Bradley R. Karas

Thermal Manipulation of Deactivation Processes in Luminescent Photoelectrochemical Cells Employing Tellurium-Doped Cadmium Sulfide Photoelectrodes.

Abstract : Temperature significantly modifies the efficiencies of luminescence and photocurrent in an n-type, single crystal, CdS:Te-based photoelectrochemical cell (PEC) employing aqueous polyselenide electrolyte. Between 20 and 100 C photocurrent (quantum yield phi sub x) from ultraband gap 501.7 nm excitation increases modestly by less than or = 20%, whereas photocurrent from bandgap edge 514.5 nm excitation increases by about an order of magnitude, reaching 50-100% of the 20 C 501.7 nm photocurrent. Undoped CdS exhibits a similar photocurrent-temperature profile. Higher temperatures thus extend the wavelength response of CdS- and CdS:Te-based PECs. In contrast to the increase in photocurrent, emissive efficiency (quantum yield phi sub r) of CdS:Te drops by a factor of approximately 10-20 over the same temperature range; this decline is relatively insensitive to potential and excitation wavelength (501.7 or 514.5 nm).

Luminescent tellurium-doped cadmium sulphide electrodes as probes of semiconductor excited-state deactivation processes in photoelectrochemical cells

Correlations among quantum efficiencies for photocurrent (φx), emission (φr), and non-radiative recombination (φnr) are discussed with reference to data from single-crystal, n-type, 100 and 1000 p.p.m. CdS: Te-based photoelectrochemical cells (PECs) employing aqueous sulphide electrolyte. These materials emit while they serve as PEC electrodes. The assumption that the proportionality of φr to φnr is unaffected by potential, leads to a simple expression relating φx to φr for monochromatic excitation. Calculated and observed emission data are in reasonable agreement; sources of deviation are discussed. Polychromatic excitation is shown to yield photocurrents and emission intensities which are approximately a weighted average of the values obtained with the constituent monochromatic frequencies. Practical implications of the φx correlation with φr are described, as are related results from other PECs.