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Thallium halides
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<p>The thallium halides include mono<a href="/facts/Halide/ujYu8kGD">halides</a>, where <a href="/facts/Thallium/v35pGMJB">thallium</a> has <a href="/facts/Oxidation_state/W53W6s6V">oxidation state</a> +1, trihalides in which thallium generally has oxidation state +3, and some intermediate halides containing thallium with mixed +1 and +3 oxidation states. These salts find use in specialized optical settings, such as focusing elements in research <a href="/facts/Spectrophotometry/hhjdQYvf">spectrophotometers</a>. Compared to the more common <a href="/facts/Zinc_selenide/FTF76u67">zinc selenide</a>-based optics, materials such as thallium bromoiodide enable transmission at longer wavelengths. In the <a href="/facts/Infrared_spectroscopy/u1Hzx617">infrared</a>, this allows for measurements as low as 350 cm−1 (28 μm), whereas zinc selenide is opaque by 21.5 μm, and zinc sulfide optics are generally only usable to 650 cm−1 (15 μm). </p>