Photoluminescence of CsMBr3:Eu2+ (M=Mg, Ca, Sr)-A novel strategy for the development of low-energy emitting phosphors

In this paper, the luminescence properties of Eu2+-doped series CsMgBr3, CsCaBr3, and CsSrBr3 have been studied. All the host compounds crystallize in perovskite-type structures with octahedrally coordinated alkaline earth sites. In each of these compounds, Eu2+ occupies the alkaline earth site and thus, they are ideal host compounds to investigate the dependence of the luminescence properties of Eu2+ upon the size of the cationic site. The emission spectra of the doped compounds are characterized by 4f65d1→4f7 transitions of Eu2+ located in the green, blue, and violet range, for M=Mg, Ca and Sr, respectively. The 5d excitation bands show a well-resolved fine structure arising from the different 7FJ levels (J=0…6) of the 4f6 core in both the t2g and eg excited states. The decay times and electron-phonon coupling were analyzed in each of these compounds. For CsMgBr3:Eu2+ an outstanding behavior in the series of the bromoperovskites is observed concerning its luminescence properties. This can be understood as a synergic effect of a small size of the cationic site and the structural feature of linear chains characteristic for this compound. Substitution of such a site could be a novel strategy for the development of low-energy emitting LED phosphors.