Fluoride Phosphor Surface Mn Gradient for Water Resistance
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Solution Overview
Problem
Conventional fluoride phosphors activated with tetravalent Mn have poor water resistance due to oxidation of surface Mn4+ to manganese dioxide, leading to degradation of luminance, making them unsuitable for long-term reliability in applications like LCD backlights and in-vehicle uses.
Innovation Solution
A method of manufacturing fluoride phosphors with a surface region having a lower concentration of tetravalent Mn compared to the inner region, represented by the formula K2[M1-aMn4+aF6], where M includes Ti, Zr, Hf, Si, Ge, or Sn, and a is between 0 and 0.2, to reduce the likelihood of MnO2 formation and enhance water resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional fluoride phosphors activated with tetravalent Mn are used to achieve narrow emission peak half width and high color purity, then color reproduction is improved, but water resistance deteriorates due to oxidation of surface Mn4+ to MnO2
Solution Approach 1:
The phosphor particle is designed with non-uniform Mn concentration distribution, where the inner region contains high Mn concentration for optimal emission characteristics, while the surface region contains low Mn concentration to prevent oxidation. This local quality differentiation resolves the contradiction between achieving narrow emission peak (requiring uniform high Mn) and water resistance (requiring Mn-free surface).
Solution Approach 2:
The phosphor particle is segmented into two distinct regions: an inner region with high Mn4+ concentration for emission and an outer surface region with low Mn4+ concentration for protection. This segmentation allows each region to fulfill its specific function, resolving the contradiction between emission performance and water resistance.
2Illumination intensity
If surface Mn4+ concentration is increased to enhance emission intensity, then luminance is improved, but oxidation to MnO2 occurs more readily, reducing durability
Solution Approach 1:
The invention creates a spatial gradient of Mn concentration within the phosphor particle, concentrating Mn4+ in the inner region to maintain high emission intensity while depleting Mn4+ from the surface region to prevent oxidation and ensure long-term durability.
Solution Approach 2:
A Mn-depleted surface layer is created beforehand to act as a protective barrier against oxidation, cushioning the high-Mn inner region from environmental damage and ensuring long-term durability while maintaining emission 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 approach results in fluoride phosphors with improved water resistance and maintained emission intensity, suitable for applications requiring durability and broad color reproduction, such as liquid crystal device backlights and in-vehicle lighting.
Implementation Method 1
mixing a first solution which contains at least Mn and F, a second solution which contains at least K and F, and a third solution which contains at least Si and F to form phosphor cores
Implementation Method 2
fluoride phosphors activated with tetravalent Mn which can emit red light with a narrow half width of the emission peak
Data Source
AI summary
A method of manufacturing a fluoride phosphor includes mixing a first solution which contains at least Mn and F, a second solution which contains at least K and F, and a third solution which contains at least Si and F to form phosphor cores whose composition is represented by a formula K2[M1-aMn4+aF6] wherein a satisfies 0<a<0.2, and M includes at least one selected from group-IV elements of Ti, Zr, and Hf and group IVB elements of Si, Ge, Sn. The phosphor cores and a fourth solution containing a reducing agent are mixed to form a surface region on each of the phosphor cores so that a concentration of tetravalent Mn on the surface region of one of the phosphor cores is lower than in an inner region of the one of the phosphor cores.