Gd/Tb/Eu alloyed double-perovskite lanthanide halides for color tunable photoluminescence and robust scintillation performance

Abstract

Double-perovskite materials with diverse elemental compositions have been developed as high-performance phosphors and scintillators. However, the low doping concentration of activator ions in the host matrix limits the flexible tuning of luminescence properties. In this work, we propose a series of gadolinium, terbium, and europium alloyed double-perovskite lanthanide chlorides (DPLCs) to achieve color-tunable photoluminescence (PL) as well as thermally and radiationally stable X-ray excited optical luminescence (XEOL). The Cs₂NaGdCl₆ host allows up to 100% and 60% doping concentrations of Tb³⁺ ions for PL and XEOL, respectively, without concentration quenching. The designed Cs₂NaTbCl₆ exhibits a high photoluminescence quantum yield of 73.5%. Optical encryption was achieved using Cs₂NaTb_0.95Eu_0.05Cl₆, which shows excitation-wavelength-dependent dynamic emission colors. Benefiting from efficient energy transfer from Gd³⁺ to Tb³⁺ in the XEOL process, Cs₂NaGd_0.4Tb_0.6Cl₆ achieves a high light yield of 27 000 ph MeV⁻¹. With the incorporation of Eu³⁺, Cs₂NaTbGd_0.35Tb_0.6Eu_0.05Cl₆ exhibits excellent thermal and radiation stability for scintillation. Moreover, DPLCs embedded in polymethyl methacrylate (PMMA) scintillator films enable high-resolution X-ray imaging with a spatial resolution of 16.6 lp mm⁻¹. This work provides a novel strategy for designing DPLCs with state-of-the-art optical applications.

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Introduction

Double-perovskite metal halides (DPMHs), known for their low-toxicity chemical components and stable crystal structures, have attracted extensive research interest due to their extraordinary luminescence properties, particularly in applications such as advanced light-emitting diodes, scintillators, and optical sensing.^1–8 As derivatives of the perovskite structure, DPMHs are formed by replacing two Pb²⁺ ions with one monovalent cation (M⁺) and one trivalent cation (M³⁺), resulting in [M⁺X₆] and [M³⁺X₆] octahedral units that collectively constitute a three-dimensional double perovskite structure with the general formula A₂M⁺M³⁺X₆. Theoretically, this framework offers considerable compositional flexibility: M⁺ can be Ag⁺, Na⁺, or Cu⁺, while M³⁺ may include Bi³⁺, Sb³⁺, or In³⁺. This enables the design of diverse perovskite materials such as Cs₂AgBiX₆, Cs₂AgInCl₆, Cs₂AgSbCl₆, and Cs₂NaBiCl₆, as well as their alloyed variants.^9–13 Despite their promise, these materials face significant challenges in spectral modulation due to intrinsic self-trapped emissions in DPMHs. To address these limitations, novel strategies such as ion doping have been successfully employed to broaden the spectral range and enhance emission intensity. For example, Mn²⁺ doping can induce broad white emission with a high photoluminescence quantum yield (PLQY), while lanthanide ions like Er³⁺, Nd³⁺, and Yb³⁺ enable near-infrared emission in DPMHs.^14–18 Although these advances have expanded both the spectral range and quantum efficiency of DPMHs, the achievement of narrow-band pure-color emission in DPMH hosts remains an area requiring further development.

