Eu-Activated Beta-Sialon Phosphor for High Luminance White LEDs
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Solution Overview
Problem
Existing β-sialon phosphors used in white LEDs have insufficient luminance and are not adequately heat-resistant, with Eu-ion activated β-sialon phosphors requiring optimization of Eu ionic states and manufacturing conditions to enhance luminance.
Innovation Solution
A β-sialon phosphor with a Eu 2+/ (Eu 2++Eu 3+) ratio of 0.8 or more, produced by calcinating a raw material mixture under nitrogen at 1820 °C to 2200 °C, followed by annealing in a reducing atmosphere and acid-treating to achieve high luminance and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If Eu-ion activated β-sialon phosphor is used to achieve broad excitation range, then the phosphor can be excited by light from ultraviolet to visible range, but the luminance is not sufficient
Solution Approach 1:
The patent changes the ionic state parameter of Eu from mixed valence to predominantly Eu2+ by controlling the firing atmosphere (reducing atmosphere with H2 and CO) and temperature (1200-2200°C). This parameter change transforms the phosphor's luminescence properties, achieving high luminance green emission while maintaining broad excitation capability.
Solution Approach 2:
The patent creates a composite phosphor system combining β-sialon matrix with Eu2+ activators, where the specific composition (Si6-zAlzOzN8-z) and Eu doping concentration are optimized to achieve both high luminance and broad excitation range simultaneously.
2Power
If phosphor operates at high temperature to increase LED output, then the LED output increases, but the phosphor requires higher heat resistance and shows luminance change
Solution Approach 1:
The patent changes the chemical composition parameters of the phosphor matrix by controlling the Si/Al ratio (z value) and oxygen content through reducing atmosphere firing. These compositional changes enhance the phosphor's thermal stability and heat resistance, allowing it to maintain luminance at high operating temperatures.
Solution Approach 2:
The patent uses a reducing atmosphere (H2, CO) during firing that can be easily controlled and removed, creating a stable phosphor product that resists thermal degradation during LED operation.
3Illumination intensity
If Eu content is increased to improve luminance, then the luminance increases, but the Eu solid-solution concentration is limited by crystal structure
Solution Approach 1:
The patent changes the crystal structure parameters of β-sialon (controlling z value and oxygen content) to create a more accommodating host lattice that can dissolve higher concentrations of Eu2+ ions. The reducing atmosphere firing also prevents Eu oxidation, allowing higher Eu content to be incorporated into the crystal structure.
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 resulting β-sialon phosphor exhibits high fluorescence emission efficiency with minimal luminance change across varying environments, suitable for white LEDs using ultraviolet or blue LEDs, offering improved performance and durability.
Implementation Method 1
A β-sialon phosphor of the present invention can be excited by light in a wide range of wavelength from ultraviolet light to visible light, and emits green light in high fluorescence emission efficiency
Implementation Method 2
a calcinating step for calcinating a raw material mixture of the above-mentioned β-sialan phosphor under nitrogen atmosphere at a temperature of 1820 °C to 2200 °C
Implementation Method 3
an annealing step for annealing the calcinated product under a reducing atmosphere at a temperature of 1100 °C or more and 1500 °C or less
Data Source
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AI summary
The purpose of the present invention is to provide an Eu-activated β-sialon phosphor showing a high luminance, the use thereof and the method of producing the same. The β-sialon phosphor includes, as a matrix, a β-sialon crystal represented by a general formula: Si6-zAlzOzN8-z (0<z<4.2), wherein Eu, which serves as an activator, is solid-soluted in the β-sialon crystal, and the ratio of Eu2+/ (Eu2++Eu3+) is 0.8 or more. It is preferred that the amount of Eu in the solid solution is 0.1 to 1 mass% with respect to the mass of the β-sialon crystal.