Photochemical generation of E′ centres from Si–H in amorphous SiO₂under pulsed ultraviolet laser radiation

Abstract

In situ optical absorption spectroscopy was used to study the generation of E' centres (≡Si•) in amorphous SiO 2 occurring by photo-induced breaking of Si-H groups under 4.7eV pulsed laser radiation. The dependence from laser intensity of the defect generation rate is consistent with a two-photon mechanism for Si-H rupture, while the growth and the saturation of the defects are conditioned by their concurrent annealing due to reaction with mobile hydrogen arising from the same precursor. A rate equation is proposed to model the kinetics of the defects and tested on experimental data.

Generation and excitation of point defects in silica by synchrotron radiation above the absorption edge

“…[12][13][14][15] While the detrimental influence of point defects on the performance of silica in applications is a well established fact, defects are still the subject of ongoing research aimed to clarify several poorly understood aspects of their generation processes, the factors determining their stability or instability, as well as some of their most basic spectroscopic properties. In regard to the formation mechanisms, while several works have investigated the generation of EЈ and NBOHC centers induced by high-power laser ͑up to 7.9 eV photon energy͒ or ionizing radiation, [16][17][18][19][20][21][22][23][24][25][26] little information is available on possible generation of these defects upon exposure of SiO 2 to low power above-edge VUV radiation.…”

Temperature dependence of the generation and decay of E′ centers induced in silica by 4.7eV laser radiation

“…Previous experiments allowed to propose the following model for the generation of E 0 centers in fused silica at room temperature [18][19][20]: the main generation process of defects is the laser-induced breaking of Si-H precursors:…”

“…Aside from E 0 center, this process generates H atoms which dimerize in H 2 and react with E 0 centers in the post-irradiation stage causing their partial decay in a time scale of a few hours [18][19][20]:…”

“…An important feature of the E 0 center, shared by other paramagnetic defects, is that it can be annealed by reaction with diffusing H 2 [10,12,[14][15][16][17][18][19][20]. This process is widely exploited in optical fibers technology where H 2 loading of the SiO 2 core material is used to prevent it from being damaged by UV light.…”

“…Since passivation of E 0 by H 2 is thermally activated as well, the presence of hydrogen may be expected to influence the temperature dependence of the formation efficiency of the defects, due to the interplay between generation and passivation. To thoroughly investigate this issue it is needed to measure in situ the kinetics of the defects in temperature-controlled experiments [16,[18][19][20], in contrast with previous works that measured only the stationary concentration of E 0 centers [4,5,[8][9][10][11] …”