Color Stable Phosphor Coating for LED Thermal Stability
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Solution Overview
Problem
Phosphors used in solid state lighting, such as InGaN LEDs, experience decreased quantum efficiency and color shift due to temperature increases, and are prone to hydrolysis under elevated temperature and humidity, leading to instability in light emission and color quality.
Innovation Solution
A color stable phosphor composition with a specific formula ((Sr1-zMz)1-(x+w)AxCeX)(Al1-ySiY)O4+y+3(x-w)F1-y-3(x-w) is developed, coated with materials like aluminum oxide or magnesium oxide, and prepared using a method involving a coating precursor at acidic or basic pH in a water-based solvent, which enhances stability and resistance to temperature and humidity changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phosphors are used in solid state lighting without coating, then the structure is simple and manufacturing is easy, but quantum efficiency decreases and color shifts at elevated temperatures
Solution Approach 1:
The patent applies composite materials by coating phosphor particles with a protective layer having different thermal expansion characteristics. The coating layer comprises a matrix material and dispersed particles, creating a composite structure that stabilizes the phosphor against thermal stress and prevents color shift while maintaining manufacturing feasibility through slurry-based application methods.
2Reliability
If phosphors are exposed to elevated temperature and humidity, then light emission stability deteriorates due to hydrolysis, but adding protective coatings increases manufacturing complexity
Solution Approach 1:
The patent utilizes parameter changes by controlling the pH of the slurry during coating application. By adjusting pH to specific ranges (acidic pH 2-4 or basic pH 9-11), the coating materials undergo controlled chemical reactions that form protective layers on phosphor surfaces, enhancing hydrolysis resistance while using simple slurry immersion processes that maintain ease of manufacture.
3Use of energy by moving object
If quantum efficiency is maintained at high temperatures, then color stability improves, but this requires complex phosphor compositions and coating procedures
Solution Approach 1:
The patent applies local quality by creating a localized protective environment around each phosphor particle through coating. The coating layer is applied locally to individual particles in slurry form, providing targeted thermal and chemical protection where needed most, while the bulk phosphor composition remains relatively simple and manufacturable.
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 phosphors that maintain high quantum efficiency and color stability across a wide range of temperatures and humidity levels, enabling the production of white light with desirable color quality and reduced sensitivity to environmental conditions, suitable for various lighting applications.
Implementation Method 1
some phosphors undergo hydrolysis reactions at an appreciable rate under conditions of elevated temperature and humidity
Implementation Method 2
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
Data Source
Figure 1
AI summary
An LED lamp includes a light source configured to emit radiation with a peak intensity at a wavelength between about 250 nm and about 550 nm; and a phosphor composition configured to be radiational!y coupled to the light source. The phosphor composition includes particles of a phosphor of formula I, said particles having a coating composition disposed on surfaces thereof; ((SR1-zMz)1-(x+w)AwCex)3(AI1-ySiy)O4+y+3(x-w)F1-y-3(x-w) I wherein the coating composition comprises a material selected from aluminum oxide, magnesium oxide, calcium oxide, barium oxide, strontium oxide, zinc oxide, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, strontium hydroxide, zinc hydroxide, aluminum phosphate, magnesium phosphate, calcium phosphate, barium phosphate, strontium phosphate, and combinations thereof; and A is Li, Na, K, or Rb, or a combination thereof; M is Ca, Ba, Mg, Zn, or a combination thereof; and 0<x=0.10, Q=y=0.5, 0=z=0.5, 0=w=x.