In Situ Eu Redox in Cs₃YCl₆ Enabling Colorful Scintillators for Multicolor Radiography and Real‐Time Dosimetry

ABSTRACT

Colorful scintillators with multilayer structures have attracted considerable attention for advanced radiography, but their layered architectures suffer from intrinsic interlayer excitation and photon crosstalk problems. Here, we design and report a single‐phased Cs₃YCl₆:Eu³⁺ scintillator with tunable blue/red emissions via in situ x‐ray‐induced Eu³⁺ reduction. Partial transient reduction of Eu³⁺ with 4f→4f transition to Eu²⁺ with 5d→4f transition in Cs₃YCl₆ is attributed to low‐lying defect states, confirmed by thermoluminescence and density functional theory calculations. Thanks to multicolor characteristics, the colorful Cs₃YCl₆:Eu³⁺ scintillator achieves x‐ray dose real‐time dosimetry within the range from 0.068 to 3.387 mGy, with a maximum relative sensitivity of 233.9% mGy^{− 1}. Furthermore, it exhibits multicolor x‐ray imaging with a resolution of 10 lp mm⁻¹, allowing simultaneous material discrimination and x‐ray dose dosimetry. This work provides a new design principle for the innovation of colorful scintillators and high‐precision multicolor x‐ray detection technologies.

We present a single‑phase colorful Cs₃YCl₆:Eu³⁺ scintillator, where X‑ray‑induced transient Eu³⁺→Eu²⁺ reduction enables intrinsic multicolor emission, and the mechanism is underpinned by shallow defect states. The scintillators serve a dual function: real‑time X‑ray dose monitoring and high‑resolution multicolor imaging for direct material discrimination.

1. Introduction

X‐ray imaging technology plays a critical role in medical diagnostics, security inspection, and industrial nondestructive testing [1, 2, 3, 4, 5]. The traditional monochrome images in x‐ray imaging rely on energy‐integrating detectors, which generate contrast between light and dark by accumulating the total x‐ray intensity. However, in this process, only the signal of x‐ray‐responsible photons is accumulated while the energy of the photons is ignored [6, 7]. This mechanism results in poor discrimination between materials of similar density and fails to meet the imaging demands of complex scenarios [8, 9]. Multicolor x‐ray imaging techniques have emerged to overcome this limitation by using scintillators with multilayer structures [10, 11]. In such architectures, the top scintillator layer is sensitive to low‐energy x‐rays and emits long‐wavelength light, whereas the underlying layer absorbs high‐energy x‐rays and produces short‐wavelength emission [12, 13]. The detailed information of substances has been more accurately distinguished under the combination of multi‐wavelength light. Nevertheless, the stacked architectures introduce some inherent interference problems, including interlayer excitation, photon crosstalk, and transmission loss, which significantly degrade energy‐resolution accuracy [14, 15]. In contrast, single‐layer multicolor scintillators structurally avoid such crosstalk issues while simplifying the fabrication process and reducing potential costs. Therefore, high‐performance single‐layer multicolor scintillators will propel next‐generation high‐precision x‐ray imaging forward.

Rare‐earth Eu ions are considered a possible approach for achieving single‐phase multicolor luminescence due to the self‐reduction behavior of Eu³⁺ to Eu²⁺ [16, 17, 18], and the tunable emissions from the two activators [19, 20]. These states enable the coexistence of red emissions of Eu³⁺ and tunable blue emissions from Eu²⁺ within a single host [21]. Notably, the self‐reduction and coexistence of Eu ions usually originate from energy traps; however, the trap depths within oxides are relatively deep, causing Eu‐doped oxides to exhibit significant afterglow emission [22, 23, 24, 25]. Such exceptionally long luminescence lifetime will lead to delays in imaging response, making it difficult to meet the requirements for real‐time imaging and reusability [26, 27]. Fortunately, the tunable trap depths in emerging low‐dimensional metal halides (perovskites) do not result in excessively long afterglow [28, 29], making them an excellent choice for the single‐layer multicolor scintillator. Therefore, achieving both the coexistence of Eu³⁺/Eu²⁺ and fast luminescence decay is of vital significance in the development of single‐layer multicolor x‐ray imaging technology.

