Highly sensitive UV-vis-NIR photothermal deflection spectroscopy (PDS) was used to investigate the pure absorption (absorptance; free from reflection or scattering losses) of the ZIF-62 materials, both crystalline and amorphous (Figure ). In PDS, the sample surface is irradiated with modulated monochromatic light in the 200 to 2500 nm range. Absorption leads to local heating, which results in the formation of a thermal lens in the inert liquid (Fluorinert FC-770, Sigma-Aldrich) surrounding the sample. This thermal lens deflects a 633 nm probe-laser guided parallel to the sample surface. This deflection is proportional to the absorption. Unlike the other employed methods, PDS is not limited by the sample thickness, surface quality (surface roughness is tolerated until thermal lens focusing becomes an issuefixed crystals on glass substrate of grain size ~200µm or less are good to measure, larger crystals become problematic), inner defects and, more important in the present case, porosity of the material. The PDS absorption data (Figure ) is transformed into an internal transmission spectrum using the Beer-Lambert equation (Figure ). While extrinsic effects such as surface reflection and scattering are always affecting the observed total transmittance, for the present case, bulk scattering effects are of particular interest, which can be judged from a comparison of PDS and conventional UV/vis/NIR spectroscopic data. Overall, internal transmittance of agZIF-62 reaches 99.48% in the visible range, which is much higher than was observed by conventional transmission spectroscopy. Comparing panels b) and d) of Figure , there appears to be a red-shift in the fundamental UV absorption edge, however, this impression is caused by the significantly higher sensitivity of PDS as low absorption. In effect, saturation occurs with respect to the photoinduced heat generation, and therefore, with respect to the focal length of the thermal lens. with agZIF-62 marked by the dark blue star.