Light Emitting Device Resin Refractive Index Gradient
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Solution Overview
Problem
Conventional methods fail to efficiently extract light from sealing resins in large display devices, particularly when LED elements increase in size, leading to reduced light extraction efficiency due to the treatment of LED elements as point light sources and the expansion of the light emitting region to include phosphors, resulting in insufficient light extraction.
Innovation Solution
A light emitting device design featuring a substrate with a semiconductor light emitting element and fluorescent particles, where the inner portion has a higher refractive index than the outer portion, and the outer portion forms a concentric hemispherical shape around the inner portion, optimizing the radius relationship to enhance light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If LED element size is increased to meet brightness requirements, then light emission intensity is improved, but light extraction efficiency deteriorates due to expansion of light emitting region and treatment as point light source
Solution Approach 1:
The patent applies local quality by creating a refractive index gradient within the sealing resin, where the refractive index varies from the center to the periphery. Specifically, the refractive index is higher near the LED element and lower toward the outer surface, forming concentric regions with different refractive indices. This gradient structure optimizes light extraction locally at each radius while accommodating the expanded light emitting region of larger LED elements, thereby resolving the contradiction between increased light emission intensity and maintained light extraction efficiency.
Solution Approach 2:
The patent changes the refractive index parameter of the sealing resin from a uniform value to a spatially varying gradient. By controlling the refractive index to decrease from the center toward the periphery (with specific relationships such as n1 > n2 > n3 for different concentric regions), the patent enables efficient light extraction across the entire expanded light emitting region of larger LED elements, preventing total internal reflection and maintaining high extraction efficiency despite increased LED size.
2Length of moving object
If sealing resin thickness is reduced to achieve thin and lightweight display devices, then device thickness and weight are improved, but light extraction efficiency deteriorates due to confined light paths
Solution Approach 1:
The patent applies local quality by creating radially varying refractive index regions within the sealing resin, with higher refractive indices near the LED element and lower refractive indices toward the outer surface. This local differentiation of optical properties enables efficient light extraction at each radial position, allowing thin sealing resin structures to maintain high light extraction efficiency by optimizing the light path at each local region rather than relying on overall thickness.
Solution Approach 2:
The patent employs a spherical or hemispherical geometry for the sealing resin structure, with concentric refractive index regions arranged radially from the LED element at the center. This curved, spherical configuration naturally guides light rays outward through the gradient refractive index profile, enabling efficient light extraction even in thin structures by following the curved optical paths rather than straight-line propagation that would be constrained in planar geometries.
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 design significantly enhances light extraction efficiency by eliminating total reflection and confinement phenomena, allowing for improved light extraction into the atmosphere, even with larger LED elements, and maintains a compact form factor suitable for thin and lightweight display devices.
Implementation Method 1
a fluorescent particle that absorbs a part of the primary light and emits secondary light
Implementation Method 2
an outer portion having a refractive index n and covering the inner portion... eliminating total reflection and confinement phenomena, allowing for improved light extraction into the atmosphere
Data Source
Figure 1~2
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Figure 5~7
AI summary
A light emitting device (10) includes: a substrate (21) having a main surface (22); a phosphor layer (31) provided on the main surface (22) and containing an LED element (26) that emits primary light and a fluorescent particle (36) that absorbs a part of the primary light and emits secondary light; and a transparent resin layer (41) having a refractive index n and covering the phosphor layer (31). The transparent resin layer (41) has an outer circumferential surface (42) that forms a boundary between the transparent resin layer (41) and the atmosphere. When a minimum circumference (101) that includes the overall phosphor layer (3 1) and is concentric with the outer circumferential surface (42) has a radius r in a cut surface where at least a part of the outer circumferential surface (42) takes a shape of an arc having a radius R, a relationship of R>r•n is satisfied. With such configuration, the light extraction efficiency is enhanced.