Recently, 0D metal halides, characterized by their strong quantum confinement effects and structural unit isolation, typically exhibit exceptional thermal stability and radiation resistance [30, 31, 32, 33, 34, 35, 36]. Among these, the rare‐earth‐based 0D metal halide Cs₃YCl₆ has emerged as an excellent host, featuring a simple energy level structure of yttrium. Herein, we successfully constructed a single‐layer multicolor scintillator, that is, Eu³⁺ doping of Cs₃YCl₆. Under x‐ray excitation, partial transient reduction of Eu³⁺ to Eu²⁺ luminescent centers occurs, simultaneously generating blue, green, and red emissions. The luminescent mechanism of monophasic enables color imaging without a multilayer architecture, enhancing imaging contrast while fundamentally circumventing photon‐crosstalk issues caused by interlayer interference. Owing to the differential growth trends of luminescence intensities across color channels with increasing x‐ray dose, we achieved highly sensitive x‐ray dose monitoring within the range of 0.06 to 3.387 mGy using the RL intensity ratio technique, reaching a maximum relative sensitivity of 233.9% mGy⁻¹. The multicolor imaging characteristics of Cs₃YCl₆:Eu³⁺ show potential for enhancing imaging contrast of biological tissue structures in medical imaging, while simultaneously enabling high‐sensitivity radiation real‐time dose monitoring. This in‐situ Eu redox strategy provides a new material design platform and technical pathway for developing high‐precision, intelligent next‐generation multifunctional medical imaging technologies.

2. Results and Discussion

Eu³⁺‐doped Cs₃YCl₆ microcrystals (MCs) were successfully synthesized via a simple room‐temperature recrystallization method. The crystals crystallized in the monoclinic structure with a space group C2/c (Figure 1a). Specifically, isolated octahedral [YCl₆]³⁻ units were completely separated by surrounding Cs⁺ ions, forming a 0D framework. Powder x‐ray diffraction (PXRD) patterns of the as‐synthesized Cs₃YCl_6:Eu³⁺ at different doping concentrations show an agreement with the standard pattern of monoclinic Cs₃YCl₆ (PDF#04–010–7421) (Figure 1b), confirming the purity of the Eu³⁺‐doped Cs₃YCl₆ MCs, and the Rietveld refinement results on the various doping concentrations are summarized in Table S1. The lattice parameters a, b, and c gradually expand with increasing doping concentration, as indicated by the doping concentration‐dependent unit cell volume (Figure S1). This signifies the successful substitution of larger Eu³⁺ ions (0.947 Å, CN = 6) for smaller Y³⁺ ions (0.9 Å, CN = 6) [37]. Elemental mapping from scanning electron microscopy (SEM) images reveals a uniform distribution of Cs, Y, Cl, and doped Eu elements within Cs₃YCl₆:Eu³⁺(Figure S2), further confirming the existence of Eu.

FIGURE 1.

(a) Schematic of the crystal structure of Cs₃YCl₆:Eu³⁺ MCs. (b) X‐ray diffraction (XRD) patterns of Cs₃YCl₆:Eu³⁺ MCs with different Eu doping concentrations. (c) The k³ weighted Eu L₃‐edge EXAFS spectra and corresponding Fourier transform fitting as a function of R of Cs₃YCl₆:Eu³⁺. The gray dashed area represents the data fitting area. (d) Photoluminescence excitation (PLE), PL, and RL spectra of the synthesized Cs₃YCl₆:Eu³⁺ MCs. (e) RL spectra of Cs₃YCl₆:Eu³⁺ microcrystalline composites at different Eu³⁺ doping concentrations. (f) Time‐resolved RL decay curve of Cs₃YCl₆:Eu³⁺ measured at 460 nm and time‐resolved PL decay curve measured at 615 nm.

