementation Method 3
a first thermally conductive element in thermal contact with at least part of the second luminescent material
Data Source
AI summary
The invention provides a lighting device (1000) comprising: —a first light source (110) configured to generate first light source light (111), having a first light source light spectral power distribution, wherein the first light source (110) comprises a laser light source (10), and wherein the first light source light (111) has an optical axis (0); —a first converter material (215), comprising a first luminescent material (210), configured to convert at least part of the first light source light (111) into first luminescent material light (211) having a first luminescent material light spectral power distribution, wherein the first luminescent material light (211) has one or more wavelengths in the green and/or yellow wavelength range; —a second converter material (225), comprising a second luminescent material (220), configured to convert part of the first luminescent material light (211) into second luminescent material light (221) having a second luminescent material light spectral power distribution different from the first luminescent material light spectral power distribution, wherein the second luminescent material light (221) has one or more wavelengths in the orange and/or red wavelength range; wherein the first light source (110), the first converter material (215), and the second converter material (225) are configured such that first light source light (111) can only reach the second converter material (225) after scattering via the first converter material (215); wherein the optical axis (O) is incident on the first converter material (215) and is not incident on the second converter material (225); and —a first thermally conductive element (410) in thermal contact with at least part of the second luminescent material (220).