Phosphor-Converted LED Sidewall Mirror and Selective Filter
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Solution Overview
Problem
Phosphor-converted LEDs designed for down-conversion of blue light suffer from blue light leakage, which diminishes the color purity of emitted light, particularly in applications requiring yellow, amber, or red light emissions.
Innovation Solution
Incorporating a selective filter with nanoparticles adjacent to the wavelength conversion material and/or a mirror layer on the sidewalls of the LED to absorb unconverted light, and optimizing the distance between the LED perimeter and substrate edge to minimize light leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a phosphor-converted LED uses down-conversion of blue light to yellow/amber/red light, then the desired color emission is achieved, but blue light leakage occurs that diminishes color purity
Solution Approach 1:
The patent extracts and removes the harmful blue light component from the emitted spectrum by placing a selective filter (absorbing layer) between the LED and the external environment. This filter specifically absorbs blue light wavelengths that leak through the phosphor conversion process, thereby eliminating the harmful factor while preserving the desired yellow/amber/red emission.
Solution Approach 2:
The patent introduces an intermediary absorbing layer composed of nanoparticles (such as silver, aluminum, or titanium dioxide) positioned between the LED phosphor and the external space. This intermediary layer mediates the light path by selectively absorbing blue wavelengths without significantly affecting the converted longer wavelengths, thus resolving the contradiction between achieving color conversion and preventing blue light leakage.
2Device complexity
If the LED is placed close to the substrate edge, then the device structure is compact, but light leakage through sidewalls increases reducing color purity
Solution Approach 1:
The patent converts the potentially harmful sidewall light leakage into a beneficial effect by applying a reflective coating to the LED sidewalls. Instead of allowing blue light to escape through the sidewalls and reduce color purity, the reflective coating bounces this light back into the phosphor layer, where it can be converted to the desired wavelength, thus turning the leakage problem into an efficiency improvement.
Solution Approach 2:
The patent modifies the optical parameters of the LED sidewalls by applying reflective materials (such as metal layers or dielectric coatings) that change the reflectivity parameter of the sidewall surface. This parameter change ensures that light attempting to escape through sidewalls is reflected back into the active region, maintaining color purity while allowing structurally compact designs.
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 solution achieves high color purity of at least 95% by effectively absorbing unconverted light, thereby enhancing the saturation and purity of yellow, amber, or red light emissions in phosphor-converted LEDs.
Implementation Method 1
A phosphor may absorb a portion of the light emitted from an LED at a given wavelength and re-emit the light at different wavelength via the principle of photoluminescence
Implementation Method 2
a selective filter is adjacent to the wavelength conversion material, where the selective filter comprises a plurality of nanoparticles for absorbing light from the LED not down-converted by the wavelength conversion material
Data Source
AI summary
A phosphor-converted light emitting device includes a light emitting diode (LED) on a substrate, where the LED comprises a stack of epitaxial layers comprising a p-n junction. A wavelength conversion material is in optical communication with the LED. According to one embodiment of the phosphor-converted light emitting device, a selective filter is adjacent to the wavelength conversion material, and the selective filter comprises a plurality of nanoparticles for absorbing light from the LED not down-converted by the wavelength conversion material. According to another embodiment of the phosphor-converted light emitting device, a perpendicular distance between a perimeter of the LED on the substrate and an edge of the substrate is at least about 24 microns. According to another embodiment of the phosphor-converted light emitting device, the LED comprises a mirror layer on one or more sidewalls thereof for reducing light leakage through the sidewalls.