Investigation of combined optical and thermal effects on phosphor converted light-emitting diodes with liquid immersion cooling

Abstract

The inclusion of phosphor into a high brightness light-emitting diode (LED) package is a complicated task since LEDs are encapsulated with a phosphor and epoxy mixture to convert blue photons to white light. Moreover, this common practice may cause high temperatures and fractures in the gold wire bonds of the chip or solder balls due to local heating and thermal stresses leading to device failures. Furthermore, at elevated junction temperatures, the light conversion efficiency of the phosphor reduces and decreases the overall optical efficiency of an LED. Although, remote phosphor technique has been already applied to LED systems, the high power requirements have needed better performing methods. Thus, an immersion liquid cooled remote phosphor-coated system has been proposed and experimentally and computationally investigated. First, a set of experiments was performed, which includes the combined effects coming from both optical and thermal improvements with the proposed liquid cooled remote phosphor-coated technique, where the total light extraction enhancement was obtained in excess of 25%. Then, the same problem has been computationally studied for investigation of solely optical enhancements, which has shown that remote phosphor-coated LED package with a liquid coolant of suitable refractive index at the optical path has enhanced the overall lumen performance about 13%, whereas the rest of the improvements of 12% were due to thermal enhancements.