EPR spectroscopy of impurity thulium ions in yttrium orthosilicate single crystals

The frequency-field and orientation dependences of the electron paramagnetic resonance (EPR) spectra are measured for impurity Tm$^{3+}$ ions in yttrium orthosilicate (Y$_2$SiO$_5$) single crystals by stationary EPR spectroscopy in the frequency range of $50$–$100$ GHz at $4.2$ K. The position of the impurity ion in the crystal lattice and its magnetic characteristics are determined. The temperature dependences of the spin-lattice and phase relaxation times are measured by pulse EPR methods in the temperature range of $5$–$15$ K and the high efficiency of the direct single-phonon mechanism of spin-lattice relaxation is established. This greatly shortens the spin-lattice relaxation time at low temperatures and makes impurity Tm$^{3+}$ ions in Y$_2$SiO$_5$ a promising basis for the implementation of high-speed quantum memory based on rare-earth ions in dielectric crystals.