Failure Mechanism of Phosphors in GaN‐Based White LEDs

Abstract

The degradation and failure mechanisms of nitride phosphor in GaN-based white LEDs are studied using an in situ multi-functional accelerated life test and different analytical technologies. The electroluminescence results show that both the intensities of the blue emission (BL) from the LED chips and the yellow emission (YL) from the phosphors decrease with the stress time increasing. However, the YL/BL intensity ratio increases with a yellow shift for the chromaticity coordinates. The reason is not only due to the degradation of the LED chip but the nitride phosphors. The generated microcracks and delamination of phosphor layer lead to the increase of blue light absorption. Except for that, we find that the reason for the decrease of the phosphor conversion efficiency is related to the oxidization of the phosphor's luminescence center Eu 2þ ions instead of phosphor thermal quenching. These findings help further understand failure mechanism of phosphors during the operation, and improve the long-term color quality for the white LEDs.

Transmission Geometry Laser Lighting with a Compact Emitter

“…Although red phosphors are less efficient and less studied quantitatively in lighting systems than the yellow phosphor Ce:YAG, they continue to improve with further research efforts. [ 50,51 ] The down‐conversion of the blue laser light to red contributes to a higher SS, reducing efficiency in comparison with the one‐phosphor system or the two‐laser system with a high efficiency red laser diode.…”

CsPb(Br/I)3 Perovskite Nanocrystals for Hybrid GaN-Based High-Bandwidth White Light-Emitting Diodes

“…When the excitation power increases, many electrons transition and transfer to adjacent nanocrystals, promoting nonradiative energy transfer and resulting in the decrease in radiative lifetime of the perovskite nanocrystals. 39,40 The fluorescence lifetime of the perovskite NC film is one order of magnitude shorter than that of the commercial phosphors, such as yttrium aluminum garnet (YAG), 9,41 confirming its potential as an optical conversion material for white LEDs.…”

“…However, the overall bandwidth of these white LEDs is only a few MHz, which severely restricts the data communication capacity of VLC systems . This low bandwidth arises from the slow optical response of conventional cerium-doped phosphors. − Furthermore, tuning the color rendering of these white LEDs is also challenging due to the limited tunability of the spectral properties of phosphors.…”

Progress of Reliability and Failure Mechanisms for GaN‐Based Light‐Emitting Diodes

“…[76] We have investigated the degradation mechanism of red nitride phosphor CaAlSiN 3 :Eu 2þ encapsulated in white LEDs using the multifunctional in situ accelerated aging test system, as shown in Figure 5. [77] Two degradation modes have been observed for nitride phosphors. The generated microcracks and delamination of the phosphor layer at the top of the LED die can increase the absorption.…”