Radiation Damage And Optical Properties Of Spinel-Type γ-AlON Transparent Ceramic

Recently, aluminum oxynitride (γ-AlON) transparent ceramic, as an important spinel structure material, is a nonstoichiometry compound at room temperature and thus rich with defect structures, which may exert remarkable influence on its properties. To the best of our knowledge, few systematical works have been conducted on the defect micro structure in y-AlON transparent ceramics, which led to the differences in material performance between the exiting literature reports. In this work, defect microstructure and its formation mechanism y-AlON crystal were investigated using the method of ultraviolet irradiation and annealing treatments by the experimental facilities of photocatalysis, fluorescence and thermoluminescence etc., and the details was as following.First, the y-AlON powders, the typical spinel structure with the average grain size of about 580 nm and particle size distribution of 300～900 nm, are non-aggregated entities. The products have a band-gap of about 5.2 eV and lots of defects such as VA1 etc. in crystal. The γ-AlON exhibited good photocatalytic properties (92%) for degrading lOmg/L methyl orange (MO) under UV iiradiation for 2 h. And the photocatalytic ability was attributed to its defect microstructures, which could promote the separation of electron-hole pairs caused by defect level transition, effectivelly.Second, γ-AlON transparent ceramic post-UV-irradiation for 15 min turned blueviolet, and an optical absorption band centerd at 550 nm, covering the whole visible light spectrum, which made the sample colored. And the radiation-induced color centers, caused by VA1 etc. defects, changed with the annealing conditions and could be completely’bleached’by annealing at 250℃Third, the defect mechanism of y-AlON crystal can be expressed as:[Al24O24N8]+ 3/202→[Al23O27N5]+3[On·]+[VA1], in which VA1 and On defects with the total concentration of 1/56 coexist. And it’s [VA1-ON], [ON’-VA1-ON] and [VA1-3ON] etc. defect clusters formed by VA1 and On under the effect of electrostatic attraction that make the sample colored.Fourth, the as-sintered y-AlON transparent ceramics show two fluorescence bands in the UV (371 nm) and visible (707 nm) regains, respectively. These optical properties of the γ-AlON are considered to be related to the [VA1-ON]", [ON’-VA1-On’] and [VA1-30N] etc. defect states. With the stable crystal structure of y-AlON, the high-temperarure annealing only have effects on defect diffusion ([VA1-30N](?)[ON-VA1-ON]+ON(?) [VA1-ON]+2ON(?)VA1+3ON), leading to the variation in the combination or relative concentration of the defect clusters. UV irradiation shows no influence on the defect micro structure and fluorescence performance of y-AlON.