To elucidate the energy transfer and reexcitation processes in Eu-doped GaN layers that are used in recently developed, highly efficient red light-emitting diodes, a systematic series of photoluminescence and time-resolved photoluminescence (TR-PL) measurements was performed. Critical insights on how “slow” Eu processes (∼µs) can compete against fast semiconductor processes (∼ps) are revealed using TR-PL with a high temporal resolution, as it is found that the initial energy transfer from GaN to the Eu3+ ions takes place rapidly, on a timescale of <100 ps. Below band-gap resonant excitation was used to identify the states into which the energy transfer occurs. For the most efficient Eu defect complexes, this transfer dominantly occurs directly into the 5 D0 state of Eu3+. Less efficient complexes also exhibit transfer into the 5 D2 state, the emission of which can be detected using photoluminescence at low temperature, indicating the importance of the excitation pathway on device efficiency. Under high excitation intensity, reexcitation can also occur, leading to a redistribution of population into the 5 D2, 5 D1, or 5 D0 states.
Physical Review B
American Physical Society
Wei, R., Mitchell, B., Timmerman, D., Gregorkiewicz, T., Zhu, W., Tatebayashi, J., Ichikawa, S., Fujiwara, Y., & Dierolf, V. (2019). Picosecond time-resolved dynamics of energy transfer between GaN and the various excited states of Eu3+ ions. Physical Review B, 100(8), 081201-1-081201-5. http://dx.doi.org/10.1103/PhysRevB.100.081201