Equivalent exploitation of four-pulse one-dimensional ESEEM and HYSCORE spectroscopies for the elucidation of BOHC defects in borate glasses supported by quantum mechanical calculations

Abstract

${\mathrm{B}}_{2}{\mathrm{O}}_{3}\ensuremath{-}{\mathrm{Li}}_{2}\mathrm{O}$ glass was exposed to ${}^{60}\mathrm{Co}$ \ensuremath{\gamma} irradiation and measured with four-pulse (4P) one-dimensional (1D) electron spin echo envelop modulation (ESEEM) spectroscopy and hyperfine sublevel correlation (HYSCORE) spectroscopy. 4P 1D ESEEM revealed the values of ${\ensuremath{\chi}}_{\mathrm{zz}}<~0.7\mathrm{MHz},$ $\ensuremath{\eta}\ensuremath{\sim}0.4{T}_{\mathrm{aniso}}<~0.8\mathrm{MHz},$ and ${A}_{\mathrm{iso}}\ensuremath{\sim}0.6\mathrm{MHz}$ for the second boron neighbor. In $a$- and $c\ensuremath{-}{\mathrm{B}}_{2}{\mathrm{O}}_{3},$ 4P 1D ESEEM uncovered the value of ${\ensuremath{\chi}}_{\mathrm{zz}}\ensuremath{\sim}2.6\mathrm{MHz}$ for the second boron neighbor. HYSCORE spectroscopy in the ${\mathrm{B}}_{2}{\mathrm{O}}_{3}\ensuremath{-}{\mathrm{Li}}_{2}\mathrm{O}$ glass revealed a weak coupling with ${\ensuremath{\chi}}_{\mathrm{zz}}<~0.7\mathrm{MHz},$ $\ensuremath{\eta}\ensuremath{\sim}0.37,$ ${T}_{\mathrm{aniso}}<~0.9\mathrm{MHz},$ and ${A}_{\mathrm{iso}}<~0.9\mathrm{MHz}$ due to the interaction of the spin with the second boron neighbor loosely bonded with the defect. An orthoborate group in the proximity of fourfold coordinated boron cluster reproduces the experimental parameters most satisfactorily.