In recent years, double-perovskite lanthanide chlorides (DPLCs) with the formula Cs₂NaLnCl₆ have been proposed for high-performance optical applications.^19,20 Through diverse activator doping in the DPLC host, multi-mode stimulated luminescence—including down-shifting, up-conversion, and X-ray emission—has been achieved.^21–25 Lanthanide ions possess distinctive 4f–4f and 4fⁿ⁻¹–5d inner-shell transitions, endowing them with exceptional photoelectric properties such as rich emission spectra, extremely narrow emission bandwidths, long luminescence lifetimes, and large Stokes shifts. Typically, increasing the doping concentration of luminescent centers leads to reduced radiative transition efficiency due to cross-relaxation between ions. However, owing to their unique crystal structure and large interatomic distances, DPLCs generally allow higher doping concentrations compared to lanthanide fluorides and oxides.^26–32 Notably, some DPLCs can accommodate lanthanide activators at nearly full concentrations. For example, Nie et al. reported that C₂NaTb_0.95Sc_0.05Cl₆ exhibits a high PLQY of 96.07% and stable luminescence under conditions of extreme temperature, humidity, and long-term UV exposure.³³ Sb³⁺/Sm³⁺-co-doped Cs₂NaLuCl₆ DPLCs achieve PLQYs of 74.58% in the visible region and 23.12% in the NIR region under optimal doping concentrations of 0.5%Sb³⁺ and 25%Sm³⁺.³⁴ Cs₂NaHoCl₆ DPLCs show a high NIR PLQY of 82.3%, achieved by suppressing non-radiative recombination losses, resulting in robust photostability against thermal quenching.³⁵ Qiu and co-workers showed that Cs₂Ag_0.1Na_0.9ErCl₆ microcrystals exhibit NIR emission at 1540 nm with a PLQY of 90 ± 6% under 379 nm excitation and a large Stokes shift exceeding 1000 nm, while Cs₂NaYb_0.4Er_0.6Cl₆ microcrystals achieve a near-unity PLQY of 98.6% under 980 nm excitation.³⁶

Furthermore, due to the high atomic numbers of Cs and lanthanide elements, DPLCs exhibit effective X-ray absorption and outstanding scintillator properties. The Tang group reported Cs₂NaTbCl₆ and Cs₂NaEuCl₆ single crystals with green and red emission, respectively, showing high light yields (LY) of 46 600 ph MeV⁻¹ and 1250 ph MeV⁻¹.³⁷ With 60% Tb³⁺ doping, Cs₂NaSc_0.4Tb_0.6Cl₆ single crystals exhibited a near-unity PLQY of 98.2% and an intense afterglow lasting up to 12 hours after X-ray excitation ceases.³⁸ However, the critical doping concentration for luminescence quenching of Tb³⁺ in Cs₂NaGdCl₆ was notably low—only 5% for photoluminescence (PL) and 7% for radioluminescence (RL).³⁹ It is also worth noting that the luminescence performance of nano-sized DPLCs still lags behind their single-crystal counterparts; for instance, Cs₂NaTbCl₆ nanocrystals showed a PLQY of only 12% and a lower light yield.^40,41

In this work, a series of gadolinium and terbium alloyed DPLCs, Cs₂NaGd_1−xTb_xCl₆, at a sub-micron scale were prepared via a supersaturation recrystallization method at room temperature. These compounds exhibit a high quenching concentration of Tb³⁺ up to 100% for PL, along with a high PLQY of 73.5%. Based on the high-performance Cs₂NaTbCl₆, Eu³⁺ ions were introduced to tune the emission color. As the excitation wavelength shifts from 275 nm to 375 nm, the emission color of Cs₂NaTb_0.95Eu_0.05Cl₆ changes from orange to red to yellow. This excitation-dependent emission behavior enables applications in optical anti-counterfeiting using binary coding. Furthermore, Cs₂NaGd_1−xTb_xCl₆ crystals exhibit outstanding scintillator performance. The quenching concentration of Tb³⁺ reaches 60% in Cs₂NaGd_0.4Tb_0.6Cl₆, yielding a high LY of 27 000 ph MeV⁻¹. With the introduction of Eu³⁺, Cs₂NaGd_0.35Tb_0.6Eu_0.05Cl₆ crystals exhibit robust RL under long-term radiation exposure. Interestingly, thermal enhancement of RL and ratiometric luminescence between Eu³⁺ and Tb³⁺ with increasing temperature were observed. Using the high-performance scintillator Cs₂NaGd_0.35Tb_0.6Eu_0.05Cl₆, a polymethyl methacrylate (PMMA) film was fabricated, achieving X-ray imaging with a high resolution of 16.6 lp mm⁻¹. This work provides a novel strategy for developing high-performance DPLC luminescent materials for advanced optical applications.

