Luminescent Photoelectrochemical Cells. 5. Multiple Emission from Tellurium-Doped Cadmium Sulfide Photoelectrodes and Implications Regarding Excited-State Communication.
WISCONSIN UNIV-MADISON DEPT OF CHEMISTRY
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Samples of single-crystal, n-type, 100 ppm Te-doped CdS CdSTe exhibit two emission bands when excited at several ultraband gap wavelengths. One emission band with lambda sub max approximates 510 nm is near the band gap of CdSTe approximates 2.4 eV and is likely edge emission. Its decay time, measured for samples immersed in sulfide solution between 295 and 333 K, is faster than the pulse from the N2-pumped dye laser approximates 7 nsec used for 458-nm excitation. The other emissive transition, lambda sub max approximates 600 nm, involves intraband gap states introduced by Te. Intensity-time curves for this band have rise times of less than 10 nsec and generally exhibit nonexponential decay values of tau sub 1e are typically 120 or - 40 and 80 or - 30 nsec at 295 and 333 K, respectively. When CdSTe is used as the photoanode in a photoelectrochemical cell employing sulfide electrolyte, both emission bands are quenched in parallel during passage of photocurrent resulting from 457.9- or 476.5-nm Ar ion laser excitation. Parallel quenching is observed at several temperatures for which the excited-state kinetic schemes are demonstrably different open-circuit emission spectra reveal that both the absolute and relative intensities of the two emission bands are affected by temperature. With increasing temperature 295-333 K the absolute intensities of both bands decline a semilog plot of the ratio of 510- to 600-nm intensity vs. T to the -1 is linear with a slope of approximates 0.2 eV, corresponding to the energy gap between the two excited states. The existence of excited-state communication is inferred from the effects of temperature and electrode potential on multiple emission.
- Atomic and Molecular Physics and Spectroscopy