Influence of different synthesis methods on morphological and optical properties of the rare earth doped fluorides

Over the last few years there has been a great interest in developing the efficient methodologies for the preparation of rare earth doped up-converting nanoparticles (UCNPs), which exhibit emission in visible part of spectra when excited by the near infrared (NIR) radiation. Due to this unique optical property, as well as the high chemical stability they could be used either as security or fluorescent biological labels. Depending on the host crystal structure and choice of the dopant, these could exhibit different luminescence response. In this work we represent the effect which hydro/solvo thermal treatment and simple co-precipitation have on structural, morphological and optical properties of NaYF4:Yb,Er UCNPs. We showed that pure cubic phase crystallizes in monodisperse spherical nanoparticles obtained through hydro/solvothermal synthesis, while co-precipitation and annealing at 500°C for 5 hours leads to the obtaining of agglomerated microparticles with hexagonal phase. Due to the difference in size and morphology of the samples, the different up-conversion mechanisms are established upon the excitation by the infrared light (λ = 978 nm), intensifying green emission (2H11/2,4S3/2 →4I15/2 ) in sample obtained through hydro/solvo thermal synthesis