Understanding and controlling chromaticity shift in LED devices
| Autor: | Robert Yaga, Karmann Mills, J. Lynn Davis, Joseph Young, Michael Lamvik, Bobashev, Curtis Perkins, Georgiy, Cortina Johnson |
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| Rok vydání: | 2017 |
| Předmět: |
010302 applied physics
Quenching business.industry Chemistry Phosphor 02 engineering and technology Nitride 021001 nanoscience & nanotechnology 01 natural sciences law.invention Wavelength law 0103 physical sciences Thermal Optoelectronics Chromaticity 0210 nano-technology business Diode Light-emitting diode |
| Zdroj: | 2017 18th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE). |
| DOI: | 10.1109/eurosime.2017.7926223 |
| Popis: | Chromaticity shift in light-emitting diode (LED) devices arises from multiple mechanisms, and at least five different chromaticity shift modes (CSMs) have been identified to date. This paper focuses on the impacts of irreversible phosphor degradation as a cause of chromaticity shifts in LED devices. The nitride phosphors used to produce warm white LEDs are especially vulnerable to degradation due to thermal and chemical effects such as reactions with oxygen and water. As a result, LED devices utilizing these phosphors were found to undergo either a green shift or, less commonly, a red shift depending on the phosphor mix in the LED devices. These types of chromaticity shifts are classified as CSM-2 (green shift) and CSM-5 (red shift). This paper provides an overview of the kinetic processes responsible for green and red chromaticity shifts along with examples from accelerated stress testing of 6″ downlights. Both CSMs appear to proceed through analogous mechanisms that are initiated at the surface of the phosphor. A green shift is produced by the surface oxidation of the nitride phosphor that changes the emission profile to lower wavelengths. As the surface oxidation reaction proceeds, reactant limitations slow the rate and bulk oxidation processes become more prevalent. We found that a red chromaticity shift arises from quenching of the green phosphor, also possibly due to surface reactions of oxygen, which shift the emission chromaticity in the red direction. In conclusion, we discuss the implications of these findings on projecting chromaticity. |
| Databáze: | OpenAIRE |
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