Enhanced photoluminescence in (Ca, Zn)TiO₃: Pr³⁺ afterglow phosphor for anti-counterfeiting application

Afterglow luminescent materials display an unusual phenomenon of delayed emission, primarily due to electron or hole traps. A lot of pioneering work on green and blue emitting afterglow luminescent materials have been reported, however, a handful of lattices are known to exhibit red emission. Red-emanating afterglow luminescent materials are desirable for tactical defence applications due to their lower sensitivity, particularly in dark conditions. A series of red-emanating CaTiO₃: Pr³⁺ phosphor materials were prepared and the role of Zn ions in escalating the photoluminescence (PL) properties was studied. Detailed characterization of the as-synthesized phosphors revealed orthorhombic structure and contraction in unit cell volume was observed upon zinc incorporation. Broad excitation spectrum and sharp peak at 618 nm (red emission) due to transition from ¹D₂ - ³H₄ were observed at room temperature. Ca_(0.9),Zn_(0.1)TiO₃: 0.25 mol% Pr³⁺ phosphor was found to emit enhanced PL intensity with an afterglow duration of 12 min. At 373 K, the optimized phosphor retained 76% of its initial emission intensity which indicates excellent thermal stability. The development of luminescent security ink followed by deposition onto various substrates was also discussed. The aqueous stability of the deposited patterns was tested on a time scale of more than 10 days. Security ink can be used for anti-counterfeiting applications such as safeguarding important documents and consumable-driven goods.