UV LED Backlight Unit Green Phosphor Conversion
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Solution Overview
Problem
Conventional backlight units for LCDs using cold cathode fluorescent lamps (CCFLs) have low color purity and require more green LEDs than red and blue LEDs, leading to increased power consumption and fabrication costs, with emission wavelength stability issues due to temperature and current variations.
Innovation Solution
A backlight unit employing a green light source comprising a UV LED and a green phosphor excited by the UV LED, with blue and red light sources also using UV LEDs and phosphors, all maintained in a 1:1:1 ratio to improve luminous efficiency and stability, using materials like ZnS, (BaSr)2SiO4, LaPO4, and BaMgAl10O17 for the phosphors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional green LEDs are used in LCD backlight units, then color purity is improved, but internal quantum efficiency becomes very low (10%) requiring twice as many green LEDs as red or blue LEDs
Solution Approach 1:
The patent changes the fundamental parameters of the green light source by transitioning from direct green LED emission to UV LED excitation of green phosphor materials. This parameter change enables achieving high color purity (x=0.20, y=0.70) while dramatically improving internal quantum efficiency to 80%, thereby reducing power consumption and the number of green light sources needed.
Solution Approach 2:
The patent employs composite phosphor materials including (Ba, Sr)2SiO4:Eu2+, LaPO4:Ce3+, and BaMgAl10O17:Eu2+ that are excited by UV LEDs. These composite phosphor systems enable simultaneous achievement of high color purity, high efficiency, and stable emission characteristics, resolving the contradiction between color purity and power consumption.
2Illumination intensity
If the number of green LEDs is increased to compensate for low efficiency, then illumination intensity is maintained, but fabrication cost increases
Solution Approach 1:
By changing from direct green LED to UV LED with green phosphor, the patent achieves high illumination intensity with fewer components. The high quantum efficiency (80%) means fewer green light sources are needed, directly reducing fabrication costs while maintaining required illumination levels.
Solution Approach 2:
The UV LED can serve multiple functions by exciting different phosphor materials to produce various colors (green, blue, red). This multi-functionality allows a single UV LED type to replace multiple different colored LEDs, simplifying manufacturing and reducing costs.
3Illumination intensity
If conventional green LEDs are used, then color purity is achieved, but emission wavelength becomes unstable due to temperature and current variations
Solution Approach 1:
The patent introduces green phosphor materials as an intermediary between UV LED and the final green light output. The phosphor absorbs UV photons and re-emits at stable green wavelengths, decoupling the emission stability from the LED's direct electrical characteristics and temperature dependencies, thereby stabilizing the output color.
Solution Approach 2:
By transitioning from direct green LED emission to phosphor-converted green light, the patent changes the physical mechanism of light generation. Phosphor materials exhibit more stable emission wavelengths under varying temperature and current conditions compared to direct LED emission, resolving the stability issue while maintaining color purity.
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
This configuration reduces the number of green LEDs needed, lowering power consumption and fabrication costs while maintaining stable color coordinates and luminous efficiency, achieving nearly twice the efficiency of conventional green LEDs.
Implementation Method 1
a green light source, which includes an ultraviolet (UV) LED and a green phosphor excited by light emitted from the UV LED
Data Source
AI summary
A backlight unit for a liquid crystal display (LCD) using a light emitting diode (LED) is provided. The backlight unit includes a blue light source, a red light source, and a green light source. The green light source includes an ultraviolet (UV) LED and a green phosphor excited by light emitted from the UV LED.