Towards tunable single-pixel LEDs with Eu-doped GaN active layers

Doping rare-earth ions in the active layers of GaN-based materials has been useful for achieving precise emission colors. In particular, Eu³⁺ can be excited electrically and emits red (~620nm) from its ⁵D₀ state, as well as green, yellow and orange from its ⁵D₁ state. By adjusting excitation conditions, the population ratio between the two states can be controlled resulting in smooth color tunability from red to yellow. Modeling work for the excitation dynamics of the defect-ion complex after creation or injection of electron hole pairs takes a local defect into account, where the carriers are captured, recombine, and transfer energy to the Eu³⁺. Multiple excitations of the same defect complex before the Eu³⁺ can relax causes the ⁵D_j states’ populations to redistribute. Furthermore, by considering the local defect as a blue emitter, our model can predict tunability parameters within a larger color space due to the mixing of the primary colors: red, green, and blue. The model assumes that the reshuffling process takes place within one complex and that energy is not transferred to others. To test the validity of this assumption, various samples co-doped with Eu³⁺ and other RE ions are studied.