Porous Ceramic Conversion Element for Electroluminescent Devices
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Solution Overview
Problem
Phosphor-converted electroluminescent devices (pcLEDs) face reduced luminance due to non-directional secondary radiation being emitted by lateral surfaces rather than the main light emission surface, leading to inefficient light distribution and luminous loss, especially with transparent conversion elements.
Innovation Solution
A translucent ceramic conversion element with a density of 97% or higher of the theoretical solid-state density and pore diameters between 250 nm and 2900 nm is used to optimize light scattering and absorption, ensuring a Lambertian radiation pattern and improved luminous efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a transparent conversion element is used, then conversion efficiency is improved, but luminance is decreased due to total reflection at lateral surfaces
Solution Approach 1:
The patent applies porous materials by incorporating a multiplicity of pores with diameters between 250 nm and 2900 nm into the ceramic conversion element. These pores act as scattering centers that redirect light paths, preventing total internal reflection at lateral surfaces and directing more light toward the main light emission surface, thereby resolving the contradiction between conversion efficiency and luminance.
Solution Approach 2:
The patent changes the physical parameters of the conversion element by controlling the pore size (250-2900 nm) and density (≥97% of theoretical density). This parameter optimization enables the material to maintain high transparency for efficient conversion while simultaneously providing sufficient scattering to improve luminance and redirect light to the main emission surface.
2Shape
If a phosphor powder layer is used, then a cosinusoidal radiation pattern is achieved, but luminous efficiency is reduced due to non-radiating absorption processes
Solution Approach 1:
The patent uses composite materials by combining ceramic material with controlled porosity (pores 250-2900 nm) to create a conversion element that achieves both cosinusoidal radiation pattern and high luminous efficiency. The composite structure provides scattering centers for directional control while minimizing absorption losses compared to phosphor powder layers.
Solution Approach 2:
The porous ceramic structure with optimized pore sizes (250-2900 nm) replaces the phosphor powder layer, maintaining the cosinusoidal radiation pattern through controlled scattering while significantly reducing non-radiating absorption processes, thereby achieving both radiation pattern control and high luminous efficiency.
3Quantity of substance
If the density of the ceramic conversion element is increased, then translucence is improved, but scattering power is reduced
Solution Approach 1:
The patent resolves this contradiction by introducing a controlled pore structure (250-2900 nm) into the high-density ceramic material (≥97% theoretical density). The pores provide scattering centers that maintain scattering power despite the high density, while the overall high density ensures sufficient translucence for efficient light conversion.
Solution Approach 2:
The patent optimizes multiple parameters simultaneously: density (≥97% theoretical density), pore size (250-2900 nm), and pore distribution. This multi-parameter optimization enables the material to achieve high translucence through dense structure while maintaining scattering power through controlled porosity.
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 solution achieves a luminous efficiency of 80% or more in electroluminescent devices, significantly increasing luminance and reducing radiation losses compared to devices with phosphor powder layers or polycrystalline ceramic bodies with unfavorable pore sizes.
Implementation Method 1
The pores between the crystallites function as scattering centers for primary and secondary radiation
Implementation Method 2
the LED emits a primary radiation of which at least one portion is absorbed by a phosphor layer (conversion element) arranged on the LED and is re-emitted as longer-wave secondary radiation
Data Source
AI summary
A conversion element (3) comprising a ceramic material (31) with a multiplicity of pores (32) provided for at least the partial absorption of at least one primary radiation (52) and for transforming the primary radiation (52) into at least one secondary radiation (53), wherein the conversion element (3) has a density greater than or equal to 97% of the theoretical solid-state density of the ceramic material (31), and the pores (32) in the conversion element (3) have a diameter substantially between 200 nm and 5000 nm.