Spectrally resolved dynamics of energy transfer in GaN:Eu

Europium(Eu) doped Gallium Nitride has demonstrated great potential as the red-emitting active layer in nitride-based light emitting diodes(LEDs). External quantum efficiency of up to 9.2% have been achieved. In such optimized layers, we performed a systematic series of temperature dependent, spectrally and time resolved photoluminescence measurements with goal to understand the energy transfer processes between the host material and the various energy levels of the Eu ions. Eu ions are affected by their local environment resulting in at least eight different centers that can be spectrally distinguished. For the most dominant centers, we find that the energy transfer to the Eu ion takes place on a time scale faster than 5 ns. Depending on incorporation site, the energy transfer leads to the population of the ⁵D₀ and/or the ⁵D₂ state. Direct energy transfer to the ⁵D₁ states is negligible. We further show that Eu ions in their long-lived ⁵D₀ state can be excited further leading the creation of electron hole pairs which subsequently relax and transfer their energy back to the Eu ions. This leads to a change in the color of the total emitted light and enables color tunability of the LEDs.