Core-Shell Particle Assemblies for LED Optical Transparency

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Solution Overview

Problem

Polymer-phosphor composites used in LED lighting systems suffer from low optical transparency and poor thermal conductivity due to refractive index differences between the polymeric matrix and phosphor fillers, leading to light scattering and overheating of phosphor particles, which limits their effectiveness in lighting applications.

Innovation Solution

The development of core-shell particle assemblies with an inorganic core and a polymeric shell, where the refractive index is adjusted by controlling the core and shell volume fractions, allowing for the incorporation of fillers that enhance thermal conductivity and wavelength conversion capabilities while maintaining optical transparency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If phosphor fillers are dispersed in a polymeric matrix to create wavelength-conversion composites, then wavelength conversion capability is achieved, but optical transparency deteriorates due to refractive index differences causing light scattering

Engineering Contradiction:

Improvewavelength conversion capabilityVSAvoidoptical transparency

Core Design Contradiction:

Adaptability or versatilityVSIllumination intensity

Solution Approach 1:

A polymeric shell is introduced as an intermediary material between the phosphor filler and the polymeric matrix. This shell has a refractive index that matches both the filler and the matrix, acting as a refractive index bridge that reduces light scattering at interfaces while allowing the phosphor to maintain its wavelength conversion function.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention creates a multi-component composite structure consisting of phosphor filler particles coated with a polymeric shell, which are then dispersed in a polymeric matrix. This composite approach allows combining materials with different properties (wavelength conversion, refractive index matching, and structural support) to achieve overall optical transparency while maintaining functionality.

Inventive Principle:

Principle #40Composite materials

2Productivity

If phosphor particles are used for wavelength conversion, then light conversion efficiency is achieved, but thermal conductivity deteriorates leading to heat accumulation and phosphor overheating

Engineering Contradiction:

Improvelight conversion efficiencyVSAvoidphosphor particle temperature

Core Design Contradiction:

ProductivityVSTemperature

Solution Approach 1:

The polymeric shell is applied locally to the surface of each phosphor filler particle, creating a localized refractive index transition zone at each particle-matrix interface. This local modification reduces light scattering without requiring changes to the bulk matrix properties, thereby maintaining optical transparency while allowing heat dissipation pathways to be optimized separately.

Inventive Principle:

Principle #3Local quality

3Ease of manufacture

If a polymeric matrix is used to disperse phosphor fillers, then ease of manufacture is improved, but thermal conductivity deteriorates due to low thermal conductivity of polymers

Engineering Contradiction:

Improveease of manufactureVSAvoidthermal conductivity

Core Design Contradiction:

Ease of manufactureVSTemperature

Solution Approach 1:

The refractive index parameter of the interface between filler and matrix is changed by introducing the polymeric shell with intermediate refractive index. This parameter change reduces optical scattering losses without affecting the ease of manufacturing, as the shell can be applied through standard coating or synthesis procedures before final composite fabrication.

Inventive Principle:

Principle #35Parameter changes

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 core-shell particle assemblies achieve improved optical transparency and thermal conductivity, enabling more efficient light conversion and heat management in LED lighting systems, addressing the limitations of traditional polymer-phosphor composites.

Implementation Method 1

The refractive index of the core-shell particle assemblies may be adjusted by controlling the core and shell volume fractions... matching the filler refractive index

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 2

Absorption of the primary light can excite the wavelength-conversion material to a higher energy state. When the wavelength-conversion material returns to a lower energy state, it emits secondary light

Methodology Applied

Scientific EffectPhotoluminescence: Photoluminescence

Implementation Method 3

heat (e.g., Stokes heat) is generated when a wavelength conversion material such as a phosphor converts primary light to secondary light... improve thermal conductivity

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Data Source

PatentUS9349921B2Index matched composite materials and light sources incorporating the same

Publication Date: 2016.05.24 OSRAM SYLVANIA INC

AI summary

Disclosed are composites that include a matrix and at least one filler. The matrix may be a core-shell particle assembly that includes an inorganic core and a polymeric shell. The refractive index of the core may be adjusted by adjusting the volume fraction of the core, such that the refractive index of the core-shell particle assembly matches or substantially matches the refractive index of the filler. Optically transparent composites that exhibit properties of the filler may therefore be achieved. Methods of making such composites and light sources including such composites are also disclosed.