Optical Absorption Spectra of Divalent Neodymium (Nd²⁺) in Bromide and Iodide Hosts

Abstract

The electronic spectra for Nd2+ ions in bromide and iodide hosts are reported for the first time. These spectra, together with the recently obtained spectra for the chloride matrix, constitute a substantial series of Nd2+ spectra in crystals. Importantly, these crystals differ in the factors important for the physical properties of the divalent lanthanide Ln2+ ions; that is, the ligand's chemical character and the symmetry of the crystal field. The available experimental data allow systematic investigations of the impact of these factors on the electronic spectra, and thus, spectroscopic properties of Nd2+ ions. These investigations are the main aim of this study. The results indicate that due to the increasing covalence of the Nd2+ environment in the Cl–Br–I series, the energy of the first f–d transition shifts into the infrared region, from 6121 cm–1 for SrCl2/Nd2+ to ca. 5260 cm–1 for SrI2/Nd2+, whereas the strength of the crystal field decreases along this series. Calculations using the parametric Hamiltonian and superposition model are carried out to quantitatively interpret the measured spectra. The simulated spectra exhibit good agreement with the experimental spectra. Using the proposed approach, a meaningful interpretation and assignment of the bands observed in the spectra has been achieved.

Divalent and trivalent neodymium photoluminescence in NaMgF3:Nd

“…Consequently, it is expected that Nd 2+ can only be stabilised in very wide-bandgap compounds (ε g ≈ 10 eV). To our knowledge, spectroscopic data related to Nd 2+ have thus far been presented only for CaF 2 :Nd [27,28], SrF 2 :Nd [28], BaF 2 :Nd [28], LiCl-KCl melts [29], SrB 4 O 7 :Nd [30], SrCl 2 :Nd [11,31], SrI 2 :Nd and SrBr 2 :Nd [32], and KMgF 3 :Nd [33], in contrast to the several thousands of compounds for which other divalent lanthanides, such as Eu 2+ [9,12,17], have been studied in detail. In the majority of the aforementioned cases, only 4f 4 → 4f 3 5d 1 absorptions were observed [28][29][30], precluding any detailed analysis of the various intraconfigurational 4f 4 → 4f 4 transitions.…”