Excitation Wavelength‐Dependent Fluorescence of a Lanthanide Organic Metal Halide Cluster for Anti‐Counterfeiting Applications

Abstract The achievement of significant photoluminescence (PL) in lanthanide ions (Ln 3+ ) has primarily relied on host sensitization, where energy is transferred from the excited host material to the Ln 3+ ions. However, this luminous mechanism involves only one optical antenna, namely the host material, which limits the accessibility of excitation wavelength‐dependent (Ex‐De) PL. Consequently, the wider application of Ln 3+ ions in light‐emitting devices is hindered. In this study, we present an organic–inorganic compound, (DMA) 4 LnCl 7 (DMA + =[CH 3 NH 2 CH 3 ] + , Ln 3+ =Ce 3+ , Tb 3+ ), which serves as an independent host lattice material for efficient Ex‐De emission by doping it with trivalent antimony (Sb 3+ ). The pristine (DMA) 4 LnCl 7 compounds exhibit high luminescence, maintaining the characteristic sharp emission bands of Ln 3+ and demonstrating a high PL quantum yield of 90–100 %. Upon Sb 3+ doping, the compound exhibits noticeable Ex‐De emission with switchable colors. Through a detailed spectral study, we observe that the prominent energy transfer process observed in traditional host‐sensitized systems is absent in these materials. Instead, they exhibit two independent emission centers from Ln 3+ and Sb 3+ , each displaying distinct features in luminous color and radiative lifetime. These findings open up new possibilities for designing Ex‐De emitters based on Ln 3+ ions.