Photoluminescence properties of Yb2+ ions doped in the perovskites CsCaX3 and CsSrX3 (X = Cl, Br, and I) – a comparative study

Markus Suta,Werner Urland,Claude Daul,Claudia Wickleder

doi:10.1039/c6cp00085a

Abstract

The Yb(2+)-doped perovskite derivatives CsMX3 (M = Ca and Sr; X = Cl, Br, and I) are ideal systems for obtaining a detailed insight into the structure-luminescence relationship of divalent lanthanides. The investigation of the respective photoluminescence properties yielded two emission bands in the violet and blue spectral range for all compounds, which are assigned to the spin-allowed and spin-forbidden 5d-4f transitions, respectively. The impact on their energetic positions is dependent on both the covalency of the Yb(2+)-halide bond and the corresponding bond length in agreement with expectations. The excitation spectra provide a detailed fine structure at low temperatures and can be partly interpreted separating the 4f(13) core from the 5d electron in the excited state. The local crystal field in CsSrI3:Yb(2+) provides a special case due to the trigonal distortion induced by the crystal structure that is clearly evident in the luminescence features of Yb(2+). The structure-property relationship of several spectroscopic key quantities of Yb(2+) in this series of halides is analyzed in detail and parallels the properties of Eu(2+) ions doped in the given perovskites.

Highlights

CsCaX3 (X = Cl, Br, and I).[5,6] Tm2+ is known to show upconversion in halides.[7,8] In particular, the relatively low number of literature studies on the photoluminescence of Yb2+ and other divalent lanthanide ions compared to Eu2+ is mainly due to the high preparative challenge in stabilizing these ions in inorganic compounds
The local crystal field in CsSrI3:Yb2+ provides a special case due to the trigonal distortion induced by the crystal structure that is clearly evident in the luminescence features of Yb2+
The occupation of the Cs+ sites can be excluded, as they provide higher coordination numbers than 6 in all halides regarded in this paper and differ significantly in both charge and size (r(Cs+) 4 1.67 Å for CN 4 6) from Yb2+

Summary

Introduction

Yb2+ exhibits a closed-shell 4f14 configuration in its ground state and it is stabilized in many solids. Contrary to the case of Eu2+, its luminescence is often quenched or related to excitonic features due to the proximity of the excited states to the conduction band of the respective host compound.[9,10]. This extraordinary behavior is known as anomalous luminescence and has been recently investigated in much detail in fluorides where exciton trapping is often encountered.[11,12,13]

Results

Discussion

Conclusion