An interplay between electronic and structural effects on the photoluminescence decay mechanisms in LaPO4·nH2O:Tb3+ and LaPO4:Tb3+ single-crystal nanorods

Abstract

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 is reported. We have observed that the changes in the white-line intensity follow a similar trend to that previously observed in the photoluminescence behaviour of these materials. Those changes have been 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-state localization) and structural (local disorder) effects is used to explain the different optical behaviour between the two series of nanorods. The XAS results indicate that the local ordering is a key factor influencing the different emission efficiencies, quenching effects and decay lifetimes observed experimentally for both series of nanorods. The present results indicate that the long lifetime decay process is 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. Implications for future use of the white-line intensity in the HERFD-XAS spectra in characterizing other luminescent materials are also discussed.