By measuring the absorption of dilute aqueous solutions of KI with various known amounts of pure iodine added, the present writers have observed that the absorption coefficient at a wavelength of about 350 mµ is nearly proportional to the amount of iodine in the solution. Making use of this fact, the amount of excess iodine in additively V-colored KI crystal has been obtained. Taking into account that two iodine atoms are associated with a V2 center, the oscillator strength of the absorption band at 365 mµ has been estimated to be 1.10±0.16 by the Smakula formula.
YOICHI UCHIDA, YOSHIO NAKAI, and TOSIRO TOMOTIKA, "On the Oscillator Strength of V2 Centers in Potassium Iodide Crystals," J. Opt. Soc. Am. 47, 246-249 (1957)