Luminescent Material Thermal Stability for White LEDs
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Solution Overview
Problem
High-output blue LEDs in white light-emitting devices generate excessive heat, causing a shift in the wavelength of emitted light, which leads to a decrease in luminous intensity and disrupts the balance between red and green luminescence, resulting in noticeable color shifts.
Innovation Solution
A luminescent material with a crystal structure similar to Sr2Si7Al3ON13, activated by Eu and containing a specific amount of Ca, is used to maintain luminous intensity and balance across varying temperatures, extending the excitation spectrum edge and reducing color shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a high current is introduced to drive a high-output blue LED, then the luminous intensity increases, but the LED generates excessive heat causing wavelength shift and luminous intensity decrease
Solution Approach 1:
The patent changes the compositional parameters of the luminescent material by incorporating specific amounts of Ca (0.01≤x≤0.20) and Eu (0.01≤y≤0.05) dopants into the Sr2Si7Al3ON13 crystal structure. This compositional modification adjusts the material's thermal properties and excitation spectrum to maintain stable luminescence under high-temperature conditions, directly addressing the temperature-induced luminous intensity decrease
Solution Approach 2:
The patent creates a composite luminescent material system by combining Sr2Si7Al3ON13 host material with Ca and Eu dopants. This composite structure leverages the synergistic effects of different elements: Sr2Si7Al3ON13 provides the crystal framework, Ca modifies the lattice structure and excitation spectrum, and Eu acts as the luminescent center, together achieving thermal stability and reduced color shift
2Temperature
If the temperature of the blue LED rises, then the wavelength of emitted light shifts toward the long wavelength side, but the excitation spectrum of the luminescent material decreases, causing noticeable luminous intensity decrease
Solution Approach 1:
The patent modifies the excitation spectrum parameters of the luminescent material through compositional adjustment. By controlling Ca content (0.01≤x≤0.20) and Eu content (0.01≤y≤0.05), the excitation spectrum is tuned to maintain high intensity across the shifted LED wavelength range (430-480 nm), ensuring that the material remains effectively excited even when LED peak wavelength shifts by 6 nm or more due to heating
Solution Approach 2:
The patent performs preliminary optimization of the luminescent material's excitation spectrum during the material design phase. The composition is pre-adjusted to anticipate and compensate for the expected LED wavelength shift under operating conditions, so that when the LED operates at high temperature and wavelength shifts occur, the luminescent material is already configured to maintain strong excitation and luminescence
3Temperature
If the temperature rises, then the balance between red and green luminescence is easily broken, but maintaining stable color balance requires a luminescent material with low temperature quenching
Solution Approach 1:
The patent optimizes the compositional parameters to achieve balanced red and green luminescence with minimal temperature dependence. The specific ranges of Ca (0.01≤x≤0.20) and Eu (0.01≤y≤0.05) are determined to produce a luminescence spectrum where the red component (560-780 nm) and green component (480-560 nm) maintain stable intensity ratios across temperature variations, preventing color balance disruption
Solution Approach 2:
The patent applies local quality modification by strategically placing Ca and Eu dopants at specific sites within the Sr2Si7Al3ON13 crystal structure. Ca occupies Sr sites to modify the local lattice environment and excitation characteristics, while Eu occupies specific cation sites to provide the luminescent centers. This localized compositional control creates regions with optimized luminescence properties that maintain color balance under thermal stress
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 luminescent material exhibits high quantum efficiency and low luminous intensity decrease even at high temperatures, ensuring stable color output and reduced color shifts in white light-emitting devices under high-load conditions.
Implementation Method 1
a luminescent material that emits red light by excitation with blue light, a luminescent material that emits green light by excitation with blue light
Implementation Method 2
a luminescent material exhibits a luminescence spectrum having a peak in a wavelength range of 570 to 670 nm when excited with light having an emission peak in a wavelength range of 250 to 520 nm
Data Source
AI summary
According to one embodiment, the luminescent material shows a luminescence peak in a wavelength range of 570 to 670 nm when excited with light having an emission peak in a wavelength range of 250 to 520 nm. The luminescent material includes a host material having a crystal structure substantially same as the crystal structure of Sr2Si7Al3ON13. The host material is activated by Eu, and includes Sr and Ca to satisfy a relationship of 0.008≦MCa/(MSr+MCa)≦0.114, where MCa is a number of moles of Ca and MSr is a number of moles of Sr.