Facile phase tuning of CsCdCl3:Mn2+ phosphor for nearly-unity quantum yield and extended afterglow
Cubic-phase CsCdCl3 microcrystals were synthesized via room-temperature solid-state synthesis, overcoming the elusiveness of this polymorph relative to the extensively reported hexagonal phase. Doping with 10% Mn2+ elevated the photoluminescence quantum yield (PL QY) to near unity and extended afterglow duration to 10 h. The cubic phase exhibits metastability toward thermal treatment, transitioning to the hexagonal phase upon heating at 100 °C. Phase transition is also sensitive to Mn2+ doping concentration, providing a facile tool to manipulate the lattice structure of octahedra dimers (hexagonal) or monomers (cubic). Phonon spectrum and lattice formation energy calculations rationalize the phase transition mechanism. The phosphor demonstrates potential for information storage, X-ray imaging, and anti-counterfeiting. Under X-ray excitation, a spatial resolution of approximately 6 lp/mm was achieved, and luminescence intensity remained unchanged after 10 min of irradiation. Stored information, including a poem and a chip pattern, was retrievable upon heating at 125 °C. A hand-printed flower-like pattern on PET substrate, composed of pristine, 10% Mn2+, and 20% Mn2+-doped CsCdCl3, exhibited tunable photoluminescence color and afterglow duration. The digit '8' hidden under UV excitation was revealed after ceasing excitation, demonstrating anti-counterfeiting capability. This work opens avenues for advanced applications in information storage, X-ray imaging, and anti-counterfeiting.