High dose optical and electrical sensor dosimeter using cobalt phthalocyanine (CoPc) thick film

Cobalt phthalocyanine films were screen-printed on glass substrates using polymer thick film technology (PTF). The films were treated with various doses of γ-radiation from ¹³⁷Cs standard source with a dose rate of 6.0 Gy/min. Measurements for I-V characteristics were performed and the capacitance values were recorded for a number of irradiated Ag/CoPc/Ag devices. The electrode-limited conduction mechanism, namely, Schottky effect was shown to be predominant for both the as-printed and irradiated samples. The ultraviolet/visible spectra were recorded for the as-printed and irradiated thick films at room temperature. It was found that the optical density increased significantly as the dose of γ-ray was increased. The optically induced electronic transitions were analysed in view of the models proposed by Mott & Davis resulting in a predominance of a direct allowed transition for the as-printed CoPc thick film and indirect allowed for the irradiated samples. In addition, there was small and insignificant decrease in the optical band gap. The dosimetric properties were established by two methods: firstly by the continuous linear decrease in the values of the capacitance and secondly by the continuous linear increase in the absorbance over a dose range of 5.4-27.0 kGy.