Polarization effects in the luminescence of cadmium selenide electrodes


Polarization properties of the emission from single-crystal, n-type CdSe samples have been examined. When excited with several ultraband gap wavelengths, a plates of n-CdSe (wurtzite structure) exhibit polarized photoluminescence (PL) spectra consistent with the reported electronic structure of the solid. The spectra consist of two bands near the band gap energy (∼1.7 eV) assignable to transitions between the conduction band and a split valence band having its two highest energy band edges separated by ∼0.022 eV; the lower energy band is preferentially polarized with E ⊥ c, while the other band displays no polarization preference. Time-resolved PL data, obtained with 620-nm excitation from a N2-pulsed dye laser, were independent of polarization. Intensity-time curves yielded a decay time (τ1/e) of ∼20 ns for both bands, providing evidence that the two emissive excited states are in thermal equilibrium. Emissive properties of n-CdSe, a-plate electrodes were also consistent with thermal equilibration. Polarized electroluminescence (EL) spectra, obtained by using the solid as a dark cathode in aqueous peroxydisulfate electrolyte, closely resemble their PL counterparts, demonstrating attainment of similar excited-state populations in the two experiments. And when the semiconductor is used as the photoanode of a photoelectrochemical cell employing diselenide electrolyte, the two PL bands resulting from 514.5- or 632.8-nm excitation are quenched in parallel by the electric field present in the semiconductor.

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Journal of Physical Chemistry