1. Institute for Scintillation Materials, State Scientific Institution, “Institute for Single Crystals,” National Academy of Sciences of Ukraine, 60 Nauki Ave., Kharkov 61001, Ukraine
2. B.I. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine, 47 Nauki Ave., Kharkov 61103, Ukraine and Max-Planck-Institut für Physik komplexer Systeme, 38 Noethnitzer Str., Dresden D-01187, Germany