The luminescence spectroscopy of atomic zinc isolated in the solid rare gases ͑Zn/RG͒ is compared with theoretical predictions obtained from the sum of diatomic Zn•RG and RG•RG pair potentials. In particular the existence of pairs of emission bands, both of which are assigned to the same gas phase electronic transition, is examined with the use of diatomic pair potentials to simulate the potential energy surfaces of the Jahn-Teller active vibrational modes of Zn in the solid rare gases Ar, Kr, and Xe. Simulations of the solid state Zn/RG luminescence are developed from a consideration of the excited state Zn( 1 P 1 )•RG n van der Waals cluster species in the gas phase. The maximum binding energy of the Zn( 1 P 1 )•RG n clusters is found in the Zn•RG 4 cluster having a square planar structure at the energy minimum. Based on the results of the cluster calculations, lattice distortions which led to a dominant interaction between the Zn atom and four of its host atoms were sought to simulate the solid state luminescence. Two such vibronic modes were identified; one a lattice mode in which four rare gas atoms contract on a single plane toward the Zn atom, referred to as the waist mode, and the other a motion of the Zn atom toward an octahedral interstitial site of the lattice, the body mode. Energy calculations of these modes were carried out for rigid and relaxed rare gas lattices allowing identification of the high energy emission bands in the Zn/RG systems as arising from the waist mode, while the lower energy bands are associated with the body mode. The model also rationalizes the differences exhibited in the time-resolved behavior of the pairs of singlet emission bands in the Zn/Ar and Zn/Kr systems, whereby the lower energy band of a given system shows a risetime of a few hundred picoseconds while the higher energy band exhibits direct feeding. The steep gradient calculated on the waist mode, feeding the high energy band, and the flat gradient found on the body mode, feeding the lower energy emission, are consistent with the existence of a risetime in the latter and its absence in the former. The close agreement found between theory and experiment indicates the validity of using pair potentials in analysis of matrix zinc spectroscopy and thereby indicates that the luminescence is controlled by localized guest-host interactions.
Luminescence spectroscopy of the metal atoms Mg, Zn and Cd isolated in solid neon is recorded using pulsed synchrotron radiation excitation of the ns 1 np 1 1 P 1 -ns 2 1 S 0 resonance (n = 3, 4 and 5 respectively) transitions. Two features, a dominant band and a red-shoulder, are identified in the UV absorption spectra of Zn/Ne and Cd/Ne. Excitation of these features yields distinct emission bands with the red-shoulder absorption producing the smaller, Stokes-shifted emission. Nanosecond decaytime measurements, made with the time correlated single photon counting technique indicate the emission bands arise from the spin singlet 1 P 1 → 1 S 0 transition. Hence, it is concluded the duplication of absorption and emission features in the Cd/Ne and Zn/Ne systems arises from metal atom occupancy in two distinct sites. In contrast, Mg/Ne luminescence consists of single excitation and emission bands, indicative of occupancy in just one site. The occurrence of distinct photophysical characteristics of the linewidths, Stokes shift and lifetimes in the Mg/Ne system, compared with those recorded for Zn/Ne and Cd/Ne, is rationalised in terms of a different site occupancy for atomic Mg. Accurate interaction potentials for the ground states of the M·Ne diatomics are used to analyse site occupancies and interpret this contrasting behavior.
The temperature dependence of the pairs of emission bands present for atomic zinc isolated in annealed solid argon, krypton, and xenon samples is examined in steady-state and time-resolved luminescence spectroscopy. The pairs of emission bands in all the Zn/RG systems exhibited a reversible temperature dependence whereby the intensity of the high-energy band decreased, while the low-energy band gained in intensity with increasing temperature. In the Zn/Ar system, the decrease in the intensity of the 218.9 nm emission band observed between 9 and 28 K was coupled with a concomitant increase in the intensity of the band at 238 nm. In this temperature range the decay times of the 218.9 nm band decreased while the 238 nm band exhibited a constant decay time of 1.41 ns and a rise time correlated with the decay of the 218.9 nm band. The interdependence exhibited by the intensities and decay times of the two emission bands is modeled by an activated nonradiative process with a barrier height of 130.6 cm Ϫ1 for population interconversion between the pairs of emitting levels on of the spin singlet adiabatic potential energy surface. Similar behavior was observed in Zn/Kr between 6.3 to 20 K, but at higher temperatures this system also exhibited enhanced intersystem crossing. Likewise, for Zn/Xe, the low-energy 399 nm emission increased in intensity at the expense of the high-energy 356 nm emission up to a temperature of 40 K. For the Zn/Kr pair of singlet emissions and the Zn/Xe pair of triplet emissions, barrier heights of 78.1 and 42.6 cm Ϫ1 were evaluated, respectively.
The pair-potentials calculations of McCaffrey and Kerins ͓J. Chem. Phys. 106, 7885 ͑1997͔͒ used with success in simulating the emission spectroscopy of the Zn-RG matrix systems are extended to examine the different temporal decay characteristics exhibited at low temperature, TϽ13 K, by the singlet emission bands in the Zn-Ar matrix system. The 238 nm band, assigned in the earlier theoretical work to the body mode Q 2 , exhibits a 0.1 ns risetime, the 219 nm band assigned to the waist mode Q 3 , is prompt. By extracting the gradients and the second derivatives of the Q 3 and Q 2 mode potentials of a Zn•Ar 18 cluster, decay rates of 3 and 2 ps, respectively, are calculated at the Franck-Condon regions of these potentials accessed in absorption, leading to effective competition between the Q 2 and Q 3 modes for relaxation of excited-state population and thereby to the coexistence of the 238 nm emission with the 219 nm band. A quasi-bound region is located at 0.32 Å in the body mode, Q 2 , which slows down the relaxation on this mode and is identified as responsible for the recorded risetime on the 238 nm emission. The temperature dependence exhibited in the Zn-Ar system at higher temperatures (TϾ14 K) in which the intensity of the 219 nm band can reversibly be put into the 238 nm band, was examined by generating the ͑PES͒ potential-energy surface for coupled Q 2 ϫQ 3 vibronic modes. The theoretically predicted activation energy barrier is 380 cm Ϫ1 , which is only in qualitative agreement with the value of 130.6 cm Ϫ1 extracted in the kinetics study. Possible reasons for the overestimation in the theoretical value are discussed.
Previous steady-state and time-resolved luminescence spectroscopy of 3p 1 P 1 atomic magnesium, isolated in thin film samples of the solid rare gases, is extended to include the higher energy 4p 1 P 1 excitation. Well-resolved site splittings are recorded in Mg/Ar samples for excitation to the 4p 1 P 1 level. A small red shift in the absorption energy to the 4p 1 P 1 level for Mg/Ar contrasts with a small blue shift on absorption to the 3p 1 P 1 level. Direct emission from the 4p 1 P 1 level is not observed in any of the rare gas matrices; instead, intense emission from the low energy 3p 1 P 1 level is. Measurements of the emission decay curves in Mg/Ar have revealed slow rates in the steps feeding the 3p 1 P 1 level following 4p 1 P 1 excitation. The reason for the differential shifting of the 4p 1 P 1 and 3p 1 P 1 levels as well as the lack of direct 4p 1 P 1 emission is thought to be related to the strong binding interaction between Mg in the 4p 1 P 1 state and the rare gases.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.