Subsequently, the local coordination environment of Eu³⁺ in Cs₃YCl_6:Eu³⁺ was further probed by Eu L ₃‐edge extended x‐ray absorption fine structure (EXAFS) spectroscopy. The k ³‐weighted EXAFS oscillation and its corresponding Fourier‐transform (FT) spectrum are displayed in Figure 1c, with detailed fitting parameters compiled in Table S2. The spectra were well fitted (R factor = 0.018), with the fitted CN in the first coordinated shell bing 6.3 ± 1.8, and the R for the Eu─Cl bond is 2.57 ± 0.02 Å. The obtained CN close to 6 indicates that Eu³⁺ is situated in a well‐defined [EuCl₆]³⁻ octahedral coordination sphere, which corroborates the successful substitution of Eu³⁺ for Y³⁺ in the host lattice without significant structural distortion [38, 39].

To further investigate its luminescence properties, the photoluminescence (PL) and radioluminescence (RL) spectra were comparatively characterized (Figure 1d). The PL spectrum exhibits characteristic peaks of Eu³⁺ at 592 and 615 nm, corresponding to the ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ electronic transitions, respectively. In contrast, the RL spectrum reveals an additional broad emission band centered at 460 nm, which is attributed to the allowed 4f⁶5d¹ → 4f⁷ transition of Eu²⁺ ions [40]. Subsequently, RL spectra of Cs₃YCl₆:xEu³⁺ samples with varying doping concentrations (x = 1%, 2%, 3%, 5%, and 7%) were further collected (Figure 1e). The results indicate that all samples exhibit a broad emission at 460 nm under x‐ray excitation. As the Eu³⁺ doping concentration increases, the intensity ratio between the red emission of Eu³⁺ ions and the blue emission of Eu²⁺ also rises correspondingly. The result demonstrates that the relative intensities of red and blue emissions in Cs₃YCl₆:xEu³⁺ can be effectively modulated by controlling the Eu³⁺ doping concentration. The lifetime of the blue emission at 460 nm in Cs₃YCl₆:Eu³⁺ under x‐ray excitation was fitted to be 489 ns, a value consistent with the characteristic 5d‐4f lifetime of Eu²⁺, thereby confirming its origin in the electronic transitions of Eu²⁺ (left of Figure 1f). Simultaneously, the red emission at 615 nm exhibits a lifetime of 826 µs, which aligns with the luminescent transition characteristics of Eu³⁺ ions (right of Figure 1f).

Notably, the blue emission at 460 nm is unique to x‐ray excitation and absent in the PL spectrum (Figure 1d), indicating a transient reduction of partial Eu³⁺ in Cs₃YCl₆:Eu³⁺ under x‐ray induction. When irradiation stops, the metastable Eu²⁺ is oxidized back to Eu³⁺. To unequivocally determine the valence state of Eu in Cs₃YCl₆:Eu³⁺ under x‐ray excitation, we employed a comprehensive approach including x‐ray absorption near‐edge structure (XANES) analysis and x‐ray photoelectron spectroscopy (XPS) (Figure S3). The high‐resolution Eu 3d XPS spectrum of the Cs₃YCl₆:7%Eu³⁺ sample is presented in Figure 2a, exhibiting four distinct peaks within the binding energy range of 1110–1170 eV. The two peaks at the lowest binding energies (1124.0 and 1154.0 eV) correspond precisely to the 3d_5/2 and 3d_3/2 energy levels of Eu²⁺, respectively, while the two higher binding energy peaks of 1135.2 eV and 1165.0 eV are attributed to the 3d_5/2 and 3d_3/2 energy levels of Eu³⁺ [41]. And the Eu‐L ₃ near‐edge absorption spectra of the Cs₃YCl₆:Eu³⁺ sample exhibit two absorption peaks at 6974 and 6983 eV (Figure 2b), corresponding to the 2p_3/2→5d energy level transitions of Eu²⁺ and Eu³⁺ [42]. Collectively, these results further confirm the transient reduction of partial Eu³⁺ to Eu²⁺ in Cs₃YCl₆:Eu³⁺ under x‐ray irradiation.

FIGURE 2.

