I. A. Mironov

Nanostructure of optical fluoride ceramics

The real structure of samples of optical fluoride ceramics is studied by atomic force, scanning electron, and transmission electron microscopy. It is shown that the optical ceramic samples based on CaF2 have a lamellar structure, and the distance between lamellae is 25–50 nm. Most likely, lamellae have a twin nature. For BaF2 ceramic, lamellae are not typical, and they are concentrated near grain boundaries.

Optical fluoride nanoceramic

Samples of the natural optical ceramic CaF2 from the Suran deposits (Southern Urals) have been studied as a model object. Nanostructure has been detected in this ceramic by the methods of electron and atomic-force microscopy. The conditions for obtaining precursors and the technological parameters of a process for obtaining a transparent fluoride ceramic with optical losses at a level of 10−2-10−3cm−1 at a wavelength around 1μm have been selected, and this is a necessary condition for creating materials for photonics elements. The fluoride nanoceramic possesses improved mechanical properties by comparison with single crystals. The ceramic is free from cleavage, has a breakdown viscosity greater by a factor of 3-6, and its microhardness is 10-15% higher. The thermal conductivity of the fluoride ceramic and of the corresponding single crystal completely coincide. The spectroscopic characteristics of the fluoride nanoceramic differ insignificantly from the characteristics of single crystals of the corresponding composition.

Thermal conductivity of single crystals of Ca1 − x Er x F2 + x and Ca1 − x Tm x F2 + x solid solutions

The thermal conductivity of single crystals of Ca1 − xErxF2 + x (x = 0.01, 0.05, 0.07, and 0.10) and Ca1 − xTmxF2 + x (x = 0.02, 0.04, and 0.06) solid solutions is studied in the temperature ranges 50–300 and 298–673 K. With increasing content of rare-earth elements, the behavior of thermal conductivity in these solid solutions changes from the characteristic of defect single crystals to glasslike. The concentration dependences of thermal conductivity for the two systems differ insignificantly.

Spectral-kinetic characteristics of crystals and nanoceramics based on BaF2 and BaF2: Ce

Optical characteristics of BaF2 and BaF2: Ce single crystals and nanoceramic materials prepared from these single crystals by uniaxial hot pressing have been studied. It has been shown that the introduction of Ce3+ ions into BaF2 hardly affects the ultrafast (∼0.9 ns) luminescence component. The integrated luminescence intensity of the BaF2: Ce nanoceramics is higher than that of the corresponding single crystal and considerably higher that the intensity of the undoped BaF2 crystal. It has been demonstrated that the slow (several hundred nanoseconds) component of the luminescence decay of BaF2: Ce is due to the energy transfer from excitons to Ce3+ ions.

Additive Coloring of CaF 2 Optical Ceramic

The specificity of additive coloring of CaF2 optical ceramic (formation of color centers in it and photothermochemical transformation of these centers in colored ceramic samples) has been considered. Under the same coloring conditions, this process occurs more slowly in ceramics rather than in crystals; at the same time, the limiting concentration of color centers that can be introduced into ceramics is much higher. The photothermochemical transformations of color centers in crystals and ceramics, which occur under illumination at different wavelengths and upon heating, have been studied. The specific features of introduction of color centers into ceramic and their transformation under illumination and heating are likely to be related to the mass twinning of ceramic grains.

Thermal conductivity of LaF3-based single crystals and ceramics

The thermal conductivity of lanthanum fluoride based single crystals and ceramics (LaF3, La0.975Nd0.025F3, and La0.95Sr0.05F2.95) has been measured at temperatures from 50 to 693 K by an absolute steady-state axial flow technique. We have not detected any anomalies indicative of “two-level systems.” The heat capacity of LaF3 single crystals has been measured in the temperature range 56–300 K. The results are used to evaluate the c-axis phonon mean free path as a function of temperature for single-crystal LaF3.

New scintillators based on barium fluoride crystals and ceramics

Experimental studies on the optical properties of new crystals and ceramics based on CeF3- and CdF2-doped barium fluoride were aimed at producing scintillators with a higher light yield level (particularly in the ultra-short wavelength range with a luminescence time of 0.6–0.8 ns) that could be used in the development of fast and low-cost optical sensors for positron emission tomography (PET). Ceramics manufactured on the basis of BaF2 single crystals with various concentrations of Ce and Cd are transparent in the 300–600 nm wavelength range; this is comparable to BaF2 single crystals.

Optical absorption in CaF{sub 2} nanoceramics

The optical characteristics of two Russian-made CaF{sub 2} ceramic samples are compared to those of single-crystal CaF{sub 2}. The results indicate that the ceramic possesses high optical quality and a small absorption coefficient ({approx}10{sup -3} cm{sup -1} at a wavelength of 1.07 {mu}m) and is suitable as a material for optical components. Experimental evidence is presented for spatial modulation of the thermally induced depolarisation in the ceramic. (nanostructures)

Optical properties and radiation damages of cerium fluoride crystals doped with alkali-earth and rare-earth elements

The most essential contribution in the investigation of CeF{sub 3} crystals having the goal to construct high precision electromagnetic calorimeters has been done by Crystal Clear Collaboration. Study of optical properties and radiation damages of Cerium Fluoride crystals doped with Ca, Ba, Sr, La, Nd, Zr and Hf in the wide range of concentrations has been performed with the goal to obtain high optical transparency of crystals at different cumulative doses under {gamma}-irradiation. Time decay curves and relative light yields of scintillators as a function of doping level were measured using X-ray excitation of samples and single photon counting method.