Investigation of the medium range structure of phosphosilicate glasses by cw-EPR, 1D-ESEEM and HYSCORE spectroscopies

6Li2O 3P2O5 6SiO2 and 6Na2O 3P2O5 6SiO2 glasses were exposed to 60Co γ-ray irradiation for the production of paramagnetic states that were studied by continuous wave(cw)-EPR, 1D-electron spin echo envelop modulation (ESEEM) and hyperfine sublevel correlation (HYSCORE) spectroscopies. The cw-EPR signal consisted of a doublet separated by ≈47 G. This doublet was assigned to the Qn=2-type center (POHC-defect). The analysis of the 1D-ESEEM peaks determined the Aiso and T⊥ parameters. Using the point dipole approximation for T⊥, the r(P–O–P)-distance was estimated to be ≈2.83 and ≈3.49 Å while the P–O–P bond angle was determined to be ≈107° and ≈168° for Li and Na containing glasses, respectively. HYSCORE spectroscopy unveiled the presence of alkali metal ions in close proximity to the phosphorus oxygen hole center (POHC). The experimental findings together with SCF-HF calculations suggested the existence of the POHC–POHC–Li/Na complex (Q2–Q2–Li/Na-structure) in the glasses. It has been demonstrated that the advanced EPR techniques extend the spatial resolution of the cw-EPR spectroscopy to the medium range structure of the amorphous state.