Results and discussion

A series of DPLC crystals were synthesized via a supersaturation recrystallization (SR) method, using an environmentally friendly solution system with deionized (DI) water as the solvent and a mixture of ethanol and ethyl acetate as the antisolvent (see details in the Experimental section, SI). As illustrated in the schematic diagram in Fig. 1a, the cubic-phase Cs₂NaTbCl₆ crystallizes in the Fm3̄m space group, wherein the hexacoordinated octahedral [TbCl₆] units provide an optimal coordination environment for luminescence from trivalent lanthanide ions.^42,43 The SR-synthesized products consist of a pure phase of Cs₂NaTbCl₆, as confirmed by the XRD pattern matching the standard ICDD card (#00-055-0604) with no detectable impurities or secondary phases (Fig. 1b). Under 275 nm UV light or X-ray irradiation, the samples exhibit strong green emission (Fig. 1c). Scanning electron microscopy (SEM) images (Fig. 1d and e) show that the Cs₂NaTbCl₆ powder possesses a polyhedral morphology, with grain sizes predominantly within 1 µm (Fig. S1, SI). EDS elemental mapping of single particle Cs₂NaTbCl₆ with a homogeneous distribution of its constituent elements is shown in Fig. S2 (SI).

Fig. 1 (a) Schematic illustration of Cs₂NaTbCl₆ crystals with a double-perovskite structure. (b) The XRD pattern of the prepared Cs₂NaTbCl₆ matches the standard card. (c) Images of Cs₂NaTbCl₆ under ambient light, UV and X-ray. (d) and (e) SEM image of the Cs₂NaTbCl₆ crystals and their high magnification images. (f) XPS survey results of Cs₂NaTbCl₆.

X-ray photoelectron spectroscopy (XPS) was employed to further analyze the chemical composition of Cs₂NaTbCl₆. The survey spectrum (Fig. 1f) shows characteristic binding energy peaks corresponding to Tb 3d, Na 1s, Cs 3d, and Cl 2p, confirming the presence of Tb³⁺, Na⁺, Cs⁺, and Cl⁻. High-resolution XPS spectra of elements are shown in Fig. S3. Specifically, the Tb 3d_3/2 peaks were fit at 1277.2 eV, while the 3d_5/2 peaks were observed at 1243.6 eV and 1240.8 eV, consistent with reported values. The Cl 2p spectrum shows characteristic doublet peaks at 200.0 eV (2p_1/2) and 198.5 eV (2p_3/2). For the monovalent cations, the Cs 3d peaks were located at 738.4 eV (3d_3/2) and 724.5 eV (3d_5/2), and the Na 1s peak was observed at 1071.9 eV.

The PL and photoluminescence excitation (PLE) spectra are shown in Fig. S4 (SI). The PLE spectrum exhibits a broad band from 270 to 300 nm, which is attributed to the transition from the valence band (VB) to the conduction band (CB), where the VB consists primarily of Cl 3p orbitals and the CB is formed by Tb 5d orbitals.^22,25,27 Additionally, several weak narrow peaks between 300 and 400 nm are assigned to the f–f transitions of Tb³⁺. In the PL spectrum, narrow emission peaks are observed at approximately 500 nm, 550 nm, 600 nm, and 625 nm, corresponding to the ⁵D₄ → ⁷F₆, ⁵D₄ → ⁷F₅, ⁵D₄ → ⁷F₄, ⁵D₄ → ⁷F₃ transitions of Tb³⁺ ions, respectively.

