Aging effects in bulk and fiber TlBr-TlI

A study of optical aging in bulk and extruded fibers of thallium bromo‐iodide (TlBr‐TlI) is presented. A variety of techniques including secondary ion mass spectrometry (SIMS), powder neutron and x‐ray diffraction, infrared spectroscopy, and electron paramagnetic resonance (EPR) spectroscopy are used to probe the chemical and structural properties of both pristine and aged material. High concentration levels of a hydrogen bearing impurity have been detected by SIMS and neutron scattering in aged TlBr‐TlI, and have been shown to be localized in the surface layers of fibers as well as bulk samples. We present EPR evidence which indicates that the hydrogen bearing impurity is water.