Thallium(I) sulfide, Tl
2S, is a chemical compound of
thallium and
sulfur
Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
.
It was used in some of the earliest photo-electric detectors by
Theodore Case who developed the so-called thalofide (sometimes spelt thallofide) cell, used in early film projectors. Case described the detector material as consisting of thallium, oxygen and sulfur, and this was incorrectly described by others as being thallium oxysulfide, which incidentally is a compound that is not known. Case's work was then built on by R.J. Cashman who recognised that the controlled oxidation of the Tl
2S film was key to the operation of the cell.
Cashman's work culminated in the development of long wave infrared detectors used during the Second World War. Reliable Tl
2S detectors were also developed in Germany at the same time.
Tl
2S is found in nature as the mineral carlinite which has the distinction of being the only sulfide mineral of thallium that does not contain at least two metals. Tl
2S has a distorted anti-CdI
2 structure.
Tl
2S can be prepared from the elements or by precipitating the sulfide from a solution of thallium(I), e.g. the
sulfate or nitrate. Thin films have been deposited, produced from a mixture of citratothallium complex and thiourea. Heating the film in nitrogen at 300°C converts all the product into Tl
2S
References
{{Sulfides
Sulfides
Thallium(I) compounds