1996 Fiscal Year Final Research Report Summary
ELEMENTARY RELAXATION PROCESSES IN PHOTO-EXCITED STATES IN THE WEAK ELECTRON-LATTICE COUPLING SYSTEM
| Project/Area Number |
06452047
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体物性Ⅰ(光物性・半導体・誘電体)
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| Research Institution | OKAYAMA UNIVERSITY |
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Principal Investigator |
NAKAMURA Kaizo OKAYAMA UNIV.PHYSICS PROFESSOR, 理学部, 教授 (40025359)
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| Co-Investigator(Kenkyū-buntansha) |
SUEMOTO Tohru TOKYO UNIV.ISSP ASSOCIATE PROF., 物性研究所, 助教授 (50134052)
ARIMOTO Osamu OKAYAMA UNIV.PHYSICS ASSOCIATE PROF., 理学部, 助教授 (70193092)
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| Project Period (FY) |
1994 – 1996
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| Keywords | EXCITON POLARITON / RELAXATION PROCESSES / ZINC DIPHOSPHIDE / ELECTRON-LATTICE INTERACTION / WEAK COUPLING SYSTEM / RESONASNCE RAMAN / INTER-SYSTEM CROSSING / MAGNETIC FIELD EFFECTS |
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| Research Abstract |
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
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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
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