Anisotropic Excitation-Modulated Multi-Color Three-photon Excited Luminescence in Ln-MOF Heterostructure

Multi-photon excited luminescence (MPEL) modulation is of great application value for optoelectronics, especially MPEL with the characteristics of multi-color emission and optical anisotropy. However, it still suffers from the obstacles in highly-integrating and orientedly-assembly of various MPEL units. Herein, a hierarchical assembly-in situ doping strategy is proposed to establish a novel lanthanide-graded metal-organic framework based heterostructure. Well-designed ligand and Ln³⁺ ions are respectively selected as the MPEL energy donor and acceptor units (MEDU and MEAU). Through utilizing the effective energy transfer between them, the as-obtained triblock heterostructure displays multi-dimensional three-photon excited luminescence (3PEL) modulation, where the emission band and intensity can be switched by manipulating excited regions and excitation polarization based on a single pump source. This is attributed to the precise integration and orientation of photonic units. As a result, the heterostructure exhibits multi-color 3PEL with a record-high MPEL color gamut (>30% of sRGB area) in MOFs and high degree of linear polarization values (max ≈88.6%). Such anisotropic 3PEL modulation shows promising potential in nonlinear optical switches, programmable logic gates, and multi-level optical barcodes. These findings open up an intriguing way to develop up-conversion luminescent materials with functions on demand toward photonic modulation.