Semiconductor Electrodes. 51. Efficient Electroluminescence at ZnS Electrode in Aqueous Electrolytes.
TEXAS UNIV AT AUSTIN DEPT OF CHEMISTRY
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Electroluminescence EL on ZnS was studied in aqueous solutions containing various redox species. For species able to generate strongly oxidizing intermediates, such as peroxydisulfate or hydrogen peroxide, bright blue luminescence was observed during cathodic polarization at potentials near to or negative of flat-band potential Vfb of ZnS. For solutions containing supporting electrolyte alone at various pHs, no emission was detectable even at potentials 7 volts negative of Vfb. This suggests that minority-carrier hole injection is responsible for the initiation of EL. The peak energy of the EL spectrum was much smaller by 1 eV than the bandgap of ZnS, suggesting that the radiative recombination is through intermediate luminescent centers. Under steady state conditions, the EL intensity was proportional to the square of the current, suggesting that EL intensity is dominated by the recombination of electron-hole pairs at luminescent centers. In the early part of a potential pulse especially the first pulse, the growth behavior of EL intensity was strongly affected by the electron trapping of the empty upper luminescent states. The location of the EL spectra depended on the current density and the EL intensity with increasing EL intensity, a significant blue shift of the emission peak was observed.
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