Influence of the local structure on the optical properties of Tb3+-doped LaPO4•nH2O and LaPO4 Single-Crystal Nanorods Prepared by Microwave-Assisted Hydrothermal Synthesis

A novel High Energy Resolution Fluorescence Detected X-ray Absorption Spectroscopy (HERFD-XAS) study at the Tb L₃-edge for the rhabdophane-type LaPO₄·nH₂O:Tb³⁺ and the monazite-type LaTbPO₄:Tb³⁺ nanorods was performed. The changes in the white-line intensity followed a similar trend to that previously observed in the photoluminescence behavior of these materials. Those changes were assigned to the localization of the terbium 5d states and the modification induced by the hybridization with the next neighbours as the terbium content is varied. The interplay between electronic (d-states localization) and structural (local disorder) effects was used to explain the different optical behaviour between the two series of nanorods. XAS results indicated that the local ordering is a key factor influencing the different emission efficiency, quenching effect and decay lifetimes observed experimentally for both series of nanorods. The present results indicated that the long lifetime decay process was accounted within a standard single Tb³⁺ ion scenario, where the structural disorder, favoured by the presence of water molecules in the structure, aids the non-radiative recombination processes.