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

Hydroxyl-doped potassium iodide polycrystals were successfully colored electrolytically for the first time using a technique of electrolytic coloration, and a lot of color centers were produced in the colored polycrystals. Systematical spectral measurement and analysis were carried out to the colored polycrystals. The mechanisms of the production and transformation of the color centers were presented. By means of measured current-time curves, the process and mechanism of the production of the color centers were explained further. Potassium bromide crystals were irradiated by gamma rays, and production and transformation of color centers were explained.Positions of absorption spectrum bands of OH^- ions and O₂^--Va⁺ color centers at room temperature in potassium iodide hosts were determined for the first time from Mollwo-Ivey plots. In the research it was found that the OH^- ions were not stable in potassium iodide hosts and were converted gradually into U and O₂^--Va⁺ color centers during the polycrystal storage in the dark at room temperature. By careful observation, the converting process from the OH^- ions to the U and O₂^--Va⁺ color centers was tracked. Under proper heat treatments, the OH^- ions in hydroxyl-doped potassium iodide polycrystals could also be converted into the U and O₂^--Va⁺ color centers and the reverse process was also observed.A lot of U, O₂^--Va⁺, Cu⁺, Cu-related impurity, I₂^-, I₂, V, F, K, R₁ and R₂ color centers were produced in the hydroxyl-doped potassium iodide polycrystals after the electrolytic coloration with a pointed cathode. Because the hydroxyl-doped potassium iodide polycrystals contain a lot of OH^- ions, the polycrystals are hardly colored electrolytically using the traditional electrolysis method. It is the unique anode matrix composed of the graphite grains to make that V color centers are produced firstly. Some V color centers are converted into F color centers under light illumination, then, some F color centers are aggregated into R1 and R2 color centers. Data of current-time were recorded in the electrolysis, with which current-time curves were plotted. After analysis, it is known by reasoning that the current components of each current zone all consists of the ionic motion and the electron exchange between halogen ions and anode matrix. The formation mechanism of the current zones in the current-time curves and the close relation between the color center production and the formation of the current zones is presented. After many researches, a best effective coloration condition at temperature 798 K, voltage 600 V and electrolysis time 45 min was found.A lot of U, V₂, V₃, Cu⁺, Cu-related impurity and F color centers were produced in the hydroxyl-doped potassium iodide polycrystals after the electrolytic coloration with a pointed anode. It is similar to the electrolytic coloration with a pointed cathode that the F color centers result from the conversion of the V color centers under illumination. The coloration mechanism of the hydroxyl-doped potassium iodide polycrystals by electrolysis with a pointed anode is given, and by plotting current-time curves, the process and mechanism of the production of the color centers in colored hydroxyl-doped potassium iodide polycrystals are explained further.Potassium bromide crystals were irradiated by gamma rays with different dose. The concentration of the color centers increases with the irradiation dose. The desired concentration of the color centers can be obtained according to the requirement in the actual application.