Facile phase tuning of CsCdCl3:Mn2+ phosphor for nearly-unity quantum yield and extended afterglow

While the hexagonal-phase CsCdCl₃ was extensively reported due to its high photoluminescence quantum yield and ultralong afterglow duration, the cubic-phase CsCdCl₃ remained elusive. Herein, the cubic-phase CsCdCl₃ microcrystals were synthesized via a solid-state synthesis at room temperature. After 10%-Mn²⁺ doping, the photo-luminescence quantum yield (PL QY) was improved to near unity and the afterglow duration was extended to 10 h. Importantly, the cubic phase was found meta-stable toward thermal treatment, where a transition to hexagonal phase was observed upon heating at 100 °C. In addition, the phase transition was also sensitive to Mn²⁺-doping concentration, which provided a facile tool to manipulate the lattice structure of octahedra dimers (hexagonal) or monomers (cubic). The mechanism of phase transition was theoretically explained through both phonon spectrum and lattice formation energy. This work opened many avenues to advanced applications such as information storage, X-ray imaging and anti-counterfeiting.