Sonochemical synthesis of up-converting β-NaYF4: Yb, Er nanoparticles

Up-converting nanoparticles (UCNPs) with unique ability to convert NIR to VIS light (anti-Stokes process) have a wide application in optoelectronics, forensic, security labeling and biomedicine. Over the past few years different methods (like co-precipitation, thermal decomposition, hydro/solvothermal synthesis, etc.) are used for synthesis of β-NaYF4: Yb/Er phase, mainly from toxic organic precursors. In this work we explore conditions for stabilization of β-NaYF4: Yb/Er phase in nanoparticles applying sonochemistry synthesis of common inorganic precursor. The XRPD analysis showed that pure β phase is possible to obtained after 120 min of ultrasonification, while for shorter processing time (30-90min), cubic α-NaYF4: Yb/Er or orthorhombic YF3 : Yb,Er phase were founded too. The SEM and TEM analysis reveal presence of elongated nanoparticles self-assembled in spindles long up to 500 nm. Evolution of particle morphological and particle composition are analysed and correlated further with intensity of green emission (2H11/2,4S3/2→4I15/2) intensity measured under excitation of 978 nm.