EFFECT OF WATER VAPOUR ON PHOTOCONDUCTIVITY OF ZINC OXIDE

The photoconductivity of zinc oxide powder has been found to be strongly dependent on the water vapour concentration of the ambient gas. The effects of water vapour have been studied over the range 2 to 2 × 104 ppm in air and in oxygen. Over this range, photoconductivity first rises with increasing concentration to attain a maximum at 100 ppm and then decreases, with a rapid fall at concentrations approaching saturation. The results suggest that at low partial pressures water vapour reacts with chemisorbed oxygen to increase the conductivity, while at higher pressures OH- ions are chemisorbed with a consequent fall in conductivity. The kinetics of the slow photoconductivity decay of zinc oxide in moist air have been studied. Decay rates can be approximated to an equation of the Elovich type with three kinetic stages. The last stage only is dependent on water vapour concentration and the results suggest that the reaction involves pairs of chemisorption sites with water molecules forming abridge between them. © 1968.