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

The achievement of significant photoluminescence (PL) in lanthanide ions (Ln³⁺ ) has primarily relied on host sensitization, where energy is transferred from the excited host material to the Ln³⁺ 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 Ln³⁺ ions in light-emitting devices is hindered. In this study, we present an organic-inorganic compound, (DMA)₄ LnCl₇ (DMA⁺ =[CH₃ NH₂ CH₃ ]⁺ , Ln³⁺ =Ce³⁺ , Tb³⁺ ), which serves as an independent host lattice material for efficient Ex-De emission by doping it with trivalent antimony (Sb³⁺ ). The pristine (DMA)₄ LnCl₇ compounds exhibit high luminescence, maintaining the characteristic sharp emission bands of Ln³⁺ and demonstrating a high PL quantum yield of 90-100 %. Upon Sb³⁺ 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 Ln³⁺ and Sb³⁺ , each displaying distinct features in luminous color and radiative lifetime. These findings open up new possibilities for designing Ex-De emitters based on Ln³⁺ ions.