A general strategy for the synthesis of rare earth fluoride nano(micro)crystals

Abstract

In this study, we developed a simple and environmentally friendly method to synthesize rare earth fluorides with the formula REF₃ (RE = La, Y), and AREF₄ (A = Li, Na, K; RE = La, Gd, Y) nano(micro)crystals via a solvothermal route for the first time in a mixture of oleic acid (OA) and n-hexanol (HA) by tuning the radio of AF/RE (A = Li, Na, K) and the reaction temperature. It was found that the specific inorganic salt (LiF, NaF, and KF) should be selected carefully to precisely control the phases of YF₃, LiYF₄, NaYF₄, and KYF₄ nano(micro)crystals. Also, the synthetic conditions, namely temperature, tends to decrease with an increase in the cation radius for the formation of the pure orthorhombic YF₃ [Li⁺ (0.60 Å) < Na⁺ (0.95 Å) < K⁺ (1.33 Å)]. In addition, phase-dependent upconversion luminescence (UCL) and decay curves of the excited state levels of ⁴S_3/2 and ⁴F_9/2 of Er³⁺ for the Yb³⁺/Er³⁺ co-doped KYF₄ (tetragonal, hexagonal, orthorhombic) nano(micro)crystals were observed with pulse laser excitation at 980 nm.