Crystal field analysis of rare-earth ions energy levels in GaN

•We report on crystal field analysis of Er ion energy levels in cubic and hexagonal GaN.•We present re-measured photoluminescence and excitation photoluminescence spectra of hexagonal GaN:Er3+.•Theoretical calculations reveal that local symmetry of Er in cubic GaN is D2, whereas in hexagonal GaN local symmetry is C3V.•Some trends in crystal field parameters of trivalent lanthanides in hexagonal GaN are discussed.

Much effort has been put to achieve optoelectronic devices based on Er doped GaN, operating on the intra-4f-shell transitions of erbium. The key issue for good understanding of energy transfer mechanisms to Er and its luminescence properties is the position of Er3+ ions in the crystalline lattice of GaN. After doping, Er3+ ions are assumed to be placed in substitutional position for Ga3+ in GaN. Although Ga is positioned in high symmetry, tetrahedral [ErN4]9 – cluster, deviations from this after doping are impossible to avoid because of a large difference in ionic radii of Ga3+ (47 pm) and Er3+ (89 pm). In this work we report on crystal field analysis of Er ion energy levels in cubic and hexagonal GaN. It is shown that local symmetry of Er in cubic GaN is D2, whereas calculations reveal that in hexagonal GaN local symmetry is C3V. Some trends in crystal field parameters of trivalent lanthanides in hexagonal GaN are discussed.