To further investigate the concentration quenching behavior in the DPLC host, a series of Gd–Tb alloyed compounds were synthesized by incorporating optically inert Gd³⁺ ions. XRD results confirm that no impurity phases were introduced as shown in Fig. S5 (SI). Due to the smaller ionic radius of Tb³⁺ (0.92 Å) compared to Gd³⁺ (0.94 Å), the diffraction peaks shift to higher angles with increasing Tb³⁺ concentration. The luminescence properties of Cs₂NaGd_1−xTb_xCl₆ were systematically studied. Fig. 2a shows the PL spectra under 275 nm excitation. The intensity of the green emission from the ⁵D₄ → ⁷F_J transitions increases gradually with higher Tb³⁺ doping levels, whereas the blue emission from the ⁵D₃ → ⁷F_J transitions decreases correspondingly. As clearly shown in Fig. 2b, the ⁵D₃-related emission is progressively suppressed with increasing Tb³⁺ content. Quantitative analysis indicates that the contribution of ⁵D₃ emission decreases dramatically from 22.4% to 1.9%, while that of ⁵D₄ emission increases from 77.6% to 98.1%. This strong anti-correlation clearly indicates efficient cross-relaxation between Tb³⁺ ions. The PLQY reaches 73.5% for Cs₂NaTbCl₆, originating from the highly radiative ⁵D₄ level, while Cs₂NaGd_0.9Tb_0.1Cl₆ shows a PLQY of only 25.6% (Fig. S6, SI), showing the high concentration quenching threshold of Tb³⁺ in the DPLC host. The transient PL lifetime was further measured to investigate the energy transfer process in Cs₂NaGd_1−xTb_xCl₆. As shown in Fig. 2c, the lifetime of the ⁵D₃ level decreases with increasing Tb³⁺ concentration, decreasing from 2.52 ms to 19.6 µs (see Table S1, SI). This reduction can be attributed to efficient cross-relaxation between Tb³⁺ ions (⁵D₃ + ⁷F₆ → ⁵D₄ + ⁷F₀), as illustrated in Fig. 2d. Specifically, the ⁵D₃ lifetime decreases from 7.16 ms in Cs₂NaGd_0.9Tb_0.1Cl₆ to 6.29 ms in Cs₂NaGd_0.6Tb_0.4Cl₆ (Fig. S7, SI). However, no further decrease is observed at higher Tb³⁺ concentrations, indicating the absence of concentration quenching.

Fig. 2 (a) PL spectra of Cs₂NaGd_1−xTb_xCl₆ under an excitation wavelength of 275 nm. (b) The emission ratio from ⁵D₃ and ⁵D₄ levels over total emission. (c) Photoluminescence decay curves for the ⁵D₃ level (437 nm). (d) Energy-level diagram for Tb³⁺ ions in Cs₂NaGd_1−xTb_xCl₆ showing a possible route of luminescence quenching and cross-relaxation.

To further tailor the luminescence properties, 5% Eu³⁺ ions were incorporated into Cs₂NaTbCl₆ to achieve tunable emission colors. The excitation spectra of Cs₂NaTb_0.95Eu_0.05Cl₆ are presented in Fig. 3a. The excitation band monitored at 548 nm (corresponding to Tb³⁺ emission) is consistent with that of pure Cs₂NaTbCl₆. For Eu³⁺, the excitation spectrum monitored at 596 nm comprises a broad band between 250 and 350 nm, attributed to the Cl–Eu charge transfer band, along with several narrow peaks in the 350–450 nm range, associated with the 4f–4f transitions of Eu³⁺. The emission spectrum under 315 nm excitation—where only Eu³⁺ ions are excited—is shown in Fig. 3b, highlighting the characteristic photoluminescence of Eu³⁺. The sample exhibits orange-red emission, with a prominent peak at 596 nm originating from the ⁵D₀ → ⁷F₁ transition, and additional typical Eu³⁺ emissions between 611 and 624 nm corresponding to the ⁵D₀ → ⁷F₂ transition. Benefiting from the distinct excitation characteristics of Tb³⁺ and Eu³⁺, Cs₂NaTb_0.95Eu_0.05Cl₆ shows tunable emission colors. As depicted in Fig. 3b, varying the excitation wavelength from 275 nm to 375 nm alters the intensity ratio between Tb³⁺ and Eu³⁺ emission (I_Tb/I_Eu), leading to shifts in the overall emission profile. As the excitation wavelength increases from 275 nm to 305 nm, the I_Eu/I_Tb ratio gradually increases, with Eu³⁺ emission dominating between 305 nm and 335 nm. Upon further red-shifting to 375 nm, the emission intensities of Tb³⁺ and Eu³⁺ become comparable, yielding a balanced emission. As a result, the emitted color transitions sequentially from orange to red and finally to yellow. The color changes were further annotated using the Commission internationale de l’éclairage (CIE) coordinates as shown in Fig. 3c, as the position shifted from (0.49, 0.46) to (0.58, 0.37) and then to (0.40, 0.44).

