SiAlON Phosphor Aspect Ratio Control for LCD Brightness Stability
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Solution Overview
Problem
Conventional light emitting apparatus using trivalent cerium-activated (Y, Gd)3(Al, Ga)5O12 phosphors face challenges with high input energy due to decreased luminance at elevated temperatures and aggregation issues with divalent europium-activated oxynitride green light emitting phosphors, leading to unstable brightness and chromaticity.
Innovation Solution
A phosphor particle group of divalent europium-activated β-type SiAlON phosphors with a controlled aspect ratio, where the mean value of the longer particle diameter divided by the shorter diameter is not greater than 1.75, and a gallium nitride-based semiconductor light emitting element, to enhance brightness stability and color gamut.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If divalent europium-activated oxynitride green light emitting phosphor (β-type SiAlON) is used to improve color gamut and temperature characteristic, then color gamut and temperature stability are improved, but particle aggregation occurs due to columnar crystal shape (aspect ratio > 5) preventing uniform dispersion
Solution Approach 1:
The patent changes the critical parameter of particle shape by controlling the aspect ratio to be 1.05 or less, transforming the columnar crystal morphology into a more equant shape. This parameter change resolves the aggregation issue while preserving the superior color gamut and temperature characteristics of β-type SiAlON phosphors
Solution Approach 2:
The patent addresses the asymmetry problem by making the particles more symmetric (reducing aspect ratio to 1.05 or less). The columnar asymmetry that caused aggregation is eliminated, enabling uniform dispersion in the resin matrix while maintaining the phosphor's optical properties
2Illumination intensity
If input energy is increased to achieve higher brightness, then luminous intensity is improved, but heat dissipation becomes difficult causing temperature rise and luminance degradation
Solution Approach 1:
The patent converts the harmful effect of high input energy (heat generation) into a beneficial outcome by using phosphor particles with aspect ratio 1.05 or less that disperse uniformly and maintain stable luminance at elevated temperatures. The heat that would normally degrade performance is now managed effectively, allowing high brightness operation
3Stability of the object's composition
If phosphor particles with aspect ratio greater than 5 are used, then crystal structure stability is improved, but aggregation occurs in resin preventing uniform dispersion and good brightness characteristic
Solution Approach 1:
The patent identifies aspect ratio as the critical parameter and changes it from >5 to 1.05 or less. This parameter transformation maintains the crystal structure stability of β-type SiAlON while eliminating the aggregation problem, achieving both structural integrity and uniform dispersion
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 solution results in a light emitting apparatus with significantly reduced fluctuations in brightness and chromaticity, achieving high efficiency, excellent color gamut, and improved temperature characteristics, suitable for large LCDs like thin-screen televisions.
Implementation Method 1
A light emitting apparatus using a combination of semiconductor light emitting elements and phosphors attracts attention
Implementation Method 2
a light converter absorbing a part of the primary light to emit secondary light having a wavelength longer than a wavelength of the primary light
Data Source
AI summary
Provided is a phosphor particle group of divalent europium-activated oxynitride green light emitting phosphor particles each of which is a β-type SiAlON represented by a general formula: EuaSibAlcOdNe, where 0.005≦a≦0.4, b+c=12, d+e=16, wherein a mean value of a value obtained by dividing a longer particle diameter by a shorter particle diameter is not greater than 1.75. Also provided are a light emitting apparatus using the phosphor particle group in a light converter, and a liquid crystal display television using the light emitting apparatus. With these, a high-efficiency and stable light emitting apparatus using a β-type SiAlON, and a phosphor particle group therefor are provided.