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采用冷心放肩微量提拉法(SAPMAC)生长了目前国内最大的氧化铝单晶体((?)225mm×205mm,重27.5kg)。测试了大晶坯不同部位样品的真空紫外吸收光谱(140nm～380nm)及荧光光谱。结果表明,晶体各部位样品都存在波长为163nm,178nm及230nm左右的吸收峰位;而且边缘部位样品的吸收系数更大。荧光光谱图上主要存在320nm左右的紫外荧光带和420nm附近的蓝色荧光带。进一步的研究证实了吸收色心起源于氧空位与Ti~(4+)复合存在以及Mn~(4+)、Cr~(3+)等杂质离子的电荷转移过程。计算了不同类型的色心浓度。最后提出了减小色心浓度、提高晶体光学性能的一些工艺措施。
The largest alumina single crystal (? 225mm × 205mm, weight 27.5kg) was grown in China by using the cold pulling method (SAPMAC). The vacuum ultraviolet absorption spectra (140nm ~ 380nm) and fluorescence spectra of samples from different parts of large crystal ingot were tested. The results show that there are absorption peaks at wavelengths of 163nm, 178nm and 230nm in all parts of the crystal, and the absorption coefficient of the sample in the edge part is larger. Fluorescence spectrum mainly exists around 320nm UV fluorescence band and near the blue fluorescent band 420nm. Further studies confirmed that the absorption color center originated from the charge transfer process between oxygen vacancies and Ti 4+ and impurity ions such as Mn 4+ and Cr 3+. Calculated different types of color center concentration. Finally, some technical measures to reduce the color center concentration and improve the optical properties of the crystal are proposed.