Luminescent Material for White LEDs Using Segmented Emission
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Solution Overview
Problem
Conventional white LEDs with broad-band emission spectra have limited color rendering due to the use of luminescent materials that are inefficiently excited by light in the ultraviolet to blue region, and Dy-activated materials are poorly excited by such light, requiring vacuum ultraviolet rays or electron beams for activation.
Innovation Solution
A luminescent material comprising an alkaline earth orthosilicate compound with europium and praseodymium or dysprosium activators, optimized to emit light efficiently when excited by light in the 310-420 nm range, achieving both narrowband and broadband emission spectra, thereby enhancing color rendering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a broad-band emission spectrum luminescent material is used, then the light emission coverage is improved, but the color rendering is limited
Solution Approach 1:
The patent divides the emission spectrum into multiple discrete bands by using different activators (Eu2+ for broadband, Dy3+ for narrowband green, Pr3+ for narrowband blue-green) within the same host material, rather than relying on a single broad-band emitter. This segmentation allows simultaneous achievement of wide coverage and precise color control.
Solution Approach 2:
The invention creates a composite luminescent system by incorporating multiple activator ions (Eu2+, Dy3+, Pr3+) into the alkaline earth orthosilicate host structure. This composite approach combines the advantages of broadband emission from Eu2+ with the narrowband color-pure emission from Dy3+ and Pr3+, resolving the contradiction between coverage and color rendering.
2Illumination intensity
If Dy-activated luminescent material is used, then the emission intensity is improved, but the excitability by ultraviolet to blue light deteriorates
Solution Approach 1:
The patent introduces Eu2+ as an intermediary sensitizing ion that absorbs ultraviolet to blue light effectively and transfers energy to Dy3+ and Pr3+. This intermediary mechanism solves the problem of poor direct excitation of Dy3+ by UV-blue light while maintaining high emission intensity from the rare earth ions.
Solution Approach 2:
The invention optimizes the concentration ratios of different activators (Eu2+, Dy3+, Pr3+) to control energy transfer efficiency. By adjusting these parameters, the system achieves both high excitability by UV-blue light (through Eu2+) and high emission intensity (through Dy3+ and Pr3+).
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 enables efficient light emission with improved color rendering, as it can be excited by LEDs in the near-ultraviolet to blue region, producing specific emission peaks that enhance the average color rendering index, making it suitable for white light-emitting devices.
Implementation Method 1
The luminescent material to be used in a white LED is required to be not only capable of effectively absorbing the light ranging from near-ultraviolet region to blue region (310-420 nm) which corresponds to the emission wavelength of LED chip acting as an excitation light source but also capable of efficiently emitting visible light.
Data Source
AI summary
A luminescent material is provided, which includes a compound having a composition represented by the following general formula (A):(Sra1,Bab1,Cac1,Rev1,Euw1)2SiO4 (A)wherein, Re is at least one selected from a group consisting of Pr and Dy, and a1, b1, c1, v1 and w1 satisfy following relationships:a1+b1+c1+v1+w1=1 (1),0≦a1/(1−v1−w1)≦1 (2),0≦b1/(1−v1−w1)≦1 (3),0≦c1/(1−v1−w1)≦1 (4),0<v1≦0.15 (5),0<w1≦0.02 (6).