Time-resolved spectroscopy of colloidal ZnO nanoparticles has been carried out with a laser excitation at 248 nm. UV and visible fluorescence has been analyzed. Except for the known band gap 370-nm and impurity 510-nm emissions, we have found additional continua at ∼300, 430, and 545 nm. These continua were developed in solutions of different composition, with excess Zn and OH ions, and in function of time. All but 510-nm fluorescence bands exhibit short nanosecond or subnanosecond decays. The green fluorescence at 510 nm originating from 4-nm particles in Zn-rich solutions is a much longer-lived, 1.0 μs. The band natures are discussed. Cluster size distribution and growth kinetics have been recovered from spectral measurements.

Photoluminescence of polycrystalline hexagonal boron nitride ͑hBN͒ was measured by means of time-and energy-resolved spectroscopy methods. The observed bands are related to donor-acceptor pair transitions, impurities, and structural defects. The excitation of samples by high-energy photons above 5.4 eV enables a phenomenon of photostimulated luminescence ͑PSL͒, which is due to distantly trapped conduction band electrons and valence band holes. These trapped charges are metastable and their re-excitation with low-energy photons results in anti-Stokes photoluminescence. The comparison of photoluminescence excitation spectra and PSL excitation spectra allows band analysis that supports the hypothesis of Frenkel-type exciton in hBN with a large binding energy.

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