Dual blue fluorescence and green phosphorescence of a hybrid cadmium halide for anti-counterfeiting†

Zero-dimensional (0D) metal halide-based room-temperature phosphorescence (RTP) materials have received extensive attention with wide application prospects, but they still suffer from low phosphorescence efficiency, which restricts their progress in cutting-edge photonic applications. In this work, a new zero-dimensional (0D) cadmium halide [BTPP]₂CdBr₄ (BTPP = benzyl triphenylphosphonium bromide) was successfully synthesized through a room-temperature solution method. Under excitations of 357 nm and 309 nm UV light, [BTPP]₂CdBr₄ displays dual blue fluorescence and green phosphorescence with lifetimes of 1.38 ns and 76.18 ms, respectively. The quantum yield of phosphorescence reaches 43.68%, which exceeds that of most 0D metal halide-based RTP materials. Detailed experimental characterizations and theoretical calculations demonstrate that the fluorescence and phosphorescence originate from the radiative recombination of singlet self-trapped excitons (STEs) and triplet π–π* charge transfer in the [BTPP]⁺ cation, respectively. Benefitting from its dual luminescence, [BTPP]₂CdBr₄ can be explored as a dual space- and time-resolved luminescent label with applications in anti-counterfeiting and information security, among other fields. This work provides a fundamental structural engineering strategy to design highly efficient 0D metal halide-based RTP materials.