Annotation of the results obtained in 2018
The technique of a crystal growth by the Czochralski method with extremely low concentration (5 - 100 ppm) of the doping Nd-143, Nd-145, Er-167, Tm-169, Rh-103, Yb-171 isotope is developed and was used; the host elements of the crystals contain the Li-7, Si-28, Sc-45, Y-89, Nb-93 isotopes. The monoisotopic 7LiNbO3 crystal with the use of a non-standard reactant monoisotopic 7LiOH, doped by the isotope Er-167, Rh-103, Tm-169 ions have been grown for the first time. Monoisotopic crystals of (Y1-xScx)2SiO5 containing 28-Si isotopic ions, doped by the Nd-143, Nd-145, Er-167, Tm-169, Yb-171 isotopic ions have been grown for the first time. During the project, isotopically pure crystals of Y2(28-Si)O5 and Sc2(28-Si)O5 doped with isotopes of erbium, ytterbium, neodymium with a non-zero nuclear spin with a concentration of 0.001 and 0.005 at % were grown. The presence of a non-zero nuclear spin plays a key role for quantum memory devices. The spin-spin and spin-lattice relaxation times were measured for these ions. It is found that erbium and neodymium ions can occupy positions of yttrium ion with a seven-fold nearest environment of oxygen ions, and ytterbium ions occupy positions with both a six-fold and a seven-fold environment. It is shown for the first time that the spin-lattice relaxation times of impurity rare-earth ions in Y2(28-Si)O5 and Sc2(28-Si)O5 single crystals strongly depend on the substituted position of the yttrium ion. So at T=5K, for the Yb3+ ion in a six-fold environment, the spin-lattice relaxation time is ~5 µs, for this ion in a seven-fold environment ~100 µs. The measurements of the spin-spin relaxation time showed that it time depends on the nature of the impurity rare-earth ion. So, at a temperature of 5K for the erbium ion, it is 1.06 µs., for isotope of 171-Yb it is about 28 µs., and for the 171-Yb isotope - 43 µs. It is shown that fora YVO4single crystal doped with neodymium isotopes 143-Nd and 145-Nd, the spin-spin relaxation time at 5 K are 22 µs and 43 µs, respectively, as it is in the Sc2SiO5 matrix, for which this times are ~ 42 µs both for the 143-Nd and 145-Nd isotopes. The most important results obtaining during the project include the registration of the increase of the spin-spin relaxation time of monoisotopic impurity neodymium ions 143/145-Nd in the yttrium orthosilicate single crystal grown on the basis of isotopically pure silicon 28-Si. It was found that at a temperature of 5K the spin-spin relaxation time reaches a record value, exceeding 100 µs for the resonance transition of the isotope 143-Nd in a magnetic field of 589 mT. Isotopically pure crystals Y2(28-Si)O5 and Sc2(28-Si)O5 were synthesized and studied for the first time in the framework of this RSF project.

 

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Annotation of the results obtained in 2016
- It is proved that a dissociation of initial oxides occurs in rare-earth melts, both silicates, and vanadate and, as a result, concentration of oxygen in the growth atmosphere strongly depends on melting temperature. - The technique of the automated control and change of concentration of oxygen in the growth atmosphere is developed and was for the first time used during crystal growth by the Czochralski method. - The technique of a crystal growing by the Czochralski method with extremely low concentration (5 - 100 ppm) of the doping isotope is developed and was used; the host elements of the crystals contain the isotopes of 28-Si, 45-Sc, 51-V, 89-Y, and the doping isotopes of 143-Nd, 145-Nd, 169-Tm. - Monoisotopic crystals of Sc2SiO5 and Y2SiO5 containing 28-Si isotopic ions, and the YVO4 crystals doped by the 143-Nd, 145-Nd, 169-Tm isotopic ions have been grown for the first time. - It is experimentally proved that introduction to the melt of Ca2+ ions in concentration optimal in relation to the content of yttrium, eliminates formation of the V3+, V4+ coloring centers in crystals; such kind color centers are not acceptable for a researching of magnetic properties. Monoisotopic crystals of Tm:YVO4 from the melt containing Ca2+ ions have been grown for the first time. - The grown monoisotopic crystals were investigated by Pulsed Cathodoluminescence method (PCL). The spectral PCL characteristics of monoisotopic Y2SiO5 crystals doped by the 145-Nd isotope and the Ca2+ doped 89Y51VO4 single crystals were studied in the 250 – 800 nm spectral range. - The occurrence of the oxygen vacancies in crystal structure of silicates and vanadate has been revealed by the PCL method. - It is experimentally proved that the nature of defects in the rare-earth silicates crystals is a presence of cationic and anionic vacancies, and also presence Ca2+ ions. The parameters of the effective spin Hamiltonian describing the magnetic properties of paramagnetic centers formed by impurity trivalent Nd-143 ions in two structurally nonequivalent positions in the crystal lattice Y2SiO5 are determined. It is established that the character of temperature dependences of the spin-spin relaxation time is different for different hyperfine components of the EPR spectrum of neodymium ions with different values of the resonance magnetic field. For the lines with resonance values of the magnetic field 309 588 MT the time of the spin-spin relaxation at 9K and above are the same, but at T=4 K the relaxation time for the low-field line is approximately 2.8 times shorter. Temperature dependences of the spin-lattice relaxation time of the impurity ion Nd3+ in Y2SiO5 are measured. It is established that there are three mechanisms contributing to the spin-lattice relaxation. They are direct one-phonon spin-phonon interaction, two-phonon interaction with Raman scattering and two-phonon Orbach-Aminov mechanism involving low-lying electronic level with energy of about 96 inverse cm.

