Significance Natural photochromic minerals have been reported by geologists for decades. However, the understanding of the photochromism mechanism has a key question still unanswered: What in their structure gives rise to the photochromism’s reversibility? By combining experimental and computational methods specifically developed to investigate this photochromism, this work provides the answer to this fundamental question. The specific crystal structure of these minerals allows an unusual motion of the sodium atoms stabilizing the electronic states associated to the colored forms. With a complete understanding of the photochromism mechanism in hand, it is now possible to design new families of stable and tunable photochromic inorganic materials-based devices.

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Low-temperature (LT) passivation methods (< 450 o C) for decreasing defect densities in the material combination of silica (SiOx) and silicon (Si) are relevant to develop a diverse technology (e.g. electronics, photonics, medicine), where defects of SiOx/Si cause losses and malfunctions. Many device structures contain the SiOx/Si interface(s), of which defect densities cannot be decreased by the traditional, beneficial high temperature treatment (> 700 o C). Therefore, the LT passivation of SiOx/Si has been, since long, a research topic to improve applications performance. Here, we demonstrate that a LT (< 450 o C) ultrahigh-vacuum (UHV) treatment is a potential method that can be combined with current state-of-theart processes in a scalable way, to decrease the defect densities at the SiOx/Si interfaces. The studied LT-UHV approach includes a combination of wet chemistry followed by UHV-based heating and pre-oxidation of silicon surfaces. The controlled oxidation during the LT-UHV treatment is found to provide an until now not reported crystalline Si oxide phase. This crystalline SiOx phase can explain the observed decrease in the defect density by halve.Furthermore, the LT-UHV treatment can be applied in a complementary, post-treatment way to ready components to decrease electrical losses. The LT-UHV treatment has been found to decrease the detector leakage current by factor of two.

Hackmanites are reusable and non-toxic materials for radiochromic films. They show a unique “gamma memory” function where the width of the reflectance spectrum changes permanently, but the ability to change color reversibly remains fully functional.