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Controlled synthesis and upconversion luminescence properties of LiYF4:Yb0.2Er0.02 nanoparticles

A series of high quality tetragonal LiYF4:Yb0.2Er0.02 nanoparticles were synthesized via thermal decomposition method. The influence of reaction conditions on final products has been investigated in detail. The TEM and XRD data show that the size, shape and crystallization of the samples depend on the reaction time and concentration. The upconversion luminescence (UCL) intensity gradually enhanced along with the sizes of the samples increasing. And when the reaction solvent system is oleic acid/1-octadecence (OA/ODE), the samples show smaller size and stronger emission compared with oleic acid/oleylamine/1-octadecence (OA/OM/ODE). Under 980 nm NIR laser diode excitation, all the samples show intense green emission between 510 and 570 nm wavelength from 4S3/2 → 4I15/2 and 2H11/2 → 4I15/2 transitions of Er3+ and intense red emission between 640 and 690 nm attributed to 2F11/2 → 4I15/2 transition of Er3+, both of the processes belong to two-photon energy absorption.