Phosphor-Converted LED Long-Wavelength Pass Filter
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Solution Overview
Problem
Conventional single-color LEDs, particularly green and amber LEDs, face issues with low external quantum efficiency, color purity, and temperature-dependent efficiency due to lattice mismatch, energy deficits, and light leakage, especially when using nano/micro powder-based phosphor-converted LEDs.
Innovation Solution
A phosphor-converted single-color LED design incorporating a blue light source, phosphor, and a long-wavelength pass filter with a layer stack of alternating thin films, where the uppermost and lowermost layers have optical thicknesses corresponding to 1/7 to 1/9 of the peak wavelength of blue light, reflecting blue light and transmitting light in the 500 to 700 nm range to enhance photoluminescence efficiency and color purity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If blue LEDs are used as excitation sources with nano/micro phosphor powders to emit green or amber light, then the production process is well known and easier to manufacture, but blue light leaks without exciting the phosphor powders causing poor color purity
Solution Approach 1:
A long-wavelength pass filter is introduced as an intermediary component between the blue LED and the phosphor powder. The filter selectively transmits blue light (430-480 nm) to excite the phosphor while blocking leaked blue light from reaching the observer, thereby maintaining color purity without requiring changes to the established phosphor conversion LED manufacturing process
Solution Approach 2:
The long-wavelength pass filter provides localized wavelength-selective transmission and blocking properties. It allows blue excitation light to pass through to the phosphor while blocking leaked blue light in the output direction, creating different optical properties for different directions and wavelengths without affecting the overall manufacturing process
2Manufacturing precision
If a ceramic plate phosphor is used to completely convert blue light to amber light, then color purity reaches at least 95%, but incomplete transparency causes partial reflection or loss of blue light resulting in low photoconversion efficiency
Solution Approach 1:
The long-wavelength pass filter acts as an intermediary that separates the excitation light path from the emission light path. It allows blue excitation light to pass through to the phosphor while blocking reflected and leaked blue light from reaching the observer, thereby improving photoconversion efficiency without compromising the high color purity achieved by the ceramic plate phosphor
3Use of energy by moving object
If phosphors are added to silicon matrices in larger amounts to achieve complete absorption and blocking of light, then light absorption is improved, but phosphors at high concentrations aggregate causing scattering and reflection leading to optical loss
Solution Approach 1:
The long-wavelength pass filter serves as an intermediary that enables the use of optimized phosphor concentrations. By blocking leaked blue light, the filter allows phosphors to be used at concentrations that optimize absorption without requiring excessively high concentrations that would cause aggregation and scattering losses
4Adaptability or versatility
If InGaN-based green LEDs are used, then blue LED technology can be leveraged, but external quantum efficiency drops to 30% or below due to lattice mismatch caused by increased gallium
Solution Approach 1:
The patent replaces the direct InGaN green LED approach (which suffers from lattice mismatch) with a phosphor conversion system using blue LEDs. The blue LED excites yellow phosphor to produce green light, avoiding the lattice mismatch problem entirely while leveraging the high efficiency of blue LED technology
Solution Approach 2:
The invention changes the fundamental approach from direct green light emission via InGaN to blue light excitation of phosphor. This parameter change in the emission mechanism allows bypassing the lattice mismatch limitation while maintaining technology compatibility with established blue LED manufacturing
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 and efficiency with improved temperature and current-dependent characteristics, overcoming the limitations of conventional semiconductor-based LEDs by effectively reusing blue light to excite phosphors and preventing light leakage.
Implementation Method 1
a long-wavelength pass filter disposed on the phosphor to reflect blue light and transmit light in a wavelength range of 500 to 700 nm
Implementation Method 2
the long-wavelength pass filter includes a layer stack including first thin films and second thin films laminated alternately and repeatedly, the second thin films having a refractive index higher than that of the first thin films
Implementation Method 3
a phosphor disposed on the blue light source to absorb blue light emitted from the blue light source and emit light in a wavelength range of 500 to 700 nm
Data Source
Figure 1~2
Figure 3a~3b
Figure 3c~4
AI summary
A phosphor-converted single-color LED is provided. The phosphor-converted single-color LED includes a long-wavelength pass filter having a special construction. The phosphor-converted single-color LED has high color purity and efficiency despite the use of a phosphor in the form of a nano/micro powder.