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Abstract
Sensitometric and spectroscopic techniques are used to study the effect of 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene (TAI) during the sulphur sensitization of AgBr octahedra. TAI increased the speed of an oversensitized emulsion, causing it to have a speed comparable with the optimally sulphur-sensitized emulsion at high irradiance. TAI decreased the absorption by sulphide centres at 1.5 mmole concentration but not at 1 mmole. The long wavelength sensitivity (> 500 nm) increased at 1 mmole TAI concentration, but decreased at 1.5 mmole TAI concentration, whereas the activation energy for this response was reduced at both TAI levels. These results are interpreted using a model which assumes that TAI interacts with multiple-sulphide centres to lower their ground-state energy level, but not their electron-trapping energy level. This interaction reduces the degree of free-hole/trapped-electron recombination that occurs at these centres. The enhancement of this recombination channel by high levels of sensitizer is what causes the oversensitization effect.