Mn4+ Red Phosphor Synthesis With Sub-10 μm Particle Control
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Solution Overview
Problem
Current processes for preparing red-emitting phosphors based on complex fluoride materials 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 process involving combining a source of A and a source of Mn+4 in the presence of a Hammett acidity function of at least −0.9 to form Mn+4 doped phosphors with a D50 particle size of less than 10 μm and a narrow size distribution, using microemulsion methods to create a coated phosphor with a manganese-free shell, and adjusting the molar ratios and concentrations of reactants to achieve monodisperse particles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional processes are used to prepare red-emitting phosphors, then phosphor 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 (H0 ≤ -1.5) of the reaction medium and adjusting the molar ratios of reactants (KF:H2SiF6:H2O in range 1:0.5:2 to 1:0.5:10) to achieve precise control over phosphor particle size, producing monodisperse particles with D50 between 0.1-10 μm and span ≤1.0
Solution Approach 2:
The patent implements local quality by creating specific local chemical environments through buffered hydrofluoric acid solutions with controlled Hammett acidity, where the local pH and ion concentration around nucleation sites determine the final particle size and distribution characteristics
2Reliability
If high aspect ratio nanorods are synthesized, then phosphor material can be produced, but manufacturing issues arise due to high aspect ratio and total internal reflection
Solution Approach 1:
The patent changes the morphological parameters of the phosphor particles by controlling reaction conditions (Hammett acidity, temperature, reactant ratios) to produce particles with aspect ratio ≤3/1, thereby eliminating total internal reflection issues and improving light extraction efficiency in LED applications
Solution Approach 2:
The patent converts the potential harm of particle morphology control into a benefit by using the controlled synthesis conditions to produce optimal particle shapes (low aspect ratio) that inherently prevent total internal reflection, turning a manufacturing challenge into a performance advantage
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 process produces phosphors with particle sizes less than 10 μm, achieving improved efficiency and performance in lighting and display applications by minimizing internal reflection and enhancing manufacturing compatibility.
Implementation Method 1
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
Implementation Method 2
microemulsion methods for preparing a coated phosphor having a core comprising a phosphor of formula I and a manganese-free shell comprising a metal fluoride compound disposed on the core
Implementation Method 3
annealing to enhance stability
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.