Red Emitting Luminescent Material for Warm White LEDs
Solution Overview
Problem
There is a need for red emitting luminescent materials that can be used across a wide range of applications to fabricate phosphor converted warm white LEDs with optimized luminous efficiency and color rendering, as existing materials do not adequately meet these requirements.
Innovation Solution
A luminescent material with an orthorhombic structure comprising three-dimensionally connected SiN4 and AlN4 tetrahedra, featuring two crystallographically different M-sites that allow for adjustable red emission through RE doping, particularly with Eu, and optimized Ba/Sr/Ca ratio, enhancing thermal and chemical stability and photostability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing red emitting phosphor materials are used, then red emission can be achieved, but thermal stability and chemical stability are insufficient
Solution Approach 1:
The patent employs a composite phosphor material comprising a nitride host lattice doped with rare earth metals (particularly Eu²⁺). This composite structure combines the high thermal and chemical stability of the nitride host with the red emission properties of Eu²⁺, achieving both stability requirements simultaneously. The host lattice provides structural stability while the dopant provides the desired optical properties.
Solution Approach 2:
The patent optimizes the composition parameters of the phosphor material, specifically the ratio of host material to dopant and the oxidation state of the rare earth metal. By controlling these parameters (using divalent Eu²⁺ rather than trivalent Eu³⁺, and optimizing the nitride host composition), the patent achieves enhanced thermal stability and chemical stability while maintaining red emission properties.
2Productivity
If red emitting phosphor materials are used, then red emission can be achieved, but luminous efficiency is not optimized
Solution Approach 1:
The patent changes the key parameter of using Eu²⁺ in the +2 oxidation state rather than the more common +3 state. This parameter change results in 4f-4f transitions with higher quantum efficiency and reduced energy loss through non-radiative pathways. The patent also optimizes the host lattice structure to maximize energy transfer efficiency from the host to the Eu²⁺ dopant, thereby improving overall luminous efficiency.
3Illumination intensity
If red emitting phosphor materials are used, then red emission can be achieved, but color rendering is not optimized
Solution Approach 1:
The patent utilizes the different crystallographic sites (M1 and M2) within the nitride host lattice to create local variations in the emission characteristics. By controlling the distribution of Eu²⁺ ions across these different sites, the patent achieves a broadened emission spectrum that improves color rendering while maintaining compatibility with various LED applications. The M1 and M2 sites provide slightly different local environments that contribute to spectral broadening.
4Reliability
If conventional phosphor materials are used, then light conversion can be achieved, but photostability under blue light irradiation is insufficient
Solution Approach 1:
The patent creates a composite material where the nitride host lattice provides exceptional photostability under blue light irradiation. The strong covalent bonding in the nitride structure resists photo-degradation, while the Eu²⁺ dopant maintains stable red emission. This composite structure significantly extends the operational lifetime of the LED by preventing phosphor degradation during prolonged exposure to high-energy blue pump light.
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 material enables the production of LEDs with improved lighting features, including thermal stability, high chemical stability, and optimized luminous efficiency and color rendering, suitable for various applications, including warm white pcLEDs, by tuning the emission spectrum and maintaining high photostability under blue light irradiation.
Implementation Method 1
the LED emitting primary radiation in the range from 300 to 570 nm, this radiation being partially or completely converted into longer-wave radiation by phosphors
Implementation Method 2
red emission especially occurs after excitation of RE incorporated on the smaller M(1) site
Implementation Method 3
excitation energy absorbed by RE incorporated on the smaller M(1) site may be transferred to RE on M(1) site by means of energy transfer processes
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The invention relates to an improved red light emitting material of the formula M 1-y A 1+x Si 4-x N7-x-2y O x+2y :REwhereby M is selected out of the group comprising Ba, Sr, Ca, Mg or mixtures thereof, A is selected out of the group comprising Al, Ga, B or mixtures thereof, RE is selected out of the group comprising rare earth metals, Y, La, Sc or mixtures thereof and x is =0 and =1 and y is =0 and =0.2. This material is believed to crystallize in a novel structure type that comprises two individual lattice sites for rare 10 earth metal incorporation, which leads to an improved lighting behaviour.