Backlight Phosphor Composition for Wide-Gamut Bright Displays
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Solution Overview
Problem
Existing color image display devices face challenges in achieving high color purity and brightness due to inadequate emission from backlights, particularly with yellow-emitting phosphors, which result in reduced color reproducibility and increased brightness at the expense of NTSC ratio, and the complexity of combining red, green, and blue LEDs for improved color reproduction.
Innovation Solution
A semiconductor light emitting device with specific phosphors, including a blue or deep blue emitter and phosphors with emission peaks in the 515-550 nm range for green and 610-650 nm range for red, optimized for high luminance and durability, allowing for efficient light use and improved NTSC ratio without sacrificing brightness, and a process for producing these phosphors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If yellow-emitting phosphors are used in the backlight, then brightness is increased, but color reproducibility deteriorates and NTSC ratio decreases
Solution Approach 1:
The invention segments the backlight emission into multiple wavelength components by using a blue LED combined with multiple phosphors (yellow-emitting phosphor and red-emitting phosphor) instead of a single yellow phosphor. This segmentation allows independent optimization of brightness and color reproduction by controlling the emission spectrum in different wavelength regions.
Solution Approach 2:
The invention uses a composite phosphor system consisting of multiple phosphor materials (yellow-emitting phosphor and red-emitting phosphor) combined with a blue LED. This composite approach enables the backlight to simultaneously achieve high brightness from the yellow phosphor and improved color reproducibility from the red phosphor, resolving the trade-off between brightness and color accuracy.
2Reliability
If the color filter is adjusted to increase NTSC ratio, then color purity is improved, but brightness decreases
Solution Approach 1:
The invention performs preliminary action by optimizing the backlight emission spectrum before light reaches the color filter. By adjusting the phosphor composition and excitation wavelength to match the color filter's transmission characteristics, the system maximizes light utilization efficiency, allowing high NTSC ratio to be achieved without sacrificing brightness.
Solution Approach 2:
The invention changes the parameters of the backlight system by adjusting the phosphor composition ratios, particle sizes, and excitation wavelength to optimize the emission spectrum. These parameter changes enable the system to achieve both high color purity (NTSC ratio) and high brightness by improving the spectral match between backlight and color filter.
3Reliability
If red, green, and blue LEDs are combined to improve color reproduction, then color reproducibility is improved, but device complexity increases
Solution Approach 1:
The invention merges multiple light-emitting functions into a single blue LED chip by combining it with multiple phosphor materials that convert the blue light into yellow and red wavelengths. This merging approach achieves the color reproduction benefits of multiple LEDs while simplifying the device structure and mounting process, as only one LED chip needs to be mounted rather than three separate red, green, and blue LEDs.
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 enables broad color reproducibility with high luminance and efficiency, facilitating easy white balance adjustment and maintaining image brightness, while simplifying the mounting process by using a single chip for red, green, and blue emissions.
Implementation Method 1
a blue or deep blue light-emitting semiconductor device and phosphors, in combination
Data Source
AI summary
To provide a semiconductor light emitting device which is capable of accomplishing a broad color reproducibility for an entire image without losing brightness of the entire image. A light source provided on a backlight for a color image display device has a semiconductor light emitting device comprising a solid light emitting device to emit light in a blue or deep blue region or in an ultraviolet region and phosphors, in combination. The phosphors comprise a green emitting phosphor and a red emitting phosphor. The green emitting phosphor and the red emitting phosphor are ones, of which the rate of change of the emission peak intensity at 100° C. to the emission intensity at 25° C., when the wavelength of the excitation light is 400 nm or 455 nm, is at most 40%.