(a) High‐resolution x‐ray photoelectron spectroscopy (XPS) spectra of Cs₃YCl₆:Eu³⁺ MCs, Eu 3d. (b) Eu L₃‐edge XANES spectra of Cs₃YCl₆:Eu³⁺. (c) PL spectra of Cs₃YCl₆: Eu³⁺ after x‐ray irradiation at 300 and 80 K. (d) Thermoluminescence spectra of Cs₃YCl₆ with or without Eu³⁺ doping under x‐ray excitation. (e) Phase structure and transformation analysis. (f) The formation energy of the Cs₃YCl₆:Eu³⁺ sample as a function of the Fermi level. (g) Schematic illustration of the x‐ray‐induced reduction mechanism from Eu³⁺ to Eu²⁺.

We further revealed its underlying photophysical mechanism. At 300 K, the material after x‐ray pre‐irradiation exhibits only the characteristic transitions of Eu^{3 +} under UV excitation. However, an additional blue emission at 460 nm emerges under the same conditions at low temperature (Figures 2c and S4). This behavior indicates that at room temperature (300 K), the trapped electrons acquire sufficient thermal energy to escape, leading to reoxidation of Eu²⁺ to Eu³⁺ and consequently quenching the Eu²⁺ emission. At low temperatures of 80 K, however, the thermal energy is insufficient to overcome the potential barrier and release the trapped electrons. This allows Eu²⁺ to remain stable, enabling the 4f⁶5d¹ → 4f⁷ energy level transition originating from Eu²⁺ upon 375 nm optical excitation, resulting in extra blue light emission near 460 nm. The thermoluminescence (TL) measurements on both Eu‐doped and undoped Cs₃YCl₆ samples after x‐ray irradiation were also performed (Figure 2d). The undoped sample exhibits a dominant TL peak at 200 K, whereas the Eu³⁺‐doped sample shows not only this main peak at 200 K but also an additional trap level appearing at approximately 226 K. Generally, the depth of traps (E _t) can be calculated using the following equation [43]:

$$\begin{array}{c}{E}_t\left(\mathrm{eV}\right)=\frac{T_m}{500}\end{array}$$ (1)

where T _m corresponds to the temperature at the TL peak maximum, the computational results indicate that the two trap depths are approximately 0.4 and 0.452 eV, respectively, which fall within the typical range for shallow‐level traps. As this category of traps readily releases captured carriers through thermal agitation at room temperature, the samples exhibit no significant afterglow following the cessation of x‐ray irradiation, nor do they require external stimulation to retrieve effective information. This characteristic effectively prevents signal persistence during imaging procedures, demonstrating the strong potential of Cs₃YCl₆:xEu³⁺ materials for real‐time, multicolor x‐ray imaging applications.

To further understand the RL mechanism of Cs₃YCl₆:Eu³⁺, we conducted systematic density functional theory (DFT) calculations on Cs₃YCl₆:Eu³⁺ and host samples. Figure 2e presents the isothermal cross‐sectional phase diagram of the CsCl‐YCl₃ binary system at a specific temperature, revealing the stability regions of various phases under different chemical potential conditions. The diagram demonstrates that the Cs₃YCl₆ phase maintains a broad stability region within a certain Δμ range, and the definition of Δμ is provided in the Supporting Information, indicating its favorable thermodynamic stability under experimental synthesis conditions. The blue markers represent energy data points obtained from first‐principles calculations, with their positions corresponding to the formation energies of the system at specific chemical compositions. These data enable the determination of the Fermi level at respective compositions, providing crucial references for analyzing electronic structures and defect formation tendencies.

