Optical activity levels of metal centers controlling multi-mode emissions in low-dimensional hybrid metal halides for anti-counterfeiting and information encryption

In-depth insight into the electronic competition principles between inorganic units and organic ligands proves to be extremely challenging for controlling multi-mode emissions in low-dimensional hybrid metal halides (LHMHs). Herein, an efficient blue emission from organic ligand was engineered in (DppyH)₂MCl₄ (Dppy = diphenyl-2-pyridylphosphine, M = Zn²⁺, Cd²⁺) due to the reverse type I band alignment constructed by optically inert units with nd¹⁰ shell electrons. By contrast, the optically active [MnCl₄]^2- with semi-fully filled 3d⁵ shell electrons prompts the band alignment of type II, resulting in the narrowband green emission of Mn²⁺, along with an energy transfer from DppyH⁺ to [MnCl₄]^2-. Beyond that, the band alignment of (DppyH)SbCl₄ is further reversed to type I due to the strong stereochemical activity of 5s² lone-pair electrons, resulting in the triplet-state (³P₁ → ¹S₀) self-trapped exciton (STE) emission of [SbCl₄]^-. The conclusion is that the electronic configurations of metal centers govern the optical activity levels of inorganic units, which in turn controls the multi-mode emissions by maneuvering the band alignments. This research provides an enlightening perspective on the multi-mode emissions with tunable photoluminescence and resulting electronic transitions of LHMHs, whose derived emitters can be employed in anti-counterfeiting and information encryption.