Structure and optical properties of porous silica modified by electronic excitation process

我们详细研究了气相二氧化硅的结构和发光性能。从红外和拉曼测量的结果，它已被证明，完全烧结的透明样品的网络结构，平均而言，可比的散装石英玻璃。然而，烧结的热解法二氧化硅的FESEM图像表明，所得透明样品仍然具有源自原始热解法二氧化硅颗粒的边界和界面区域。时间分辨的PL测量已经揭示了烧结的透明样品的PL光谱由位于-410、-360和-510 nm的至少三个发射带组成。这三个发光带在不同的时间尺度上分别具有不同的衰减曲线。我们认为，陷阱控制的光激发电子的扩散是负责缓慢拉伸指数PL组件。另一方面，快速纯指数PL分量是在经历上述色散扩散过程之前由电子-空穴对的辐射重组产生的。-360-nm PL带在微秒的时间尺度上显示出纯指数衰减。所观察到的纯指数衰减意味着与360 nm PL发射相关的电子态是局部化的，并且可以简单地由两态模型表示。虽然在氧化多孔硅和多孔二氧化硅中已经报道了类似的紫外光致发光带，但目前的360 nm光致发光的衰减时间（μs）比以前报道的衰减时间（μ ns）长得多，这表明这些光致发光带有不同的起源。

We have studied the structure and PL properties of sintered fumed silica in detail. From the results of infrared and Raman measurements, it has been shown that the network structure of the fully sintered transparent sample is, on average, comparable to that of the bulk silica glass. However, the FESEM image of the sintered fumed silica demonstrates that the resulting transparent sample still has boundary and interface regions derived from the original fumed silica particles. Time-resolved PL measurements have revealed that the PL spectrum of the sintered transparent sample consists at least of three emission bands located at -410, -360, and -510 nm. These three PL bands are characterized respectively by different decay curves in different times scales. We suggest that a trap-controlled diffusion of the photoexcited electrons is responsible for the slow stretched exponential PL component. On the other hand, the fast pure exponential PL component results from radiative recombinations of electron-hole pairs before experiencing the above dispersive diffusion process. The -360-nm PL band shows a pure exponential decay in the time scale of microseconds. The observed pure exponential decay implies that the electronic states related to the 〜360-nm PL emission are localized and can be represented simply by a two state model. Although similar UV PL bands have been reported in oxidized porous silicon and porous silica, the decay time (〜μs) of present 〜360-nm PL is much longer than that of the previously reported ones (〜ns), suggesting that these PL bands have different origins.