Reinterpretation of the Photoluminescence and Long Persistent Luminescence of Pristine Hexagonal and Cubic CsCdCl ₃ and with Mn ²⁺ and Fe ³⁺ Doping

The electronic spectra and luminescence decay measurements at room temperature (RT) and 77 K have been recorded for pristine hexagonal and cubic CsCdCl 3 and for this material doped with Mn 2+ or Fe 3+ . First‐principles calculations have been performed in order to rationalize the results. The RT visible emission broad band of hexagonal CsCdCl 3 is due to [MnCl 6 ] 4− emission at two different Cd 2+ sites. On cooling below RT, the Mn 2+ emission weakens in intensity, and variable intensity near‐ultraviolet emission bands are assigned to spin‐orbit coupling mixed singlet and triplet 1 D 2 , 3 D 3,2,1 (4 d 9 5 s 1 ) → 1 A 1g (4 d 10 ) ( O h ) transitions at C 3v and D 3d sites of Cd 2+ . Pristine cubic CsCdCl 3 exhibits two weak RT emission bands associated with tetrahedral and octahedral Mn 2+ impurity. Doping hexagonal CsCdCl 3 with Fe 3+ does not produce additional visible emissions and leads to quenching of Cd 2+ emissions below RT. Very weak infrared emission from Fe 3+ is observed. The thermoluminescence of cubic and hexagonal CsCdCl 3 is weak, but long‐lasting persistent luminescence is obtained upon Mn 2+ doping at a several percent level. Optical applications for anti‐counterfeiting and information encryption are suggested.