Therefore, the reversible valence transition (Eu³⁺ ⇌ Eu²⁺) observed under x‐ray excitation can be rationally explained by a defect formation energy theory. As shown in Figure 2f, under equilibrium conditions at room temperature, the Fermi level is pinned at approximately 0.45 eV, where the formation energy of Eu_Y ⁰ (Eu³⁺) is significantly lower than that of Eu_Y ⁻¹ (Eu²⁺). Consequently, Eu ions are stabilized predominantly in the trivalent state (Eu³⁺) at Y lattice sites. Concurrently, Cl vacancies (V _Cl) and Cs vacancies (V _Cs) exhibit relatively low formation energies, serving as the dominant intrinsic defects that provide the necessary trap centers for carrier capture. Upon x‐ray irradiation, the system is strongly excited, generating a high concentration of energetic electron–hole pairs. The electron concentration in the conduction band increases dramatically under this non‐equilibrium condition. Shallow defects near the conduction band readily capture electrons, forming negatively charged defect states. Density of states (DOS) indicates that the Eu 5d states hybridize significantly with the conduction band and extend deeply into its bottom (Figure S5), which substantially lowers the energy barrier for electron transfer from the conduction band to Eu sites. Thus, electrons can be efficiently transferred from the conduction band or defect states to Eu³⁺, inducing the transient reduction of a portion of Eu³⁺ ions [44] (Figure 2g). After the x‐rays turned off, external energy input ceased, and the system returned to thermal equilibrium. Electrons and holes recombine, and the high electron population in the conduction band and defects is depleted. The extra electron in Eu²⁺ is returned to the conduction band or transferred to hole/defect centers via thermal activation, leading to the spontaneous reoxidation of Eu²⁺ back to Eu³⁺. Therefore, Eu²⁺ exists only as a metastable state after x‐ray removal, with its lifetime governed by the trap depth and thermal activation processes.

Generally, distinct luminescent centers exhibit different responses to x‐ray irradiation due to their unique electronic structures. Although both Eu²⁺ and Eu³⁺ emissions in Cs₃YCl₆:3%Eu³⁺ demonstrate intensity enhancement with increasing radiation dose under x‐ray irradiation, their respective growth rates differ significantly. This divergence results in distinguishable luminescence colors across varying dose levels, enabling preliminary qualitative identification of x‐ray dose through visualization analysis. A scintillating screen based on Cs₃YCl₆:3%Eu³⁺ MCs was fabricated, and its dose–luminescence response relationship was systematically investigated. Specifically, the MCs were uniformly dispersed in methanol and fabricated into a single‐matrix multicolor scintillating screen via a spin‐coating process. The scintillating screen exhibits bright orange‐red emission under UV excitation (Figure S6). The RL spectra of the single‐matrix Cs₃YCl₆:3%Eu³⁺ scintillator under x‐ray tube voltages ranging from 10 to 37 kV, with the current fixed at 50 µA (Figure S7a). Under x‐ray excitation, the scintillator exhibits characteristic multicomponent luminescence: the broad emission centered around 460 nm originates from the 5d–4f transition of Eu²⁺, while the sharp‐line emissions at 535 and 612 nm correspond to the ⁵D₁→⁷F₂ and ⁵D₀→⁷F₂ characteristic transitions of Eu³⁺, respectively. Notably, the three RL components exhibit distinctly different growth trends as the x‐ray dose increases (Figure S7b). Specifically, the blue RL intensity demonstrates a significantly higher growth rate compared to the green and red components, resulting in a systematic shift in the overall emission color of the sample with increasing tube voltage. This color evolution process can be quantitatively described through CIE 1931 chromaticity analysis (Figure 3a,b). As the x‐ray tube voltage increasing from 10 to 37 kV, the chromaticity coordinates progressively shift from (0.332, 0.341) to (0.244, 0.182), forming a distinct trajectory on the chromaticity diagram that corresponds to a continuous transition from bluish to purplish‐red emission.

FIGURE 3.

(a) The evolution of CIE coordinates in Cs₃YCl₆:3%Eu³⁺ scintillator corresponding to RL spectra under different x‐ray tube voltages. (b) The corresponding x‐ray imaging colors calculated from the x, y, z chromaticity coordinates in (a). (c) The dependence of RL intensity at 460, 535, and 615 nm on x‐ray dose. (d) The fitting curve of the blue‐to‐green emission intensity ratio versus x‐ray dose for the Cs₃YCl₆:3%Eu³⁺ scintillator. (e) The relative sensitivity (Sr) curves of different luminescence intensity ratios versus x‐ray dose for the Cs₃YCl₆:3%Eu³⁺ scintillator. (f) The error values between the calculated and actual doses under different tube voltages.

