Core-Shell Red-Emitting Phosphors for Stable LED Color
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Solution Overview
Problem
LED packages containing blends of red-emitting phosphors experience issues such as phase segregation and light scattering due to refractive index mismatch between phosphors and binder materials, necessitating the development of color-stable phosphors that mitigate these problems.
Innovation Solution
The development of coated phosphors with a Mn 4+ doped shell composed of coordination compounds, such as K2SiF6:Mn4+, surrounded by fluoride ions and charge-compensated by counter ions, which are prepared by contacting a core phosphor with a source of Mn4+ and M in a HF solution, followed by exposure to a fluorine-containing oxidizing agent at elevated temperatures to enhance color stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If blends of red-emitting phosphors are used in LED packages, then white light production is achieved, but phase segregation and light scattering occur due to refractive index mismatch
Solution Approach 1:
The patent applies homogeneity by matching the refractive index of the phosphor material to the binder material. The complex fluoride phosphors are specifically formulated to have refractive indices between 1.30-1.70, which are matched to the binder materials used in LED packages. This refractive index matching eliminates phase segregation and light scattering, creating a homogeneous mixture that maintains stability over time while producing white light.
2Use of energy by moving object
If complex fluoride phosphors are used, then luminous efficacy is maximized, but color stability becomes a concern
Solution Approach 1:
The patent employs composite materials by creating complex fluoride phosphors with specific compositions (e.g., K2SiF6:Mn4+, Rb2GeF6:Mn4+, Cs2TiF6:Mn4+). These composite fluoride materials combine multiple elements to achieve both high luminous efficacy (quantum efficiency exceeding 85% under blue excitation) and color stability. The fluoride-based composite structure provides a stable crystal field that maintains consistent emission characteristics while delivering high energy 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 coated phosphors achieve improved color stability and reduced light scattering, enabling efficient production of white light without the need for additional phosphors, with tailored emission spectra and enhanced luminous efficacy.
Implementation Method 1
These materials absorb blue light strongly and efficiently emit between about 610-635 nm with little deep red/NIR emission
Implementation Method 2
contacting a core phosphor with a source of Mn4+ and M in a HF solution, followed by exposure to a fluorine-containing oxidizing agent at elevated temperatures
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A coated phosphors that include a shell comprising a first Mn4+doped phosphor of formula (I) directly disposed on a core comprising a second phosphor. The second phosphor is a material other than a compound of formula (I) or formula (II) wherein A is, independently at each occurrence, Li, Na, K, Rb, Cs, or a combination thereof; M is, independently at each occurrence, Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Hf, Y, La, Nb, Ta, Bi, Gd, or a combination thereof; x is the absolute value of the charge of the [MFy] ion; and y is 5, 6 or 7.