Grafting organic antenna onto rare earth hydroxynitrate nanosheets for excitation-dependent and greatly enhanced photoluminescence by multi-modal energy transfer

Abstract

Abstract Excitation-dependent photoluminescence is most frequently encountered in quantum dot systems and organic-inorganic metal halide hybrids. Here, we report a new paradigm for excitation-dependent luminescence by grafting picolinic acid (pa) onto the single-crystalline nanosheets of RE(OH)2.94(NO3)0.06·nH2O (RE = Y/Tb, Y/Eu, Y/Tb/Eu). Grafting of pa through an interaction between COO− group of pa and RE3+ ions on the surface of nanosheets, did not change the morphology and the crystal structure of the original nanosheets, and the grafting content of pa reached the maximum value at R = 0.25 (R, the molar ratio of pa to nanosheets). Effective intramolecular energy transfer from coordinated ligands to the activated RE3+ ions, called the antenna effect, can give rise to an enhanced photoluminescence upon light irradiation. In this work, multi-modal energy transfer of pa → Eu3+, pa → Tb3+ → Eu3+, and the reconstructed Tb3+ → Eu3+ resulted from the antenna effect of pa contributed to the excitation-dependent luminescence behavior and greatly enhanced emission intensity. The luminescence reversibly undergoes repeated cycles by switching the excitation wavelength, indicating the grafted nanosheets are the potential materials of switched “on/off” optical sensors. The use of the energy transfer to the activated RE3+ ions through the antenna effect recommends a new paradigm for luminescence improvement and excitation-dependent luminescence.