A general strategy for the synthesis of rare earth fluoride nano(micro)crystals
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 4S3/2 and 4F9/2 of Er3+ for the Yb3+/Er3+ co-doped KYF4 (tetragonal, hexagonal, orthorhombic) nano(micro)crystals were observed with pulse laser excitation at 980 nm.