The luminescence of Cs3Bi2Cl9 and Cs3Sb2Cl9

The luminescence properties of Cs3Bi2Cl9, α-Cs3Sb2Cl9, and β-Cs3Sb2Cl9 are reported and compared with those of Cs3Bi2Br9. The first two compounds have comparable luminescence properties which can be described in terms of a band model. Deep center emission is observed for both compounds, whereas edge emission is observed only for Cs3Bi2Cl9. The optical transitions of β-Cs3Sb2Cl9 are localized on the Sb3+ ion. The orientation of the lone-pair orbitals of the ns2 ions seems to play an important role in the formation of the cationic valence band. The α-β transformation must therefore have a considerable influence on the spectral properties of Cs3Sb2Cl9.