Electrolytic Coloration Of Potassium Bromide Polycrystals And Mechanism Of Production And Transformation Of Color Centers

OH--doped potassium bromide polycrystals were successfully colored electrolytically for the first time by using a technique of electrolytic coloration, and a lot of color centers were produced in the colored polycrystals. Spectral measurement and analysis were performed systematically to the colored polycrystals, and some spectra were decomposed reasonably. By using measured current~time curves, process and mechanism of production of color centers were further explained.Absorption spectrum bands of O-, OH-, U, Cu+ and centers were observed in absorption spectrum of polycrystal before electrolysis, herein a position of absorption spectrum peak at room temperature was determined by using a Mollwo-Ivey plot.A lot of V2, V3, Cu+, O2--Va+, I-2, I2 and F centers were produced in hydroxyl-doped potassium bromide polycrystals after electrolytic coloration with a pointed cathode. Because the hydroxyl-doped potassium bromide polycrystals contain a lot of OH- ions, the polycrystals cannot be colored electrolytically using the traditional electrolysis method. With the unique anode matix composed of the graphite grains,under appropriate electrolysis temperatures and voltage,the V centers are produced firstly from polycrystal region near anode. F centers are produced through photo-conversion of V centers under illumination. Therefore, the original center produced by electrolysis is V center and not previous F center. From measured current~time curves, it is known that current components of each current zone all consists of ionic motion and electron exchange between halogen ions and anode matrix. Formation mechanisms of current zones and their close relationship with production of color centers were explained. After many researches, a best effective coloration condition at temperature 435 oC, voltage DC 900V and time 100 min was obtained.A lot of V2, V3, Cu+, O2--Va+, I-2, I2 and F centers were also produced in the polycrystals after the electrolytic coloration with a pointed anode. It is similar to electrolytic coloration with a pointed cathode that F centers result from conversion of V centers under illumination. Coloration mechanism of hydroxyl-doped potassium bromide polycrystals by electrolysis with a pointed anode is given. Current-time curves were given, and formation mechanism of current zones is similar to that in case by electrolysis using a pointed cathode.