Nature of Localized Excitons in CsMgX3 ( X=Cl , Br, I) and Their Interactions with

Markus Suta

¹

,

Flavie Lavoie-Cardinal

²

,

Jacob Olchowka

³

et al.

Abstract

In this paper, the luminescence properties of self-trapped excitons (STEs) of undoped and Eu 2+ doped perovskite-type materials CsMgX3 (X = Cl, Br, I) are presented. The three compounds crystallize isostructurally in a hexagonal crystal system that exhibits an intrinsic pseudo one-dimensionality. This feature has a highly stabilizing effect upon the localization of excitons. Similarities to the properties of STEs in alkali halides are drawn that are justified by band structure and density of states (DOS) calculations.The luminescence spectra of all three halides are characterized and interpreted despite of their high complexity with many emissive transitions. It is illustrated that both self-trapped excitons (STEs) and impurity-localized self-trapped excitons (IL-STEs) are responsible for the features in the spectra . The impurity localization of the STEs is proven by doping the hosts with Sr 2+ ions instead of Eu 2+ ions. The decay times in the µs range indicate that emission predominantly occurs from a triplet state of the STEs with a prominent afterglow component for the IL-STEs that ideally suits a trapping model along the one-dimensional chains of the halides. Moreover, by thermal activation, the excitons tend to annihilate at the Eu 2+ traps thereby inducing an energy transfer to the Eu 2+ ions. Due to this action, an extreme increase of the intensity of the Eu 2+ -based 4f 6 5d-4f 7 emission at room temperature could be observed, which might be a general explanation for unusual temperature-dependent emission intensities of Eu 2+ ions. In general, an understanding of the basic optical properties of the STEs may give some new insights into the mechanism of currently used X-ray storage phosphors as well as scintillators.

Halide Pb-Free Double–Perovskites: Ternary vs. Quaternary Stoichiometry

“…A further class of ternary inorganic perovskites that has been recently investigated is represented by alkali earth metal ions in the B site of the perovskite CsMX 3 (here M = alkali earth ions; X = halides) [88] and its interactions with rare earth metals, both as dopants and in alloys, the latter with interesting applicability as scintillators [89]. Among the others, the PL properties of such mixed systems were studied for Eu 2+ [90,91] and for Yb 2+ [92].…”

Impact of 1,10-Phenanthroline-Induced Intermediate Valence on the Luminesence of Divalent Europium Halides

“…The outer 5d subshell is not shielded and therefore influenced by the ligand and/or solvent. These properties were extensively studied in halides, where the divalent state can be stabilized. − …”