祖母绿为绿柱石族中铬(Cr)、 钒(V)共同致色的宝石种, 合成历史悠久, 技术不断改进, 新配方产品不时出现。 近期市场上出现一种新型水热法合成祖母绿, 颜色亮丽, 外观可与哥伦比亚天然祖母绿媲美, 经初步分析发现其为V致色合成祖母绿。 为了探究其特征, 运用激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)、 紫外-可见-近红外(UV-Vis-NIR)分光光度计进行详细研究, 旨在获得其化学成分中致色元素含量及UV-Vis-NIR吸收光谱特征, 分析致色原因, 并寻求与天然祖母绿的相区别的方法, 为检测机构提供重要数据信息。 化学成分研究表明, 该合成祖母绿为纯V致色, 具有富V贫铁(Fe)的特征, 铜(Cu)在不同批次样品中, 含量差别较大, 而Cr及其他致色元素含量大多低于检测限。 作为对比的传统富Fe型水热法合成祖母绿样品, 则具有高Cr高Fe的特征。 此外, 含有较高的镍(Ni)及微量钛(Ti), 锰(Mn), Cu, 而V含量则低于检测限。 新型合成祖母绿的紫外-可见吸收光谱呈现典型的钒元素的吸收光谱特征, 在紫区430 nm、 橙红区617 nm处显示两个宽大的吸收带。 此外在约390和680 nm附近分别有一肩峰, 多数样品在756 nm处有一弱吸收峰。 430 nm吸收带归属于V³⁺的d电子[³ T_1g(³ F)→³ T_1g(³ P)]自旋允许跃迁, 617 nm吸收带归属于V³⁺的d电子的³ T_1g(³ F)→³ T_2g(³ F)自旋允许跃迁, 756 nm吸收峰为Cu²⁺所致, 该吸收光谱特征与传统富Fe型合成祖母绿明显不同。 天然祖母绿大多具Fe³⁺, Fe²⁺及Cr³⁺的吸收光谱组合特征, 较容易与该合成祖母绿区分; 少数纯V致色天然祖母绿, 虽然同样具有V元素特征的吸收峰, 但由于同时具有在810830 nm附近Fe²⁺的特征吸收带, 也能与富V型合成祖母绿区别。 近红外区, 主要在1 402, 1 467和1 895 nm处显示I型水相关吸收峰, 也可与天然祖母绿区别。 紫外-可见-近红外光谱是鉴定天然祖母绿与合成祖母绿的一个有效手段, 但要结合其他鉴定信息, 如包裹体、 分子振动光谱等, 避免新合成配方祖母绿的出现而导致错误的鉴定结论。

Emerald is a species of beryl in which chromium (Cr) and vanadium (V) are co-colored, with a long history of synthesis, continuous technological improvements and the emergence of new formulations. Recently, a new type of synthetic hydrothermal emerald with a bright color whose appearance is comparable to natural emeralds from Colombia has shown up in the market. After initially analyzing the emerald, it was a vanadium color-causing synthetic emerald. In order to investigate its characteristics, a detailed study was carried out using LA-ICP-MS and UV-Vis-NIR spectrophotometer, aiming to obtain the content of chromogenic elements and analyze the chromogenic reason in its chemical composition and UV-Vis-NIR absorption spectra. Digging differentiation from natural emeralds, we could provide vital data for testing institutions. The chemical composition showed that these synthetic emeralds were pure vanadium-colored, characterized by vanadium-rich and iron-poor, with copper (Cu) varying widely among the different batches, while Cr and other color-causing elements were mostly below the detection limit. The conventional iron-rich hydrothermal synthesized emerald samples used for comparison were characterized by chromium-rich and iron-rich. In addition, it contained high nickel (Ni) and traces of titanium (Ti), manganese (Mg) and Cu, while the vanadium content was below the detection limit. The UV-Vis absorption spectra of the new synthetic emeralds revealed typical absorption spectral features of vanadium, with two broad absorption bands centered at 430 nm in the violet region and 617 nm in the orange-red region, in addition to a shoulder peak near about 390 and 680 nm respectively, and a weak absorption peak at 756 nm for most samples. 430 nm absorption band was attributed to the d electrons spin-allowed transition [³ T_1g(³ F)→³ T_1g(³ P)] of V³⁺ , the 617 nm absorption band was attributed to d electrons spin-allowed leap [³ T_1g(³ F)→³ T_2g(³ F)] of V³⁺, and the 756 nm absorption peak was due to Cu²⁺, and this spectral absorption feature was different from that of the conventional iron-rich synthetic emerald. Most natural emeralds have a combination of Fe³⁺, Fe²⁺ and Cr³⁺ absorption spectra, which can be easily distinguished from these synthetic emeralds. A small amount of the pure vanadium-colored natural emeralds also have the characteristic absorption peaks of vanadium, but they can be separated from the vanadium-rich synthetic emeralds because they also have the characteristic absorption band of Fe²⁺ around 810830 nm. The NIR region, mainly showing type I water-related absorption peaks at 1 402, 1 467 and 1 895 nm, can also be differed from natural emeralds. UV-Vis-NIR spectroscopy is an effective means of identifying natural emeralds from synthetic emeralds. However, it should be combined with other identification evidence, such as inclusions and molecular vibration spectroscopy techniques, avoiding the appearance of new synthetic formulations of emeralds that could lead to erroneous identification conclusions.