An enhanced absorption edge from pressure-densified vitreous SiO2

Vacuum ultraviolet absorption experiments have been done on specimens of v- SiO2, permanently densified under the high pressure of 5 GPa and at tempera tures from 450 degreesC to 900 degreesC. The curves of log of absorption co efficient alpha, versus photon energy (h) over bar omega, from specimens of density 2.52-2.61 g cm(-3), had absorption tails from 6.0 to 7.7 eV that h owever depended not on density; and they were similar to the absorption tai ls from undensified v-SiO2 of density 2.20 g cm(-3). At 7.7 eV, and alpha a bout 10 cm(-1), all curves began to rise linearly. However the curves from densified specimens rose faster, and alpha from these was about 100 cm(-1) at 8.1 eV. Some absorbing structure common to both densified and undensifie d v-SiO2 seems to be the cause of the linear absorption. But the greater sl ope, the enhanced absorption, from the densified specimens is a sign perhap s of the development of new sub-structures. (C) 2001 Elsevier Science B.V. All rights reserved.