Luminescent Photoelectrochemical Cells: VII . Photoluminescent and Electroluminescent Properties of Cadmium Sulfo‐Selenide Electrodes

Abstract

Samples of single crystal, n‐type emit when excited with ultra‐bandgap excitation. The 295 K bandgaps monotonically decrease with from ∼2.4 eV for to ∼1.7 eV for . Photoluminescence (PL) spectra are sharp and have band positions which vary nearly linearly with composition: . The energetic proximity to the bandgap, temperature dependence, and decay times are all consistent with a description of the PL as edge emission. Measured PL efficiencies, , are ∼10−4 in air. When the samples are used as photoanodes in photoelectrochemical cells (PEC's) employing aqueous polysulfide electrolyte, the emission intensity can be quenched by the passage of photocurrent. The extent of quenching can be correlated with the photocurrent quantum efficiency. Electroluminescence (EL) can be initiated by using the samples as dark cathodes in aqueous, alkaline, peroxydisulfate electrolyte at potentials cathodic of ∼−0.9 to −1.1V vs. SCE. The EL spectral distribution for a given sample is similar to that observed in PL experiments and indicates that the same emissive excited state is involved. At high resolution EL and PL spectra can differ in a manner which shows evidence of self‐absorption effects: The EL spectra are slightly broader than their PL counterparts with the spectral mismatch almost exclusively in the high energy tail. This suggests that EL occurs, on average, nearer the semiconductor‐electrolyte interface. Measured EL efficiencies exceed 10−4 or 10−5 at −1.50V vs.SCE, but are smaller near the EL threshold potentials. Comparisons with values are discussed.