Light Emitting Device Phosphor Layering for Secondary Absorption
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Solution Overview
Problem
Conventional light emitting devices using sulfide phosphors suffer from secondary absorption, leading to reduced luminous efficiency due to the use of conventional red phosphors like CaS:Eu, which absorb green light emitted by sulfide phosphors, necessitating a solution for improved light extraction and luminance efficiency.
Innovation Solution
Incorporating KSF or MGF phosphors as red phosphors, which absorb blue light with minimal secondary absorption, and positioning them closer to the light emitting element within a sealing resin, while the green sulfide phosphor is placed farther away to reduce heat influence and maintain high luminous efficiency, thereby enhancing light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional red phosphors (CaS:Eu, (BaSr)3SiO5:Eu) are used with green sulfide phosphor, then the device structure is simple, but secondary absorption occurs reducing luminous efficiency
Solution Approach 1:
The device is divided into distinct functional layers: a light emitting element layer, a sealing resin layer containing red phosphor particles, and a green sulfide phosphor layer. This segmentation allows the red phosphor to be positioned where it can absorb blue light directly from the light emitting element without interfering with green light emission, thereby eliminating secondary absorption while maintaining structural organization.
Solution Approach 2:
The sealing resin acts as an intermediary medium that contains and positions the red phosphor particles. This intermediary structure enables the red phosphor to perform its function of converting blue light to red light while being spatially separated from the green sulfide phosphor layer, preventing harmful secondary absorption interactions.
2Productivity
If green sulfide phosphor is placed close to light emitting element, then light extraction efficiency is high, but thermal degradation occurs
Solution Approach 1:
The device structure separates the green sulfide phosphor layer from the light emitting element by introducing a sealing resin layer in between. This segmentation allows the green sulfide phosphor to maintain high light extraction efficiency while being thermally protected from the light emitting element, as the sealing resin acts as a thermal barrier.
3Loss of energy
If red phosphor is placed close to green sulfide phosphor, then device structure is compact, but secondary absorption increases
Solution Approach 1:
The device is segmented into distinct layers with the red phosphor-containing sealing resin layer positioned between the light emitting element and the green sulfide phosphor layer. This segmentation eliminates secondary absorption by preventing spatial overlap between red and green phosphor emission regions, while the layered structure maintains a compact overall device volume.
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 use of KSF or MGF phosphors reduces secondary absorption, achieving high luminous efficiency and color purity with reduced phosphor thickness, improving light extraction and maintaining brightness while minimizing thermal degradation.
Implementation Method 1
a light emitting element adapted to emit a blue light
Implementation Method 2
a sulfide phosphor configured to emit a green light upon absorbing a portion of the blue light emitted from the light emitting element
Implementation Method 3
The sealing resin includes at least one of a KSF phosphor or a MGF phosphor
Implementation Method 4
a sealing resin covering the light emitting element
Data Source
AI summary
A device includes a light emitting device including: a light emitting element adapted to emit a blue light, a sealing resin covering the light emitting element, and a sulfide phosphor-containing layer disposed separate from the sealing resin; and a diffusion plate disposed between the sealing resin and the sulfide phosphor-containing layer, the diffusion plate being spaced apart from the sealing resin.