Fig. 3 (a) PLE spectra of Tb³⁺ ions (548 nm) and Eu³⁺ (596 nm). (b) PL spectra of Cs₂NaTb_0.95Eu_0.05Cl₆ under various excitation wavelengths. (c) CIE coordinates of the Cs₂NaTb_0.95Eu_0.05Cl₆ emission.

Utilizing the excitation wavelength-dependent luminescence of Cs₂NaTb_0.95Eu_0.05Cl₆, we developed an optical encryption system based on binary coding that synergistically integrates Cs₂NaTb_0.95Eu_0.05Cl₆ and Cs₂NaEuCl₆. As evidenced in Fig. S8 (SI), under 315 nm UV irradiation, Cs₂NaTb_0.95Eu_0.05Cl₆ exhibits distinct orange emission, whereas Cs₂NaEuCl₆ maintains red luminescence; conversely, both compounds display homogeneous red emission at 365 nm excitation. Within this encryption system, we leveraged the dynamic PL color of DPLCs to implement binary state encoding. When subjected to modulated UV excitation wavelengths, a distinct emission color (from red to orange) was assigned to bit state “1”, while unchanged emission profiles were designated as bit state “0”. For demonstration in Fig. 4, capital letters “I K U N” are converted to binary sequences and spatially mapped onto a 4 × 8 matrix with Cs₂NaTb_0.95Eu_0.05Cl₆ and Cs₂NaEuCl₆ representing bit “1” and “0” positions, respectively (Fig. 4a). Under 365 nm UV (encryption mode), a uniform red emission conceals the information; during 315 nm decryption, elements exhibiting orange transition are decoded as “1”, while persistently red-emitting elements register as “0”, successfully reconstructing the original characters from the binary sequences 01001001 (I), 01001011 (K), 01010101 (U), and 01001110 (N) (Fig. 4b).

Fig. 4 (a) Binary sequences of the capital letters “I K U N”. (b) Luminescence images of a 4 × 8 matrix with Cs₂NaTb_0.95Eu_0.05Cl₆ and Cs₂NaEuCl₆ under 365 nm and 315 nm.

The scintillation properties of a series of Cs₂NaGd_1−xTb_xCl₆ compounds were systematically investigated. The X-ray XEOL spectra are presented in Fig. 5a. In the Gd–Tb alloyed samples, a narrow emission peak with a full width at half maximum (FWHM) of 2.4 nm is observed at 312 nm in the UV region and is shown in Fig. S9, originating from the Gd³⁺ transition ⁶P_7/2 → ⁸S_7/2. Additional narrow peaks in the ranges of 350–450 nm and 475–650 nm are assigned to the ⁵D₃ → ⁷F_J and ⁵D₄ → ⁷F_J transitions of Tb³⁺ ions, respectively. The intensity ratio between the ⁵D₄ → ⁷F_J and ⁵D₃ → ⁷F_J emissions increases with Tb³⁺ concentration, consistent with their photoluminescence (PL) characteristics. A weak broad band between 350 and 450 nm in low Tb³⁺ concentration samples (Cs₂NaGd_0.9Tb_0.1Cl₆ and Cs₂NaGd_0.8Tb_0.2Cl₆) can be attributed to the self-trapped exciton (STE) emission of the host lattice. Taking the commercial scintillator Bi₄Ge₃O₁₂ (BGO) as a reference, a high LY of 27 000 photons ph MeV⁻¹ was achieved in the Cs₂NaGd_0.4Tb_0.6Cl₆ sample, Fig. S10 (SI). We propose that Gd³⁺ introduces an intermediate energy level between the conduction band and the 4f levels of Tb³⁺, thereby reducing energy loss during the transfer process.

