Eaton Sandra S, Mitchell Debbie G, Eaton Gareth R
Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210.
Appl Magn Reson. 2025 Feb;56(1-2):73-90. doi: 10.1007/s00723-024-01716-1. Epub 2024 Sep 10.
The blue color that has made lazurite (lapis lazuli) a prized mineral is due to the same S radical that is in synthetic ultramarine blue (UMB), which has been proposed as a CW EPR standard. Continuous wave and pulsed EPR spectra and relaxation times of S are compared for three commercial sources of synthetic UMB, for samples of lapis lazuli from Afghanistan, Chile, Colorado USA, and Pakistan, and a solution in DMSO:dioxane. The spin concentrations in the UMB samples were high, in the range of 3×10 to 5×10 spins/g. The field-swept echo detected spectra of UMB samples have lineshapes at 4.2 K that depend on the field at which phase adjustment is performed, indicating strong spin-spin interaction. The spectra of the minerals included large spectral contributions from Mn, in addition to S for which the concentrations were 6×10 to 2.9×10 spins/g. Features in the spin-echo detected spectra attributed to forbidden Mn transitions were confirmed by comparison with Mn spectra in CaO powder. Large distributions in relaxation times caused derived results to depend strongly on the experimental acquisition windows for echo decay and inversion recovery curves. Short phase memory times are attributed to spin-spin interactions and to motion of the S in the lattices. Relatively weak temperature dependence of spin lattice relaxation rates below about 25 K is attributed to substantial spin-spin interaction and cross relaxation. The strong spin-spin interaction is not present for 0.4 mM S in DMSO:dioxane. The shorter T for S than for SO or SO is attributed to stronger spin orbit coupling.
使青金石（天青石）成为珍贵矿物的蓝色，是由与合成群青蓝（UMB）中相同的S自由基造成的，合成群青蓝已被提议作为连续波电子顺磁共振（CW EPR）标准。比较了三种商业来源的合成UMB、来自阿富汗、智利、美国科罗拉多州和巴基斯坦的青金石样品以及二甲基亚砜：二氧六环溶液中S的连续波和脉冲EPR光谱以及弛豫时间。UMB样品中的自旋浓度很高，在3×10至5×10自旋/克范围内。UMB样品的场扫描回波检测光谱在4.2 K时的线形取决于进行相位调整的场，表明存在强自旋-自旋相互作用。除了浓度为6×10至2.9×10自旋/克的S之外，矿物光谱还包括来自Mn的大量光谱贡献。通过与CaO粉末中的Mn光谱比较，证实了自旋回波检测光谱中归因于禁戒Mn跃迁的特征。弛豫时间的大分布导致推导结果强烈依赖于回波衰减和反转恢复曲线的实验采集窗口。短相位记忆时间归因于自旋-自旋相互作用以及S在晶格中的运动。在约25 K以下，自旋晶格弛豫率相对较弱的温度依赖性归因于大量的自旋-自旋相互作用和交叉弛豫。在二甲基亚砜：二氧六环中0.4 mM的S不存在强自旋-自旋相互作用。S的T比SO或SO短归因于更强的自旋轨道耦合。
