天然蓝宝石红外光谱中经常会出现与OH有关的3 309 cm-1吸收峰, 此峰对于鉴别蓝宝石热处理具有一定指示意义。 目前对于3 309 cm-1峰在蓝宝石色带上的强度分布情况尚缺乏研究且其归属尚存在争议。 山东昌乐产出的蓝宝石蓝色普遍偏深且色带发育, 其红外光谱中通常存在3 309 cm-1吸收峰。 针对昌乐蓝宝石色带区域3 309 cm-1峰的强度分布以及此峰与微量元素的关系进行研究, 并进一步推测此峰的归属。 谱学测试技术方面, 创新性使用红外光谱面扫描技术测试3 309 cm-1峰在色带区域的强度分布。 谱学分析方面, 创新性结合蓝宝石的电荷补偿理论与色带区域的微量元素分布情况, 对3 309 cm-1峰的归属进行了分析推测。 结果发现, 3 309 cm-1峰在色带上的强度分布呈现出从面扫描区域的左下角到右上角不断增强的趋势, 沿着此峰增强的方向, 使用激光剥蚀电感耦合等离子体质谱仪(LA-ICP-MS)测试了5个点的微量元素含量。 根据电荷补偿理论, 在蓝宝石晶体中, Ti4+会优先跟Mg2+进行电荷补偿, 如果Ti4+含量高于Mg2+, 那么跟Mg2+电荷补偿之后剩余的Ti4+会跟Fe2+进行电荷补偿, 形成Fe2+-Ti4+对产生蓝色调。 色带中无色区域的Ti含量较低且全部的Ti4+与Mg2+进行电荷补偿, 所以无色区域中没有Fe2+-Ti4+对且结合红外光谱面扫描数据发现该区域内3 309 cm-1峰很弱。 蓝色区域的Fe2+-Ti4+对含量决定了蓝色的深浅, 蓝色区域的3 309 cm-1峰强度明显高于无色区域, 但深蓝色区域此峰强度并非一定比蓝色区域强, 3 309 cm-1峰强与Fe2+-Ti4+对的含量无必然联系。 3 309 cm-1峰强分布表现出随着Ti含量升高而增强的现象, 即3 309 cm-1峰强与Ti元素的含量呈正相关性。 推测是含有Ti和OH的缺陷簇导致了3 309 cm-1吸收峰的产生。 Fe2+的作用是与Ti4+形成电荷补偿对产生蓝色, 与3 309 cm-1吸收峰的产生并没有必然联系。

The infrared absorption peak at 3 309 cm-1 caused by the vibration of OH often appears in natural sapphire. This peak is significant for the identification of heat treatment sapphire. The color of sapphire produced in Changle County, Shandong Province is often dark blue, and the color zones are usually well developed. The absorption peak at 3 309 cm-1 is often found in FTIR spectrum of Changle Sapphire. At present, the intensity distribution of this peak in color zones of sapphire is still not studied, and the assignment of this peak is still controversial. In this paper, the intensity distribution of peak at 3 309 cm-1 in Changle sapphire color zones and the relationship between this peak and trace elements are studied, and the assignment of this peak is further speculated. In spectroscopic technology, FTIR area scanning was innovatively used to analyze the intensity distribution of peak at 3 309 cm-1 in the color zones. In the spectroscopic analysis, the assignment of the peak at 3 309 cm-1 was creatively predicted based on the charge compensation theory in sapphire and the distribution of trace elements in the color zones. We found that the intensity distribution of this peak showed a trend of increasing from the lower left corner to the upper right corner in the scanning area. Along the direction of this peak increasing, we measured the trace elements contents at five points by Laser Ablation Inductively Coupled Plasma Mass Spectrometer. Based on the charge compensation theory, Ti4+ prefers to compensate with Mg2+ in sapphire. If the content of Ti4+ is higher than Mg2+, almost all Mg2+ will compensate with Ti4+ and remaining Ti4+ will compensate with Fe2+ to form Fe2+-Ti4+ pairs which produce the blue color. The content of Ti in the colorless region is low, and all Ti4+ will compensate with Mg2+. So there is almost no Fe2+-Ti4+ pair in colorless region and the peak at 3 309 cm-1 is very weak. The contents of Fe2+-Ti4+ pairs in the blue region determine the depth of blue. The intensity of 3 309 cm-1 peaks in the blue region is obviously higher than that in colorless region, but the intensity of this peak in the dark blue region is not necessarily stronger than that in the blue region. The intensity of this peak has no certain relationship with the contents of Fe2+-Ti4+ pairs in sapphire. The intensity distribution of this peak shows a positive correlation with the contents of Ti. The more the Ti contents are, the stronger the is peak. We found this peak was positively correlated with the content of Ti, and we further speculated that the defect cluster containing Ti and OH produced the peak at 3 309 cm-1. The Fe2+ is not necessary to produce a peak at 3 309 cm-1 but to compensate with the Ti4+ to produce the blue color.