White Light Emitting Device Using Semiconductor Nanocrystals
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Solution Overview
Problem
Conventional white light-emitting diodes (LEDs) face a trade-off between high luminous efficiency and high color rendering index, with low red color rendering index due to low luminous efficiency of red light emitters, and existing attempts to improve color rendering using red phosphors result in decreased efficiency due to wide invisible light spectra.
Innovation Solution
A white light-emitting device comprising a blue light source, a phosphor, and semiconductor nanocrystals, where the phosphor and nanocrystals are dispersed in different matrices to form an emission layer, achieving a high R1-R8 average color rendering index and R9 red color rendering index of greater than or equal to 90, with the nanocrystals having a narrow light emitting spectrum and high luminous efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a red phosphor is applied to improve color rendering index, then color rendering index is improved, but luminous efficiency is decreased due to wide invisible light spectrum
Solution Approach 1:
The patent changes the spectral parameters by using a red semiconductor nanocrystal with a narrow full width at half maximum (FWHM) of 30-50 nm, compared to the wide spectrum of conventional red phosphors. This parameter change allows the red emission to be concentrated in the visible range (620-750 nm), improving color rendering index while avoiding energy loss in invisible wavelengths, thus resolving the contradiction between color rendering and luminous efficiency
Solution Approach 2:
The patent employs a composite material system consisting of a blue light source (440-460 nm) combined with a red semiconductor nanocrystal (620-650 nm) and a yellow phosphor. This composite approach creates a synergistic effect where each component contributes to both color rendering and efficiency: the blue LED provides high efficiency primary emission, the red nanocrystal enhances color rendering without significant energy loss, and the yellow phosphor fills the spectral gap, achieving both high color rendering index and maintained luminous efficiency
2Loss of energy
If single color light at 555 nm is emitted to increase luminous efficiency, then luminous efficiency is increased, but color rendering index is decreased
Solution Approach 1:
The patent merges multiple light emission components: blue light (440-460 nm) from LED, red light (620-650 nm) from semiconductor nanocrystal, and yellow light from phosphor. This combination merges the high efficiency of single-color blue LED emission with the color rendering benefits of multiple wavelengths, achieving both high luminous efficiency and high color rendering index simultaneously
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 solution achieves high luminous efficiency and improved color rendering indices without deteriorating luminous efficacy, enabling white light emission with a color temperature of 2500 K to 4000 K, while maintaining commercially viable efficiency.
Implementation Method 1
The phosphor and the semiconductor nanocrystal may absorb light from the blue light source and emit light
Implementation Method 2
The phosphor may have a light emitting spectrum of about 510 nm to about 650 nm and luminous efficiency of greater than or equal to about 70%
Implementation Method 3
The semiconductor nanocrystal may have a light emitting spectrum of about 620 nm to about 650 nm and luminous efficiency of greater than or equal to about 50%
Data Source
AI summary
A light emitting device including: a blue light source; a phosphor; and a semiconductor nanocrystal, and emits white light having a R1-R8 average color rendering index (“CRI”) of greater than or equal to about 90, and a R9 red color rendering index (R9) of greater than or equal to about 90.