Your asking about near IR wavelength.
I'm sure you'll find absorbance numbers in optical material data. Of course the structure matters. Crystalline SiO2 (fused silicia, quartz) has a good transparency around 1.5 µm, absorption of IR quality quartz fibre optic is measured in dB/km. Silicon has a low pass wavelength of about 1 µm and still some absorption at 1.5 µm. You should be able to calculate a loss tangent from optical data (after correction for reflection losses).