Highly Tuneable Photochromic Sodalites for Dosimetry, Security Marking and Imaging

Abstract

Photochromic sodalites are considered for a plethora of possible applications, such as UV indexing and X‐ray imaging, but for many of these the materials are yet to be optimized. UV indexing can be improved through incremental adjustment of the activation energy of coloration from 300 to 410 nm through replacement of sulfur with selenium. By combining this and other methods of tuning presented in the literature, the excitation threshold and photochromism color can be tuned independently of one another. The range of possible absorption maxima is expanded to 420–680 nm, or almost the entire visible spectrum. Mixing low‐cost and easy‐to‐synthesize sodalites further broadens the possible range of colors and facilitates development of a unique sodalite mix capable of quantifying the doses of two types of UV radiation simultaneously. Finally, the response to X‐rays of these highly tuned sodalites is investigated, and it is found that they can be sensitized to produce clear, high‐contrast X‐ray images at significantly lower doses of radiation than those required by classic photochromic sodalite, Na8(AlSiO4)6(Cl,S)2.

Inorganic photochromic materials: Recent advances, mechanism, and emerging applications

“…The photochromism in robust oxides is usually ascribed to the reversible formation of F‐centers [81] . An F‐center is a type of crystallographic point defect where an anionic vacancy is occupied by one or more unpaired electrons [82,83] .…”

“…The return of the electron from $${\mathrm{V}}_{\text{Cl}}^{-}$$ to $${\mathrm{S}}_{2}^{-}$$ corresponds to the bleaching process (red curves in Figure 3a). Also, the photochromic behavior in sodalite‐based minerals can be regulated through modifying the structure or composition as this will impact the energy of the orbitals involved in the transition [28,81,90,91] . This includes the coloration energy, absorption energy and decoloration energy [46] .…”

“…For example, Byron et al. showed that the energy gap between the F‐center's highest occupied molecular orbital to the lowest unoccupied molecular orbital can be tuned though anion substitution, cation substitution or the combination of both [81] . This causes the maximum absorption peak of the colored sample to shift from 426 to 682 nm (Figure 3b), thus achieving a highly tunable photochromic color from white to almost any other desired color (Figure 3c).…”

Realizing Multicolor and Stepwise Photochromism for On-Demand Information Encryption

“…The last two groups usually show repeatability and reversibility superior to those of the first one. Up to now, photochromic inorganic materials are limited to single color change unless a mixture of several materials is used. − In pursuit of a high level of information security, novel photochromic materials with multicolor variation in a single matrix are highly desirable, facilitating the controllable read-out of optical information.…”

“…Multicolor photochromism in a single matrix requires multiple color centers. Crystal defects play the key role as trap centers to capture, store, and release electron (or hole) carriers in trap-related photochromic materials. ,− A robust crystal with high defect tolerance is a promising candidate to realize a controllable regulation of several color centers and reversible coloration–discoloration performance. For instance, apatite-type material with the framework A 10 (BO 4 ) 6 X 2 features a wide variety of compositions, leading to diverse defects which can be formed due to the different ion substitutions, easy formation of anionic vacancies (V O and V X ), and the presence of one-dimensional X channels.…”