Abstract
The CaAlSiN3:Eu2+ red phosphor and its silicone/phosphor composite are very promising materials used in the high color rendering white light-emitting diode (LED) packaging. However, the reliabilities of CaAlSiN3:Eu2+ and its composite are still being challenged by phosphor hydrolysis at high humidity application condition. A fundamental understanding of the interface adhesion between silicone and CaAlSiN3:Eu2+ is significant for the developments and applications of this material. In this work, the mechanical properties of silicone/pristine CaAlSiN3:Eu2+ and silicone/hydrolyzed CaAlSiN3:Eu2+ composites are experimentally measured and compared firstly, in which both the tensile strength and Young’s modulus of composite are increased after the hydrolysis reaction. Then, the first principles Density Functional Theory (DFT) calculations are used to investigate the adhesion behaviors of the silicone molecular on both the pristine and the hydrolyzed CaAlSiN3[0 1 0] at atomic level. The results show that: (1) The silicone molecular is weakly adsorbed on the pristine CaAlSiN3[0 1 0] via Van der Waals (vdW) interactions, while silicone molecular is much stronger absorbed on the hydrolyzed CaAlSiN3[0 1 0] due to the formation of hydrogen bonding at the interface; (2) The transient state calculations indicate that the sliding energy barrier of silicone on the hydrolyzed CaAlSiN3[0 1 0] is higher than that on the pristine one, as the increased adsorption energy and surface roughness. Generally, the findings in this paper can guide the phosphor selection, storage and process in LED packaging, and also assist in improving the reliability design of LED package used in high moisture condition.
Highlights
As a new generation light source, phosphor converted white lightemitting diodes, generally constructing by a blue light-emitting diode (LED) chip coated with the phosphor, are being applied in many fields, like indoor and outdoor lighting, healthcare, automotive headlamp and high-resolution displays and so on [1,2]
In the tensile test described in part 2.1, the mechanical properties of silicone/hydrolyzed CaAlSiN3:Eu2+ composite were obtained and compared to the silicone/ pristine CaAlSiN3:Eu2+ composite
The hydrolysis reaction of CaAlSiN3:Eu2+ increases its surface roughness, and the tensile tests further show that both tensile strength and Young’s modulus of silicone/hydrolyzed CaAlSiN3:Eu2+ composite are enhanced after hydrolysis reaction
Summary
As a new generation light source, phosphor converted white lightemitting diodes (pc-WLEDs), generally constructing by a blue LED chip coated with the phosphor, are being applied in many fields, like indoor and outdoor lighting, healthcare, automotive headlamp and high-resolution displays and so on [1,2]. When the LED operates under harsh application environments, the silicone/phosphor interface is always suffering degradation under conditions of high temperatures [4], high blue light illumination, and high humidity [5,6,7,8,9,10,11]. CaAlSiN3:Eu2+ has attracted much attention for its application in warm white or high color rendering [12,13,14]. Phosphors generally have high thermal quenching temperature and good thermal stability, the reliability of CaAlSiN3:Eu2+ red phosphor is still being challenged by the high humidity application condition. Our research team experimentally found the hydrolysis phenomenon of CaAlSiN3:Eu2+ red phosphor, that can lower the crystallinity of CaAlSiN3 and increases its thermal quenching effect [20]
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