Alexander A. Grabar

The results of conductometric and pH studies in the time evolution for the water and aqueous solutions of ethyl irradiated with different sort of nuclear particles are presented. Such parameters of liquids are determined by the peculiarities of the radiation fragmentation of their molecules. The influence of small and large doses of radiation on these parameters was studied using a microtron M-30 (18 MeV) and radiation stands (Pu-Be, 137Cs) capable of generating electron (e–), neutron (n), γ-, and mixed nuclear radiation. The high sensitivity of conductometric studies of irradiated liquids to nuclear e-, n-, and γ-irradiation has been established. It has been shown that, after irradiation, the physical properties of water are restored, and new chemical compounds can form in aqueous alcohol solutions according to the Lego game principle. The biological activity of irradiated liquids was also studied using several common test microorganisms. Data on the radiation-induced fragmentation of liquids are essential for understanding their biological activity.

Tin hypothiodiphosphate (Sn2P2S6) is a ferroelectric semiconductor with electro-optic and photorefractive relevance. The lattice contains Sn2+ ions and (P2S6)4− anionic groups. In the present work, an Sn2P2S6 crystal is doped with Te during growth. Our results show that the Te ions occupy Sn sites and S sites, where they serve as electron and hole traps, respectively. Electron paramagnetic resonance (EPR) spectra from five trapped holes and one trapped electron are observed at low temperatures after exposure to 633 nm light. Spin-Hamiltonian parameters are extracted from the angular dependence of each spectrum. Holes are localized on (P2TeS5)4− units and form (P2TeS5)3− anions, with the five defects corresponding to Te on different S sites within the anion. These defects have large g shifts caused by the tellurium spin–orbit coupling parameter. Four of the five also have an isotropic hyperfine interaction with one Sn ion, which suggests that they have an adjacent Sn vacancy (leaving just one close Sn neighbor). Three trapped-hole spectra are photoinduced at 20 K and two appear after removing the light, warming to 120 K, and then returning to 20 K. Electrons are trapped in pairs at Te4+ ions occupying Sn2+ sites when the crystal is exposed to 633 nm light while at 20 K. The Te2+ ions that are formed have no observable EPR spectrum. Warming to 100 K releases one electron from Te2+ ions that have an adjacent Sn vacancy, and an EPR spectrum from Te3+ ions (5s25p) is seen when the crystal is returned to lower temperatures.

Electron paramagnetic resonance (EPR) is used to establish the role of iodine as an electron trap in tin hypothiodiphosphate (Sn₂P₂S₆) crystals. Iodine ions are unintentionally incorporated when the crystals are grown by the chemical-vapor-transport method with SnI₄ as the transport agent. The Sn₂P₂S₆ crystals consist of Sn²⁺ ions and (P₂S₆)⁴⁻ anionic groups. During growth, an iodine ion replaces a phosphorus in a few of the anionic groups, thus forming (IPS₆)⁴⁻ molecular ions. Following an exposure at low temperature to 633 nm laser light, these (IPS₆)⁴⁻ ions trap an electron and convert to EPR-active (IPS₆)⁵⁻ groups with S = 1/2. A concentration near 1.1 × 10¹⁷ cm⁻³ is produced. The EPR spectrum from the (IPS₆)⁵⁻ ions has well-resolved structure resulting from large hyperfine interactions with the ¹²⁷I and ³¹P nuclei. Analysis of the angular dependence of the spectrum gives principal values of 1.9795, 2.0123, and 2.0581 for the g matrix, 232 MHz, 263 MHz, and 663 MHz for the ¹²⁷I hyperfine matrix, and 1507 MHz, 1803 MHz, and 1997 MHz for the ³¹P hyperfine matrix. Results from quantum-chemistry modeling (unrestricted Hartree–Fock/second-order Møller–Plesset perturbation theory) support the (IPS₆)⁵⁻ assignment for the EPR spectrum. The transient two-beam coupling gain can be improved in these photorefractive Sn₂P₂S₆ crystals by better controlling the point defects that trap charge.

For the first time, we demonstrated successful post-synthesis incorporation of metal dopants at elevated temperature into a host structure of Sn₂P₂S₆, known as the grandfather of dichalcogenide ferroelectrics with a formula M₂P₂X₆ (M = metal and X = chalcogen).

We determine both the lifetime and the mobility of photoexcited charge carriers in Sn2P2S6 using holographic time of flight in diffusion mode. From the build-up dynamics of space charge gratings created by pulsed interband illumination at 532 nm, we find a charge carrier lifetime of 2.6 ± 0.5 ns and a charge carrier mobility along the x-axis of 2.4 ± 0.6 cm2 V−1 s−1 at room temperature. This mobility is assigned to holes as more mobile carriers in tin hypothiodiphosphate (SPS), and it is found to decrease for decreasing temperature, a behavior consistent with small-polaron hopping.