Phosphor Particle Size Distribution for LCD Backlight Color Rendering
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Solution Overview
Problem
Conventional white light-emitting devices have inadequate color rendering properties and color reproducibility, particularly in the red region, and suffer from low luminous efficiency when used as illumination sources or backlights for small-sized LCDs, due to the instability of certain luminescent materials and poor luminous component distribution.
Innovation Solution
A light-emitting device utilizing a combination of phosphor particles with controlled median diameters, including divalent-europium-activated nitride red phosphor particles, divalent-europium-activated oxynitride green phosphor particles, and trivalent-cerium-activated silicate green phosphor particles, to enhance luminous efficiency and color rendering properties by optimizing the distribution and emission peak wavelengths within a luminescence converter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional luminescent materials (SrGa2S4:Eu2+ and SrS:Eu2+) are used to improve color rendering properties, then general color rendering index (Ra) improves to 70-90, but chemical stability deteriorates as these materials are easily decomposed when irradiated with ultraviolet light
Solution Approach 1:
The patent replaces unstable but high-performance luminescent materials (SrGa2S4:Eu2+ and SrS:Eu2+) with more stable alternatives that have shorter operational lifetimes or lower performance, accepting a trade-off to achieve chemical stability. Specifically, it uses luminescent materials with higher resistance to UV decomposition even if their color rendering index is slightly lower, ensuring long-term reliability of the light-emitting device.
Solution Approach 2:
The patent employs composite luminescent material systems that combine multiple materials with different properties. By creating a composite structure, it achieves both adequate color rendering properties and improved chemical stability, as the composite system can distribute the stress of UV irradiation across multiple components rather than relying on a single unstable material.
2Reliability
If red luminescent materials are added to improve color rendering properties and NTSC ratio, then color reproducibility improves, but brightness deteriorates due to poor luminous component distribution
Solution Approach 1:
The patent applies local quality by optimizing the spatial distribution and concentration of red luminescent materials within the luminescence converter. Instead of uniform distribution, it creates localized regions with specific material compositions and concentrations, allowing red light emission to be concentrated where it most effectively improves NTSC ratio without excessively reducing overall brightness. This localized optimization enables selective enhancement of color rendering properties in specific spectral regions.
Solution Approach 2:
The patent changes key parameters of the luminescent material system, including the wavelength peak, half-value width, and concentration of red luminescent materials. By adjusting these parameters, it achieves a balance where the red light component is sufficiently strong to improve NTSC ratio to 70% or more, while the overall luminous efficiency and brightness are maintained at acceptable levels through optimized material selection and configuration.
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 significantly improves brightness and color rendering properties, achieving higher NTSC ratios and correlated color temperatures, making the device suitable for general illumination and small-sized LCD backlights.
Implementation Method 1
a luminescence converter for absorbing the primary light and emitting secondary light having a longer peak wavelength as compared with the primary light
Data Source
AI summary
A group of phosphor particles for a light-emitting device contains a plurality of types of phosphor particles having different emission peak wavelengths, while phosphor particles of a type having a relatively longer emission peak wavelength have a relatively larger median diameter as compared with phosphor particles of a type having a relatively shorter emission peak wavelength.