Spectroscopic and energy transfer studies of Eu3+ centers in GaN

Photoluminescence (PL), photoluminescence excitation (PLE), and time-resolved PL spectroscopies have been carried out at room temperature and 86 K on transitions from D-5(2), D-5(1), and D-5(0) excited states to numerous F-7(J) ground states of Eu-doped GaN films grown by conventional solid-source molecular beam epitaxy (MBE) and interrupted growth epitaxy MBE. Within the visible spectral range of 1.8-2.7 eV, 42 spectral features were observed and assignments were attempted for each transition. PL and PLE indicate that four Eu3+ centers exist in the GaN lattice whose relative concentration can be controlled by the duration of growth interruption. The energy levels for these four sites are self-consistently obtained, and time-resolved photoluminescence measurements reveal details about the radiative and nonradiative relaxations of excitation among these levels. The data indicate a near-resonant cross relaxation among these sites. The D-5(2) and D-5(1) states are observed to decay nonradiatively by filling the D-5(0) state with characteristic times of 2.4 and 2.8 mu s, respectively. The D-5(0) state is found to relax in a manner that depends slightly on the final state and dopant site. (C) 2007 American Institute of Physics.