Fluoride Phosphor Composition for Brightness and Chromaticity Uniformity
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Solution Overview
Problem
Existing fluoride phosphors used in light emitting devices face challenges in achieving a narrow half-value width and high color purity, particularly in liquid-crystal display device backlights, due to issues with particle size distribution and activator concentration leading to inefficiencies and chromaticity variations.
Innovation Solution
A fluoride phosphor with controlled average and maximum particle sizes, combined with a specific composition including Group 4, 13, and 14 elements, alkali metals, and Mn, is developed to enhance dispersibility and uniformity, reducing the amount required for desired emission characteristics and inhibiting chromaticity variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If fluoride phosphor with narrow particle size distribution is used, then color purity is improved, but manufacturing complexity increases
Solution Approach 1:
The production process is divided into multiple stages: first preparing fluoride particles with average size 5-30 μm, then performing pulverization treatment to obtain final particles with average size 0.1-7 μm. This segmentation allows independent optimization of each stage, achieving narrow particle size distribution (ratio of maximum to average particle size > 1) while managing manufacturing complexity through systematic process division.
2Illumination intensity
If higher activator concentration is used, then brightness is improved, but chromaticity variation increases
Solution Approach 1:
The patent precisely controls the activator concentration parameter, setting the number of moles of Mn to be more than 0 and less than 0.2 when the number of moles of alkali metal is 2. This specific parameter range optimizes the balance between brightness emission intensity and chromaticity stability, preventing both insufficient activation and excessive activation that would cause chromaticity variation.
3Productivity
If larger particle size is used, then luminous flux is improved, but uniformity in wavelength conversion layer decreases
Solution Approach 1:
The patent specifies different particle size characteristics for different aspects: average particle size of 0.1-7 μm for overall uniformity and maximum particle size of 1-18 μm for luminous flux. The controlled ratio of maximum to average particle size (> 1) ensures that particles are not too large to create uniform distribution in the wavelength conversion layer, while still providing sufficient surface area for high luminous flux output.
4Quantity of substance
If fluoride phosphor content is reduced, then cost is lowered, but emission intensity decreases
Solution Approach 1:
The patent uses a composite fluoride phosphor composition containing alkali metal elements (more than 0.8 and less than 1 when number of moles of Mn is 2), Mn (more than 0 and less than 0.2), and F (more than 5 and less than 7). This composite structure with specific compositional ratios enhances the phosphor's emission efficiency, allowing reduced fluoride phosphor content while maintaining desired emission intensity through the synergistic effect of multiple elements.
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 controlled particle size and composition fluoride phosphor improves brightness, reduces chromaticity variation, and enhances uniformity in wavelength conversion layers, leading to improved luminous flux and color stability in light emitting devices.
Implementation Method 1
a phosphor used in a light emitting device for liquid-crystal display device backlight application is required to have an emission peak with a narrow half-value width as well as a high color purity
Data Source
AI summary
A fluoride phosphor, comprising fluoride particles having an average particle size of 0.1 μm to 7 μm and a maximum particle size of 1 μm to 18 μm, wherein a ratio of the maximum particle size with respect to the average particle size is higher than 1. The fluoride particles have a composition containing an element M containing at least one selected from the group consisting of Group 4 elements, Group 13 elements, and Group 14 elements; an alkali metal; Mn; and F. In the composition, when the number of moles of the alkali metal is 2, the number of moles of Mn is more than 0 but less than 0.2, the number of moles of the element M is more than 0.8 but less than 1, and the number of moles of F is more than 5 but less than 7.