Phosphor Converted LED Layered Phosphor Thickness Tolerance
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Solution Overview
Problem
Current warm white phosphor converted LEDs (pcLEDs) face challenges in achieving optimized luminous efficiency and color rendering due to variations in phosphor layer thickness, leading to deviations from the Planckian locus and non-white emission colors.
Innovation Solution
A light emitting device comprising a blue emitting LED, a first ceramic phosphor layer with an emission wavelength between 500 nm and 560 nm, and a second phosphor layer with a color point u' between 0.24 and 0.35 and a peak emission of λp > 600nm, utilizing a material of the general formula M1-x-y-zSi1+zAl1-zN3-zOz:Eu2+, where M is Ca, Sr, or a mixture, with specific doping levels for Ce and Eu, to enhance color rendering and compensate for layer thickness variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If variations in phosphor layer thickness are used in current warm white pcLEDs, then manufacturing flexibility is improved, but color rendering deteriorates due to deviation from Planckian locus
Solution Approach 1:
The patent changes the spectral parameters of the phosphor materials by selecting a green phosphor with specific emission characteristics (500-560nm) and an orange phosphor with specific color coordinates (u' between 0.24-0.35). This parameter selection makes the system tolerant to thickness variations while maintaining color stability near the Planckian locus.
Solution Approach 2:
The patent uses a composite phosphor system combining green-emitting ceramic phosphor (e.g., Lu3Al5O12:Ce or SrSi2O2N2:Eu) and orange-emitting phosphor (e.g., CaAlSiN3:Eu). This composite material approach creates synergistic effects where the specific combination compensates for thickness variations and maintains color rendering.
2Illumination intensity
If red phosphor layer thickness is increased to improve color rendering, then color saturation is improved, but emission color stability deteriorates due to deviation from white light
Solution Approach 1:
The patent selects an orange phosphor with peak emission >600nm and specific color coordinates (u' between 0.24-0.35) that provides optimal color saturation while maintaining stability. This specific parameter range prevents over-saturation that would cause deviation from the Planckian locus.
Solution Approach 2:
The patent assigns different functional qualities to different phosphor layers: the green phosphor provides the base emission and the orange phosphor provides targeted color enhancement in the red region. This local functional differentiation allows color saturation improvement without compromising overall emission stability.
3Loss of energy
If phosphor interaction is reduced through layered structure, then luminous efficiency is improved, but color rendering precision deteriorates due to thickness variations
Solution Approach 1:
The patent selects phosphor materials with emission spectra that are optimally spaced to minimize overlap and interaction losses. The green phosphor (500-560nm) and orange phosphor (>600nm) have sufficient spectral separation to reduce absorption losses while their specific emission characteristics maintain color point stability.
Solution Approach 2:
The patent divides the phosphor system into distinct layered regions with green phosphor and orange phosphor separated in space. This segmentation reduces harmful interactions between phosphors while the specific material selection ensures that color rendering remains stable despite variations in individual layer thicknesses.
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 provides improved lighting features, including enhanced color rendering and tolerance to red phosphor layer thickness variations, resulting in stable white pcLEDs with a CRI > 75 and broad band emission suitable for various applications.
Implementation Method 1
comprising a blue emitting LED
Implementation Method 2
a first phosphor layer exited at the emitting wavelength of the LED, which ceramic phosphor has an emission wavelength within a range of between 500 nm and 560 nm
Implementation Method 3
a second phosphor layer having a color point u' in the range between 0.24 and 0.35 and a peak emission of the phosphor layer of λp > 600nm
Data Source
Figure 1
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Figure 3~4
AI summary
The invention is directed to a light emitting comprising a blue emitting LED, a first phosphor layer exited at the emitting wavelength of the LED, which phosphor has an emission wavelength within a range of between 500 nm and 560 nm, and a second phosphor layer having a color point u´ in the range between 0.24 and 0.35 and a peak emission of the phosphor layer of ?p > 600nm of the emission spectra,especially a pcLED comprising a combination of a green emitting luminescent ceramic material and a second phosphor material having a broad emission spectra. The second phosphor material can comprise a compound of the general formula M1-x-y-zSi1+zAl1-zN3-zOz:Eu2+ xCe2+ y, whereby M is selected from the group consisting of Ca, Sr or mixtures thereof and 0.0001 = x = 0.005; 0.001 = y = 0.05and 0 = z = 0.25.