Journal of Alloys and Compounds 432 (2007) 18–22 Theoretical investigations of the optical spectra and EPR parameters for Yb 3+ ions in GaN epilayer M. Dammak ∗ , S. Kammoun, R. Maalej, T. Koubaa, M. Kamoun Groupe de Physique Th´ eorique, Laboratoire de Physique Appliqu´ ee, D´ epartement de Physique, Facult´ e des Sciences de Sfax, 3018 Sfax, Tunisia Received 9 May 2006; received in revised form 31 May 2006; accepted 1 June 2006 Available online 11 July 2006 Abstract In this paper, the crystal-field energy levels of Yb 3+ in GaN epilayer are calculated using crystal-field theory. The perfect agreement between measured and calculated energy values obtained, under C 3v point symmetry assumption, allows us to conclude that we deal with an isolated Yb 3+ ion in the GaN lattice. The crystal field parameters of Yb 3+ ions in this host are calculated and compared to those obtained for Yb 3+ in CaF 2 in C 3v symmetry site. The respective strength crystal field parameter permits to calculate the maximum splitting of the 2 F 7/2 ground state, which is in good agreement with the observed value. The 2 F 5/2 missing experimental energy level is calculated and the predicted emissions from this level are calculated and can be attributed in the emission spectra. The lowest Kramer’s doublets are found to be E 1/2 for Yb 3+ ion in trigonal symmetry site. The EPR g factors g // and g ⊥ and hyperfine structure constants A // and A ⊥ are investigated using the perturbation formulas. The admixture of different states is induced. © 2006 Elsevier B.V. All rights reserved. PACS: 71.70.ch Keywords: GaN; Yb 3+ ; Crystal-field; EPR parameters 1. Introduction Rare earth (RE) doped semiconductor materials have been extensively studied over the last decade due to their potential in light-emitting device applications [1–3]. Particularly an impor- tant effort research has been devoted to III–V semiconductors doped with rare earth. One of the problems encountered for these materials is the decrease of the PL intensity at higher tem- perature. Since this thermal quenching was more severe for the smaller band gap materials, wider band gap semiconductors like III–V nitrides appear to be especially promising host materials for rare earth doping [4]. The applications of III–V semiconductors are strongly depen- dent on the presence of optical active ions, which are intently incorporated in the host crystal. Trivalent rare earth (Re 3+ ) ions are the most commonly used as activator center. Especially, the Yb 3+ ions appear as a potential candidate for laser materials. ∗ Corresponding author. Tel.: +216 74274923; fax: +216 74274437. E-mail address: madidammak@yahoo.fr (M. Dammak). Compared with Re 3+ doped laser materials, Yb 3+ -doped materi- als have some advantages due to the simple energy level structure of the Yb 3+ ions. Indeed, rare earths implanted into GaN can be activated as luminescent centers emitting in the near-infrared region. Espe- cially, an important effort in the solid-state laser materials field being devoted to the research of new Yb 3+ -doped crystalline materials [5]. Several groups have investigated the photoluminescence, the cathodoluminescence and electroluminescence of GaN doped rare earth ions [6–17]. In some cases, the observed intensities for the RE luminescence transitions have been compared to theoretical predictions from lattice sum calculations in order to asses the symmetry properties of the participating RE defects. It was found that the luminescence spectra of Pr [16,18–20] and Sm [21] are compatible with C 3v symmetry, while Tb lumi- nescence was probably related to defects of D 2 symmetry [22]. In the case of the Eu, C 3v [15] and D 2 [18] symmetries were suggested. In any case, extracting symmetry information of rare earth centers is considered to be difficult because contributions from 0925-8388/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2006.06.002