Producing high-purity zinc oxide for photonics technologies

Abstract

The authors developed a procedure for synthetizing high-purity zinc oxide by precipitation from a solution with the subsequent high-temperature treatment in oxygen. Metallic zinc additionally purified by vacuum distillation, nitric acid and aqua ammonia with total impurities not exceeding 10–4 % wt. were used as incoming substances for the synthesis. It is found that to produce a single-phase product as zinc oxide powder containing no nitrate and amine complexes, the precipitation should be conducted at a zinc concentration in solution of 2 mol/l and pH = 7.5. Impurities of iron, chromium, aluminum, barium, molybdenum and sodium are removed at the stage of forming the intermediate precipitate at pH = 5. The yield of the final high-purity product is 59%. A scanning electron microscopy method was used to study precipitate morphology before high-temperature annealing and after it. It is shown that the final product is powder formed from well-faceted crystallites represented by hexagonal prisms, 0.5–0.7 μm in diameter and 1.7–2.1 μm in length. The analysis of luminescence spectra indicated that synthetized and purified ZnO after high-temperature annealing showed low luminescence with a maximum value of 678 nm, while commercial ZnO powder was characterized by intensive luminescence with a maximum value of 522 nm, attributed to defects of non-stoichiometry and/or yttrium impurities. Chemical purity of zinc oxide synthetized and purified according to the developed procedure, as shown by inductively coupled plasma mass spectrometry, was 99.9993 % wt. by 67 impurity elements.The authors acknowledge K. I. Runina, an employee of the Department of Chemistry and Technology of Crystals, for her help with spectral studies.The research was conducted as part of funding applied research project of Mendeleev University of Chemical Technology of Russia No. ВИГ 2022-081.