J. Nakahara

Broad Raman scattering and luminescence in β-carotene solution

Resonant secondary radiation spectra of dilute β-carotene solution (10−4–10−5 M) are measured under stationary excitation. The excitation energy is varied within 0–0 and 0–1 transition energies in the S2–S0 transition of β-carotene. When the excitation energy is varied from the peak of the 0–0 absorption band to the low-energy side at 60 K and 175 K, (a) the line shape of 0–0 emission band changes from symmetric to asymmetric, and (b) the intensity of luminescence rapidly decreases as compared with the intensity of Raman scattering by ν1, ν2, and ν3 intramolecular vibronic modes of β-carotene. When the 0–1 absorption band is excited, we successfully separate luminescence and broad Raman component (BR), which is resonant Raman scattering of low-frequency phonon modes in solution. The line shape of the density of vibronic states weighed by the coupling strength between electronic states in a dye molecule and vibrations of the surrounding atoms (WDOS) is determined by BR. Taking into account inhomogeneous br...

Pressure dependence of low-frequency light scattering in carbon disulfide

Abstract The pressure dependence of low-frequency vibrational density of states, ρ ( ω ), for liquid and crystalline carbon disulfide (CS 2 ) is determined by measurement of light-scattering spectra using diamond anvil cell. In the liquid, a broad band is observed and in crystalline CS 2 , sharp peaks are observed under high pressure. Molecular dynamics calculations predicted that these sharp spectra come from the librational mode. We indicate experimentally that the origins of spectra obtained in liquid and crystalline CS 2 are the same.

Magneto-photoluminescence in Cd1−xMnxTe

Abstract Photoluminescence (PL) spectra near the fundamental absorption edge are investigated in Cd 1− x Mn x Te ( x = 0.03 to 0.3) at 4.2 K in magnetic fields up to 23 T for Faraday configuration. For PL of free excitons and neutral-donor(acceptor)-bound-exciton transitions in low concentration of Mn ( x = 0.03 and 0.05), diamagnetic shifts are observed in the region of high magnetic fields. In the case of x = 0.1 and 0.3 the decrease in energy of these PL peaks is observed in the region of high magnetic fields with increasing magnetic fields corresponding to magnetization steps and large phenomenological temperature T 0 describing spin interaction. We determine exchange integrals and T 0 using the magnetic field dependence of PL peaks. For x ≤ 0.1 PL spectra of self-trapped magnetic polaron are observed but they disappear at low magnetic fields as ∼1 T.

OPTICAL KERR EFFECT IN CARBON DISULFIDE UNDER HIGH PRESSURE

The optical heterodyne spectroscopy of optical Kerr effect (OKE) in liquid carbon disulfide (CS2) was performed under various high pressures using a diamond anvil cell (DAC). The relaxation time of orientation was determined up to 1.20 GPa at 295 K using OKE signals. It increased from 1.6 ps at atmospheric pressure to 10.7ps at 1.20 GPa. Low-frequency light scattering (LFLS) spectra were measured in order to compare the intermolecular dynamical processes in liquid CS2 with those of crystalline CS2. A damped oscillation in OKE is found as a precursor of librational motion observed in crystalline state. This change shows that the intermolecular dynamical processes in the liquid vary gradually to that in crystal with increasing pressures.

Temperature Dependence of Inhomogeneous Broadening and Mn2+ Photoluminescence Energy Shift in CdMnTe

Energy shift in Mn2+ photoluminescence relating with an excitation energy was observed in CdMnTe at low temperature. The shift is considered as the selective excitation of inhomogeneously broadened states. Using this shift we estimated the inhomogeneous broadening of the d-d transition in Mn2+ ions. The temperature dependence of the inhomogeneous broadening is discussed.

Growth of zincblende MgSZnSe superlattices and their heterointerface properties

Abstract MgS naturally forms the rocksalt structure, but zincblende MgS ZnSe superlattices were grown with atmospheric-pressure MOVPE. The lattice constant of zincblende MgS was determined to be 5.59 A from a series of X-ray measurements. The purging effect during the growth of MgS ZnSe heterointerfaces was studied. While purging with a Se precursor resulted in the formation of an extra MgSe-related interface layer, purging with a Zn precursor improved the abruptness of the heterointerfaces.

Large Lattice Distortion and Infrared Photoluminescence in Cd1-xMnxTe

The infrared photoluminescence near 1.15eV (IR PL) in Cd 1-x Mn x Te is investigated under high pressures up to 20kbar and at wide temperature range. Using a configuration coordinate model, we propose that relaxed excited states of Mn 2+ have two minima, and the excited states of IR PL has larger lattice relaxation than that of excited states of Mn 2+ PL. Also distorted ground state without metastable states is the final states of IR PL. Thermal barrier from Mn 2+ excited state to excited state of IR PL is 36meV

The energy relaxation in intermediate state of second-order optical processes in dye molecules in solution

Abstract The excitation energy dependence of the peak energy of the 0-0 luminescence band of β-carotene in isopentane has been measured at various temperatures. It is analyzed using the two-dimensional configuration coordinate model. Assuming that the nature of the intermediate state interaction for a second-order optical process in this system is in slow modulation, we calculate the amplitude of the energy modulation using the value of the observed Stokes shift and compare it to that derived from the analysis of the excitation profiles of Raman scattering and luminescence. They are in good agreement with each other, which indicates that the observed energy shift of the luminescence and the excitation profiles of second-order optical processes can be understood by the stochastic motion on the adiabatic potential curves.

Temperature dependence of luminescence in mixed crystals

Abstract It is reported that the temperature dependence of integrated luminescence intensity in Al x Ga 1- x As and Cd 1- x Mn x Te obeys 1/(1+ A exp ( T / T 0 )). By analogy with the discussions of temperature dependence of luminescence in amorphous materials, we presume that a mobility edge and localized tail states exist at the edge of amalgamation bands of mixed crystals. The tail states below their edge become narrower at larger x (0.4⪖ x ⪖0.1 in the present study). The same dependence is observed for the luminescence from magnetic polarons bound to potential fluctuations (BM).

Observation of ‘broad Raman’ component in resonant secondary radiation

Abstract The broad Raman component in resonant secondary radiation in β-carotene solution is observed for the first time. The characters obtained are as follows: the line shape is independent of excitation energy; the Stokes to anti-Stokes intensity ratio is n(ω)+1: n(ω) with a Bose factor n(ω); the width at Stokes side is about 150 cm −1 ; the integrated intensity decreases toward off-resonant excitation. The broad Raman component has the detailed information on electron–phonon interaction and optical dephasing.