磷灰石是珠宝市场上常见的宝石品种, 因颜色丰富而广受欢迎。 变色磷灰石是稀有品种且价格高昂, 该品种在D65光源（色温6 500 K）下呈黄绿色, A光源（色温2 856 K）下呈粉红色, 其可见光光谱的谱学特征与变色成因未被详细研究。 基于此, 将一颗变色磷灰石晶体, 沿其平行c轴和垂直c轴方向各切下一个薄片并双面平行抛光, 分别测试其可见光光谱与微量元素。 结果发现, 其可见光光谱中谱峰较多: 位于583和578 nm处的吸收双峰强度最强, 位于748和738 nm处的吸收双峰强度中等, 分别位于688和526 nm处的吸收峰, 强度较弱。 还有一些非常微弱的吸收峰, 分别位于514, 483, 473和443 nm处。 位于748和738 nm处的吸收双峰与583和578 nm处的吸收双峰共同造成了红橙光区的透射窗, 583和578 nm处的吸收双峰与526 nm处的吸收峰共同造成了黄绿光区的透射窗。 D65光源和A光源由于相对光谱功率分布不同, 在不同透射窗的透过有所不同, 导致变色磷灰石在不同光源下呈现出不同颜色。 D65光源中黄绿光成分较多, 透过黄绿光区透射窗的成分较多, D65光源下磷灰石呈黄绿色, A光源中红光成分较多, 通过红橙光区透射窗的成分较多, A光源下磷灰石呈粉红色。 因此, 磷灰石的变色效应与位于748和738 nm处的吸收双峰, 位于583和578 nm处的吸收双峰以及位于526 nm处的吸收峰相关。 根据微量元素数据与稀土元素的晶体场理论, 这些吸收峰是由稀土元素钕（Nd）导致。 根据不同晶体方向样品的可见光光谱特征, 平行c轴方向变色效果更好, 建议加工变色磷灰石晶体时宝石台面应尽量平行c轴。 该研究结合微量元素与可见光光谱分析了变色磷灰石的变色成因, 并为其加工切割方向提供了指导。

Apatite is a kind of common gem species in jewelry market. It is popular because of its rich color. Apatite with the Alexandrite effect is rare and expensive. It shows yellow green under the D65 light source and pink under the A light source. Characteristics in the visible spectrum and Alexandrite effect origin of this apatite have not been studied in detail. Based on this, the sample of this study is an apatite crystal with the Alexandrite effect. Two thin slices were cut parallel and perpendicular to the c-axis, respectively. The two samples were polished, and their visible spectra and trace elements data were collected. The results show there are many peaks the in visible spectrum of Alexandrite effect apatite. There are double absorption peaks at 583, 578 nm with strong intensity, double absorption peaks at 748, 738 nm with middle intensity, two absorption peaks at 688 and 526 nm with weak intensity and some very weak absorption peaks at 514, 483, 473 and 443 nm. The absorption peaks at 748, 738, 583, 578 nm create a transmission window in red orange region, and the absorption peaks at 583, 578, 526 nm create another transmission window in the yellow green region. Due to different relative spectral power distributions between D65 and A light sources, the transmittance through transmission windows is also different, which leads to different colors of apatite. D65 light source has the more yellow green light, passing through transmission window in yellow green region, so apatite shows yellow green color. A light source has more red light, passing through another transmission window in red orange region, so apatite shows pink. Therefore, the Alexandrite effect of apatite is caused by the absorption peaks at 748, 738, 583, 578 and 526 nm. Based on trace elements data and crystal field theory of rare earth elements, it was found that these absorption peaks were caused by neodymium (Nd). It was found that the Alexandrite effect was better in the orientation parallel to the c-axis based on visible spectra. It is suggested that the table of the gemstone should be cut parallel to the c-axis. This research combines trace elements and visible spectra to analyze the Alexandrite effect origin of apatite. It also provides guidance for cutting apatite crystal.