ELEMENTARY RELAXATION PROCESSES IN PHOTO-EXCITED STATES IN THE WEAK ELECTRON-LATTICE COUPLING SYSTEM

为了研究激子极化激元的内部结构和光激发态弛豫过程的动力学，我们研究了单斜晶系二磷化锌β-ZnP 2晶体的共振二次发射。β-ZnP_2晶体是目前已知的电子-晶格耦合最弱的模型体系。在本课题的研究过程中，我们得到了如下结果：1）在从n= 2，3，4等高激子态的弛豫过程中，谐振2LO拉曼过程与普通1 LO散射过程一样也是重要的。2)在三重态激子发光的激发光谱中，我们发现了非常尖锐的类氢系列，直到n=9。另一方面，从三重态到单重态激子极化激元发光的转换只发生在新的尖锐激子系列n <greater than or equal>3，这是不同的s-类系列，但与d-类来自s-d混合。日 ...更多信息 这一结果对激子的内部结构提出了新的问题。3)在磁场作用下，激发光谱中的这些峰显示出尖锐精细的特征塞曼分裂。在三重态激子发光光谱中也观察到精细的二色性塞曼图案。这些结果在布拉格举行的国际发光会议上发表。一个研究生课程的学生在此基础上获得了理学博士学位。4)已经观察到三重态激子发光的衰减时间为纳秒量级，太短而不能用非常小的振子强度10^来解释<-6>。从详细的分析中发现，三重态激子容易形成激子分子。反斯托克斯激发谱实验表明，三重态激子有可能通过吸收声学声子而转变为单重态。这是迄今为止在中强电子-晶格耦合系统中没有发现的新弛豫过程。结合多特蒙德的Froehlich教授在超拉曼实验中测定的三重态激子极化激元的色散曲线，使弛豫速率的数值分析成为可能。5)在另一种多晶型α-ZnP_2中，通过发光温度的变化，清楚地证实了双声子辅助的间接激子发光。这一结果已在德国国际激子会议上发表，并发表在JPSJ上，目前正与东京ISSP大学合作进行β-ZnP_2发光的温度变化实验，与京都大学合作进行时域实验，与多特蒙德大学合作进行非线性光谱实验。少

We have investigated the resonant secondary emission from the monoclinic zinc diphosphide beta-ZnP2 crystal in order to clarify the internal structure of exciton polariton and also the dynamics of the relaxation processes in the photo-excited states. The crystal beta-ZnP_2 is proved to be the model system of the weakest electron-lattice coupling as far as we are aware of. In the course of this project, we have obtained following results ;1) In the relaxation from the higher exciton states as n=2,3,4 etc., the resonant 2LO Raman process is also important as is the ordinary 1LO scattering process. 2) In the excitation spectrum of the triplet exciton luminescence, we found very sharp Hydrogen-like series up to n=9. On the other hand, conversion from the triplet state to the singlet exciton polariton luminescence occurs only from the new sharp exciton series for n<greater than or equal>3, which is different from s-like series, but associated with d-like ones derived from the s-d mixing. Th … More is result poses a new problem upon the internal structure of the exciton. 3) Under the magnetic field, those peaks in the excitation spectra shows sharp fine characteristic Zeeman splitting. Fine dichroic Zeeman patterns are also observed in the triplet exciton luminescence spectra. These results were presented at the International Conference on Luminescence in Prague. A graduate course student obtained D.Sc.on the basis of there results. 4) Decay time of triplet exciton luminescence has been observed to be of the order of nanosecond, too short to be explained by using the very small oscillator strength of 10^<-6>. From the detailed analysis, it is found that the triplet excitons easily form exciton molecules. There is a possibility that triplet excitons are transferred into the singlet state by absorbing acoustic phonons which was suggested by the experiment of anti-Stokes excitation spectra. This is the new relaxation process so far not found in the intermediate and strong electron-lattice coupling systems. Together with the dispersion curve of triplet exciton polariton determined by the hyper-Raman experiment by Prof.Froehlich in Dortmund, numerical analysis of relaxation rate seems to become possible. 5) In another polymorph alpha-ZnP_2, two-phonon assisted indirect exciton luminescence is clearly confirmed through the temperature change of luminescence. This result was presented at the international conference of exciton in Germany and also published in JPSJ.Collaboration is still in progress in ISSP Univ.Tokyo on the temperature change experiment of the luminescence in beta-ZnP_2 , also in Kyoto on the time domain experiments and in Dortmund Univ.on the nonlinear spectroscopy. Less