Natural blue sapphire is a gem species of corundum, which has high economic value due to its beauty and rarity. Color is the most important factor affecting the price of sapphire and mainly caused by trace elements. However, there is little quantitative data currently available to demonstrate the correlation between trace elements and colorimetric parameters of natural blue sapphire. In this study, the UV-Vis-NIR spectra and colorimetric parameters were collected by UV-Vis-NIR spectrophotometer while the chemical composition was analyzed by laser-ablation inductively coupled plasma mass spectrometry. The results show that the content ratio of (FeO_T + TiO₂)/MgO has negative correlation with b^* but positive correlation with C_ab^*, illustrating its obvious effect on the blue color saturation of natural blue sapphire. In addition, the existence of Cr can produce purple hue and the content of Cr shows positive correlation with hue-angle h_ab only in the low range (5-15 ppm), which implies the content of Cr has a limited influence on the hue of natural blue sapphire and the effect may be more complicated as the content of Cr increases above 15 ppm. This investigation can provide quantitative data for scientific color grading and additional applications of natural blue sapphire.

中文翻译：

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天然蓝宝石微量元素与比色参数的相关性研究

天然蓝宝石是刚玉的宝石种，因其美丽、稀有而具有很高的经济价值。颜色是影响蓝宝石价格的最重要因素，主要由微量元素引起。然而，目前很少有定量数据可以证明天然蓝宝石的微量元素与比色参数之间的相关性。在这项研究中，紫外-可见-近红外光谱和比色参数通过紫外-可见-近红外分光光度计采集，化学成分通过激光烧蚀电感耦合等离子体质谱分析。结果表明，(FeO _T  + TiO ₂ )/MgO的含量比与b ^*呈负相关，与C呈正相关。_ab ^*，说明它对天然蓝宝石的蓝色饱和度有明显的影响。此外，Cr的存在会产生紫色色调，Cr的含量仅在低范围（5-15 ppm）与色调角h _ab呈正相关，这意味着Cr的含量对色调的影响有限。天然蓝色蓝宝石，随着 Cr 含量增加到 15 ppm 以上，效果可能会更加复杂。这项调查可以为科学颜色分级和天然蓝色蓝宝石的其他应用提供定量数据。