Scalable synthesis of core-shell MOF single crystals with spatially segregated multicolour luminescence for optical encoding.

The development of millimetre-scale optically resolvable tags that combine information density with mass-producible uniformity is crucial for advanced anti-counterfeiting and colour barcoding. Despite the excellent luminescence tunability of metal-organic framework (MOF) materials, the scalable fabrication of single-crystal MOFs with spatially defined multicolour emission remains a major challenge. Here, we report a scalable solution-phase epitaxial growth strategy to construct multicolour luminescent heterostructures based on uniform Ce3+-MOF (IAM19-1) single crystals. Through sequential and regioselective overgrowth of different emissive lanthanide (e.g., Tb3+, Eu3+) doped MOF shells, we programmatically construct core-shell architectures within individual crystals, where distinct lanthanide-emitting domains (e.g., Tb3+ for green, Eu3+ for red) are programmed with separation distances tailored for optical discrimination. This method overcomes the spatial and scalability limitations of traditional postsynthetic modification routes, yielding more than 0.1 g quantities of single-crystal heterostructures with sharp, well-defined luminescent domains. Under UV excitation (254 nm), these heterostructures exhibit bright, domain-specific multicolour photoluminescence, where each colour corresponds to a pre-defined spatial region. Leveraging this unique spatial-optical coupling feature, we successfully construct a high-capacity optical encoding system for anti-counterfeiting. This work establishes a scalable materials platform for fabricating luminescent millimetre-scale tags with complex, embedded optical information, bridging the gap between bottom-up crystal engineering and practical device applications in security.