Annual Report 2012 - Latvijas Universitātes Cietvielu fizikas institūts

enables sensitive and selective detection of interstitial O 2 . Advantages of this method
and results of evaluation of oxygen exchange between interstitial O 2 and the a-SiO 2
network are presented.
OXYGEN-EXCESS-RELATED POINT DEFECTS IN GLASSY/AMORPHOUS
SiO 2 AND RELATED MATERIALS
L. Skuja, (a) K. Kajihara, (b) M. Hirano, (c) and H. Hosono (c,d)
(a)
Institute of Solid State Physics, URiga, Latvia
(b)
Department of Applied Chemistry, Graduate School of Urban Environmental
Sciences, Tokyo Metropolitan University, 1-1 Minami-Osawa,
Hachioji 192-0397, Japan
(c)
Frontier Collaborative Research Center, Mail Box S2-13, Tokyo Institute of
Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
(d)
Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta,
Midori-ku, Yokohama 226-8503, Japan
An insight is given into recent experimental advances in the spectroscopic studies of
oxygen-excess intrinsic defects, in glassy SiO 2 and α-quartz. By controlling excess
oxygen in a-SiO 2 , and the conditions of F 2 -laser irradiation, SiO 2 glass samples can be
obtained with optical absorption almost exclusively dominated by single defect, oxygen
dangling bonds ("non-bridging oxygen hole centers" or NBOHCs), without the presence
of complementary Si dangling bonds (generic “E’-centers”). This allows for a more
accurate determination of the spectral shape of NBOHC optical absorption in UV and
vacuum UV spectral regions. The temperature dependence of NBOHC electron
paramagnetic resonance (EPR) signal intensity is stronger than predicted by Curie’s law
(1/T) even at temperatures at and below 77K. Dangling bonds are characteristic of an
amorphous state and do not exist in a regular crystal lattice. However, site-selective
luminescence shows that highly ordered NBOHCs exist in particle-irradiated α-quartz,
evidently either on the border between the damage tracks and the crystalline phase or as
a part of Si vacancies. They are different from the common “glass-like” NBOHCs in a-
SiO 2 by giving distinct sharp zero-phonon lines with characteristic energies in
luminescence spectra instead of a continuous distribution of lines. Two distinct types of
luminescent NBOHCs, associated with the long and short Si-O bonds in α-quartz are
suggested. EPR data corroborate the presence of oriented NBOHCs in neutron-irradiated
α-quartz and confirm distinct NBOHCs at the sites of “long” and “short” Si-O bonds in
α-quartz.
Scientific publications
1. L. Skuja, K. Kajihara, M. Hirano, H. Hosono, Oxygen-excess-related point defects in
glassy/amorphous SiO 2 and related materials Nuclear Instruments and Methods in
Physics Research Section B. v.286, p.159-168 (2012) .
2. K.Kajihara, L.Skuja, H. Hosono, 18 O-labeled interstitial oxygen molecules as probes
to study reactions involving oxygen-related species in amorphous SiO 2 , J. Non-
Crystalline Solids vol. 358 3524–3530 (2012).
3. I Mihailovs, J Kreicberga, V Kampars, S Miasojedovas, S Juršenas, L Skuja and M
Rutkis, Hyper-Rayleigh scattering and two-photon luminescence of phenylamineindandione
chromophores, IOP Conf. Series: Materials Science and Engineering, vol.
38 p.012035 (2012) .
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