Zero-Dimensional Hybrid Zinc Halides with Bright Self-Trapped Exciton Emission for Switchable Encryption and Decryption
Zero-dimensional (0D) hybrid metal halides are promising for optoelectronic displays, bioimaging, and anti-counterfeiting due to strong exciton localization and self-trapped exciton (STE) emission. However, low-toxicity, biocompatible zinc halides with blue emission remain scarce, hindered by structural isolation of [ZnBr4]2− tetrahedra, electron-phonon coupling, lattice distortion, and nonradiative relaxation. Here, we synthesize MPAZnBr4 (MPA = N-(3-aminopropyl) morpholine), a 0D zinc bromide halide. Single-crystal X-ray diffraction reveals a monoclinic P21/c space group with a = 6.65190 Å, b = 16.11210 Å, c = 13.79640 Å, β = 94.5700°, Z = 4, and a calculated density of 2.394 g/cm3. The isolated [ZnBr4]2− tetrahedra are hydrogen-bonded to MPA cations, with the shortest Br···Br contact of 4.76 Å indicating weak inter-cluster electronic coupling. Upon photoexcitation, MPAZnBr4 exhibits bright blue emission centered at 450 nm with a full width at half maximum of 135 nm. Wavelength-dependent emission mapping confirms a single radiative pathway, while temperature-dependent photoluminescence identifies triplet STE emission with a thermal quenching activation energy of 55 meV. The extensive hydrogen-bonding network imparts remarkable structural stability, showing negligible photoluminescence decay under prolonged excitation or storage. As a proof-of-concept, we demonstrate switchable and rewritable information encryption and decryption, enabling complex luminescent patterns. These findings provide a strategy for constructing highly stable, low-toxicity blue-emissive Zn-based 0D metal halides for advanced photonic and information-security applications.