Re-Excitation of Trivalent Europium Ions Doped into Gallium Nitride Revealed through Photoluminescence under Pulsed Laser Excitation

The behavior of trivalent europium (Eu3+) ions doped into gallium nitride (GaN) was investigated under intense excitation conditions to explore the excitation energy transfer characteristics in the presence of large carrier densities. Under such conditions, strong emission from the higher excited 5D1 and 5D2 states of the Eu3+ ions was observed in highly efficient AlGaN/Eu-doped GaN multiple quantum wells grown by organometallic vapor phase epitaxy. This behavior was studied using a variety of excitation sources and conditions. Most notably, when a femtosecond-pulse laser was used, the excitation of the Eu3+ ions into the higher energy states became significant only with a second excitation pulse arriving within the lifetime of the 5D0 state. We propose that an already excited Eu3+ ion is promoted from its 5D0 excited state into the higher 5DJ states where it relaxes and can emit from the 5D1 and 5D2 states.