Efficient Room‐Temperature Phosphorescence via Engineering Heavy‐Atom Effect and Band‐Edge Arrangement in 0D d ¹⁰ Metal (M=Zn, Cd) Halides for Anti‐Counterfeiting

Advancing room‐temperature phosphorescence (RTP) is pivotal for optoelectronics, yet a key challenge lies in precisely controlling exciton dynamics to boost RTP efficiency. This study presents a strategic approach to enhance RTP in 0D d 10 metal halides by engineering the inorganic units [MBr 4 ] 2– ( M ═Zn, Cd). Using a π‐conjugated ligand as organic template, we constructed a pair of isostructural hybrid bromides with 0D “host‐guest” structure, namely (PTPP) 2 MBr 4 (PTPP = Pentyltriphenylphosphonium, M ═Zn and Cd). They exhibit the cyan afterglow originating from the RTP emission of PTPP + (T 1 →S 0 ), whose efficiency and lifetime surpass those of the pristine organic chromophore due to enhanced structural rigidity. Importantly, the substitution of Zn 2+ by heavier Cd 2+ triggers a dual role: a stronger heavy‐atom effect and a band‐edge arrangement transform from Type II to reverse Type I. The phosphorescence quantum yields (Φ P ) increase dramatically from 10.2% ( M ═Zn) to 45.75% ( M ═Cd). The Cd 2+ ‐system provides more efficient intersystem crossing (ISC) channels (S 1 →T n ) and faster ISC rate, accounting for superior RTP efficiency. Furthermore, they can be employed in multi‐level anti‐counterfeiting and information encryption. This work elucidates the dual functionality of d 10 metal center in modulating spin‐orbit coupling and electronic structure, providing new insights for the rational design of RTP materials.