Coated Red Line Phosphors for LED Stability
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Solution Overview
Problem
Red-emitting manganese doped phosphors in solid state lighting are prone to color instability and non-uniformity due to susceptibility to high temperature and humidity conditions, limiting their stability and performance in LED applications.
Innovation Solution
A process involving a phosphor of formula A x [MF y ]:Mn 4+ coated with a manganese-free composite layer, comprising a compound of formula II and a metal fluoride, such as calcium fluoride, to enhance stability and performance, including a fluorine-containing oxidizing agent treatment to improve quantum efficiency and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If red-emitting manganese doped phosphors are used in solid state lighting, then high quantum efficiency and color rendering can be achieved, but color instability and non-uniformity occur under high temperature and humidity conditions
Solution Approach 1:
The patent applies composite materials by combining the red-emitting manganese doped phosphor core with a protective shell layer made of aluminum oxide or aluminum nitride. This core-shell composite structure maintains the high quantum efficiency of the manganese doped phosphor while the protective shell prevents degradation under high temperature and humidity conditions, thereby resolving the contradiction between energy efficiency and reliability.
Solution Approach 2:
The protective shell layer acts as an intermediary between the manganese doped phosphor and the harsh environment (high temperature and humidity). This intermediate layer protects the phosphor from direct exposure to degrading conditions while allowing the phosphor to maintain its optical properties, thus preserving color stability without compromising quantum efficiency.
2Illumination intensity
If red-emitting manganese doped phosphors are used to achieve high color rendering index, then good color quality can be obtained, but susceptibility to degradation under high temperature and humidity limits performance
Solution Approach 1:
The core-shell composite structure with aluminum oxide or aluminum nitride shell protects the manganese doped phosphor core from environmental degradation while preserving its red emission properties. This maintains the high color rendering index and color quality without suffering from heat and humidity induced degradation.
Solution Approach 2:
The aluminum oxide or aluminum nitride shell creates an inert protective environment around the manganese doped phosphor, isolating it from harmful external factors such as moisture and oxygen that cause degradation under high temperature and humidity conditions, thereby preserving color rendering performance.
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 phosphor particles exhibit significantly improved stability, with reduced color instability and enhanced performance under high temperature and humidity conditions, maintaining high quantum efficiency and color rendering index, suitable for use in LEDs and other light sources.
Implementation Method 1
Light emitted from the LED is converted to light that is useful for illumination purposes by coating or covering the LED with a phosphor layer. By interposing a phosphor excited by the radiation generated by the LED, light of a different wavelength, e.g., in the visible range of the spectrum, may be generated.
Implementation Method 2
including a fluorine-containing oxidizing agent treatment to improve quantum efficiency and thermal stability
Data Source
Figure 1~2
Figure 3~4
AI summary
A process for coating a phosphor of formula I: Ax [MFy]:Mn4+ includes combining the phosphor of formula I in particulate form with a first solution including a compound of formula II: Ax[MFy] to form a suspension and combining a second solution with the suspension, the second solution including a precursor including an element selected from the group consisting of calcium, strontium, magnesium, yittrium, barium, scandium, lanthanum, and combinations thereof. A population of particles having a core including a phosphor of formula I and a manganese-free composite coating disposed on the core, and a lighting apparatus (10) including the population of particles are also presented.