S. P. Chernov

Growth of congruently melting Ca0.59Sr0.41F2 crystals and study of their properties

AbstractHomogeneous crystals of Ca0.59Sr0.41F2 alloy (sp. gr., Fm

UV and VUV spectroscopic study of Na0.4Y0.6F2.2 crystals doped with rare-earth ions

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Growth and some properties of Ce3+-doped LiYbF4 single crystals

m, a = 0.56057 nm), corresponding to the point of minimum in the melting curve in the CaF2-SrF2 phase diagram, have been grown by the vertical Bridgman method. The optical, mechanical, electrical, and thermophysical properties of Ca0.59Sr0.41F2 and MF2 crystals (M = Ca, Sr) have been studied and comparatively analyzed. Ca0.59Sr0.41F2 crystals are transparent in the range of 0.133–11.5 μm, have refractive index nD = 1.436, microhardness Hμ = 2.63 ± 0.10 GPa, ion conductivity σ = 5 × 10−5 S/cm at 825 K, and thermal conductivity k = 4.0 W m−1 K−1 at 300 K. It is shown that the optical properties of Ca0.59Sr0.41F2 crystals are intermediate between those of CaF2 and SrF2, whereas their mechanical and electrical characteristics are better than the latter compounds.

The possibilities of pumping UV lasers by synchrotron radiation

Crystalline materials that are transparent in the vacuum UV spectral region and currently used have been reviewed. Transmission of crystals of solid solutions with the fluorite structure Ca1−xRxF2+x (R = Sc, Y, La, Yb, Lu) in the UV and vacuum UV spectral regions has been investigated. It is shown that application of different methods of purification of fluorides from some impurities can significantly improve the optical quality of fluoride multicomponent crystals in the short-wavelength spectral region.

Spectral luminescence properties of Ca1 − xSrxF2:Ce3+ (0 < x <1) crystals

The short-wavelength transmission spectra of Na0.4R0.6F2.2 crystals with R = Y, Yb, or Lu have been investigated. For these crystals, the VUV transmission cutoffs are 78750, 58820, and 75200 cm−1, respectively. The 4fn–4fn−15d absorption and excitation spectra of Na0.4Y0.6F2.2 crystals activated with Ce3+, Pr3+, Nd3+, Er3+, Tm3+, and Yb3+ ions have been analyzed in the range 30000–80000 cm−1. The energy positions of the lowest levels of the 4fn−15d configurations of these ions in the fluorite crystal matrix Na0.4Y0.6F2.2 are determined. The absorption band in the spectral range 60600–70000 cm−1 in Na0.4(Y, Yb)0.6F2.2 crystals is due to the charge transfer from F− to Yb3+. It is shown that the environmental symmetry of Ce3+ ions in Na0.4R0.6F2.2 (R = Y, Yb, Lu) crystals is almost identical.

Spectroscopic investigations of wide-band fluoride crystals doped with ions of some rare-earth elements under X-ray excitation

MgF2 single crystals have been grown from melt by the Bridgman technique in a fluorinating atmosphere. To control the presence of oxygen impurity, it was first suggested to measure the ionic conductivity in MgF2 crystals by impedance spectroscopy. The characteristics of ionic conductivity of “as grown” (i.e., without thermal treatment) crystals and crystals obtained by commercial vacuum technology practically coincide: the volume conductivity σv = 1.4 × 10−7 S/cm at 773 K and the ion-transport activation energy Ea = 1.40 ± 0.05 eV. Annealing MgF2 crystals during electrophysical studies upon heating from 293 to 823 K in vacuum (residual pressure ∼1 Pa) for 4 h led to their partial pyrohydrolisis. The influence of this thermal treatment of MgF2 crystals on their optical transmission is studied in the wavelength range of 115–300 nm.

VUV-spectroscopy of Ce3+ -doped crystals with fluorite-type structure

LiYbF4 single crystals, nominally pure and doped with Ce3+ ions, of optical quality and up to 60 mm in diameter, have been grown by vertical directed crystallization. The optical and mechanical properties of the crystals have been studied. The refractive index dispersion for LiYbF4 in the range of 0.4–0.6 μm can be described by the dependence n2(λ) − 1 = Aλ2/(λ2 − λ02), where A = 1.14 and 1.21 and λ0 = 0.074 and 0.080 μm for no and ne, respectively. The sample microhardness exceeds 2.6 GPa. LiYbF4 crystals are transparent in the range of 0.17–9 μm and have an absorption band in the range of 0.9–1.2 μm. It is shown that LiYbF4 crystals doped with Ce3+ ions can be used as optical cut-off UV filters in the operating range λ = 0.25−0.28 μm.

VUV spectroscopy of Ce3+-doped Na0.4Lu0.6F2.2 single crystals

Abstract Creation of lasers in VUV and X-ray region of spectrum is one of the most actual tasks of modern quantum electronics. Use of powerful synchrotron radiation will allow to achieve generation of lasers in the high-energy part of the spectrum. Estimations of possible pumping of wide bandgap crystals (made for NaCl) show that such generation may be obtained with the help of synchrotron radiation of storage rings VEPP in Novosibirsk. The usage of VEPP-3 will allow to achieve a pumping density twice over threshold. Specific power of such a generation in regime of free generation will be about 103 W / cm3. The wide fluorenscence line of proposed active media will make it possible to achieve powerful ultrashort impulses in the VUV-region and tunable generation. Other possible active media for lasers with synchrotron radiation pumping are also discussed. Active media for UV and VUV lasers are intensively explored nowadays. The possibilities of pumping these lasers by powerful synchrotron radiation are discussed. An active medium must be able to absorb pumping radiation, must be transparent for radiation at the wavelength of generation and must be stable under radiation, etc. It will be rather useful to use solid active media, because they have several merits, such as great partial density of energies, convenient use, etc. But, up to now, there are no solid state UV and VUV lasers. So the first task is to look for such active media, which will be luminescent in the UV and VUV regions. Such media are large bandgap crystals with luminescence emission in the ultraviolet region. The possibility of achieving ultraviolet luminescence of large bandgap crystals is currently explored with electron beam1,2) (giving a high density of excitation) or X-ray sources3,4). Vacuum ultraviolet luminescence of crystals of rare gases was also explored with synchrotron excitation. Recently, excitation of luminescence of several crystals was achieved with the help of VUV-lasers6,7) which allow to achieve high densities of excitation in the region of fundamental absorption. Later, we shall report about the exploration of UV and VUV luminescence of crystals pumped by powerful VUV laser, about the observation of luminescence of crystals of oxides, pumped by powerful X-ray synchrotron radiation and we shall give estimations of achieving laser generation from large bandgap crystals, pumped by powerful X-ray synchrotron radiation. Results of our experiments and other works have made possible to estimate the possibilities of generation from several crystals, pumped by synchrotron radiation.