釕摻雜鈦酸鉍的光激發性質

Abstract

本論文是研究鈦酸鉍晶體摻雜不同濃度釕（Ruthenium）的一些光激發性質。 光折變晶體，尤其是 硫化物（sillenite）晶體，顯露的性質對非線性光學利用很有前途。 不過它們光激發吸收的物理過程還沒完全瞭解。 跟BSO (Bi12SiO20)和BGO (Bi12GeO20)比較，BTO沒有被深入的研究。 而且，過去還沒有釕摻雜鈦酸鉍（BTO：Ru）的研究。 本論文會提到在非線性光學材料裡的能帶結構跟電荷移動。 再來我們用單能階與雙能階的模型來解釋光折變效應和光致色變效應這兩個現象。 最後提出一個模型來說明BTO：Ru 的光激發性質：能帶結構有一個深能階，兩個淺能階；光激發吸收的過程類似雙能階的。 為了多瞭解釕摻雜對鈦酸鉍光學性質的效果，我們做了光致色變效應的光譜，光激發吸收的動態響應，和光電導率實驗。鈦酸鉍摻雜低濃度（1018/cm3）的釕還跟無摻雜很像，只是它的光吸收比較高。 到一個等中的濃度(1019/cm3)，除了吸收增加以外，吸收光譜也移動到比較長的波長。 表示釕摻雜增加淺能階的載子數目，所以紅光的光激發吸收效應增強。

The present thesis examines the light induced properties of bismuth titanate Bi12TiO20 (BTO) with various concentrations of ruthenium doping. Photorefractive crystals, in particular sillenites, display promising characteristics for use in non-linear optics applications, however information available on light-induced absorption in these is not yet complete. BTO has been less extensively studied than the other two sillenites, BGO and BSO, and studies on the dopant ruthenium for BTO have not previously been reported. Basic description of charge transport and structure of energy levels within the band-gap of materials displaying non-linear optical phenomena shall be presented. The photorefractive effect and the photochromic effect are discussed, and explained in terms of one- and two-level models, respectively. A band structure analogous to the two-level model but with two relatively shallow levels is hypothesized as the mechanism responsible for light induced absorption in BTO crystals. Photochromic effect spectroscopy, light induced absorption, and photoconductivity experiments were carried out in order to further understand the effect of ruthenium doping on BTO optical properties. BTO with a ruthenium concentration of 1018/cm3 is quite similar to the undoped BTO, only with higher optical absorption. A higher concentration (1019/cm3), however, not only increases the absorption but also shifts the absorption shoulder to longer wavelengths. The addition of ruthenium results in the increase of shallow centres, and consequently a stronger light induced absorption effect, which in the present case is in the red region.