 

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Annotation of the results obtained in 2017
- It is proved that a dissociation of initial oxides occurs in rare earth melts, both silicates, and vanadate and, as a result, concentration of oxygen in the growth atmosphere strongly depends on melting temperature. - The technique of the automated control and change of concentration of oxygen in the growth atmosphere is developed and was for the first time used during crystal growth by the Czochralski method. - The technique of a crystal growing by the Czochralski method with extremely low concentration (5 - 100 ppm) of the doping isotope is developed and was used; the host elements of the crystals contain the isotopes of 28-Si, 45-Sc, 51-V, 89-Y, and the doping isotopes of 143-Nd, 145-Nd, 169-Tm. - Monoisotopic crystals of Sc2SiO5 and Y2SiO5 containing 28-Si isotopic ions, and the YVO4 crystals doped by the 143-Nd, 145-Nd, 169-Tm isotopic ions have been grown for the first time. - It is experimentally proved that introduction to the melt of Ca2+ ions in concentration optimal in relation to the content of yttrium, eliminates formation of the V3+, V4+ coloring centers in crystals; such kind color centers are not acceptable for a researching of magnetic properties. Monoisotopic crystals of Tm:YVO4 from the melt containing Ca2+ ions have been grown for the first time. - The grown monoisotopic crystals were investigated by Pulsed Cathodoluminescence method (PCL). The spectral PCL characteristics of monoisotopic Y2SiO5 crystals doped by the 145-Nd isotope and the Ca2+ doped 89Y51VO4 single crystals were studied in the 250 – 800 nm spectral range. - The occurrence of the oxygen vacancies in crystal structure of silicates and vanadate has been revealed by the PCL method. - It is experimentally proved that the nature of defects in the rare-earth silicates crystals is a presence of cationic and anionic vacancies, and also presence Ca2+ ions. Sc2SiO5, Y2SiO5, and YVO4 single crystals doped with monoisotopic 143Nd3+ and 145Nd3+ ions and Y2SiO5 single crystals doped with trivalent thulium ions have been studied by continuous wave and pulse EPR methods. The directions of the principal magnetic axes of the paramagnetic centers formed by the impurity ions, the principal values of the g-tensor determining the dependence of the energy of the electron levels on the magnetic field, and hyperfine constants determining the interaction between the electron and nuclear spins of rare earth ions were determined based the angular dependences of the ESR spectra. The energy of the first excited electron singlet level of the ground 3H6 manifold of the Tm3+ ions in Y2SiO5 crystal equal to 50.0 GHz was directly measured by recording EPR spectra at zero magnetic field. The directions of the principal magnetic axes of the two magnetically nonequivalent thulium ions substituting ytterbium ions in one of the two crystal different positions, the principal values of the g-tensor and hyperfine tensor were determined based on the orientation dependences of the EPR spectra. It is found that the spectral diffusion is the main physical mechanism limiting the time of phase memory of the thulium impurity ions in Y2SiO5 and neodymium impurity ions in YVO4 single crystals at temperatures less than 10 K. The influence of spectral diffusion can be suppressed by using of special sequences of the microwave pulses (Dynamical Decoupling).

 

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