Phase transitions and chromium( iii ) luminescence in perovskite-type [C 2 H 5 NH 3 ][Na 0.5 Cr x Al 0.5−x (HCOO) 3 ] (x = 0, 0.025, 0.5), correlated with structural, dielectric and phonon properties

) octahedral units and this feature explains a much stronger distortion of the former units and a weak effect of a trivalent cation type on the phase transition temperature. The dielectric studies have confirmed the occurrence of phase transitions of dipolar character and dipole relaxation processes. The optical studies show that EtANaCr and EtANaAlCr exhibit efficient Cr(iii)-based emission characteristics for intermediate-ligand field strength.