LaCeTb Phosphor Brightness Stability at High Temperature
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Lanthanum, cerium, and terbium phosphors used in luminescent devices experience degradation in luminescence properties, particularly brightness, during high-temperature manufacturing and operation, leading to unstable performance.
Innovation Solution
A phosphor based on lanthanum, cerium, and terbium phosphate with controlled particle size, low lithium and boron content, and a specific preparation process involving controlled pH precipitation, calcination, and heat treatment under a reducing atmosphere with lithium tetraborate to maintain brightness stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phosphors are subjected to high temperatures during manufacturing, then the phosphor structure is formed, but the luminescence brightness degrades
Solution Approach 1:
The patent applies parameter changes by precisely controlling the calcination temperature (at most 1000°C) and heat treatment temperature (1050-1150°C) to achieve optimal crystal structure formation while preventing brightness degradation. The pH control during precipitation (maintained below 2) also represents parameter optimization to ensure proper phosphor formation without excessive temperature exposure
Solution Approach 2:
The patent employs preliminary action through controlled pH precipitation before calcination, where the phosphor precursor is prepared in advance with proper pH control (pH < 2) to ensure optimal crystal structure formation. This preliminary preparation allows the subsequent high-temperature treatment to proceed without causing brightness degradation, as the structure is pre-optimized
2Stability of the object's composition
If phosphors undergo high-temperature heat treatment, then the crystal structure is improved, but the brightness stability deteriorates
Solution Approach 1:
The patent resolves this contradiction by optimizing the heat treatment parameters: temperature range (1050-1150°C) and duration (2-4 hours) are precisely controlled to achieve complete crystal structure transformation to monazite phase while maintaining brightness stability. The addition of lithium tetraborate (0.1-0.5% by mass) acts as a flux to facilitate crystal growth at controlled rates, ensuring structural perfection without brightness degradation
Solution Approach 2:
Lithium tetraborate serves as an intermediary substance during heat treatment. It acts as a flux that mediates the crystal structure transformation, allowing the phosphor to achieve stable monazite structure at controlled temperatures while preventing direct harmful interactions that would cause brightness degradation. The flux creates a protective environment during the phase transformation
3Illumination intensity
If phosphors are used in luminescent devices, then they emit green light, but the brightness degrades over time
Solution Approach 1:
The patent maintains bright green light emission over time by optimizing the composition parameters (La-Ce-Tb ratio, phosphate content) and thermal treatment parameters. The controlled calcination and heat treatment create a stable crystal structure that resists degradation during operation, ensuring consistent luminescence intensity throughout the device's operational lifetime
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 phosphor exhibits stable brightness across temperature variations, with a variation of no more than 4% from 25°C to 200°C, enhancing its luminescence properties and performance in luminescent devices.
Implementation Method 1
c) the precipitate is calcined at a temperature of at most 1000°C
Implementation Method 2
d) the precipitate resulting from step c) is heat treated under a reducing atmosphere, in the presence of lithium tetraborate (Li 2 B 4 O 7) in a mass quantity of at most 0.2%, at a temperature between 1050°C and 1150°C and for a period of between 2 hours and 4 hours
Implementation Method 3
They emit a bright green light when irradiated by certain energetic radiation of wavelengths shorter than those of the visible range (UV or VUV radiation for lighting or visualization systems)
Data Source
AI summary
The phosphor of the invention is based on a lanthanum cerium terbium phosphate, and it is characterized in that the phosphate consists of particles having a mean size of at most 4 µm, in that it has a lithium content of at most 30 ppm, a boron content of at most 30 ppm and in that it has a variation of brightness between the brightness measured on the phosphor at 25°C and that measured on the same phosphor at 200°C of at most 4%.