Investigation of Photoconductivity in ZnS and CdS Phosphors with Microwave Methods

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Abstract
Microwave techniques are applied to measure the photoconductivity of activated CdS and ZnS phosphor powders. Polarization effects, which are a source of error in dc and low‐frequency ac measurements, and surface effects introduced by electrodes are eliminated by the use of microwaves. The conduction‐band electron density is determined by a waveguide perturbation calculation from the measurement of wave‐propagation characteristics in the phosphors. For radiation at 5150 Å and incident light intensity of 170 μW/cm2, there is a density of 1014 conduction electrons per unit volume (cm3) in a CdS (Cl, Cu) powder. In ZnS (Cl, Cu), the electron density is 3×1013 at 8700 μW/cm2 intensity in the 3600 to 6000 Å wavelength band. When long‐wavelength ir radiation is added to the exciting light the photoconductivity is decreased.