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TIME-RESOLVED SPECTROSCOPY ON ULTRAFAST NONRADIATIVE RELAXATION OF TRANSITION METAL IONS IN SOLIDS

固体中过渡金属离子超快非辐射弛豫的时间分辨光谱

基本信息

批准号：
02640247
负责人：
SUZUKI Yoshiro
金额：
$ 1.09万
依托单位：
TOHOKU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1990
资助国家：
日本
起止时间：
1990 至 1991
项目状态：
已结题

项目摘要

Trivalent cerium impurities (Ce^<3+>) in YAG crystals were selected as a model system to investigate the de-excitation mechanism of d electrons in solids. The 4f electrons at the ground state were pumped to the second-lowest 5d state (5d_b) by UV laser pulses. Then, observed were the growths of the yellow-green (YG) emission from the lowest 5d state (5d_a) by a streak camera, as well as the growths of the excited state absorption (ESA) from the 5d_a to higher excited states by a pump & prove method.Each measurement gave consistent results. The growth times (tau) at temperatures below 80K were as long as 50ps. The tau decreased above 80K to be less than 5ps at 300K. The constant tau below 80K was interpreted from a tunneling process from 5d_b to 5d_a, while the decreasing tau above 80K was from a thermally-activated process. It follows that the nonradiative transition (NRT) between 5d states occurs not dynamically, but statically after completing a thermal equilibrium in the initial 5d state.The above results predict the existence of UV emission from the metastable 5d_b state to the 4f ground state. The UV emission was successfully detected at 350 to 400nm. Agreement of the decay time of the UV emission with the tau of the ESA and YG emission supports the static mechanism of the NRT for 5d electrons.To apply the time-resolved spectroscopy to a variety of d electron systems, extension of the pumping wavelengths and improvement of the pumping methods were required. As the former examination, F^+_ centers were shown to be available for an IR pulse source, while, as the latter, a method of time-delayed double excitation was demonstrated by making use of two pulse lasers.

以YAG晶体中的三价铈杂质（Ce^<3+>）为模型体系，研究了固体中d电子的退激机制。基态的4f电子被紫外激光抽运到次低的5d态（5d_b）。然后用条纹照相机观测了黄绿（YG）发射从最低5d态（5d_a）的增长，用抽运法观测了激发态吸收（ESA）从5d_a到更高激发态的增长，每次测量都得到了一致的结果。在低于80 K的温度下的生长时间（τ）长达50 ps。τ在80 K以上降低到300 K时小于5 ps。在80 K以下的常数τ解释为从5d_b到5d_a的隧穿过程，而在80 K以上的减小的τ解释为热激活过程。结果表明，5d态之间的无辐射跃迁（NRT）不是动态发生的，而是在初始5d态达到热平衡后静态发生的，这预示了从亚稳态5d_b到4f基态的紫外辐射的存在.在350 ~ 400 nm处成功地检测到紫外发射。5d电子NRT的衰减时间与ESA和YG发射的τ的一致性支持了5d电子NRT的静态机制.为了将时间分辨光谱应用于各种d电子系统，需要扩展泵浦波长和改进泵浦方法.作为前一种检验，F^+心可用于红外脉冲光源，而作为后一种检验，通过使用两个脉冲激光器，证明了时间延迟双激发的方法。