Developments in Ceramic Materials Research

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T. T. Basiev, V. A. Demidenko, K. V. Dykel’skii et al.
At the same time analysis of the modern trends in photonics shows that within the next
few years the devices on the basis of fluoride materials will play an important role. Physical
basics of this thesis are:
− transparency in wide spectral range from 0.16 to 11 µm;
− reduced rates of multiphonon relaxation in impurity ions due to low phonon spectra;
− long lifetimes of metastable levels;
− easy activation of fluoride composition by large concentrations of rare – earth ions
(up to 10 21 см -3 );
− high thermal conductivity of fluorides;
− unlike another classes of materials which has wide window transparency such as
chlorides and halcogenides, fluorides have better mechanical properties and higher
water – resistance.
Due to the advantages of the fluorides listed above the latter are used in form of single
crystals for production of active and passive elements of laser systems, for medicine, ecology,
information science and in particular as unique elements of tunable lasers.
Main drawback of the most fluoride crystals is crystal cleavage, which hinders their use
in practice. The more clear and more perfect the crystal the lower radiation stability and
mechanical resistance and resistivity to the thermal tension. Another drawback is a
difficulty of synthesis of numerous complex fluorides in the form of optically homogeneous
crystals [25]. The necessity of preparation of optical fluoride based elements as the devices
of modern photonics with high radiation resistance and high optical homogeneity will lead
to the development of the technology of optical nanoceramics. As shown in Ref. [13]
during the last 5 years the formation of new field of science named physicochemistry and
technology of the nanofluorides was launched. This direction has practical application
(catalysts, effective phosphors, etc). Synthesis of the fluoride nanoceramics is in
compliance with this direction. The development of the technology of laser fluoride
ceramics is in progress right now [26 – 29].
For example, the translucent colorless optical fluorite (CaF2) from the Suran deposit
(Russia) is quite an interesting object (Figure 1a). It has a cryptocrystalline structure and is
actually a natural analog of the optical ceramics. This fluorite characterized by a high
homogeneity and purity and associates with the sellaite mineral (MgF2). The age of the
deposit is about 1 billion years. Typical factor of the Suran cryptocrystalline optical fluorite
(SCOF) is its unusually high “shock resistance” which manifests itself in the process of
fragmentation of this material. Microstructure of the chip of the samples of natural fluoride
ceramics measured by atomic force microscopy (AFM) method [30] is presented in Figure 2.
Transmission spectrum of the SCOF in the IR range is identical to the same spectrum of
single crystal. X – ray diffraction (XRD) (diffractometer DRON – 2, CuKα radiation) shows
complete disorder in orientation of grains. AFM and cathode luminescence studies shows that
SCOF samples consists of the differently oriented grains with size from several to dozens of
microns and that unlike for the CaF2 single crystals the grains have a layered – type structure
(Figure 2a). Chemical etching of the SCOF sample shows small grains with the size of 50 –
200 microns within the dimensions of layers (Figure 2b). This result correlates with the data