Immersion Cooling of Suspended and Coated Nano-Phosphor Particles for Extending the Limits of Optical Extraction of Light Emitting Diodes

Abstract

Abstract GaN LEDs are usually encapsulated with a cured phosphor-epoxy mixture for the light conversions from blue to white light. However, during this conversion, significant self-heating problems may occur due to insufficient cooling capabilities against the increasing power demand. Moreover, possible fracture and ultimate device failures were intersected with large displacements inside the LED package with these self-heating problems. Thus, including phosphor in a high brightness LED package is complex. Therefore, three coating technologies were investigated for an LED package's higher lifetime and ultimate optical output. Those are phosphor dispersed inside the liquid coolant as particles, remote phosphor-coated under the dome, and remote phosphor-coated under the dome with immersion cooling with dielectric liquid coolant. Their results were compared with the commonly used over chip coating application chosen as the baseline case in the current study. Furthermore, computational models and experimental studies were performed for proposed coating configurations. The chosen baseline case has shown higher junction temperatures, lower conversion efficiency, and undesirable color shifts at critical temperatures. As the first proposed technique, dispersed phosphor particles inside the dielectric liquid coolant have resulted with almost similar conversion efficiency but with a lower thermal enhancement on the LED junction than the baseline case. The second technique, remote phosphor system has resulted in better junction temperatures and 23% higher optical extraction than the baseline case. On the other hand, the remote phosphor with immersion cooling has shown the lowest junction temperature levels and extended the lumen extraction limits of white LEDs above 53% as the third proposed technique.