Excitation states and defect formation in high purity silica glass under gamma-ray or excimer-laser irradiation

本研究的目的是阐明a-SiO_2中点缺陷的结构和光学性质，以及在电离辐射或激光光子作用下的形成机制。重点放在（i）预先存在的抗磁性缺陷和辐射诱导的顺磁性缺陷的表征，以及（ii）建立的抗磁性缺陷和辐射诱导的顺磁性缺陷之间的联系。本研究的主要内容如下：1.确认了与过量氧有关的缺陷和光学吸收带。确定了两种形式的过量氧：过氧键和间隙氧。在3.8eV处的光吸收带与过氧键有关。2.对7.9eV光子诱导的新的顺磁缺陷进行了表征。通过对ESR谱的计算机模拟分析，确定顺磁缺陷为ClO_x自由基（x= 2，3）。3.在7.9eV脉冲激光激发下，对一系列SiO_2样品进行了时间分辨光致发光（PL）测量。研究了几个PL谱带与点缺陷的相关性。4.研究了6.4eV准分子激光在一系列石英样品上诱导的顺磁缺陷。氧的化学计量和羟基含量上的缺陷物种和它们的浓度的影响进行了观察。5.利用电子自旋共振（ESR）和紫外-真空紫外（UV-VUV）光吸收测量，以6.4eV和7.9eV光子和γ射线为辐照源，研究了顺磁缺陷产生的光子能量依赖性。研究了激光诱导顺磁缺陷与反磁缺陷之间的关系。6.用ESR和UV-VUV吸收测量研究了氢对E'心光生的影响。发现氢的存在增强了中性氧空位产生E'心的能力。

The purpose of this study is to clarify the structural and optical properties of point defects in a-SiO_2, and their formation mechanisms under ionizing radiations or laser photons. The emphasis is placed on (i) the characterization of preexisting diamagnetic defects and radiation-induced paramagnetic defects, and (ii) the establishment of the link between the diamagnetic defects and radiation-induced paramagnetic defects. The outline of the present study is as follows.1.Defects and optical absorption bands associated with excess oxygen are identified. Two forms of excess oxygen are identified: peroxy linkage and interstitial oxygen. An optical absorption band at 3.8 eV is associated with peroxy linkages.2.Characterization of new paramagnetic defects induced by 7.9-eV photons is performed. With the help of computer simulation analyses of the ESR spectra, the paramagnetic defects are identified to be ClO_x radicals (x=2,3).3.Time-resolved photoluminescence (PL) measurements are carried out on a series of silicas under 7.9-eV pulsed laser excitation. Correlations of several PL bands with point defects are studied.4.Paramagnetic defects induced by 6.4-eV excimer laser are studied on a series of silicas. Effects of the oxygen stoichiometry and hydroxyl content on the defect species and their concentrations are observed. It is shown that precursor transformation dominates in laser-induced defect formation.5.Photon-energy dependence of the creation of paramagnetic defects is investigated by means of ESR and uv-vuv optical absorption measurements, using 6.4-eV and 7.9-eV photons, and gamma rays as irradiation sources. Correlations between the preexisting diamagnetic defects and laser-induced paramagnetic defects are investigated.6.The effect of hydrogen on the photogeneration of E' centers is studied by means of ESR and uv-vuv absorption measurements. It is found that the creation of E' centers from neutral oxygen vacancies is enhanced in the presence of hydrogen.