Mechanism exploration of abnormal dual luminescence in Mn2+-doped NaZr2(PO4)3 phosphate phosphors and their prospective anti-counterfeiting applications

Mn 2+ -doped dual-emission luminescent materials have recently attracted significant interest. However, the distribution of Mn 2+ ions is highly dependent on the host crystal structure, the lattice sites, and the doping concentration. How to analyze and clarify the dual-emission mechanism of Mn 2+ has become a major challenge; thus, this work synthesized NaZr 2 (PO 4 ) 3 : Mn 2+ phosphate phosphors and systematically investigated their doping behavior and luminescence mechanisms. The synthesized NaZr 2 (PO 4 ) 3 : Mn 2+ phosphate phosphors exhibited dual broadband emission centered at 480 nm and 565 nm, respectively. Density functional theory (DFT) calculations confirmed the existence of different Mn doping configurations and their corresponding formation energies. The results revealed that at low concentrations, the Mn ions (Mn1) preferentially substitute Na sites; while at high concentrations, the later Mn ions (Mn2) substitutes Zr sites and interact with pre-existing Mn1 to form Mn-Mn dimer. Notably, the emission spectra of the phosphors were sensitive to both Mn 2+ doping concentration and excitation wavelength. The Commission Internationale de l′Éclairage (CIE) chromaticity coordinates could be tuned within the range of (0.2463, 0.3478) to (0.4128, 0.4733), enabling adjustable luminescence from cyan to yellow. Furthermore, leveraging the dual-wavelength emission and high contrast characteristics of this phosphor, we fabricated an anti-counterfeiting dot matrix displaying the information "WIT" via ASCII code and achieved clear fingerprint visualization. This work clarifies the doping site preference of Mn 2+ and the underlying mechanism of dual luminescence, paving the way for the applications of transition metal phosphors in fields such as information encryption and fingerprint visualization.