Analysis of absorption and luminescence spectra of U3+ doped Cs2NaYCl6 and Cs2LiYCl6 single crystals

Abstract

Uranium (3+) doped single crystals of Cs2NaYCl6 and Cs2LiYCl6 with a 2.0% and 0.1% U3+ concentration have been obtained by the Bridgman-Stockbarger method. Luminescence spectra of the crystals were recorded at 160, 70, and 15 K. The emission bands observed in the visible and near infrared regions have been assigned to transitions from the lowest components of the I11/24, F3/24, and G7/24 multiplets to the crystal-field components of the I9/24 ground level. Absorption spectra were recorded from 4 000 to 25 000 cm−1 at 4.2 K. The zero phonon transitions were identified from an analysis of the vibronic side bands as well as in least-squares fits by applying a semiempirical Hamiltonian representing the combined atomic and crystal-field interactions for an ion of the 5f3 configuration and Oh symmetry. Eight energy level parameters were varied simultaneously in the least-squares adjustments yielding a mean error of 57 and 61 cm−1 for U3+:Cs2LiYCl6 and U3+:Cs2NaYCl6, respectively. The analysis of the spectra enabled the assignment of 25 crystal field levels for U3+:Cs2NaYCl6 and 27 for U3+:Cs2LiYCl6. The received total splitting of the ground level is equal to 625 and 595 cm−1, respectively.

Ab initio theoretical studies on U3+ and on the structure and spectroscopy of U3+ substitutional defects in Cs2NaYCl6, 5f 26d1 manifold

“…8,9 Also, the relative low energy of the 5 f nϪ1 6d 1 levels of the actinide impurity ions makes the analysis of the 5 f →5 f spectra more complex. 10 5 f →6d absorption and 6d→5 f emission transitions have been observed in actinide ion impurities ͑e.g., Pa 4ϩ :Cs 2 ZrCl 6 , 11,12 U 3ϩ :Cs 2 NaYCl 6 , 10 or Cm 3ϩ :Cs 2 NaYCl 6 , 13 ͒ but they are often not well understood and detailed assignments have only been made in the 5 f 1 →6d 1 case. 12 In these circumstances, wave function-based ab initio methods of quantum chemistry are indicated, provided that they include all the relevant interactions: all the bonding interactions within the cluster formed by the impurity and its first coordination shell, including electron correlation effects and scalar and spin-orbit coupling relativistic effects, and the embedding interactions between the cluster and the rest of the host.…”

“…20 In this paper, we present the results of AIMP theoretical calculations of the large 5 f 2 6d 1 manifold of U 3ϩ in the Cs 2 NaYCl 6 host. They are aimed at interpreting the rich 5 f 3 →5 f 2 6d 1 absorption bands that have been reported by Karbowiak et al 10 and lack a detailed assignment. The results on the same manifold of free U 3ϩ ion are also presented; they are an important reference for the interpretation of the levels of the U 3ϩ impurities in solid hosts and they are not available in the literature.…”

Structure and spectroscopy of Pa4+ defects in Cs2ZrCl6. An ab initio theoretical study

“…[1][2][3][4] Contrary to the case of 5 f →5 f transitions, they are often not well understood. 3,4 In effect, the 5 f →5 f transitions are identified with the help of the crystal field theory ͑CFT͒. In these systems the number of CFT parameters is very large, usually above 20, and they cannot be fitted to the experimental data without experiencing numerical problems.…”

“…However, this shortcoming is often by-passed by fixing many of these parameters to reasonable values. 3 Trying to follow the same procedure for the 5 f →6d transitions is usually impossible, due to the much larger number of CFT parameters. In consequence, the 5 f →6d transitions are often unassigned.…”

5f−6dorbital hybridization of trivalent uranium in crystals of hexagonal symmetry: Effects on electronic energy levels and transition intensities

“…29 So far, energy-level analyses for these systems are performed only for the low-energy 5f n states without consideration of configuration interaction. 10,30,31 The configuration interaction is also excluded in previous analysis of the 5f 3 -5f 2 6d transitions for U 3+ : SrCl 2 ͑Ref. 29͒ and U 3+ : LiYF 4 .…”