HF-Free Mn4+ Phosphor Synthesis via Precipitation and Oxidation
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Solution Overview
Problem
The preparation of red-emitting phosphors based on complex fluoride materials activated by Mn4+ often requires significant quantities of highly toxic hydrofluoric acid, which is economically and environmentally disadvantageous.
Innovation Solution
An HF-free process for preparing Mn4+ doped phosphors involves combining an A+ cation, an anion of formula MFy, and a Mn n+ source in an acidic solution, followed by precipitation of a Mn n+ containing phosphor precursor and subsequent contact with a fluorine-containing oxidizing agent at elevated temperatures to form the Mn4+ doped phosphor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hydrofluoric acid is used as solvent in the preparation process, then the phosphor can be prepared with good quality, but the process becomes highly toxic and environmentally hazardous
Solution Approach 1:
The patent removes hydrofluoric acid from the preparation process entirely, replacing it with alternative reagents such as ammonium fluorosulfonate and other fluorine-containing compounds that do not produce the same toxic effects, while still achieving the desired phosphor synthesis
Solution Approach 2:
The patent introduces intermediate compounds such as ammonium fluorosulfonate and uses multi-step synthesis pathways with intermediate precipitation and purification stages to achieve the final phosphor product without requiring direct use of hydrofluoric acid
2Productivity
If significant quantities of hydrofluoric acid are used, then the phosphor preparation can proceed effectively, but the economic cost and environmental impact increase
Solution Approach 1:
The patent changes the chemical parameters of the preparation process by using alternative reagents with different chemical properties, such as ammonium fluorosulfonate instead of hydrofluoric acid, and adjusts reaction conditions like temperature, pH, and concentration to maintain effective synthesis without toxic materials
Solution Approach 2:
The patent employs readily available, non-toxic reagents that can be easily disposed of or treated as waste, replacing the expensive and hazardous hydrofluoric acid, thereby reducing both economic cost and environmental burden
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
This process reduces the use of toxic hydrofluoric acid, enhances color stability and quantum efficiency of the phosphors, and maintains high luminous efficacy, making it economically advantageous and environmentally safer.
Implementation Method 1
contacting the Mn n+ containing phosphor precursor with a fluorine-containing oxidizing agent at elevated temperatures to form the Mn 4+ doped phosphor
Implementation Method 2
combining in an acidic solution, an A+ cation, an anion of formula MFy, and a Mn n+ source in molar ratios of A+ : Mn n+ : F of from about 2:1:6 to about 2.5:1:6, followed by precipitation of a Mn n+ containing phosphor precursor
Data Source
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Figure 5
AI summary
The present invention relates to a process for preparing a Mn4+ doped phosphor of formula I Ax[MFy]:Mn+4 I includes combining in an acidic solution, an A+ cation, an anion of formula MFy, and a Mnn+ source comprising a fluoromanganese compound, precipitating a Mnn+ containing phosphor precursor from the acidic solution, and contacting the Mnn+ containing phosphor precursor with a fluorine-containing oxidizing agent in gaseous form, at an elevated temperature, to form the Mn4+ 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, Hf, 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 n is 2 or 3.