Quenched‐in Photoluminescent Color Centers in NaI

Crystals of NaI, KI, and KCl have been quenched from temperatures as high as 450 °C by rapid immersion in liquid nitrogen. In the case of NaI, very strong absorption bands at 255 nm (Q1) and 226 nm (Q2) may be produced by quenching the crystal from about 360 °C. The excitation spectrum for a characteristic luminescence at 375 nm, is identical, within the limits of experimental accuracy, with bands produced by stoichiometric excess iodine. Similar results were obtained for quenched KI, although the luminescent quantum efficiency was smaller. Negative results were obtained for quenched KCl. Analysis of the observed properties leads to the conclusion that the defect responsible for the 375 nm luminescence is, or is related to, the single cation vacancy.