Choon Sup Yoon

Bio: Choon Sup Yoon is an academic researcher. The author has contributed to research in topics: Electric field gradient & Quadrupole. The author has an hindex of 1, co-authored 1 publications receiving 13 citations.

Local structure of LiB3O5 single crystal from 7Li nuclear magnetic resonance

Abstract: The local structure of LiB3O5 single crystal was investigated with 7Li (I=3/2) nuclear magnetic resonance measurements. We observed four different spectra, which could be divided into two groups corresponding to two kinds of lithium atoms, LiA and LiB, lying at crystallographically equivalent sites and magnetically inequivalent sites. From these results, the quadrupole coupling constants and the asymmetry parameters were determined at room temperature and are e2qQ/h=143±1 kHz and η=0.6±0.1 for 7Li. The directions of the principal axes of the electric field gradient tensors were also determined. The spectra for the two groups have the same principal values of the electric field gradient tensor, but different orientations, and originate from magnetically inequivalent sites. Also, the 7Li spin-lattice relaxation rate was measured, and the measured relaxation rate was found to be proportional to the temperature. The temperature-dependent single phonon process is considered to be more effective than the Raman ...

Thermally stimulated recombination processes and luminescence in Li6(Y,Gd,Eu)(BO3)3 crystals

Abstract: The thermally stimulated recombination processes and luminescence in crystals of the lithium borate family Li6(Y,Gd,Eu)(BO3)3 have been investigated. The steady-state luminescence spectra under X-ray excitation (X-ray luminescence spectra), the temperature dependences of the X-ray luminescence intensity, and the glow curves for the Li6Gd(BO3)3, Li6Eu(BO3)3, Li6Y0.5Gd0.5(BO3)3: Eu, and Li6Gd(BO3)3: Eu compounds have been measured in the temperature range 90–500 K. In the X-ray luminescence spectra, the band at 312 nm corresponding to the 6 P J → 8 S 7/2 transitions in the Gd3+ ion and the group of lines at 580–700 nm due to the 5 D 0 → 7 F J transitions (J = 0–4) in the Eu3+ ion are dominant. For undoped crystals, the X-ray luminescence intensity of these bands increases by a factor of 15 with a change in the temperature from 100 to 400 K. The possible mechanisms providing the observed temperature dependence of the intensity and their relation to the specific features of energy transfer of electronic excitations in these crystals have been discussed. It has been revealed that the glow curves for all the crystals under investigation exhibit the main complex peak with the maximum at a temperature of 110–160 K and a number of weaker peaks with the composition and structure dependent on the crystal type. The nature of shallow trapping centers responsible for the thermally stimulated luminescence in the range below room temperature and their relation to defects in the lithium cation sublattice have been analyzed.