On the Problem of Inhomogeneous Spatial Distribution of the Redox Index of Polyvalent Iron Ions in the Volume of Ultrapure Synthetic Quartz Materials

We show that the strong spatial inhomogeneity of absorption (the change from the maximum to the minimum value was more than 50 times on a spatial scale of the order of 200–300 μm), which was observed in our earlier studies of ultrapure synthetic quartz glasses and a synthetic quartz crystal at a wavelength of 1070 nm, can be related to an inhomogeneous spatial distribution of the redox state of iron traces. Using experimental data on absorption of metal impurities in the studied glasses, we present a calculation of the iron ion concentration, which is of the order of a few ppb. This is several times better than the limit of detection of the mass spectrometry method used for certification of ultrapure quartz glasses. Based on the results of the mass spectrometry measurements of concentrations given by manufacturers and the values of the maximum (10⁻⁵ cm⁻¹) and minimum (10⁻⁷ cm⁻¹) absorption coefficient we have measured, we calculated the maximum possible concentrations of the Fe²⁺ and Cu²⁺ ions and OH groups in quartz glasses and hydrothermal synthetic crystalline quartz.