Mechanism and Application of X-ray Induced Photochromic Materials: A Review

doi:10.15541/jim20250025

Abstract

Abstract:

X-ray induced photochromic (XP) materials, characterized by their radiation dose-dependent coloration properties, exhibit broad application potential in national defense and security, nuclear energy development and utilization, industrial nondestructive testing, and medical imaging. In recent years, scientists worldwide have developed diverse XP material systems, conducted in-depth investigations into their radiation-induced coloration mechanisms, and explored their specialized applications, highlighting the urgent need for a comprehensive review on their working principles and application domains. This article systematically summarizes the material systems exhibiting XP behavior, categorizing them based on chemical composition and coloration characteristics. Their advantages and limitations are comparatively analyzed, while their underlying mechanisms, such as color center formation and redox processes, are analyzed. Furthermore, their potential applications in X-ray detection, medical diagnostics, and industrial monitoring are introduced. Finally, their future research directions are proposed to develop new XP materials with enhanced performance and broader scenario adaptability. This review holds significant implications for guiding subsequent research on optimizing XP materials and accelerating their commercialization process, thereby facilitating the practical implementation of XP technologies.

Key words: photochromic material, X-ray, radiation-induced coloration, chromic mechanism, radiation dosage measurement, review

CLC Number:

TQ174

YUAN Long, JIA Ru, YUAN Meng, ZHANG Jian, DUAN Yu, MENG Xiangdong. Mechanism and Application of X-ray Induced Photochromic Materials: A Review[J]. Journal of Inorganic Materials, 2025, 40(10): 1097-1110.

Figures/Tables 8

Fig. 1 Electromagnetic spectrum with the red box indicating the wavelength range corresponding to X-rays, and the curve above representing the electromagnetic wave energy

Table 1 Advantages and disadvantages of XP materials[14-21]

Material system	Advantage	Disadvantage	Mechanism
Organic XP material (Iodine modified isomers based on 9,9'-(6-iodophenoxy- 1,3,5-triazine-2,4-diylbis (9h carbazole)^[14], diarylethene- type photochromic compounds^[15], etc.)	Easy to regulate optical properties; Flexible, tunable photosensitive band and reaction rate through chemical modification; Lightweight, easy to shape, and suitable for various carriers	Poor stability and susceptibility to environmental factors such as humidity and oxygen; Low thermal stability	Reversible photoisomeri- zation or open-closed-loop reaction of organic molecules under X-ray excitation to achieve color change by adjusting the electronic transition energy level of the molecule
Organic inorganic hybrid XP material (Zn(II)-viologen coordination polymers^[16], methylviologen-templated layered bimetal phosphate^[17], Eu-MOF^[18], etc.)	Combining flexibility of organic materials with stability of inorganic materials; Multifunctional and adjustable based on the ratio of organic and inorganic parts; Wide radiation response range tunable optical properties through material design	Complex synthesis, stability of interface bonding needs to be further improved; Complexity of material composites resulting in difficulty in mass production and repeatability control	Based on the interfacial charge transfer or energy transfer between organic and inorganic components, the synergistic initiation of structural reorganization or redox reaction leads to color change
Inorganic XP material (NaLuF₄:Ho^3+[19], WO₃^[20], BaMgSiO₄^[21], etc.)	High stability, high temperature resistance, and corrosion resistance; Strong responsiveness to high- energy radiation such as X-rays; Good thermal, light, and chemical stability, excellent long-term performance	Usually, less obvious color change than that of organic materials, difficult in controlling reversibility; Poor flexibility, difficult in processing into complex structures	X-rays induce lattice defects or metal ion valence state changes, changing the band structure of the material or forming a color center, and finally achieving color change

Table 1 Advantages and disadvantages of XP materials[14-21]

