Multi-Emissive Lanthanide-Based Coordination Polymers for Potential Application as Luminescent Bar-Codes

Isostructural lanthanide-based coordination polymers that are obtained by reactions in water of a lanthanide chloride and the sodium salt of 5-methoxyisophthalate (mip^2–) have the general chemical formula [Ln₂(mip)₃(H₂O)₈·4H₂O]_∞ with Ln = Nd–Er except Pm plus Y (symbolized by [Ln₂(mip)₃]_∞). Some of these homo-lanthanide compounds present very high luminescence brightness. The weak intermetallic energy transfer between lanthanide ions observed in these compounds allows the design of hetero-lanthanide coordination polymers with tunable luminescence properties. A molecular alloy that involved six different lanthanide ions (Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺) has been prepared and its luminescent properties have been studied. This compound, under a unique irradiation wavelength (λ_exc = 325 nm), exhibits almost 20 emission peaks in both the visible and the NIR regions at room temperature. This unprecedented richness of the emission spectrum could be of great interest as far as luminescent bar-codes are targeted.