To achieve precise detection of x‐ray dose, the RL intensity ratio between Eu²⁺ and Eu³⁺ was employed for quantitative analysis. With the current fixed at 50 µA, the x‐ray tube voltage was increased from 10 to 26 kV, corresponding to a dose range from 0.068 to 3.387 mGy (Figure S8a–c). With rising dose, the luminescence intensities at 460 (blue), 535 (green), and 612 nm (red) exhibit linear growth (Figure 3c), with the highest growth rate being shown by the blue emission and the lowest by the green emission. Further analysis of the intensity ratios between different wavelength pairs (I _Blue/I _Green, I _Blue/I _Red, I _Red/I _Green) versus dose (Figure S8d) reveals that I _Blue/I _Green demonstrates the highest sensitivity and most pronounced response to dose variation. Therefore, the I _Blue/I _Green ratio in Cs₃YCl₆:3%Eu³⁺ scintillator can serve as an effective indicator for dose monitoring. The intensity ratio between blue and green RL is well‐fitted using the following Equation (2):

$$\begin{array}{c}\frac{I_{blue}}{I_{green}}=4.6656-3.6248e^{-\frac{x}{1.1755}}\end{array}$$ (2)

The Cs₃YCl₆:3%Eu³⁺ scintillator demonstrates promising potential for x‐ray dose detection, as shown in Figure 3d. To further evaluate its sensitivity, the relative sensitivity (S _r) was calculated using the following Equation (3):

$$\begin{array}{c}{S}_r=\left|\frac{1}{FIR}\frac{dFIR}{dx}\right|=\left|\frac{1}{I_{Blue}/I_{Green}}\frac{d\left(I_{Blue}/I_{Green}\right)}{dx}\right|\end{array}$$ (3)

As anticipated, the blue‐to‐green intensity ratio (I _Blue/I _Green) demonstrates the most pronounced response to x‐ray dose variation, exhibiting the highest relative sensitivity (Figure 3e). The calculated maximum S _r value reaches 233.9% mGy^{− 1}, indicating its exceptional sensitivity performance for low‐dose biomedical x‐ray detection. To evaluate the accuracy and practical applicability of the Cs₃YCl₆:3%Eu³⁺ scintillator in x‐ray dosimetry, we systematically acquired RL spectra at random tube voltages (ranging from 11.2 to 18.5 kV) and derived corresponding x‐ray dose values based on the I _Blue/I _Green ratio. The intensity ratios were converted into estimated dose values using a predetermined fitting formula (Equation 1), while reference dose measurements were simultaneously obtained under identical geometric conditions using a calibrated x‐ray detector. The results demonstrate that across all tested voltages, the deviation between the dose values calculated from the I _Blue/I _Green ratio and the experimentally measured values remains below 0.1 mGy (Figure 3f). The close agreement between these datasets confirms the excellent quantitative accuracy and reliability of this material under practical detection conditions.

To further evaluate the imaging capability of Cs₃YCl₆:3%Eu³⁺ scintillator in material discrimination, a test mold comprising materials with varying densities was designed and fabricated (Figure 4a). The pattern consists of a 2‐mm‐thick rectangular iron plate with cavities engraved in the shapes of the letters “S”, “C”, “U”, and “T”. These cavities were filled with three materials of progressively decreasing x‐ray attenuation coefficients: the “S” cavity was left unfilled and the “C”, “U”, and “T” cavities were filled with titanium alloy (4.51 g cm⁻³), aluminum (2.7 g cm⁻³), and the epoxy fiberglass (1.75 g cm⁻³), respectively. The thickness of the filler material in the “C”, “U”, and “T” cavities was uniformly 0.4 mm. X‐ray color imaging of the mold was performed using LuAG:Ce and Cs₃YCl₆:3%Eu³⁺ scintillators (Figure 4b). It was observed that the conventional LuAG:Ce scintillator exhibits low color contrast between aluminum and fiberglass, making clear discrimination difficult. In contrast, the Cs₃YCl₆:3%Eu³⁺ scintillator clearly displayed color differences between aluminum and glass fibers in the images due to its radiation dose‐dependent luminescence color shift, achieving high‐contrast differentiation of materials with similar densities. The advantage of this material for multicolor X‑ray imaging and material identification is thus highlighted. Multicolor X‑ray imaging spectra were systematically acquired for both scintillators on the four materials with different densities (Figure 4c). A single broad peak was observed in the LuAG:Ce spectrum, where signal variations are manifested only as overall intensity changes. Consequently, in the chromatic images, different materials merely exhibit differences in brightness, resulting in low color contrast and ineffective material discrimination based on hue. In contrast, three distinct emission bands, each corresponding to radioluminescence in different wavelength ranges, are presented by the Cs₃YCl₆:3%Eu³⁺ scintillator.

