Mn4+ Red-Emitting Phosphor Synthesis for Sub-10 μm Particle Control
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Solution Overview
Problem
Current processes for preparing red-emitting phosphors based on complex fluoride materials, such as K2SiF6:Mn4+, often result in particles larger than 10 μm with broad size distributions, which can cause manufacturing issues in LED packaging and reduce efficiency due to total internal reflection.
Innovation Solution
A method involving combining a source of A (Li, Na, K, Rb, or Cs) with a source of Mn in the presence of H2MF6, under controlled conditions to produce Mn4+ doped phosphors with a monodisperse population of particles less than 10 μm in size and a narrow particle size distribution, and optionally coating these phosphors with a manganese-free metal fluoride shell using microemulsion techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional processes are used to prepare red-emitting phosphor particles, then the particles can be produced, but the particle size becomes greater than 10 μm with broad distribution
Solution Approach 1:
The patent applies parameter changes by controlling the Hammett acidity function (Ho ≥ -0.9) of the first solution, adjusting the molar ratios of reactants, and optimizing reaction temperature and time to achieve precise particle size control below 10 μm with narrow distribution
Solution Approach 2:
The patent uses an intermediary approach by employing a specific acidic solution with controlled Hammett acidity function as a medium to facilitate the reaction between K2SiF6 and Mn sources, enabling precise nucleation and growth control that produces monodisperse particles with D50 < 10 μm
2Manufacturing precision
If high aspect ratio nanorods are produced, then the particle size can be reduced, but manufacturing problems occur in LED packaging
Solution Approach 1:
The patent applies local quality by controlling the aspect ratio to be about 3/1 or less, creating particles with optimized local dimensional characteristics that are small enough for LED packaging while maintaining uniformity and avoiding the manufacturing issues associated with high aspect ratio nanorods
Solution Approach 2:
The patent changes the morphological parameters by controlling the reaction conditions (Hammett acidity, molar ratios, temperature) to produce particles with aspect ratio ≤ 3/1, transforming the particle shape from high aspect ratio nanorods to more suitable forms for LED packaging applications
3Manufacturing precision
If particles with high aspect ratio are used, then particle size can be small, but total internal reflection reduces efficiency
Solution Approach 1:
The patent changes the geometric parameter of aspect ratio to about 3/1 or less, which reduces total internal reflection losses while maintaining small particle size, thereby improving light extraction efficiency and reducing energy loss in LED applications
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 method achieves phosphor particles with a D50 size of less than 10 μm, aspect ratio of 3/1 or less, and improved efficiency in lighting and display applications by minimizing internal reflection and enhancing manufacturing feasibility.
Implementation Method 1
wherein a value of a Hammett acidity function of the first solution is at least −0.9
Data Source
AI summary
A process for preparing a Mn+4 doped phosphor of formula I Ax [MFy]:Mn+4 I includes combining a first solution comprising a source of A and a second solution comprising H2MF6 in the presence of a source of Mn, to form the Mn+4 doped phosphor; wherein A is Li, Na, K, Rb, Cs, or a combination thereof; M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd, or a combination thereof; x is the absolute value of the charge of the [MFy] ion; y is 5, 6 or 7; and wherein a value of a Hammett acidity function of the first solution is at least −0.9. Particles produced by the process may have a particle size distribution with a D50 particle size of less than 10 μm.