Spectra and energy levels of Tb3+(4f 8) in GaN

The cathodoluminescence spectra of Tb3+ ions implanted and annealed in GaN epilayers have been analyzed and modeled according to its incorporation into a substitutional Ga lattice site having D2 point group symmetry. High-resolution emission spectra obtained at 11 K between 380 and 750 nm are identified as transitions from the G65,D35 combined manifold and the D45 manifold to individual energy (Stark) levels of the FJ7 multiplet manifolds. All intense peaks and nearly all weaker peaks and bands are associated with emission from Tb3+ ions in a similar site. The observed crystal-field splitting of the F67,F57, and F47 manifolds is much too large for any lattice-sum predictions based on Tb3+ ions in C3v sites. Calculated splittings and relative intensities based on a site symmetry of D2 give the best overall agreement with the observed data.