Analysis of the local temperature distribution in color conversion elements of phosphor converted light-emitting diodes

- A microscopic thermal model of the phosphor layer of LEDs is provided.
- The degradation of the heat transfer between phosphor and encapsulant is discussed.
- The degradation of the heat transfer between CCE and LED die is discussed.
- A temperature increase upon degradation is a source for potential color shifts.

Long-term stability, efficiency, and reliability of LED-based luminaires strongly depend on thermal management also inside the color conversion layer (CCE) which frequently consists of a transparent encapsulant with embedded microsized phosphor particles. Due to their limited quantum efficiency and Stokes-shift related losses these particles heat-up the CCE and need to be cooled just by heat conduction through the underlying LED chip which itself is heated by its own power loss. Significant research work has been devoted to determine the temperature distribution within the CCE using macroscopic thermal models by considering homogeneously distributed materials properties inside the CCE. By contrast, focus in this paper is to gain a deeper understand of thermal aspects on the base of microscopic thermal models considering the discontinuous set-up of the CCE. In turn, influences of degradation of the heat transfer between phosphor particles and encapsulant and between CCE and LED chip on the temperature distribution inside the CCE are studied in detail.