Beta-Sialon Phosphor Eu Valence Control
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Solution Overview
Problem
The β-sialon phosphor activated with Eu faces limitations in further increasing luminance, as simply increasing the Eu2+/Eu3+ ratio does not effectively enhance fluorescence properties.
Innovation Solution
Introducing an intermediate chemical state of Eu, referred to as Eum, within a specific ratio range (0.1 < Eum/(Eu2++Eu3+) < 0.4 and Eu2+/Eu2++Eu3+ > 0.7, and employing a production method involving multiple firing and annealing steps, including acid treatment, to optimize the Eu states and crystallinity for higher luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the Eu2+/Eu3+ ratio is increased to improve luminance, then the fluorescence emission efficiency improves, but the luminance cannot be further increased due to saturation effects
Solution Approach 1:
The patent changes the parameter of Eu valence state from binary (Eu2+/Eu3+) to ternary (Eu2+, Eu3+, and intermediate state Eum). By controlling the ratio of Eum within 0.05-0.40, the patent achieves enhanced luminance that overcomes the saturation effect of simply increasing Eu2+/Eu3+ ratio. This parameter expansion allows fine-tuning of fluorescence properties beyond the traditional two-state system.
2Illumination intensity
If multiple firing and annealing steps are introduced to optimize Eu states, then luminance and stability improve, but the manufacturing process becomes more complex
Solution Approach 1:
The patent applies preliminary action by performing a first firing step before the second firing step to pre-form the β-sialon phase and incorporate Eu. The first firing at 1700-2000°C creates a foundation structure that facilitates subsequent phase transformation and Eu state optimization in the second firing step, leading to better control over Eu valence states and reduced need for extensive process adjustments.
Solution Approach 2:
The patent employs periodic action through multiple discrete firing and annealing steps. The process alternates between high-temperature firing (1900-2100°C) to transform phases and form Eum, and annealing (1000-1700°C) to stabilize the structure. This periodic cycling between different thermal conditions enables progressive optimization of Eu states and crystal structure, achieving high luminance through controlled阶段性 transformations.
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 approach results in a β-sialon phosphor with enhanced luminance, stability, and reduced luminance change under varying conditions, suitable for high-performance white LEDs.
Implementation Method 1
the β-sialon phosphor... is efficiently excited by ultraviolet to blue light and emits green light
Implementation Method 2
the divalent Eu2+ can efficiently absorb excitation energy by an absorption band of 4f-5d acceptable transition and can emit light
Implementation Method 3
the Eu present in the phosphor has an intermediate chemical state other than Eu2+ and Eu3+, and when the Eu in this intermediate state is present within a certain range, the luminance of the phosphor is increased
Data Source
AI summary
Provided is a β-sialon phosphor having a β-sialon as a host crystal and containing Eu as a luminescent center, wherein when chemical states of Eu are classified into three states: Eu2+, Eu3+ and an intermediate state thereof (hereinafter, referred to as Eum), a ratio of them present in the β-sialon phosphor satisfies the relationships: 0.1<Eum/(Eu2++Eu3++Eum)<0.4 and Eu2+/(Eu2++Eu3+)>0.7.