Light-Emitting Device Segmented Phosphor Layers
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Solution Overview
Problem
Conventional light-emitting devices exhibit low light extraction efficiency due to light emitted from phosphor particles being absorbed by the LED chip, as part of the light travels radially and returns toward the chip.
Innovation Solution
A light-emitting device structure featuring a first light-transmissive member without phosphor on the upper surface of the LED, a second light-transmissive member with phosphor on top of the first, and a third member covering the lateral surfaces, which reflects and directs light to enhance extraction efficiency by minimizing absorption and optimizing phosphor excitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphor particles are disposed directly on the LED chip to convert light wavelength, then wavelength conversion efficiency is improved, but light extraction efficiency deteriorates due to radial light emission returning to and being absorbed by the chip
Solution Approach 1:
The device segments the phosphor-containing structure into multiple layers: a first light-transmissive member without phosphor closest to the chip, a second light-transmissive member with phosphor above it, and a third light-transmissive member with phosphor covering lateral surfaces. This segmentation prevents direct contact between phosphor and the chip, allowing light to be converted at a distance and reducing re-absorption by the chip while maintaining conversion efficiency.
Solution Approach 2:
The invention transitions from a single-layer phosphor structure to a three-dimensional multi-layer configuration. The third light-transmissive member extends over lateral surfaces of the chip, creating a spatial arrangement where phosphor is positioned in multiple dimensions away from the chip surface, enabling light extraction in multiple directions and reducing re-absorption.
2Productivity
If phosphor is placed close to the LED chip for efficient excitation, then phosphor excitation efficiency is improved, but light absorption by the chip increases due to radial light travel
Solution Approach 1:
The first light-transmissive member acts as an intermediary between the LED chip and the phosphor-containing second light-transmissive member. This intermediate layer allows UV light from the chip to pass through and excite the phosphor while preventing blue light emitted by the phosphor from directly returning to and being absorbed by the chip, thus maintaining excitation efficiency while reducing harmful re-absorption.
3Device complexity
If a single encapsulating material containing phosphor is used, then device complexity is reduced, but light extraction efficiency deteriorates due to light returning to and being absorbed by the chip
Solution Approach 1:
The single encapsulating material is segmented into three distinct light-transmissive members with different phosphor compositions and positions. The first member contains no phosphor, the second member contains phosphor for primary wavelength conversion, and the third member contains phosphor for additional color rendering. This segmentation resolves the contradiction by improving light extraction efficiency through spatial separation while managing complexity through functional differentiation.
Solution Approach 2:
The device uses composite material structures where each light-transmissive member is composed of different materials with specific optical properties. The first member is a phosphor-free light-transmissive material, the second member contains phosphor particles in a light-transmissive matrix, and the third member similarly combines phosphor with light-transmissive material. These composite structures enable optimized light extraction while maintaining manageable device complexity through material selection.
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 structure significantly improves light extraction efficiency by reducing light absorption and enhancing phosphor excitation, leading to improved color rendering properties and reliability of the light-emitting device.
Implementation Method 1
a light-reflective member 4 located in a region defined by lateral surfaces 21, 22, 23, and 24 of the recess 2 and an upper surface of the resin frame portion 31
Implementation Method 2
a second light-transmissive member 25 disposed on the upper surface of the first light-transmissive member 15 and containing a first phosphor 61
Data Source
Figure 1A~1B
Figure 1C~1E
Figure 2A~2F
AI summary
A light-emitting device includes: a light-emitting element; a first light-transmissive member located on an upper surface of the light-emitting element and containing substantially no phosphor; a second light-transmissive member located on an upper surface of the first light-transmissive member and containing a first phosphor; and a third light-transmissive member covering an upper surface of the second light-transmissive member and a lateral surface of the tight-emitting element and containing a second phosphor; wherein a refractive index of a resin material serving as a base material of the second light-transmissive member is higher than a refractive index of a resin material serving as a base material of the first light-transmissive member; and wherein a refractive index of a resin material serving as a base material of the third light-transmissive member is equal to or higher than the refractive index of the resin material serving as the base material of the second light-transmissive member.