National Gallery of Art, Washington, DC 20565, USA.
Appl Spectrosc. 2011 Aug;65(8):939-51. doi: 10.1366/11-06230.
A comprehensive study of the luminescence properties of cadmium pigments was undertaken to determine whether these properties could be used for in situ identification and mapping of the pigments in paintings. Cadmium pigments are semiconductors that show band edge luminescence in the visible range and deep trap luminescence in the red/infrared range. Emission maxima, quantum yields, and excitation spectra from the band edge and deep trap emissions were studied for sixty commercial cadmium pigments that span the color range from yellow to red (reflectance transition 470 to 660 nm). For paints containing cadmium pigments, luminescence from deep traps was more readily observable than that from the band edge, although the yield varied widely from zero to around 4.5%. Optimal excitation for emission is found to be in the visible for both pigments in powder form and mixed with a medium. The maxima of the deep trap emission shift with the band gap energy, providing a potentially useful way to assign pigment type even when used in pigment mixtures. The usefulness of the results of the study on mockups was demonstrated by the mapping of cadmium pigments of different hues with the aid of calibrated luminescence imaging spectroscopy in a painting by Edward Steichen, entitled Study for 'Le Tournesol' (1920). Analysis of the luminescence image cube reveals at least six unique spectral components, associated with emission from white pigments, paint binder, and cadmium red and yellow pigments. The results were compared with those from X-ray fluorescence spectrometry (XRF) and fiber-optic reflection spectroscopy (FORS) and the results obtained on paint samples containing cadmium pigments. These results show that, when present, the emission from traps can be used as an analytical tool to identify cadmium pigments, to distinguish among cadmium sulfide, cadmium zinc sulfide, and cadmium sulfoselenide, and to map cadmium pigments, even in mixtures.
进行了一项关于镉颜料发光性能的综合研究，以确定这些性能是否可用于绘画中颜料的原位识别和定位。镉颜料是半导体，在可见范围内表现出带边发光，在红色/红外范围内表现出深阱发光。研究了六十种商业镉颜料的带边和深阱发射的发射最大值、量子产率和激发光谱，这些颜料的颜色范围从黄色到红色（反射过渡 470 到 660nm）。对于含有镉颜料的油漆，深阱发光比带边发光更容易观察到，尽管产率从零到 4.5%左右变化很大。发现对于粉末状和与介质混合的两种颜料，最佳激发是在可见光范围内。深阱发射的最大值随带隙能量而变化，即使在颜料混合物中使用，也提供了一种潜在有用的方法来分配颜料类型。在爱德华·斯泰肯的一幅题为《向日葵》（1920 年）的画作中，借助校准的发光成像光谱学，对不同色调的镉颜料进行了定位，证明了模拟研究结果的有用性。发光图像立方体的分析揭示了至少六个独特的光谱成分，与白色颜料、涂料粘合剂以及镉红和镉黄颜料的发射有关。结果与 X 射线荧光光谱法（XRF）和光纤反射光谱法（FORS）以及含有镉颜料的油漆样品的结果进行了比较。结果表明，当存在时，陷阱发射可作为一种分析工具来识别镉颜料，区分硫化镉、锌硫化镉和硒化镉，并对镉颜料进行定位，即使在混合物中也是如此。
