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We report an experimental study by electron paramagnetic resonance  EPR  of  -ray irradiation induced\udpoint defects in oxygen deficient amorphous SiO2 materials. We have found that three intrinsic  E  , E  , and\udtriplet  and one extrinsic   AlO4 0  paramagnetic centers are induced. All the paramagnetic defects but E  \udcenter are found to reach a concentration limit value for doses above 103 kGy, suggesting a generation process\udfrom precursors. Isochronal thermal treatments of a sample irradiated at 103 kGy have shown that for T\ud 500 K the concentrations of E   and E   centers increase concomitantly to the decrease of  AlO4 0. This\udoccurrence speaks for a hole transfer process from  AlO4 0 centers to diamagnetic precursors of E  centers\udproving the positive charge state of the thermally induced E   and E   centers and giving insight on the origin\udof E   from an oxygen vacancy. A comparative study of the E   center and of the 10 mT doublet EPR signals\udon three distinct materials subjected to isochronal and isothermal treatments has shown a quite general linear\udcorrelation between these two EPR signals. This result confirms the attribution of the 10 mT doublet to the\udhyperfine structure of the E   center, originating from the interaction of the unpaired electron with a nucleus of\ud29Si  I=1/2 . Analogies between the microwave saturation properties of E   and E   centers and between those\udof their hyperfine structures are found and suggest that the unpaired electron wave function involves similar Si\udsp3 hybrid orbitals; specifically, for the E   the unpaired electron is supposed to be delocalized over four such\udorbitals of four equivalent Si atoms. Information on the structural model of the triplet center are also obtained\udindicating that it could consist of the same microscopic structure as the E   but for a doubly ionized state

physical review. b, condensed matter and materials physics

Characterization of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mmultiscripts><mml:mi mathvariant="normal">E</mml:mi><mml:none /><mml:mo>′</mml:mo><mml:mi>δ</mml:mi><mml:none /></mml:mmultiscripts></mml:math>and triplet point defects in oxygen-deficient amorphous silicon dioxide

Characterization ofE′δand triplet point defects in oxygen-deficient amorphous silicon dioxide