Heat- and light-induced transformations of Yb trapping sites in an Ar matrix

Abstract

The low-lying electronic states of Yb isolated in a solid Ar matrix grown at 4.2 K are characterized through absorption and emission spectroscopy. Yb atoms are found to occupy three distinct thermally stable trapping sites labeled "red," "blue," and "violet" according to the relative positions of the absorption features they produce. Classical simulations of the site structure and relative stability broadly reproduced the experimentally observed matrix-induced frequency shifts and thus identified the red, blue, and violet sites as due to respective single substitutional (ss), tetravacancy (Tv), and hexavacancy (Hv) occupation. Prolonged excitation of the (1)S → (1)P transition was found to transfer the Yb population from hv sites into Tv and ss sites. The process showed reversibility in that annealing to 24 K predominantly transferred the Tv population back into Hv sites. Population kinetics were used to deduce the effective rate parameters for the site transformation processes. Experimental observations indicate that the blue and violet sites lie close in energy, whereas the red one is much less stable. Classical simulations identify the blue site as the most stable one.

Computational study of the stable atomic trapping sites in Ar lattice

“…This is also in full agreement with experiment, which proved the existence of two sites with octahedral/cubooctahedral and tetrahedral host environment [13] established from the phonon broadening [8,9]. Another example studied in similar way [10] is Yb@Ar with ab initio values = 5.03 ρ Å and N site (left) and = 7 N site (right). Guest atom is shown as the red sphere surrounded by octahedron formed by six removed host atoms.…”

“…Thus, Ar atoms of the movable set can adapt themselves to the force induced by embedded atom G, while the atoms of fixed set maintain the long-range periodic order of the host crystal. In contrast to our previous applications [10,19], where the sizes of the sets were chosen once by convergency of the results, we need here more flexibility to handle the variation of the guest-host interaction potential automatically. So the present model allows for slight tuning at each potential parameter choice, as described in the Sec.…”

“…Partial resolution of the phonon structure of the narrow b 4 D, a 4 D and a 6 D emission bands of atomic manganese by McCaffrey group [8,9] revealed the tetrahedral ( d T ) and octahedral ( h O ) symmetry of the host envi-ronment for two sites observed. Energy order of three stable sites occupied by Yb in Ar were established from the lightand heat-induced site interconversion kinetics [10]. Of course, classical modeling is very helpful for trapping site characterization, especially if addresses kinetic [11,18] or thermodynamic [10,19] stability of the predicted sites.…”

“…Energy order of three stable sites occupied by Yb in Ar were established from the lightand heat-induced site interconversion kinetics [10]. Of course, classical modeling is very helpful for trapping site characterization, especially if addresses kinetic [11,18] or thermodynamic [10,19] stability of the predicted sites. Fortunately, crystallographic intuition helps a lot.…”

“…In the present contribution we report on the computational search of the thermodynamically stable atomic trapping sites in the Ar crystal. As an atomistic model, we used the one proposed before [10,19]. It describes an ideal crystal, but provides enough flexibility for accommodating a guest in the vacancies of different volume.…”