Abstract
Paramagnetic states in glass (a-) and crystal (c-) B2O3 were induced by γ-irradiation and studied by cw-EPR, HYSCORE and pulsed-ENDOR spectroscopies at 20 K. A `four-line-plus shoulder' spectrum was detected by cw-EPR in a- and c-B2O3. The cw-EPR spectra were simulated assuming AIa-B2O3=(39.44, 43.45, 22.00 MHz) and AIc-B2O3=(20.44, 40.00, 32.00 MHz). Pulsed ENDOR revealed a strong coupling AI-ENDOR=(−25, −36, −46 MHz) for a- and c-B2O3. A weaker coupling was detected by HYSCORE and pulsed ENDOR spectroscopies with AIIa-B2O3andc-B2O3=(5.5, 5.6, 6.4 MHz). HYSCORE spectroscopy determined two weak hyperfine couplings of AIIa-B2O3-1=5.8 MHz and AIIa-B2O3-2=2 MHz when recorded with a τ-value of 248 and 168 ns, respectively. Computer simulation of the spectra together with SCF–HF and MNDO calculations determined that the unpaired electron is trapped by an oxygen-dangling bond attached to three-fold coordinated boron. The hfs tensors AIIa-B2O3-1 and AIIa-B2O3-2 for a-B2O3 originate from an adjacent 11B atom within two different boroxol rings. The hfs tensor AIIc-B2O3 was attributed to the interaction of the unpaired electron with the next 11B atom that is three-fold coordinated. We report here the complementary use of the cw-EPR, HYSCORE, and pulsed-ENDOR spectroscopies in detecting hyperfine couplings in a glass and crystal.
Published Version
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