White LED Phosphor Layer for CCFL Color Reproduction
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Solution Overview
Problem
Conventional white LEDs used in liquid crystal display devices have a different luminescent color profile compared to CCFLs, leading to suboptimal display quality and color reproduction when replacing CCFLs, requiring costly redesign of color filters and phosphors that are not fully compatible with existing CCFL technology.
Innovation Solution
A white LED comprising ultraviolet or purple light emitting diodes or lasers combined with a phosphor layer containing specific green, blue, and red phosphors, such as trivalent cerium- and terbium-activated rare earth boride, divalent europium-activated halophosphate, and europium-activated lanthanum oxysulfide phosphors, which provide a color reproduction range comparable to CCFLs and enhance brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional white LEDs with different luminescent color profile are used to replace CCFLs, then environmental sustainability is improved (mercury elimination) and service life is extended, but color reproduction quality deteriorates and display characteristics worsen
Solution Approach 1:
The patent employs a composite phosphor system combining multiple phosphor materials (yellow phosphor with peak wavelength 560-580nm and red phosphor with peak wavelength 610-650nm) to create a white LED that reproduces CCFL-like color characteristics while maintaining LED advantages of longevity and environmental friendliness
2Object-affected harmful factors
If white LED with different color profile is used to replace CCFL, then environmental harm is reduced (mercury elimination), but adaptability to existing color filters deteriorates
Solution Approach 1:
The patent adjusts key spectral parameters of the white LED by selecting phosphors with specific peak wavelengths (yellow: 560-580nm, red: 610-650nm) to match the color reproduction range of CCFL, enabling compatibility with existing color filters while eliminating mercury
3Device complexity
If blue light emitting diode is used to produce white light with yellow phosphor, then device complexity is reduced (single LED type, no color mixing mechanism), but color reproduction quality deteriorates compared to ultraviolet diode with three color phosphors
Solution Approach 1:
The patent uses a composite phosphor approach with yellow and red phosphors excited by blue LED to achieve a spectral power distribution that closely matches CCFL, providing good color reproduction (Ra≥90, R9≥90) while maintaining the simplicity of a single LED type without complex color mixing mechanisms
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 allows for the use of existing CCFL color filters, maintaining comparable color reproduction and brightness, eliminating the need for costly redesign and ensuring environmental sustainability by eliminating mercury usage.
Implementation Method 1
A white LED comprising at least one light emitting element selected from ultraviolet light emitting diodes, purple light emitting diodes, ultraviolet light emitting lasers, and purple light emitting lasers
Implementation Method 2
a phosphor layer, characterized in that the phosphor layer comprises a green phosphor satisfying general formula (1), a blue phosphor satisfying general formula (2) or (3), and a red phosphor satisfying general formula (4)
Data Source
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AI summary
Disclosed are a white LED, which has color reproducibility comparable with that of a cold-cathode tube and improved brightness, and a backlight and a liquid crystal display device comprising the white LED. The white LED comprises at least one light emitting element selected from ultraviolet light emitting diodes, purple light emitting diodes, ultraviolet light emitting lasers, and purple light emitting lasers, and a phosphor layer. The phosphor layer comprises a green phosphor satisfying formula 1, a blue phosphor satisfying formula 2 or 3, and a red phosphor satisfying formula 4 or 5: a trivalent cerium- and terbium-activated rare earth boride phosphor represented by formula 1: M1-x-yCexTbyBO3 wherein M represents at least one element selected from Sc (scandium), Y (yttrium), La (lanthanum), Gd (gadolinium), and Lu (lutetium); and x and y are respective numbers of 0.03 < x < 0.3 and 0.03 < y < 0.3; a divalent europium-activated halophosphate phosphor represented by formula 2: (M2, Eu)10(PO4)6.Cl2 wherein M2 represents Mg (magnesium), Ca (calcium), Sr (strontium), or Ba (barium), or a divalent europium-activated aluminate phosphor represented by formula 3: a(M3, Eu)O·bAl2O3 wherein M3 represents Mg (magnesium), Ca (calcium), Sr (strontium), Ba (barium), Zn (zinc), Li (lithium), Rb (rubidium), or Cs (cesium); and a and b are respective numbers of 0 < a, 0 < b, and 0.2 ≤ a/b ≤ 1.5; and a europium-activated lanthanum oxysulfide phosphor represented by formula 4: (La1-x, Eux)2O2S wherein x is a number satisfying 0.01 < x < 0.15), or a europium-activated yttrium oxysulfide phosphor represented by formula 5: (Y1-x, Eux)2O2S wherein x is a number satisfying 0.01 < x < 0.15.