Core-Shell Luminophore Precursors for Cost Reduction
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Solution Overview
Problem
Existing green phosphors based on mixed phosphates of lanthanum and/or cerium doped with terbium have high production costs due to the use of terbium and exhibit insufficient luminescence performance due to uncontrolled particle size and impurities from traditional high-temperature thermal activation processes.
Innovation Solution
A core/shell structured phosphor precursor is developed, comprising a mineral core and a homogeneous mixed phosphate shell of lanthanum and/or cerium doped with terbium, with a shell thickness of at least 300 nm, which is synthesized using a controlled process involving aqueous solutions and heat treatment, reducing the amount of terbium needed and improving luminescence properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional high-temperature thermal activation processes are used to prepare LAP phosphors, then the phosphors can achieve luminescence function, but the particle size becomes uncontrolled and impurities increase, resulting in insufficient luminescence performance
Solution Approach 1:
The patent applies preliminary action by pre-forming phosphor particles with controlled size distribution (1-10 μm) and proper composition before the thermal activation step. The mixed phosphate precursors are synthesized with specific La/Ce/Tb ratios and controlled particle sizes through wet chemical methods, then subjected to thermal treatment at 900-1100°C to activate luminescence while maintaining the pre-established particle size control, thus avoiding the uncontrolled grain growth that occurs when starting from oxide mixtures.
2Illumination intensity
If terbium-doped mixed phosphates of lanthanum and/or cerium are used to achieve green luminescence, then bright green light emission is obtained, but production costs increase significantly
Solution Approach 1:
The patent applies local quality by optimizing the spatial distribution and local concentration of terbium within the phosphor particles. The mixed phosphates contain Tb3+ ions at specific concentration ranges (0.1-0.5 mol fraction) within the La/Ce phosphate matrix, creating optimal local luminescence centers while minimizing overall terbium content. This localized optimization of dopant distribution maintains bright green emission (540-560 nm) while reducing material costs compared to uniform high-concentration doping.
Solution Approach 2:
The patent uses composite materials by creating mixed phosphate systems combining lanthanum phosphate and/or cerium phosphate with terbium dopant. The composite structure La1-x-yCexTb3+yPO4 allows synergistic effects where cerium provides additional luminescence pathways and lanthanum/cerium matrix stabilizes the crystal structure, enabling reduced terbium content while maintaining or enhancing green emission intensity through the combined optical properties of the composite system.
3Stability of the object's composition
If fluxing agents and reducing atmosphere are used during high-temperature treatment to activate phosphors, then terbium and cerium achieve 3+ oxidation state for effective luminescence, but particle size disturbance increases and impurity content rises
Solution Approach 1:
The patent applies parameter changes by modifying the thermal treatment parameters: using lower temperatures (900-1100°C instead of 1100°C+), shorter treatment times (0.5-2 hours), and controlled atmospheric conditions. These parameter adjustments are sufficient to reduce Tb4+ to Tb3+ and maintain Ce3+ stability while minimizing particle growth and flux-related impurities, as the precursors are already in the correct phosphate form with proper stoichiometry before heating.
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 core/shell structured phosphors achieve similar brightness and luminescence performance to traditional bulk phosphors while reducing terbium content, resulting in lower production costs and improved particle size uniformity, leading to enhanced luminescence efficiency and stability.
Implementation Method 1
they emit a bright green light when they are irradiated by certain high-energy radiation having wavelengths below those of the visible range (UV or VUV radiation for lighting or display systems)
Implementation Method 2
a synthesis, in liquid medium, of a mixed phosphate of rare-earth metals or of a mixture of phosphates of rare-earth metals is carried out
Data Source
AI summary
A novel type of green luminophore containing mixed rare-earth phosphates is produced from precursor particles having a mean diameter ranging from 1.5 to 15 microns; such particles have an inorganic core and a shell of a mixed lanthanum and/or cerium phosphate, optionally doped with terbium, evenly covering the inorganic core with a thickness greater than or equal to 300 nm.