Photoluminescence in Cerium-Doped Fluoride Borate Crystals

Abstract

Antizeolite fluoride borates LiBa 12 (BO 3 ) 7 F 4 (LBBF) doped by Ce 3+ ions demonstrate photoluminescence (PL) and hold promise for use as phosphors in white light-emitting diodes. In this study, we present the results of modeling the electronic and optical properties of Ce-containing LBBF structures where doping atoms are located at different sites of the host lattice. We also consider the presence of F-centers, which exhibit trap states located within the band gap. We further investigate the nonadiabatic excited state electronic dynamics to elucidate electron-relaxation pathways. The nonadiabatic couplings (NACs) calculations provide transition probabilities facilitated by the nuclear movement. The relaxation rates of electrons and holes are calculated using Redfield's theory of the formalism of the reduced density matrix (RDM). The PL spectra are calculated using molecular dynamics (MD) sampling and time-integrated methods along the excited state trajectory based on NACs. Mechanisms of PL in LBBF:Ce 3+ crystals are interpreted using both computational and experimental observations. This work illustrates the dependence of transition energies, intensities, and relaxation rates of Ce-containing LBBF crystals on a selection of doping sites. In addition to analysis of emission band contributed by cerium, this work allows to identify and reproduce spectral lines hypothetically corresponding to the interband and intraband transitions in F-centers of borate crystals, available in the absence of a metal center.

LiBa12(BO3)7F4 (LBBF) crystals doped with Eu3+, Tb3+, Ce3+: structure and luminescence properties

“…Density functional theory calculations (HSE06) of the electronic structure of Ce-containing LBBF crystals lend support to this suggestion and demonstrate a decrease in the energy of conduction band minimum in the interval from 5.3 eV for undoped LBBF to 4.2-4.5 eV for LBBF:Ce 3+ , depending on the lattice site in which the Ce 3+ ion is located. 41 The transmission spectra of LBBF:Eu 3+ , Tb 3+ ,Ce 3+ and LBBF:Eu 3+ ,Tb 3+ , showing the long-wavelength shift of the absorption edge for LBBF:Eu 3+ ,Tb 3+ ,Ce 3+ crystal, are in good agreement with these results (Fig. S1 †).…”

Signature of low-dimensional quasi-F centers in zirconium-rich electrides

“…Further, an exploration regarding the optical activity of such electrides is highly desirable to investigate their emission properties, and the chromatic change in the lattice crystal contributed by such quasi-F centers or localized IAEs. 52…”