用光致发光研究不同通量辐照磷酸二氢钾晶体的缺陷

Photoluminescence spectrum study of defects of potassium dihydrogen phosphate crystals irradiated by different laser fluences

磷酸二氢钾晶体中的缺陷对晶体的激光诱导损伤起着重要作用.晶体的激光诱导损伤限制了大功率激光系统的发展.本文用真空紫外光致发光发射谱研究了不同通量辐照下磷酸二氢钾晶体的缺陷.与11.5 J/cm^2辐照下的晶体及退役元件相比,9 J/cm^2辐照下晶体的荧光谱中在231.55 nm处出现了一个新峰.它可能源于自捕获激子的辐照湮灭.9.0 J/cm^2辐照晶体中主要是短链结构,而退役元件的损伤较复杂,有短链、中链和长链结构.短链中的P—O键比长链中的短,磷的3s轨道与氧的2p轨道重叠增加,则自捕获激子的辐照湮灭增强.结果显示出退役元件与9 J/cm^2辐照下晶体的结构不同.对研究磷酸二氢钾晶体的激光诱导损伤机制有重要意义.

The laser-induced damage to potassium dihydrogen phosphate(KDP) crystal restricts the development of high power laser systems and attract the attention of researchers. The defects are essential for the understanding of the laser-induced damage to KDP crystals. The defects in KDP crystals are commonly related to H2 PO4-groups. The defects of KDP crystal have been studied extensively, however the changes of defects of KDP crystal with low fluence and high fluence have not been investigated sufficiently. The synchrotron radiation technology is a sensitive method of detecting the defects. The vacuum ultraviolet photoluminescence(PL) emission spectra can provide microscopic structural changes in KDP crystals. In this work, we investigate the defects of KDP crystals irradiated with different fluences by vacuum ultraviolet PL emission spectra. The vacuum ultraviolet spectra are obtained at the 4 B8 beam line in Beijing synchrotron radiation facilities. Each KDP crystal spectrum is measured from 200 to 400 nm and 400 to 800 nm. The emission spectra of KDP crystal irradiated with different fluences are fitted for illustration. Each Gaussian curve represents a kind of defect. Comparing the retired components with KDP crystal irradiated by 11.5 J/cm2, the new band at 231.55 nm emerges in the spectra of KDP crystal irradiated by 9.0 J/cm2. The intrinsic luminescence band is assigned to the radiative annihilation of self-trapped excitons. According to our previous work, the short chain structures mainly exist in the crystal irradiated by 9.0 J/cm2, and the long chain structure is mainly in the crystal irradiated by 11.5 J/cm2. The retired components have the short, medium and long chain. The length of P-O bond in the short chain is shorter than that in the long chain structure. The overlap between phosphorus 3 s orbitals and oxygen 2 p increases, and the radiative annihilation of STEs becomes stronger. So the band at231.55 nm emerges in the spectrum of KDP crystal irradiated by 9.0 J/cm2. It suggests that the structure of the retired component and the structure of KDP crystal irradiated by 9.0 J/cm2 are different. The results provide an insight into the defects in KDP crystals. It is meaningful to study the mechanism of laser-induced damage to KDP crystal.