ИСТИНА

Metal fluorides are used in various fields as ionic conductors, as carriers for catalysts, as laser materials, and so on. There are many methods for synthesis of metal fluorides. However often it is important to obtain a metal fluoride with cer-tain morphology or in a defined crystalline modification which causes difficulties. A traditional method for obtaining double fluorides is solid-phase synthesis which needs to use high temperatures and as a consequence pyrohydrolysis of metal fluo-rides takes place. Another problem is the low homogeneity of the products. There-fore, a very important task is to find new methods for the synthesis of metal fluo-rides. In our work we propose a new method for metal fluorides synthesis by de-composing metal trifluoroacetate hydrates in the presence of beta-cyclodextrin (CD). This method allows synthesizing metal fluorides at relatively low tempera-tures and the products obtained have homogeneous distribution of elements. This new synthetic approach was used to produce double fluorides M2YbF7, M4Yb3F17 (M = Ca, Sr, Ba). It is important to note that the decomposition of the correspond-ing metal trifluoroacetates hydrates without CD does not lead to the formation of these fluorides, and the formation of a mixture of simple metal fluorides was ob-served. Also this synthetic way was used to produce complex fluorides NaRF4 (R = Y, La, Lu) doped by Yb3+ and Er3+. NaYF4: Yb3+, Er3+ is one of the most efficient near-IR–to-visible up-conversion phosphors. There are a lot of works concerning this system. At the same time, a similar systems NaRF4 (R = La, Gd, Lu) are much less studied, which is associated with the complexities of their synthesis. In our work we have shown that NaYF4 samples obtained in the presence of CD are more homogeneous and have more uniform pore size distribution than those obtained without CD. At the same time, the addition of CD prevents the pyrohydrolysis pro-cess. It is interesting to note that NaLaF4 synthesis proceeds at a higher temperature (600 C instead of 420 C for NaYF4) and the effect of the presence of CD still re-quires further research. In the case of NaLuF4 the decomposition of reaction mix-ture in the presence or absence of CD leads to the formation of orthorhombic or hexagonal modification, respectively. So we propose a new soft chemistry synthetic method for preparation of metal fluorides with homogeneous distribution of elements. Advantages of this method are availability of precursors and low temperature of the process. The work was supported by RFBR, grant number 14-03-01032.