Particle based investigation of self-heating effect of phosphor particles in phosphor converted light emitting diodes

Abstract

Since 2003, self-heating effect of phosphor which reduces the efficacy and reliability of phosphor conversion (Pc) light emitting diodes (LEDs), has been a growing research area of opto-thermal Pc-LED modeling. However, few studies have focused on the particles based nature of the phosphor self-heating. Based on a new approach, accurate Monte Carlo ray tracing simulations are performed in regions of interest over discretized control volumes where only a single phosphor particle is exposed to the light radiation. Governed by the Mie scattering effects, heat generation values of phosphor particles showed strong dependency on their optical and geometrical properties. Additionally, based on the emissive behavior of the LED, space above the LED can be divided into two irradiance levels; near and far scale regions. In near scale region, where irradiance levels are above 0.1 W/mm(2), phosphor particles exhibited significant self-heating in milli-Watt scale values. Derived self-heating values are imported to simplified thermal models where phosphor particles showed a temperature rise in excess of 100 degrees C more than LED chip which can lead to considerable conversion efficiency loss and a reduction in lifetime. Higher temperatures are expected in higher irradiance levels where matrix material carbonization can also occur causing fire hazards.