1 Introduction Considerable interest has been paid to ZnO-based II-VI semiconductors because of their suitable properties for short wavelength optoelectronic applications. Since stimulated emission and room temperature lasing from an electron-hole plasma (EHP) and an exciton-exciton collision process with a low threshold were observed in ZnO epitaxial thin films [1, 2], investigation to reveal dynamics of such high density carriers are highly desired both in fundamental interest and applications. Many attempts to clarify the carrier dynamics have been carried out by femtosecond spectroscopy [3][4][5][6]. However, carrier diffusion which might affect determination of the carrier relaxation and lifetime has been neglected so far. Here, we report on both the relaxation and diffusion of the photoexcited high density carriers in the EHP state in ZnO epitaxial thin films studied by femtosecond transient grating spectroscopy.

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The effective ion-exchange capacities of ion-exchange materials were determined by measuring the change in the equilibrium conductivity of a column packed with analyte. The developed instrumental method can provide effective ion-exchange capacities for both cation and anion exchangers with simple operations. The cation-exchange capacity of a weak-acid cation-exchange resin (TSKgel SuperIC-Cation column) depended on the conditioning pH and the molar concentration of the conditioning agent. Plots of effective cation-exchange capacities over the conditioning pH exhibited three inflection points, suggesting the presence of two carboxy groups and one phenolic OH group in the resin, probably due to the inherent base polymer. This method was applied to several commercial analytical columns for ion chromatography, and could provide scientifically useful results for characterizing the resin properties.