Electrolytic coloration of hydroxyl-doped sodium chloride crystals

Electrolytic coloration of air-grown sodium fluoride crystals

“…3. These current-time curves are similar to those of the hydroxyl-doped sodium chloride crystals [7] and offer three obvious zones. …”

“…In the past electrolysis research, it was believed impossible to color electrolytically directly anion-doped crystal such as hydroxyl-or oxygencontaining one because the anions result in electrolytic coloration not to start. However, in our recent work, it is proved that the hydroxyl-doped sodium chloride crystals and lithium-doped strontium fluoride crystals can be colored electrolytically using our homemade electrolysis apparatus at appropriate coloration temperatures and electric field strengths [7,8]. In this work, it is shown that the air-grown sodium fluoride crystals containing more hydroxyl and oxygen impurities also can be colored electrolytically using the same apparatus with a pointed cathode at various temperatures and electric field strengths.…”

“…In general, the anions in the crystals were previously considered as the main obstruction for coloring the crystals by using the electrolysis, and some successful electrolytic colorations used pure or cation-doped sodium fluoride [5,6], sodium chloride and potassium chloride crystals [13], mainly benefited the substantial elimination of the hydroxyl impurities, the hydroxyl-free or the hydroxyl neutralization by the cation ions. However, our recent results show that the hydroxyldoped sodium chloride crystals and lithium-doped strontium fluoride crystals penetrated with the oxygen impurities can been colored electrolytically at appropriate temperatures and electric field strengths with our homemade electrolysis apparatus by using a pointed cathode [7,8].…”

“…As the case in the electrolytic coloration of the hydroxyldoped sodium chloride crystal [7], the secondary alkali cathode can be hardly formed due to the obstruction of the anions in the air-grown sodium fluoride crystal. Therefore, the electrolysis beginning benefits the used electrode structure, namely, the V color centers were firstly produced from the graphite anode matrix because the production of the V color centers does not need the secondary alkali cathode.…”

“…The samples were polished optically with waterless abrasive, and then stored in a desiccator with drier until electrolytic coloration due to hygroscopicity of the sodium fluoride crystal. The samples were colored electrolytically at various temperatures and DC electric field strengths using the same electrolysis apparatus as the previously used one [7,8], using a pointed tungsten cathode and a flat stainless steel anode. Some graphite powders damped with alcohol were filled between the sample and anode in order to ensure good contact.…”