FIGURE 4.

(a) The imaging object comprises a rectangular structure fabricated from materials of varying densities. (b) A comparative x‐ray imaging study of the object in panel (a) using LuAG:Ce and Cs₃YCl₆:3%Eu³⁺ scintillators. (c) X‐ray imaging spectra of LuAG:Ce and Cs₃YCl₆:3%Eu³⁺ scintillators for materials with different densities. (d) The error values between the calculated and actual doses for x‐rays transmitted through different materials. (e) Multicolor x‐ray imaging of a pen tip using Cs₃YCl₆:3%Eu³⁺ scintillator. (f) RGB values along the red dashed line in panel (e), CS: spring; PS: plastic section.

Owing to the varying X‑ray attenuation capabilities of the different materials, the excited RL intensities of these bands also differ. This characteristic generates color contrast in the images, enabling density‑based discrimination via spectral features. By substituting the I _Blue/I _Green ratio from the imaged area of each material into Equation (1), the dose of x‑rays reaching the scintillator after penetrating the material was inversely calculated. Under identical x‑ray irradiation conditions, the transmitted dose through each material was also measured with a radiation detector. The results show a deviation within 0.3 mGy of the measured dose (Figure 4d), successfully achieving the integrated combination of multicolor x‐ray imaging and real‐time dose monitoring.

In a practical demonstration, multicolor x‐ray imaging of a pen‐tip structure was performed (Figure 4e). Owing to the differences in x‐ray absorption coefficients among the constituent materials, a distinct color contrast was observed in the image: the spring and the metal tip appeared dark blue, while the plastic body was shown as purplish‐red. The background, where no object absorbed x‐rays, exhibited white emission because the high‐energy x‐rays fully excited all luminescent centers (Eu³⁺ and Eu²⁺) in the scintillator, resulting in a balanced enhancement of the blue, green, and red emission bands, which superimposed to produce white light. This visually intuitive color imaging clearly differentiated the material components, with a spatial resolution of 10 lp mm⁻¹ (Figure S9). For quantitative analysis, RGB intensity profiles at positions 1–4 along the red dashed line in Figure 4e were extracted (Figure 4f). The data reveal significant variations in the R and G values at different positions, directly reflecting the differences in imaging color originating from the intrinsic material properties. These results further confirm the potential of the scintillator for multicolor discrimination and high‐precision material identification in complex structures.

3. Conclusion

In conclusion, we develop a single‐phase Cs₃YCl₆:Eu³⁺ scintillator, in which intrinsic multicolor emission is enabled by in situ x‐ray‐induced reduction of Eu³⁺ to Eu²⁺, thereby eliminating the photon‐crosstalk limitations associated with conventional multilayer architectures. This reversible valence transition, mediated by shallow defect states, is corroborated by thermoluminescence spectroscopy and density‐functional‐theory calculations. The scintillator achieves high‐sensitivity real‐time monitoring of x‐ray dose within a low‐dose range of 0.068 mGy to 3.387 mGy, with a maximum relative sensitivity of 233.9% mGy⁻¹. Meanwhile, multicolor x‐ray imaging has been demonstrated with a spatial resolution of 10 lp mm⁻¹, exhibiting superior color‐imaging contrast relative to conventional LuAG:Ce scintillators and enabling simultaneous material discrimination and dose monitoring within a single platform. This work provides a feasible design strategy and theoretical foundation for developing novel multifunctional x‐ray detection materials.

Author Contributions

Yongqi Zhao: investigation, writing – original draft, writing – review and editing. Chenliang Li: investigation. Lihan Chen: investigation. Baoling Tang: investigation. Yutong Hu: investigation. Kai Han: investigation, writing – original draft, methodology, writing – review and editing. Zhiguo Xia: conceptualization, methodology, investigation, writing – original draft, writing – review and editing.

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Supporting File: anie72622‐sup‐0001‐SuppMat.docx.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.