The anhydrous solid trehalose: Low-temperature EPR study of glassy and boson peak modes

Electron spin–lattice relaxation times (T1) were measured by X-band electron paramagnetic resonance (EPR) spectroscopy in irradiated trehalose glass (TR-G) and trehalose-β crystalline state (TR-C) from 5 to 290 K. Throughout the whole temperature interval studied, a consistently shorter T1 was observed in TR-G than TR-C while the largest difference was detected below ca. 80 K. Here, the theoretical analysis within the soft potential model pointed to the two mechanisms responsible for a more efficient energy exchange between the spin system and the lattice in TR-G: the thermally activated dynamics of glassy modes and the Raman process with boson peak (BP) modes. In this context, the glassy polymorph of anhydrous trehalose corroborates the idea that the boson peak, being a universal property of amorphous/disordered solids, can be studied by EPR even at X-band frequencies. It is further suggested that the mechanisms, involving glassy/soft/BP modes, which provide additional channel for the electron spin coupling with the lattice in glassy as compared to the crystalline state, could be proposed as a universal phenomenon aiming to explain the electron spin relaxation in disordered matrices at temperatures above a few Kelvin in general.