Abstract
Silicone/phosphor composite, which serve as mechanical protection and light conversion material, is an integral part of white light-emitting diode (LED) package. In this paper, a comprehensive study is conducted to investigate the effect of humidity and phosphor on moisture absorption, hygroscopic swelling, mechanical behavior, as well as thermal properties of silicone/phosphor composite in comparison with the pure silicone. SEM/EDAX and FTIR were performed to identify the phosphor and silicone compositions. Through moisture sorption test, it has been observed that the addition of phosphor significantly lowers the capacity of moisture absorption, but accelerates the diffusivity of moisture absorption. The hygroscopic swelling test showed that the phosphor has little effect on the swelling compared to the pure silicone sample. Both moisture absorption/desorption and hygroscopic swelling/de-swelling are reversible. Strain ramp test revealed that the phosphor enhances the stiffness of the composite. The moisture absorption, however, has negligible impact on mechanical stiffness for both pure and composite samples. Finally, thermal expansion test showed that the coefficient of thermal expansion does not change with the addition of phosphor into pure silicone.
Highlights
High power phosphor-converted white light-emitting diodes have been accepted as an important substitute for traditional lighting sources due to their high luminous efficiency, low power consumption, longer lifetime and their environmental friendliness [1, 2]
A comprehensive study is conducted to investigate the effect of humidity and phosphor on moisture absorption, hygroscopic swelling, mechanical behavior, as well as thermal properties of silicone/phosphor composite in comparison with the pure silicone
Thermomechanical analysis (TMA) was used to determine the linear coefficient of thermal expansion (CTE) for pure silicone and silicone/phosphor composite samples were measured from 25 °C to 300 °C
Summary
High power phosphor-converted white light-emitting diodes (pc-WLEDs) have been accepted as an important substitute for traditional lighting sources due to their high luminous efficiency, low power consumption, longer lifetime and their environmental friendliness [1, 2]. Fan et al [20, 21] studied the interaction of silicone and phosphor, and showed that moisture could be the reason behind degradation of silicone/phosphor composite due to pH change. It further causes the degradation of light-conversion efficiency of phosphors and the transmittance of silicone. A comprehensive study is conducted to investigate the effect of humidity and phosphor on moisture absorption, hygroscopic swelling, mechanical behavior, as well as thermal properties of silicone/phosphor composite in comparison with the pure silicone. A series of tests, including in situ moisture absorption/ desorption, hygroscopic swelling, strain ramp test, as well as thermal expansion measurement, were conducted
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