Inhomogeneous nature of UV absorption bands of bulk and surface oxygen-deficient centers in silica glasses

Luminescent silicon nanocrystals produced by near-infrared nanosecond pulsed laser ablation in water

“…In particular, on the basis of the comparison with literature data, both PL bands are assigned to oxygen deficient centers in amorphous SiO 2 [28]. In fact, these luminescent defects are observed in irradiated or oxygen-deficient silica, both in bulk and in porous film with high specific surface [29,30]. The most accepted defect model is the twofold coordinated Si, =Si••, where the symbol (••) stands for two paired electrons [31].…”

Photoluminescence time decay of surface oxygen deficient centers in un‐doped and Ge‐doped silica

“…4,8. An absorption band around ∼5.3 eV in the silica and one at 5.4 eV in the Ge-doped sample prove the presence of two-fold coordinated centers stabilized on the surface [4,6]. Photoluminescence measurements were done with pulsed excitation in the range from 4.5 eV to 9.0 eV by synchrotron light at the SUPERLUMI station on the I-beamline of HASYLAB at DESY (Hamburg) [10].…”

“…In a subsequent luminescence study it was shown that each of these centers is characterized by optical absorption around 5 eV, and two photoluminescence (PL) bands around 4 eV and 3 eV, attributed to singlet-singlet and triplet-singlet radiative relaxations connected by a non radiative intersystem-crossing (ISC) process [1][2][3][4][5][6][7][8]. This process has been studied by stationary and time resolved photoluminescence measurements and it has been shown that it is affected by the temperature and by the inhomogeneity of the amorphous matrix [5][6][7][8]. The two-fold coordinated >Si: and >Ge: centers can be stabilized on the surface of pressed porous silica [4], and they are characterized by an enhanced ISC process with respect to the bulk variant [2][3][4].…”

Oxidation of silicon nanoparticles produced by nanosecond laser ablation in liquids

“…We note that this defect is also present at the silica surface with spectroscopic features slightly different from the defect in the bulk. In particular, the ISC rate is more active at the surface than in the bulk, as demonstrated by the different ratio between the 2.7 eV and 4.4 eV PL intensities [12]. Since these characteristics are not observed in our colloidal solution, we rule out the contribution of surface defects.…”