Fig. 5 The XEOL spectra of Cs₂NaGd_1−xTb_xCl₆ (a) and Cs₂NaGd_0.35Tb_0.6Eu_0.05Cl₆ (b). (c) The XEOL intensity of Cs₂NaGd_0.35Tb_0.6Eu_0.05Cl₆ under long-term X-ray radiation showing stability. (d) The integrated XEOL intensity of Cs₂NaGd_0.35Tb_0.6Eu_0.05Cl₆ at various temperatures.

Furthermore, Eu³⁺ ions were incorporated to achieve radiation-stable and temperature-dependent XEOL. The Eu³⁺ emission in the XEOL spectra (Fig. 5b), observed between 611 and 624 nm, corresponds to the ⁵D₀ → ⁷F_J transition. In Fig. 5c, Cs₂NaGd_0.35Tb_0.6Eu_0.05Cl₆ exhibits radiation stability, maintaining a constant luminescence intensity under 50 keV X-ray irradiation over 50 on–off cycles without attenuation, indicating its potential for long-term application. Notably, this compound also exhibits extraordinary thermally enhanced luminescence: the integrated emission intensity at 433 K is 1.2 times that at room temperature, and remains 1.1 times higher even at 473 K (Fig. 5d). Detailed temperature-dependent XEOL spectra of Cs₂NaGd_0.35Tb_0.6Eu_0.05Cl₆ are provided in Fig. S11 (SI), along with the intensity ratio between Eu³⁺ and Tb³⁺ (IR = I_Eu/I_Tb). As temperature increases, the IR value gradually rises from 1.4 to 2.2. Based on the temperature-dependent IR, Cs₂NaGd_0.35Tb_0.6Eu_0.05Cl₆ was proposed as a self-calibrating luminescent thermometer and its performance was further evaluated through ratiometric intensity measurements under XEOL. The relationship between IR and temperature is shown in Fig. S10b (SI) and can be fitted with the equation IR = 0.00376T + 0.43882, with a correlation coefficient R² of 0.993. The absolute sensitivity (S_a) and relative sensitivity (S_r) were calculated as S_a = 0.0038 K⁻¹, and S_r reaches a maximum value of 0.0034% K⁻¹ at 293 K.

The physical mechanism underlying X-ray induced luminescence in Cs₂NaGd_1−xTb_xCl₆ is schematically illustrated in Fig. 6. Upon X-ray irradiation, high-energy photons interact primarily with heavy atoms (Cs and lanthanide elements) through photoelectric and Compton effects, generating a large number of high-energy electrons and holes. These charge carriers subsequently undergo thermalization, producing a substantial quantity of secondary electrons and holes. Through transport and relaxation processes, they migrate into the conduction and valence bands, where they are eventually captured by luminescent centers. The high energy level ⁶P_7/2 of Gd³⁺ is situated near the conduction band, allowing carriers to be readily transferred to Gd³⁺ ions. This intermediate level reduces energy loss during transfer and enhances energy transfer efficiency. In this process, Tb³⁺ ions can directly receive electrons from the CB or through non-radiative relaxation from Gd³⁺, resulting in the characteristic emission of Tb³⁺ activators. Furthermore, in the case of Eu³⁺ co-doping, the variation in luminescence can be attributed to energy transfer from the donor Tb³⁺ to the acceptor Eu³⁺. As temperature increases, the energy transfer efficiency from Tb³⁺ to Eu³⁺ is enhanced. This indicates that elevated temperature effectively promotes energy transfer between Tb³⁺ and Eu³⁺, which is primarily ascribed to a thermally driven phonon-assisted energy transfer.

Fig. 6 Schematic illustration of the XEOL mechanism of Cs₂NaGd_0.35Tb_0.6Eu_0.05Cl₆.

