Probing the Dielectric Effects on the Colloidal 2D Perovskite Oxides by Eu³⁺ Luminescence

Solution-processing technique of two-dimensional (2D) materials requires the knowledge of the dielectric effects on mutual interaction of each component and the layer structure variation. This research uses the magnetic dipole (MD) transition of intentionally doped Eu³⁺, which is dependent on the dielectric environments, as an optical probe to study the dielectric effects on the colloidal charge-bearing [Ca_1.8Eu_0.1Na_0.1Nb₃O₁₀]^- perovskite nanosheets (NSs) in various solvents. Results reveal that the solvent molecules with longer alkyl chain could more easily impact the ligands on the surface of the NSs, leading to a weaker interaction between the ligands and the NSs as well as less distortion of Eu³⁺ site (Ca²⁺ site) at the inner layer of the NSs. The large-sized ligands would impede the stacking of the NSs, while H⁺ would make the H⁺-modified NSs restack more easily. With the assistance of density functional theory (DFT) simulation, it is found that the ligands or the dielectric solvents could distort or relax the surface covalent polyhedra [NbO₆]^7- to a larger extent than the inner polyhedra. Small-sized ligands and a large thickness with more atomic layers of the NSs can resist structural variation caused by solvents. The acquired knowledge in this research benefits the understanding of the solution-processing technique for industrial application of 2D materials.