Detection of X‐Ray Doses with Color‐Changing Hackmanites: Mechanism and Application

Abstract

Hackmanites, a variety of sodalite with the general formula Na8Al6Si6O24(Cl,S)2, are a family of nature‐based smart materials having the ability for reversible photochromism upon UV or X‐ray exposure. Being nontoxic, cheap, and durable, hackmanite would be an optimal material for the visual detection of the presence of X‐rays in simple portable systems. However, its X‐ray‐induced coloring abilities are so far known only qualitatively. In this work, a combination of experimental and computational methods is used to reveal the mechanism of X‐ray‐induced color changing in these materials. Finally, their use is demonstrated both in color intensity‐based X‐ray dosimetry and photochromic X‐ray imaging.

Realizing nondestructive luminescence readout in photochromic ceramics via deep ultraviolet excitation for optical information storage

“…[8][9][10][11][12] Although most reported photochromic materials are organic compounds by far, inorganic photochromic materials possess some inherent advantages over the organic-based materials in the aspects of thermal stability, chemical resistance and fatigue properties, and hence have attracted more attention in recent years. [13][14][15][16][17][18][19][20][21] Currently, the research on inorganic photochromic materials mainly focuses on transition metal oxides (WO3, MoO3, TiO2, Nb2O5 and V2O5), [22][23][24][25][26][27] ferroelectrics (Na0.5Bi4.5Ti4O15, Na0.5Bi2.5Nb2O9, Bi4Ti3O12, KSr2Nb5O15, SrBi2Nb2O9 and K0.5Na0.5NbO3), 10,11,18,20,21,[28][29][30][31][32][33][34][35][36][37] and other robust oxides (BaMgSiO4, Sr2SnO4 and (Ca,Sr,Ba)5(PO4)3F). [38][39][40][41][42][43][44] For these materials, light-induced changes in physical properties such as refractive index, electron conductivity, magnetic properties, refractive index or absorption spectrum can be regarded as the digital code of "0" and "1", respectively.…”

The structural origin of the efficient photochromism in natural minerals

“…In the last few years, the facility to tune the composition of these minerals has been reported experimentally and computationally ( 19 , 24 , 27 ). While these works were done mainly to investigate the effect of composition on the final color of the F-center and almost only based on the hackmanite structure, we understand from the study presented here that all the characteristics associated with the photochromism of the aluminosilicate minerals can be controlled: The activation energy: by selecting the oxidation state of the sulfur activator by adapting the oxidoreduction condition during the synthesis or by using another alkaline ion instead of Na + ( 19 ); The F-center color: by selecting the appropriate Na 4 polyhedron (hackmanite, tugtupite vs. scapolite) and the composition of the β-cage ( 22 ); and The bleaching energy and the kinetic of the phenomenon: by modifying the flexibility of the Na 4 polyhedra first by selecting the structure (hackmanite, tugtupite vs. scapolite) then by tuning the β-cage volume upon chemical modifications.…”

Engineering aluminosilicate's photochromism by quantum chemistry

“…This material has already proven its reliability as a UV, X-ray, and Gamma dose monitor. 3,4 The coloration of the material is due to the reversible formation of F-centers (i.e., trapped electron) in the structure.…”

“…F-center's absorption: after both geometry relaxation and intersystem crossing allowed by a large spin-orbit coupling between 1 [S 2 À , V Cl À (a 1 )] and 3 [S 2 À , V Cl À (a 1 )]) states (cf. ESI †), the F-center trapped in a tetrahedral box made by the sodium atoms has a quantized level of energy, allowing an absorption in the visible range: 3…”

“…Bleaching (or deactivation): the trapped electron is in a metastable state but stable enough so that we can observe the color up to few hours. 8 By absorbing light in the visible range (or under heating), it will reversibly go back onto the sulfur species, and the material will bleach (i.e., loss of color): 3 [S 2 À , V Cl À (a 1 )] -1 [S 2 2À , V Cl (a 1 )]. The energy related to the process is labelled bleaching energy and allows to go back from the colored to the white form.…”