Hydrothermal synthesis of optically active rare earth fluorides

Abstract

Hydrothermal method has great interest in recent years for synthesis of nano- and micro- crystals of upconverting rare earth (RE) fluorides, with controlled morphology and high purity, under high temperatures and pressures. Some surfactants (ethylenediaminetetraacetic acid (EDTA), polyvinylpyrrolidone (PVP), oleic acid (OA)) along with different type of solvents are added in order to control size, morphology and crystalline phases of particles. In this work Yb3+/Er3+ co-doped YF3 and NaYF4 fine powders were synthesized using the hydro/solvo thermal method in the present of EDTA as a complexing agent. Effect of the processing parameters on the particles crystal structure, morphology and optical properties were estimated on the basis of X-ray diffractometry (XRPD), scanning electron microscopy (SEM) and photoluminescence measurement. It was shown that in terms of increased concentration of RE ions in aqueous solvent media the hexagonal β-NaYF4:Yb3+/Er3+ phase with the most efficient green emission were synthesized. On the other side, the occurrence of cubic α-NaYF4:Yb3+/Er3+ and orthorhombic YF3:Yb3+/Er3+ were observed with a decrease of the RE ions when ethanol is used as a solvent. All of the samples provide intense green emission after been excited with infrared light (λ = 978 nm), which is assigned to the Er3+ (2H11/2, 4S3/2) → 4I15/2 electronic transitions.