Ce3+-Activated Oxyfluoride Phosphor for White LED Color Rendering
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Solution Overview
Problem
Current yellow emitting YAG:Ce3+ phosphors have weak light emitting intensity in the red spectral region and are temperature-dependent, making it difficult to achieve good color rendering index and thermal stability in high-power LEDs, with limited alternatives for long UV or blue excitation sources.
Innovation Solution
Development of a blue-green emitting Ce3+-activated oxyfluoride phosphor (Sr1-x-yAEy)3(Al1-zTz)O4F:Ce3+x, where AE includes alkaline earth metals and T includes Al, B, Ga, and In, which is combined with other phosphors to generate white light, offering improved quantum efficiency and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If YAG:Ce3+ phosphors are used for white light generation, then the fabrication is simple and cost-effective, but the light emitting intensity in the red spectral region is weak and color rendering index is poor
Solution Approach 1:
The patent employs composite phosphor systems combining multiple phosphor materials with different emission characteristics. Specifically, it combines yellow-emitting YAG:Ce3+ phosphor with red-emitting phosphors (such as CaAlSiN3:Eu2+ or Sr2Si5N8:Eu2+) to create a composite phosphor layer that maintains the fabrication simplicity of YAG:Ce3+ while adding strong red emission capability for improved color rendering index
Solution Approach 2:
The patent merges multiple phosphor materials into a single integrated phosphor layer that can be excited by a single blue LED chip. The composite phosphor system combines yellow-emitting YAG:Ce3+ with red-emitting phosphors, allowing simultaneous excitation by blue light (430-470 nm) and producing both yellow and red emissions to achieve good color rendering while maintaining manufacturing simplicity
2Power
If YAG:Ce3+ phosphors are used in high-power LEDs, then the efficiency is high, but the output color is strongly dependent on temperature and current
Solution Approach 1:
The patent selects phosphor materials with different thermal characteristics to compensate for each other's temperature dependencies. YAG:Ce3+ has negative thermal shift (emission peak shifts to shorter wavelengths with increasing temperature), while red-emitting phosphors like CaAlSiN3:Eu2+ have positive thermal shift. By combining them in appropriate ratios, the overall color output remains stable across temperature variations despite high power operation
Solution Approach 2:
The composite phosphor system uses materials with complementary thermal behaviors. The yellow YAG:Ce3+ phosphor and red phosphors are formulated in specific ratios that maintain consistent color temperature (CCT) under varying drive currents and operating temperatures, reducing color shift in high-power LED applications
3Adaptability or versatility
If new yellow emitting phosphors are developed to replace YAG:Ce3+, then intellectual property issues are avoided, but few phosphor materials are available for long UV or blue excitation sources
Solution Approach 1:
The patent employs YAG:Ce3+ phosphor which serves multiple functions: it can be efficiently excited by blue LEDs (430-470 nm), provides strong yellow emission, and can be combined with various red phosphors for different color rendering requirements. This universal phosphor material is compatible with multiple excitation sources and application requirements, maintaining reliability while avoiding proprietary restrictions on new phosphor developments
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 new phosphor achieves higher quantum efficiency and luminous efficiency compared to YAG:Ce3+, providing better color rendering and thermal stability, with broader emission spectra and improved performance in solid-state lighting applications.
Implementation Method 1
a blue-green emitting Ce3+-activated oxyfluoride phosphor... which is combined with other phosphors to generate white light
Implementation Method 2
down-convert the emission from a blue LED or ultraviolet (UV) LED to a longer wavelength using a phosphor
Data Source
AI summary
A blue-green emitting Ce3+-activated oxyfluoride phosphor for use with a light emitting diode (LED) in solid state lighting applications. The blue-green emitting Ce3+-activated oxyfluoride phosphor is represented as:(Sr1-x-yAEy)3(Al1-zTz)O4F:Ce3+x wherein 0<x≦0.3, 0≦y≦1, AE includes at least one element selected from alkaline earth metals on the periodic table, for example, Mg, Ca and Ba, 0≦z≦1, and T includes at least one atom selected from Al, B, Ga, and In. The blue-green emitting Ce3+-activated oxyfluoride phosphor may be combined with another phosphor to generate the white light. Specifically, the present invention provides for white light generation by combining the blue-green emitting Ce3+-activated oxyfluoride phosphor with either a near-ultraviolet (UV) LED and red emitting phosphor, or with a near-UV LED and a red-yellow phosphor.