abstract
We present a case study on the vibrational coupling of lattice phonons to the electronic 4f(7) (S-8(7/2))-4f(6)5d(1) (e(g)) transition of divalent europium in the hydrides and deuterides LiMH3 and LiMD3 (M = Sr and Ba). For low doping concentrations, these compounds show extraordinarily well-resolved vibronic fine structures at low temperatures. Besides luminescence emission spectroscopy of the europium doped compounds, we carried out inelastic neutron scattering (INS) experiments of the europium-free compounds. The phonons coupling to the electronic transition are identified, and a good agreement between the vibronic and the INS data is found. The frequencies of the low-energy acoustic modes do not significantly change upon replacing hydride by deuteride, whereas a decrease by a factor of approximately root 2, can be observed for the higher energy optic modes. Furthermore, we compare these experimental results to density functional calculations performed with the Vienna Ab initio Simulation Package. Knowledge of the phonons of a host material is of great importance because phonons have a large influence on the optical properties, such as line widths or luminescence quenching. Hydride-containing host lattices are an ideal model system because H-1 can easily be replaced by D-2 so that isotope effects can be investigated.
keywords
BILBAO CRYSTALLOGRAPHIC SERVER; TOTAL-ENERGY CALCULATIONS; ALKALINE-EARTH HYDRIDES; VIBRONIC TRANSITIONS; DIVALENT EUROPIUM; EU(II) LUMINESCENCE; VIBRATION-SPECTRA; LITHIUM HYDRIDE; HOST LATTICES; EMISSION
subject category
Chemistry; Science & Technology - Other Topics; Materials Science
authors
Lefevre, G; Herfurth, A; Kohlmann, H; Sayede, A; Wylezich, T; Welinski, S; Vaz, PD; Parker, SF; Blach, JF; Goldner, P; Kunkel, N
our authors
Pedro Miguel Duarte Vaz
Collaboratoracknowledgements
The authors would like to thank the ISIS Neutron and Muon Source for beamtime at TOSCA and Jean-Francois Engrand for constructing a sample holder for low-temperature PL measurements using ampoules. N.K. and T.W. would like to thank the Fonds der Chemischen Industrie for a Liebig and a doctoral fellowship (Li 197/02) and Prof. Fassler for hosting our group. A.H. and H.K would like to thank the DFG for financial support (KO1803/7-1). P.G., N.K, S.W., and T.W. thank the Bavarian French Academy Center for a mobility aid for their French German collaboration (Az. FK03-2017). Furthermore, AS., H.K., and N.K. thank the Universite d'Artois for financial support for a French German exchange.