Phosphor Composition for Red Emission in White LEDs
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Solution Overview
Problem
Current white LED illumination systems, particularly those using high luminance blue LEDs and yellow phosphors like YAG:Ce, suffer from insufficient red emission in the visible light region, leading to bluish white light and poor color rendering properties, while systems using near ultraviolet/ultraviolet LEDs and multiple phosphors face challenges with excitation efficiency and luminance.
Innovation Solution
A phosphor with a broad emission spectrum peak from yellow to red (580 nm to 680 nm) and excellent excitation band from near ultraviolet/ultraviolet to visible light (250 nm to 550 nm) is developed, containing boron and/or fluorine, which improves emission intensity and uniformity by accelerating solid reactions and suppressing sintering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high luminance blue LED and yellow phosphor (YAG:Ce) are combined, then luminance efficiency is improved, but red emission is insufficient leading to poor color rendering
Solution Approach 1:
The patent changes the chemical composition parameters of the phosphor material by incorporating specific ratios of Sr, Ca, Al, Si, N, and Eu elements. This compositional parameter change transforms the phosphor's emission characteristics to provide both yellow and red emission bands, resolving the contradiction between luminance efficiency and red emission intensity.
Solution Approach 2:
The patent creates a composite phosphor material combining multiple elements (Sr, Ca, Al, Si, N, Eu) in specific proportions. This composite structure enables the phosphor to exhibit dual emission characteristics (yellow and red) when excited by blue LED, simultaneously achieving high luminance efficiency and improved color rendering.
2Illumination intensity
If multiple phosphors (R, G, B) are combined with near ultraviolet/ultraviolet LED, then color rendering is improved, but excitation efficiency and luminance decrease
Solution Approach 1:
The patent extracts and eliminates the need for multiple separate phosphors (R, G, B) by developing a single composite phosphor material that inherently provides both yellow and red emission. This simplifies the system while maintaining excitation efficiency and luminance when combined with blue LED.
Solution Approach 2:
The composite phosphor material performs multiple functions simultaneously: it provides yellow emission for luminance efficiency and red emission for color rendering improvement. This multi-functional phosphor replaces the need for multiple specialized phosphors, maintaining high luminance while improving color rendering.
3Use of energy by moving object
If yellow phosphor YAG:Ce is used with blue LED, then excitation efficiency is improved, but emission spectrum lacks red region leading to bluish white light
Solution Approach 1:
The patent modifies the emission spectrum composition by adjusting the phosphor's chemical parameters. The inclusion of Eu element and specific ratios of Sr, Ca, Al, Si, and N changes the emission characteristics to include red region (600-680 nm) while maintaining yellow region emission, thus achieving balanced white light without compromising excitation efficiency.
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 phosphor enhances emission intensity and color rendering properties, enabling high luminance white light with improved color tone stability and reduced green phosphor insufficiency, achieving a balanced blue and yellow color tone.
Implementation Method 1
the phosphor excited by the light having an emission spectrum with a peak in the range from ultraviolet to blue color generated from the LED are combined
Data Source
AI summary
To provide a phosphor having an emission spectrum with a broad peak in a range from yellow color to red color (580 nm to 680 nm) and an excellent excitation band on the longer wavelength side from near ultraviolet/ultraviolet of excitation light to visible light (250 nm to 550 nm), and having an improved emission intensity. The phosphor is provided, which is given by a general composition formula expressed by MmAaBbOoNn:Z, (wherein element M is more than one kind of element having bivalent valency, element A is more than one kind of element having tervalent valency selected from the group consisting of Al, Ga, In, Tl, Y, Sc, P, As, Sb, and Bi, element B is more than one kind of element having tetravalent valency, O is oxygen, N is nitrogen, and element Z is more than one kind of element selected from rare earth elements or transitional metal elements, satisfying m>0, a>0, b>0 o≧0, and n=2/3m+a+4/3b−2/3o), and further containing boron and/or fluorine.