Luminescence of Atomic Barium in Rare Gas Matrices: A Two-Dimensional Excitation/Emission Spectroscopy Study

Abstract

A detailed characterization is made of the distinct sites occupied by atomic barium isolated in the three rare gas hosts Ar, Kr, and Xe in excitation scans extracted from the recorded total 6s6p P → (6s)S fluorescence. Extensive use has been made of two-dimensional excitation/emission (2D-EE) spectroscopy to achieve a comprehensive characterization for the wide variety of sites present in the Ba/RG matrix systems. The 2D-EE technique has proved to be a very powerful method to probe the effects of strong intersite reabsorption when extensive spectral overlap occurs between emission and resonance 6s6p P ← (6s)S absorption of barium atoms occupying multiple sites. Two-dimensional excitation/emission scans have also been used in this study to monitor the effects of sample annealing and thereby identify the thermally stable sites of isolation. Sites of the same type occupied by atomic barium in the three host solids are identified in resolved excitation spectra and are associated on the basis of the observed matrix shift versus host polarizability. Following site associations, the photophysical properties of each matrix site were characterized revealing that the Stokes shift was greatest in the blue site, smallest for the violet site, and intermediate for the green site. The emission temperature dependences and excited state lifetimes were recorded, indicating that measured radiative lifetimes of 4-5 ns were in good agreement with the gas phase value of 8.4 ns when corrected for the effective field of the solids. The only exception to this was the blue site in Ba/Xe, where a nonradiative quenching channel exists even at 9.8 K that competes effectively with the nanosecond fluorescence. An unusual, asymmetric 2 + 1 excitation band has been recorded for atomic barium in the three rare gas hosts in addition to the threefold split, Jahn-Teller bands typically observed for P ← S absorptions of matrix-isolated metal atoms. Possible assignments of the sites responsible for these band shapes are made on the basis of recent spectral simulations obtained from molecular dynamics calculations on the Ba/Xe system.

High Resolution Spectroscopy of Neutral Yb Atoms in a Solid Ne Matrix

“…In the rigid crystal environment of C 4v symmetry, they should appear as two degenerate ZPLs and a single ZPL (with associated substructures if multiple phonons are excited) according to the projection of J onto the site axis Ω = ±1 and 0, falling into E and A 1 irreducible representations, respectively. The electron-phonon Jahn-Teller interaction should lift the remaining degeneracy, producing a 2+1 or 1+2 generic band structure, as was observed for the axial trapping site of the Ba atom [36][37][38]. For the site of C 2v symmetry, CFS produces three individual ZPLs.…”

“…The absorption bands due to 6s → 6p transitions in Figs. 4 (a) and (b), appear as broad, weakly structured features, typical of allowed or weakly forbidden outerelectron transitions [19,36,39]. Upon s → p electron promotion, the atom-matrix interaction changes dramatically and becomes strongly anisotropic, so that multiple phonon excitations superimpose relatively large crystal field splittings.…”

Theoretical Study of Ground-State Barium–Rare Gas Van der Waals Complexes: Combining Rule Modeling and Ab Initio Calculations

“…This technique enables the unique identification of individual barium atoms in a solid xenon matrix, which is essential for the nEXO project’s goal of searching for neutrinoless double beta (0νββ) decay with a high sensitivity. , This significant application of MIS has sparked interest in exploring the behavior of atomic barium within inert gas matrices. Recently, a study utilizing two-dimensional excitation–emission (2D-EE) spectroscopy and absorption spectroscopy has been conducted to characterize the luminescence of atomic barium isolated in krypton (Kr), argon (Ar), and xenon (Xe) RG solids. − This research has offered detailed insights into the distinct sites occupied by atomic barium in these RG hosts. Furthermore, investigation of barium in He-nanodroplets, , in solid and liquid helium, and isolated on large RG clusters , has provided insights into excited P states forming bubbles in liquid helium or size exclusion effects, compelling surface attachment on argon clusters.…”