Optical performances degradation of InGaN/GaN MQW LEDs related to fluorescence shift of copolymer-based silicone coating

R. Baillot; L. Béchou; C. Belin; T. Buffeteau; I. Pianet; C. Absalon; O. Babot; Y. Deshayes; Y. Ousten

doi:10.1117/12.893528

22 September 2011 Optical performances degradation of InGaN/GaN MQW LEDs related to fluorescence shift of copolymer-based silicone coating

R. Baillot, L. Béchou, C. Belin, T. Buffeteau, I. Pianet, C. Absalon, O. Babot, Y. Deshayes, Y. Ousten

Author Affiliations +

Proceedings Volume 8123, Eleventh International Conference on Solid State Lighting; 81230G (2011) https://doi.org/10.1117/12.893528
Event: SPIE Optical Engineering + Applications, 2011, San Diego, California, United States

Abstract

Accelerated ageing tests (1500h/85°C/30mA) performed on packaged InGaN/GaN MQW LEDs have reported a fluorescence shift of silicone oil responsible for optical losses. Electrical and optical characteristics highlight a 65% loss of optical power. Through measurements of the copolymer silicone coating fluorescence emission spectra, we demonstrate that the polymer fluorescence (induced from the blue light emitted from the chip) enlarges the LED emission spectrum (7%) and shifts central wavelength (5 to 7 nm). To understand such a fluorescence shift, Attenuated Total Reflection, Nuclear Magnetic Resonance (NMR), mass spectrometry and Differential Scanning Calorimetry (DSC) have been performed. The copolymer molecular structure has been affected after ageing. Actually, NMR and Mass spectrometry evidences the disappearance of low molecular weight molecules and the presence of high molecular weight molecules after ageing. Such a mechanism is associated with the polymerization of the silicone oil after ageing. Indeed, DSC has confirmed that silicone oil polymerization process is activated by temperature. Finally, both polymerization of the silicone oil due to temperature and fluorescence shift activated by photothermal process have been identified as the main failure mechanisms responsible for optical power degradation.

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R. Baillot, L. Béchou, C. Belin, T. Buffeteau, I. Pianet, C. Absalon, O. Babot, Y. Deshayes, and Y. Ousten "Optical performances degradation of InGaN/GaN MQW LEDs related to fluorescence shift of copolymer-based silicone coating", Proc. SPIE 8123, Eleventh International Conference on Solid State Lighting, 81230G (22 September 2011); https://doi.org/10.1117/12.893528

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