Fluorescence properties have been studied for Mn:ZnS crystallites with average diameter of 4 nm prepared by an aqueous colloidal method under 266 nm light excitation. The intensity ratio of the blue band at ∼430 nm to the orange band at ∼590 nm has decreased after the preparation on a time scale of hours in aqueous solution. On the other hand, hyperfine structures of Mn 2+ in the electron paramagnetic resonance spectrum have increased markedly on the same time scale in solution samples. These phenomena are attributed to the redistribution of defect centers in nanocrystals. Such phenomena have not been observed in samples incorporated into poly(vinyl alcohol). The orange emission is mainly due to the 6 A 1 r 4 T 1 transition of Mn 2+ , while the blue emission is tentatively assigned to the donor-acceptor pair transition in which the acceptor is related to the Zn 2+ vacancy. Fluorescence decay times of the blue and orange bands have been found to be ∼10 ns and ∼1 ms, respectively, the latter being the same as in the bulk samples. A weak fluorescent component with fast kinetics observed in the orange region has been identified as a tail of the blue band. No lifetime shortening of the Mn 2+ emission due to quantum confinement has been observed, contrary to reports in the literature.

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The ultrafast photoinduced dynamics of photoactive yellow protein in aqueous solution were studied at room temperature by femtosecond fluorescence spectroscopy using an optical Kerr-gate technique. Coherent oscillations of the wave packet were directly observed in the two-dimensional time-energy map of ultrafast fluorescence with 180 fs time resolution and 5 nm spectral resolution. The two-dimensional map revealed that four or more oscillatory components exist within the broad bandwidth of the fluorescence spectrum, each of which is restricted in the respective narrow spectral region. Typical frequencies of the oscillatory modes are 50 and 120 cm(-1). In the landscape on the map, the oscillatory components were recognized as the ridges which were winding and descending with time. The amplitude of the oscillatory and winding behaviors is a few hundred cm(-1), which is the same order as the frequencies of the oscillations. The mean spectral positions of the oscillatory components in the two-dimensional map are well explained by considering the vibrational energies of intramolecular modes in the electronic ground state of the chromophore. The entire view of the wave packet oscillations and broadening in the electronic excited state, accompanied by fluorescence transitions to the vibrational sublevels belonging to the electronic ground state, was obtained.