Effect of hydrothermal time on the forming specific morphology of YPO4:Eu3+ nanoparticles for dedicated luminescent applications as optical markers

A way to control the desired shape and microstructure of YPO4:Eu3+ nanoparticles through the precipitation method followed by a hydrothermal treatment is reported. This method is useful for achieving very high control over the YPO4:Eu3+ formation process with the selection of appropriate synthesis parameters. In detail, the autoclave processing time allows control of the shape and size of nano-needle-shaped particles independently in both directions, as confirmed by X-ray powder diffraction, FT-IR Spectroscopy and Electron Transmission Microscopy. In order to analyse the effect of the nanoparticles' surroundings on the excitation and relaxation processes of luminescent ions, Eu3+ ion was used as a dopant, whose specific properties allow the study of changes in their local surroundings by analysing emission spectra. As additionally shown, the shape and size of the nano-needles were correlated with the luminescence properties of the particles, which are particularly influenced by the presence of water and by its effect on emission processes from dopant ions located in the near-surface zone of the nanoparticles. These results proved that the shape of particles influenced the distance between Eu3+ ions in the phosphor, such distance affected the specific emission properties, i.e. the lifetime of excited levels of Eu3+ ions.