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We propose a vertical transport of the photo-excited carriers under the influence of the two dimensional carrier gas (2DCG) in GaAs Ga 1−x Al x As heterojunctions before excitonic recombination. The vertical transport is responsible for a long photoluminescence (PL) rese time of the excitonic transitions as well as for the PL intensity oscillations with magnetic field. The vertical transport is proved for the first time by resonant PL intensity variation at the cyclotron resonance condition of the 2DCG, by which the effective masses of two dimensional electrons as well as two dimensional holes in the n- and p-type heterojunctions are determined.

The magnetization M of Sn 1− x Eu x Te:EuTe, x ≦0.02, has been measured at 4.2 K in fields H up to 23 T. The average pair exchange interaction is antiferromagnetic with a value of about 0.5 K. For x -values greater than 0.014 the M vs. H curves show a definite knee with approximately linear behavior above and below the knee. The knee in the magnetization data and a cusp in the susceptibility at about 10 K are related to the presence of EuTe clusters in our samples.

We have observed dispersive two-phonon Raman scattering of polaritons by LO and acoustic phonons near the lowest exciton state of ZnTe. From the Stokes shifts of these Raman lines, it has been found that the scattering process switches from an acoustic phonon followed by one LO phonon to the reversed one: a LO phonon followed by an acoustic one.

Luminescence spectra of excitonic molecules in CuCl resonantly created by nano-second dye laser excitation are measured at 4.2 K changing the lenghts of the excited region. The spectra are dominated by stimulated emission. The gain coefficient for the MT line is saturated more easily than that for ML, though the former is larger under unsaturated conditions. These gain characteristics explain well various stimulated emission effects observed.

Mn 3 d states in Cd 1- x Mn x Y ( Y = S, Se and Te have been investigated by using synchrotron radiation photoemission. The Mn 3 d partial density-of-states spreads over the whole valence bands as a result of strong p-d hybridization with a prominent peak at 3.3–3.4 eV below the valence band maximum. Degree of hybridization between the majority-spin Mn 3 d and anion p states increases on going from Te to S.

Fluorescence decay has been studied in rhodamine 6G (R6G) molecules adsorbed on a Ag electrode. The fluorescence from the lowest-excited singlet-state ( S 1 ) of the adsorbed R6G consists of the decay component less than 50 psec and of 4.5 nsec. Intense Raman scattering (RS) are also observed. The fast-decaying fluorescence arises from the R6G's adsorbed on the Ag surface within a distance of 50A, which simultaneously give rise to the intense RS. The slowly-decaying fluorescence is due to layers of the R6G's well separated from the Ag surface. The relationship between the surface enhancements of fluorescence- and RS-intensities in the adsorbed R6G is discussed.

Fluorescence spectra due to the free excitons have been studied in CdS at 4.2 K under various excitation levels. It has been found that the triplet-exciton emission intensity relative to the singlet line is enhanced remarkably with the excitation power density. This effect is reasonably explained by the mixing of the singlet with the triplet through the many body interaction. The density of optically generated excitons is determined from the magnetic field dependence of the triplet emission intensity.

Absorption bands have been found at 655 and 830 nm in a Mn2+-doped ZnS crystal under intense optical excitation. From the close correlation to the orange fluorescence, these bands are ascribed to the transitions from the emitting state 4 T 1 ( 4 G) of Mn2+. This observation of the excited-state absorption makes it possible for the first time to locate higher excited levels of impurity ions hidden behind the strong fundamental absorption of the host material by a direct optical absorption method. Assignments for the terminal states of the observed absorption transitions are discussed.

Population and spin relaxation rates concerned with exciton luminescence and multiple LO-phonon emission lines are studied in ZnTe at 77 K by means of optical circular polarization correlation between the exciting and emitted lights. The decay times of the LO lines are determined to be much less than 10 -11 sec, which are definitely shorter than the obtained exciton lifetime of 10 -10 -10 -9 sec. It is concluded that the LO lines are not due to hot luminescence but due to resonance Raman scattering.

Spectral responses of magneto-photoconductivity have been studied on the semimagnetic semiconductor Cd 0.8 Mn 0.2 Te at T=4.2 K. In external magnetic fields up to 60 k0e, anomalously large shifts of E g toward lower energy with dramatic change of spectral shape and decrease of the binding energy of bound excitons were observed. Magnetic field dependence of photoconductivity shows that their various behaviours are not due to change of mobility, but mainly due to that of carrier number in external magnetic fields. Sign of the Hall effect indicates that dominant photocarriers are electrons and the value of Hall mobility of photoelectrons reaches about 5000 cm 2 /V·s at T=4.2 K in semimagnetic semiconductor Cd 0.8 Mn 0.2 Te.

The degree of circular polarization of the free-exciton luminescence line has been measured in GaSe excited by circularly polarized light at 4.2 K under longitudinal magnetic field. The result shows that the spin relaxation time of exciton is field-dependent but the spin memory before reaching the exciton ground state is almost unaffected by the applied longitudinal magnetic field.

Optic phonons in CuClCuBr mixed crystals have been studied by means of Raman scattering and infrared absorption measurements. It is concluded that this system belongs to the two-mode type. The observed behaviour of the phonon mode is accounted for by the modified random-element-isodisplacement model fairly well. In connection with this interpretation, the origin of the double peak in the pure CuCl is discussed.