Electron spin relaxation governed by Raman processes both for Cu2+ ions and carbonate radicals in KHCO3 crystals: EPR and electron spin echo studies

Resonance local phonon mode and electron spin-lattice relaxation of formate-type free radicals studied by electron spin echo in Cd(HCOO)2·2H2O crystal

“…Temperature dependence of the relaxation rate 1/T 1 is similar for the both radicals and is presented in figure 7 together with the relaxation rate for Cu 2+ in Cd(HCOO) 2 •2H 2 O we measured previously [4]. The striking observation is that Cu 2+ -ion relaxation rate grows rapidly with temperature compared to the free radicals in the same crystal matrix.…”

“…with Debye temperature evaluated as Θ D = 193 K [4]. The three theories presented above assume that the relaxation is due to two-phonon Raman process, as in the case of Cu 2+ , but differently describe coupling to the phonons.…”

“…We have recently found [4] that carbonate radicals − CO 2 in KHCO 3 crystal relax in the same way as copper(II) ions introduced to the host crystal, i.e. via the Raman two-phonon processes indicating strong coupling between radiation defect motions and lattice vibrations.…”

“…− CO 2 radicals have not been ESR studied in Cd(HCO 2 ) 2 •2H 2 O where it was found that in heavily γ-irradiated crystal the Cd + ions are formed [20]. Electron spin-lattice relaxation of − CO 2 has been measured in KHCO 3 [4] and in natural calcite [7]. Some speculations on relaxations mechanisms were presented for NaHCO 2 on the basis of the ENDOR studies [13].…”