Spectroscopic and energy transfer studies of Eu3+ centers in GaN

Abstract

Photoluminescence (PL), photoluminescence excitation (PLE), and time-resolved PL spectroscopies have been carried out at room temperature and 86K on transitions from D25, D15, and D05 excited states to numerous FJ7 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 1.8–2.7eV, 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 D25 and D15 states are observed to decay nonradiatively by filling the D05 state with characteristic times of 2.4 and 2.8μs, respectively. The D05 state is found to relax in a manner that depends slightly on the final state and dopant site.