Most thallium is used by the electronics industry in photoelectric cells: Improvements in the production of thallium sulphide photoconductive cells (1946).
Thallium oxide is used to produce special optical components with a refractive index gradient: Thallium-Containing Optical Glass (1982), and also low softening temperature glass Mercury thallium fluorophosphate glasses (1983).
An alloy of mercury and indium containing about 14% thallium has a melting point of 23°C lower than mercury alone. This can be used in low temperature thermometers and switches: Mercury-indium-thallium alloys (1963).
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All patent information has been obtained from Espacenet (European Patent Office).