Crystal Engineering 5 (2002) 203–208 www.elsevier.com/locate/cryseng Crystal field splitting of highly excited electronic states of the 4f n–1 5d electronic configuration of trivalent rare earth ions in wide band gap crystals A.C. Cefalas a,* , S. Kobe b , Z. Kollia a , E. Sarantopoulou a a National Hellenic Research Foundation, 48 Vassileos Constantinou Avenue, Athens, 11635, Greece b Department of Nanostructured Materials, Jozef Stefan Institute, Jamova 39, 1001 Ljubljana, Slovenia Abstract The energy position and the spacing of the levels of the 4f n–1 5d electronic configuration of the trivalent rare earth ion dopands in wide band gap fluoride crystal, depend on the symmetry and the type of the host matrix. Crystal field splitting of the 4f 2 5d electronic configuration of the Nd 3+ ions in SrF 2 crystals have been observed in the VUV region of the spectrum. The absorption bands were due to the interconfigurational 4f 3 →4f 2 5d dipole allowed transitions between the ground state with 4f 3 electronic configuration of the Nd 3+ ions and the Stark components of the 4f 2 5d electronic configuration. The VUV spectra can be interpreted by applying the crystal field model, and taking into consideration both that lanthanide contraction of the 4f n–1 5d electronic configuration of the rare earth ions is taking place, and that the contribution of the positively charged ions in the total electric field, is effectively decreased with increasing numbers of the electrons in the 4f n electronic configuration due to effective charge shielding.  2003 Elsevier Science Ltd. All rights reserved. Keywords: Vacuum ultraviolet; 157 nm; Rare earth ions; Stark splitting 1. Introduction The absorption and the excitation spectroscopic characteristics of the trivalent rare earth (RE) ions in the VUV spectral region, activated in wide band gap fluorine * Corresponding author. Tel.: +30-210-7273839/40; fax: +30-210-7273842. E-mail address: ccefalas@eie.gr (A.C. Cefalas). 1463-0184/02/$ - see front matter  2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S1463-0184(02)00030-8