Material system	Advantage	Disadvantage	Mechanism
Organic XP material (Iodine modified isomers based on 9,9'-(6-iodophenoxy- 1,3,5-triazine-2,4-diylbis (9h carbazole)^[14], diarylethene- type photochromic compounds^[15], etc.)	Easy to regulate optical properties; Flexible, tunable photosensitive band and reaction rate through chemical modification; Lightweight, easy to shape, and suitable for various carriers	Poor stability and susceptibility to environmental factors such as humidity and oxygen; Low thermal stability	Reversible photoisomeri- zation or open-closed-loop reaction of organic molecules under X-ray excitation to achieve color change by adjusting the electronic transition energy level of the molecule
Organic inorganic hybrid XP material (Zn(II)-viologen coordination polymers^[16], methylviologen-templated layered bimetal phosphate^[17], Eu-MOF^[18], etc.)	Combining flexibility of organic materials with stability of inorganic materials; Multifunctional and adjustable based on the ratio of organic and inorganic parts; Wide radiation response range tunable optical properties through material design	Complex synthesis, stability of interface bonding needs to be further improved; Complexity of material composites resulting in difficulty in mass production and repeatability control	Based on the interfacial charge transfer or energy transfer between organic and inorganic components, the synergistic initiation of structural reorganization or redox reaction leads to color change
Inorganic XP material (NaLuF₄:Ho^3+[19], WO₃^[20], BaMgSiO₄^[21], etc.)	High stability, high temperature resistance, and corrosion resistance; Strong responsiveness to high- energy radiation such as X-rays; Good thermal, light, and chemical stability, excellent long-term performance	Usually, less obvious color change than that of organic materials, difficult in controlling reversibility; Poor flexibility, difficult in processing into complex structures	X-rays induce lattice defects or metal ion valence state changes, changing the band structure of the material or forming a color center, and finally achieving color change

Fig. 2 Reversible formation mechanism of color center[45] (a) LAS-Sm relationship between diffuse reflectance intensity and X-ray dose rate accompanied by its corresponding photos; (b) EPR spectra of O element in initial state, photochromic state, and decolorized state; (c) Photochromic and luminescent modulation mechanism of LAS-Sm fluorescent powder; (d) Morphology of leaves and roses after irradiation with gradually prolonged time or different dose rates in bright and dark fields

Fig. 3 Redox reaction mechanism[20,25] (a) Digital photos of WO3 powder under different X-ray irradiation times[20]; (b, c) XPS (Al-Kα) nuclear level spectra of WO3 powder before (b) and after (c) X-ray irradiation[20]; (d) General model for X-ray induced photochromism of transition metal oxides[25]

Fig. 4 Photoelectron transfer mechanism of defects associated with cross-relaxation[19] (a) Photos of NaLuF4: Ho3+ NCs doped with different concentrations of Ho3+ ions at different X-ray irradiation doses; (b) Color changing mechanism of NaLuF4: Ho3+ NCs

Fig. 5 Application of XP materials in X-ray detectors[18,21,27,57] (a-c) X-ray detection performance of single component and heterojunction detectors under 15 keV X-ray and -50 V bias[57]: (a) Current density of single component and heterojunction as a function of incident dose rate; (b) Dose dependent current density of single component and heterojunction with dashed line representing a signal-to-noise ratio (SNR) of 3; (c) Comparison of dark current density, sensitivity, and detection limit (LOD) of several advanced polycrystalline perovskite X-ray detectors; (d) Single crystal exposed to Cu-Kα X-ray (λ at 0.154056 nm, generator power at 2.97 kW) discoloration photo[18]; (e) Colour images of Al-Kα X-rays over time after 1 min of irradiation[27]; (f) Reflectance of BaMgSiO4 after exposure to different doses of X-rays (1.875 Gy·min-1)[21]; (g) Relationship between ΔR1 (coloring) and comprehensive X-ray irradiation dose[21]; (h) Dosimetric behavior of BaMgSiO4 under different X-ray irradiation intensities[21]; (i) Concept validation dosimeter for colorimetric detection of radiation dose[21]

Fig. 6 XP materials for X-ray imaging applications[26,28,36] (a) X-ray image of a tape measure[28]; (b) Pig trotters with a large flashing screen[28]; (c) Dynamic X-ray image of a chopper[28]; (d) High resolution Xr LEI illustrated by schematic diagram of 3D electronic imaging achieved by a flexible detector integrated with nano scintillators (Firstly, insert the detector into the 3D electronic circuit board for conformal coating; Next, the image of the electronic board is projected onto the detector; After stopping the X-ray, the detector is transferred to a hot substrate for thermal stimulation and subsequent luminescence imaging)[36]; (e) Xr LEI (voltage 50 kV) of 3D electronic board using prototype NaLuF4:Tb (15%, in mol) @NaYF4 detector[36]; (f) Photos of organic gel scintillators immersed in water under visible light and 365 nm ultraviolet light[26]; (g) Photos of snails under visible light and organic gel scintillators conducting self-healing X-ray imaging in water[26]

Fig. 7 Application of XP materials in the field of information storage and anti-counterfeiting[35] (a) BNN:Er ceramic for reading, writing, and erasing processes of optical information; (b) Dual mode for fast optical storage; (c) Dynamic encryption for optical storage model

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