White Light Emitting Device Phosphor Layer Segmentation
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Solution Overview
Problem
Conventional white light emitting devices using near ultraviolet LEDs face challenges in achieving high light emitting efficiency due to reabsorption issues and differing emission spectra of red-emitting phosphors activated by Eu2+ and Eu3+, leading to inefficient light output and color rendering problems.
Innovation Solution
A white light emitting device is designed with a semiconductor light emitting element emitting near ultraviolet light, a first phosphor layer containing a blue-emitting phosphor and a Eu3+-activated red-emitting phosphor, and a second phosphor layer containing a green-emitting phosphor, arranged in a specific laminated structure to minimize reabsorption and enhance light efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a red-emitting phosphor activated by Eu2+ is used, then light emitting efficiency is improved, but reabsorption in the visible light region increases causing reddish coloring
Solution Approach 1:
The device segments the phosphor layer into multiple layers with different phosphor materials. The first phosphor layer contains a red-emitting phosphor (CaAlSiN3:Eu2+) close to the UV-LED to maximize absorption efficiency, while the second phosphor layer contains a green-emitting phosphor (β-SiAlON:Eu2+) positioned farther away. This segmentation reduces reabsorption of green light by the red phosphor, preventing excessive reddish coloring while maintaining high light emitting efficiency.
2Object-generated harmful factors
If a red-emitting phosphor activated by Eu3+ is used, then reabsorption is reduced improving color rendering, but light emitting efficiency decreases due to weak absorption of near ultraviolet light
Solution Approach 1:
The patent positions the red-emitting phosphor (CaAlSiN3:Eu2+) in the first layer closest to the UV-LED excitation source, where it can efficiently absorb near ultraviolet light. The green-emitting phosphor is placed in the second layer farther from the UV-LED. This spatial segmentation ensures that the red phosphor captures UV energy effectively while minimizing reabsorption of the emitted red light by other phosphors, thus maintaining both high efficiency and good color rendering.
3Device complexity
If multiple phosphors are mixed in a single layer, then device structure is simplified, but reabsorption between phosphors increases reducing light efficiency
Solution Approach 1:
The patent divides the phosphor layer into at least two separate layers: a first phosphor layer containing a red-emitting phosphor and a second phosphor layer containing a green-emitting phosphor. This segmentation prevents reabsorption of light between different phosphor materials that would occur in a mixed single-layer configuration, thereby maintaining high light emitting efficiency while achieving a relatively simple overall device structure.
Solution Approach 2:
Instead of mixing phosphors horizontally in a single layer, the patent arranges different phosphors in vertical layers at different positions relative to the UV-LED. The first phosphor layer is positioned closer to the UV-LED than the second phosphor layer, creating a vertical dimension for phosphor arrangement that optimizes light absorption paths and minimizes reabsorption while keeping the device structure compact.
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 significantly improves light emitting efficiency and color rendering properties by reducing reabsorption and optimizing the emission spectrum, resulting in a higher luminance output compared to conventional devices.
Implementation Method 1
a semiconductor light emitting element configured to emit near ultraviolet light
Implementation Method 2
a first phosphor layer containing a blue-emitting phosphor configured to emit blue light by the near ultraviolet light
Implementation Method 3
a blue-emitting phosphor configured to emit blue light by the near ultraviolet light
Implementation Method 4
a green-emitting phosphor configured to emit green light by the near ultraviolet light
Implementation Method 5
a red-emitting phosphor activated by trivalent europium and configured to emit red light by the near ultraviolet light
Data Source
AI summary
Disclosed is a white light emitting device including a semiconductor light emitting element configured to emit near ultraviolet light having a peak wavelength ranging from 380 to 410 nm, a first phosphor layer and a second phosphor layer. The first phosphor layer contains a blue-emitting phosphor configured to emit blue light by the near ultraviolet light, and a red-emitting phosphor activated by trivalent europium and configured to emit red light by the near ultraviolet light. The second phosphor layer contains a green-emitting phosphor configured to emit green light by the near ultraviolet light. The semiconductor light emitting element, the first phosphor layer and the second phosphor layer are laminated in this order to emit white light.