Polar solvent-induced transformation of terbium-based metal halides towards optical anti-counterfeiting and polarity sensing

Metal halide perovskites demonstrate excellent photoluminescence and have shown great potential in developing eco-friendly and reversible anti-counterfeiting materials based on polar solvent-induced photoluminescent color changes. However, it remains challenging to simultaneously achieve high quantum yield, excellent stability, and highly sensitive detection of trace polar solvents such as methanol. In this study, a novel terbium-based metal halide 20 % Sb 3+ : Cs 5 TbCl 8 ·6H 2 O was synthesized via solid-phase milling. Sb 3+ doping significantly enhanced its PL performance and stability. The 20 % Sb 3+ : Cs 5 TbCl 8 ·6H 2 O sample showed bright yellow emission with a PLQY of 68.3 % under UV irradiation and reversible water-induced yellow-to-green transition. This enabled the achievement of dual-patterned information encryption and anti-counterfeiting applications by using water-induced 20 % Sb 3+ : Cs 5 TbCl 8 ·6H 2 O and 20 % Sb 3+ : Cs 3 TbCl 6 @PMMA. Furthermore, due to the high charge density of the rare earth ion Tb 3+ and its strong affinity for polar solvents, an ultra-sensitive PL response was achieved for 20 % Sb 3+ : Cs 5 TbCl 8 ·6H 2 O in organic solvents of different polarities. Liquid-phase methanol induced the most pronounced ΔEA value (0.083) among 17 solvents, enabling highly sensitive detection with a limit of 0.01 % after 30 s ultrasonication. Complementary to its solution performance, the material also demonstrated exceptional responsiveness to methanol vapor, where a rapid and reversible PL transition occurred within 7.2 s at 60 °C. This work offers a feasible strategy for designing stimuli-responsive luminescent materials.