Reinterpretation of the Photoluminescence and Long Persistent Luminescence of Pristine Hexagonal and Cubic CsCdCl₃ and with Mn²⁺ and Fe³⁺ Doping

The electronic spectra and luminescence decay measurements at room temperature (RT) and 77 K have been recorded for pristine hexagonal and cubic CsCdCl₃ and for this material doped with Mn²⁺ or Fe³⁺. First-principles calculations have been performed in order to rationalize the results. The RT visible emission broad band of hexagonal CsCdCl₃ is due to [MnCl₆]⁴⁻ emission at two different Cd²⁺ sites. On cooling below RT, the Mn²⁺ emission weakens in intensity, and variable intensity near-ultraviolet emission bands are assigned to spin-orbit coupling mixed singlet and triplet ¹D₂, ³D_3,2,1 (4d⁹5s¹) → ¹A_1g (4d¹⁰) (O_h) transitions at C_3v and D_3d sites of Cd²⁺. Pristine cubic CsCdCl₃ exhibits two weak RT emission bands associated with tetrahedral and octahedral Mn²⁺ impurity. Doping hexagonal CsCdCl₃ with Fe³⁺ does not produce additional visible emissions and leads to quenching of Cd²⁺ emissions below RT. Very weak infrared emission from Fe³⁺ is observed. The thermoluminescence of cubic and hexagonal CsCdCl₃ is weak, but long-lasting persistent luminescence is obtained upon Mn²⁺ doping at a several percent level. Optical applications for anti-counterfeiting and information encryption are suggested. © 2026 The Author(s). Aggregate published by SCUT, AIEI, and John Wiley & Sons Australia, Ltd.