Phosphor Composition for High-Temperature LED Stability
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Solution Overview
Problem
Conventional red- and orange-emitting phosphors used in light emitting diodes (LEDs) experience efficiency decline and stability issues at high temperatures and high illumination, particularly in applications like traffic lights and automotive lights, where the performance of Sr2Si5N8:Eu2+ phosphors degrades significantly.
Innovation Solution
Development of new phosphor formulations such as (Ba1-xSrx)2Si5N8:Eu2+, (Ba1-xCax)2Si5N8:Eu2+, and (Ba,Ca,Sr)2Si5N8:Eu2+ that improve temperature and photo-stability, with optimal compositions of Ba, Ca, and Sr, and the inclusion of Al and O to broaden the emission spectrum and enhance crystallinity, leading to more stable and efficient red- and orange-emitting LEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional red- and orange-emitting phosphors (such as Sr2Si5N8:Eu2+) are used in LEDs, then the devices can emit light in the desired wavelength range, but the efficiency and stability decline significantly at high temperatures and high illumination conditions
Solution Approach 1:
The patent modifies the chemical composition parameters of the phosphor material by incorporating multiple alkaline earth metals (Ba, Sr, Ca) in specific ratios, along with Al and O substitutions. This changes the crystal structure parameters and electronic properties of the phosphor, enabling it to maintain high emission efficiency and stability under high temperature and illumination conditions where conventional phosphors fail.
Solution Approach 2:
The patent creates a composite phosphor material system combining multiple elements (Ba, Sr, Ca, Si, N, O, Al, Eu) in a unified crystal structure. This composite approach leverages the complementary properties of different elements: Ba and Sr provide high emission efficiency, Ca enhances thermal stability, Al and O improve crystallinity and structural stability, and Eu serves as the luminescent center. The synergistic interaction within this composite material resolves the contradiction between efficiency and stability.
2Productivity
If the phosphor composition is optimized for high emission efficiency, then the light output is enhanced, but the temperature and photo-stability deteriorate
Solution Approach 1:
The patent systematically adjusts compositional parameters including the ratios of Ba to Sr to Ca, the amount of Al substitution, and the O content. By optimizing these parameters within specific ranges, the phosphor achieves a balance where high emission efficiency is maintained while temperature and photo-stability are significantly improved compared to conventional compositions.
Solution Approach 2:
The patent introduces local structural modifications within the phosphor crystal lattice through Al substitution and O incorporation. These local changes in specific crystallographic positions enhance the overall thermal and photo-stability of the material without significantly compromising the emission efficiency, as the luminescent centers (Eu ions) remain intact and functional.
3Reliability
If the phosphor is designed for durability under high illumination, then the emission intensity loss is reduced, but the emission spectrum narrowness increases
Solution Approach 1:
The patent modifies the phosphor composition to include Al and O, which broaden the emission spectrum while maintaining high durability under illumination. The specific parameter adjustments in the Ba-Sr-Ca ratio and the amount of Al/O incorporation enable the phosphor to achieve both wide emission spectrum and high stability, resolving the trade-off between spectrum breadth and illumination durability.
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
These new phosphor formulations demonstrate improved stability and emission efficiency at high temperatures and high illumination, with reduced loss of emission intensity over time, making them suitable for applications requiring precise color consistency and durability.
Implementation Method 1
The luminescence process involves absorbing the primary light by a photoluminescent phosphor material, which excites the atoms of the phosphor material, and emits the secondary light.
Implementation Method 2
absorbing the primary light by a photoluminescent phosphor material, which excites the atoms of the phosphor material, and emits the secondary light
Data Source
AI summary
A semiconductor light emitting device is combined with a wavelength converting material. The semiconductor light emitting device is configured to emit first light of a first peak wavelength. The wavelength converting material is configured to absorb at least a portion of the first light and emit second light of a second peak wavelength. In some embodiments, the first wavelength converting material is (Ba1-xSrx)2-y-0.5zSi5N8-zOz:Euy2+ where 0.2<x<0.3, (Ba1-xCax)2-y-0.5zSi5N8-zOz:Euy2+ where 0.01<x<0.2, or M2Si5-aAaN8-aOa:Eu2+ where M=Sr, Ba, Ca; A=Al, B, Ga, Sc; and 0.01<a<0.2.