Utilizing the high-performance DPLC materials, an X-ray imaging system was further developed. Scintillator films were fabricated by embedding Cs₂NaGd_0.35Tb_0.6Eu_0.05Cl₆ particles into a PMMA matrix. These flexible films were prepared using a blade-coating method. First, the pre-synthesized DPLC particles were uniformly dispersed in a toluene solution containing dissolved PMMA. The mixture was then poured onto a cleaned glass substrate and spread using a blade coater with a controlled slit width. After heating at 60 °C for 30 minutes, the solidified film was peeled off from the substrate, yielding the final scintillator film. To investigate the X-ray detection limit of the proposed scintillator screen, we have included a plot of the signal-to-noise ratio (SNR) as a function of the X-ray dose rate in Fig. S12 (SI). As shown, the SNR exhibits a linear dependence on the dose rate, and the data were well fit by a linear regression. Following the conventional definition, the X-ray detection limit is determined at SNR = 3, which corresponds to a dose rate of 73.1 nGy s⁻¹ films. A schematic diagram of the custom-built X-ray imaging system is shown in Fig. 7a. The scintillator films show high resolution, as quantitatively confirmed using a standard line-pair test card in Fig. 7b. As shown in Fig. 7c, a resolution of 16.6 lp mm⁻¹ can be clearly distinguished, which is further validated by analyzing the corresponding gray-value profiles. As a proof, modulation transfer function (MTF) measurement using an X-ray image of the edge of a copper film was performed, as shown in Fig. S13 (SI). The calculated MTF value of 0.2 corresponds to a spatial frequency of 16.8 lp mm⁻¹, which is consistent with the resolution observed in standard line-pair phantom images. To evaluate practical applicability, X-ray imaging of representative objects was conducted. Notably, the prepared scintillator screen exhibits excellent flexibility, as shown in Fig. 7d. To evaluate its practical performance, we captured an X-ray image of an encapsulated circuit board. A comparison between the ambient light photograph (Fig. 7e) and the X-ray image (Fig. 7f) reveals clear contrast variations, which arise from differences in X-ray absorption among various materials, such as metals and plastics. In particular, the DPLCs@PMMA scintillator screen achieves high-resolution imaging as shown in Fig. 7g, enabling clear visualization of the metallic wire as small as approximately 0.5 mm, as further confirmed by the corresponding gray value analysis.

Fig. 7 (a) Schematic illustration of a home-made X-ray imaging system. The X-ray imaging of the standard line-pair card (b) and the corresponding gray value (c). (d) A curly scintillator screen based on DPLCs and PMMA. Images of a circuit board recorded under ambient light (e) and X-ray (f). (g) The gray value collected from the X-ray image of the circuit board.

Conclusions

This work shows the successful synthesis of high-quality DPLC crystals via an eco-friendly supersaturation recrystallization route. The obtained Cs₂NaTbCl₆ exhibits a high PLQY of 73.5%. By doping with Eu³⁺, we achieved widely tunable emission colors and excitation-dependent dynamic luminescence. Based on Cs₂NaTb_0.95Eu_0.05Cl₆, a typical example of an optical encryption system was demonstrated. The proposed DPCLs show exceptional performance as scintillators, featuring a high light yield, excellent thermal stability, and thermally enhanced radioluminescence. Furthermore, a ratiometric luminescence thermometer based on XEOL was developed. The practical applicability of these DPLCs was verified through the fabrication of flexible composite films, which enabled high-resolution X-ray imaging, showcasing great potential in non-destructive testing. This study provides a valuable strategy for designing high-performance lanthanide-based perovskites toward advanced optical and scintillation applications.

Author contributions

Su Zhou: writing – original draft, conceptualization, methodology and data curation. Linshuai Li: formal analysis and data curation. Gaoqing Chen: data curation. Jingtao Zhao: supervision and methodology. Lei Lei: conceptualization and writing – review & editing.

Conflicts of interest

There are no conflicts to declare.

Data availability

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

Supplementary information (SI) is available. Experimental section, EDS mapping, XPS spectra, XRD, decay curves, PL, PLE and XEOL spectra are provided in SI. See DOI: https://doi.org/10.1039/d5qi02185e.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (52172164, 62475248, and 12404468) and the Zhejiang Provincial Natural Science Foundation of China under Grant No. LQN25E020001.

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