Bandpass Filter Multilayer Dielectric Light Extraction
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Solution Overview
Problem
Light emitting devices with phosphor-containing layers suffer from reduced efficiency due to light reflection and emission losses, necessitating a solution to enhance light emission efficiency while minimizing energy and size requirements.
Innovation Solution
A bandpass filter comprising a multilayer film with alternating dielectric layers is applied over the phosphor-containing layer on the light emitting element side, optimizing transmittance for the light emitting element's peak wavelength and reducing transmittance for the phosphor's peak wavelength across a wide range of incident angles, thereby improving light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a phosphor-containing layer is added to broaden the light spectrum, then color rendering properties are improved, but light reflection loss increases and efficiency decreases
Solution Approach 1:
A bandpass filter is introduced as an intermediary component between the light emitting element and the phosphor-containing layer. This filter selectively transmits the excitation light wavelength while reflecting the phosphor emission wavelength, mediating the interaction between these two components to prevent energy loss while maintaining color rendering functionality.
Solution Approach 2:
The optical parameters (transmittance and reflectance) of the bandpass filter are specifically designed to change based on wavelength. The filter exhibits high transmittance at the light emitting element's peak wavelength to minimize reflection loss, while showing high reflectance at the phosphor's peak wavelength to redirect emitted light back into the phosphor layer, thereby improving overall efficiency.
2Productivity
If a bandpass filter is applied to reduce light reflection loss, then light emission efficiency is improved, but device complexity increases
Solution Approach 1:
The bandpass filter is constructed as a multilayer film structure segmented into multiple thin dielectric layers with alternating refractive indices. This segmentation allows the filter to achieve complex optical functionality through simple layer stacking, where each layer contributes to the overall wavelength-selective transmittance and reflectance characteristics without requiring complex mechanical or electronic components.
3Productivity
If the bandpass filter allows high transmittance for light emitting element wavelength, then light extraction efficiency is improved, but transmittance for phosphor wavelength must be reduced
Solution Approach 1:
The bandpass filter's optical parameters are wavelength-dependent, creating different transmittance values for different wavelengths. At the light emitting element's peak wavelength, the filter maintains high transmittance to maximize light extraction efficiency. At the phosphor's peak wavelength, the filter exhibits high reflectance to prevent energy loss by redirecting the phosphor emission back into the phosphor layer for re-absorption and re-emission.
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 bandpass filter design significantly enhances light emission efficiency by ensuring high transmittance for the light emitting element's wavelength across various incident angles and minimizing reflection from the phosphor's wavelength, leading to improved brightness and energy efficiency in light emitting devices.
Implementation Method 1
The bandpass filter has a transmittance of 60% or more for light having a light emission peak wavelength of the light emitting element at an incident angle of 0 to 85°, and another transmittance of 40% or less for light having a light emission peak wavelength of the at least one type of phosphor for at an incident angle of a Brewster's angle (θb) of the bandpass filter+5° (θb+5°) to 85°.
Implementation Method 2
The bandpass filter has a transmittance of 60% or more for light having a light emission peak wavelength of the light emitting element at an incident angle of 0 to 85°, and another transmittance of 40% or less for light having a light emission peak wavelength of the at least one type of phosphor for at an incident angle of a Brewster's angle (θb) of the bandpass filter+5° (θb+5°) to 85°.
Implementation Method 3
the phosphor absorbs the light emitted from the light emitting element, and converts the absorbed light into another light with a different wavelength (in a different color)
Data Source
AI summary
Provided is a bandpass filter for a light emitting device that can improve the light emission efficiency in use for a light emitting device, and a light emitting device that can obtain the high light emission efficiency by using the bandpass filter. The light emitting device includes a substrate; a light emitting element disposed over the substrate; a phosphor-containing layer containing at least one kind of phosphor; and a bandpass filter disposed over a surface of the phosphor-containing layer on the light emitting element side, the bandpass filter including a multilayer film having a plurality of first and second dielectric layers, the second dielectric layer being disposed over the first dielectric layer. The bandpass filter has a transmittance of 60% or more for light having a light emission peak wavelength of the light emitting element at an incident angle of 0 to 85°, and another transmittance of 40% or less for light having a light emission peak wavelength of at least one kind of phosphor at an incident angle of a Brewster's angle (θb)+5° (θb+5°) to 85° of the bandpass filter.