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Which limited optical uses have thallium compounds had?

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A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors.
boron group element Modern version of the periodic table of the elements (printable).

Thallium compounds have several limited optical applications due to their unique physical and chemical properties. These uses include:1

  • Infrared Optics: Mixed bromide-iodide crystals (TlBr and TlI) are used to fabricate lenses, windows, and prisms for infrared optical systems because they effectively transmit infrared light.1
  • Photodetectors: Thallium sulfide (Tl₂S) serves as a key component in highly sensitive photoelectric cells, while thallium oxysulfide is utilized in infrared-sensitive photocells known as thallofide cells.12
  • Optical Glass and Gems: Thallium(I) oxide (Tl₂O) is employed as an ingredient in highly refractive optical glasses and as a coloring agent in the production of artificial gems.1
  • Scintillation Counters: Thallium compounds are used to dope or activate alkali halide crystals, such as sodium iodide, to create inorganic phosphors. These materials are essential for detecting radiation in scintillation counters.1