Energy absorption and transfer behavior of guest benzoate sensitizers in the interlayer space of Tb3+-doped layered yttrium hydroxide host

The energy transfer behavior from guest organic molecules to Tb3+ activators was systematically investigated using various benzoate derivatives with high ultraviolet (UV)-harvesting ability and ready exchangeability into interlayer galleries of layered yttrium hydroxide host, Y1·80Tb0·20(OH)5X∙nH2O (X = benzoate and its amino, hydroxy, chloro, cyano, and nitro derivatives of 2(ortho)-, 3(meta)-, and 4(para)-isomers). The difference in the interlayer arrangement of X anions depending on the types and positions of functional groups was found to be a critical factor for the energy transfer, sensitizing the luminescence of Tb3+. Despite the energy-level matching between the triplet state of X and the excited state of Tb3+, the difference in triplet state energy could not solely explain the significant change in energy transfer in the host-guest system. Instead, the interaction of X guests with host layers would be a major factor that determines the transfer of UV energy absorbed for the S0 → S1 transition of X to the 5D4 excited energy level of Tb3+. In contrast, when the triplet state of X was significantly lowered by the nitro group, the inverse transfer from Tb3+ to X was followed by energy dissipation, resulting in luminescence quenching, irrespective of the difference in interlayer interaction.