High-Efficiency Luminescence of Mn²⁺-Doped Two-Dimensional Hybrid Metal Halides and X-Ray Detection

Abstract

Mn²⁺ doping in metal halide perovskites enables host-to-dopant energy transfer, creating new emission pathways for optoelectronic applications. However, achieving high-efficiency luminescence in 2D systems remains challenging. We synthesized Mn²⁺-doped 2D PEA₂CdCl₄ via the hydrothermal method, characterizing its properties through PL spectroscopy, quantum yield measurements, and DFT calculations. Flexible films were fabricated using PDMS and PMMA matrices. The 15% Mn²⁺-doped crystal showed orange–red emission with 90.85% PLQY, attributed to efficient host-to-Mn²⁺ energy transfer and ⁴T₁→⁶A₁ transition. Prototype LEDs exhibited stable emission, while PDMS films demonstrated flexibility and PMMA films showed excellent X-ray imaging capability. This work demonstrates Mn²⁺ doping as an effective strategy to enhance luminescence in 2D perovskites, with potential applications in flexible optoelectronics and X-ray scintillators.

1. Introduction

Organic–inorganic hybrid metal halides (OIHMH) exhibit excellent optoelectronic properties due to their soft lattice and have broad application prospects in many fields [1,2,3,4,5,6,7,8,9,10,11,12]. Soft lattices refer to crystalline frameworks with high phonon anharmonicity, where weak intermolecular forces (e.g., hydrogen bonds, van der Waals) enable structural flexibility under stimuli. Thanks to the rich diversity of organic materials, various combinations can be achieved between organic and inorganic components, resulting in a range of optoelectronic properties. As a result, OIHMHs have found widespread applications in optoelectronic devices, anti-counterfeiting technology, and information decryption. Among them, two-dimensional organic–inorganic hybrid metal halides are widely used in optoelectronic devices due to their excellent carrier mobility, high light absorption capacity, and photoelectric conversion rate [13,14]. These optical properties are closely related to the unique combination of organic and inorganic components [15]. Therefore, it is an effective optimization method to adjust and improve the optical properties of cadmium-based hybrid metal halides by changing organic or inorganic components. For example, metal halides are modified by adjusting the size of the A-site organic component. The softening of metal halides by organic components will cause instantaneous defects in the excited state, and strong electron–phonon coupling leads to large Stokes shifts and broadband emission [16]. Another method is to change the luminescence color or improve the luminescence efficiency of halides by doping metal ions containing lone pair electrons (such as Pb²⁺, Sn²⁺, Ge²⁺, Sb³⁺, and Bi³⁺) or transition metal ions with d electrons (such as Mn²⁺, Cu²⁺ and Zn²⁺). Therefore, it is necessary to explore a general method to improve the optical properties of cadmium-based metal halides by ion doping.

From a structural point of view, different types of hybrid halides largely determine the observed unusual physical properties [17]. The structural type of the two-dimensional hybrid material depends on the charge of the organic cations between the layers. For the two-dimensional Ruddlesden–Popper (R-P)-phase hybrid perovskite of A’₂A_n−1B_nX_3n+1, where A’ and A are organic cation with different sizes, B is a metal ion, and X is a halogen anion [18]. Each inorganic metal layer is displaced by an octahedral [BX₆]⁴⁻, showing in-plane displacement. The coupled organic bilayers effectively isolate the inorganic sublattice layer, and the reduction in interaction makes it easier for two-dimensional materials to produce exciton emission directly caused by single-layer spatial electron confinement (n = 1).

The polar structure of the R-P phase and the resulting structural distortion provide a rotary knob for adjusting the electronic structure, thereby affecting the optical properties [19]. However, there are few studies on hybrid R-P-phase Cd-based metal halides. According to previous studies, Mn²⁺ is an important photoactive luminescent ion [20,21]. Its unique 3d⁵ electronic configuration endows Mn²⁺ ions with a rich energy level structure and strong spin–orbit coupling, which can produce distinct characteristic luminescence under ultraviolet excitation, especially in the red and near-infrared regions. Moreover, Mn²⁺ ions can effectively enhance the energy transfer efficiency from the host-bound exciton to the d electron of Mn²⁺ ions. This greatly enhances the energy conversion efficiency and reduces the non-radiative recombination loss. Therefore, exploring Mn²⁺-doped Cd-based hybrid metal halides is of great significance. Its unique 3d⁵ electronic configuration endows Mn²⁺ ions with rich energy level structure and strong spin–orbit coupling, which can produce distinct characteristic luminescence under ultraviolet excitation. In addition, Mn²⁺ ions can effectively improve the energy transfer efficiency from the host-bound exciton to the d-orbital of Mn²⁺ ions. This greatly enhances the energy conversion efficiency and reduces the non-radiative recombination loss [22]. Therefore, it is very meaningful to explore an effective way to activate cadmium-based hybrid metal halides. However, PEA₂CdCl₄ is susceptible to degradation under humidity and light conditions, leading to reduced reliability in long-term use. Meanwhile, its low photoluminescence (PL) efficiency due to material defects and insufficient excited state dynamics limits its application in optoelectronic devices such as solar cells and LEDs. PEA₂CdCl₄, as a material based on an R-P structure [23], possesses good doping and modification potential. Through rational doping and surface modification, its luminescence performance can be significantly improved and its application in the field of optoelectronics can be expanded. Doping with Mn²⁺ ions can significantly improve the photovoltaic performance and stability of PEA₂CdCl₄ and enhance its practical application prospects.

In this work, the orthorhombic-phase PEA₂CdCl₄ crystal was synthesized by a typical hydrothermal method, and the optical properties of the two-dimensional R-P-phase metal halide PEA₂CdCl₄ were further enhanced by appropriate Mn²⁺ ions doping. The Mn²⁺:PEA₂CdCl₄ prepared by this method exhibits a red emission at 616 nm under 269 nm excitation, the full width at half maximum (FWHM) is 82 nm, and the optimal doping concentration is 15%. Temperature-dependent emission spectra reveal the obvious activation of Mn²⁺ ions and the small activation energy (ΔE_a = 10.38 meV), which proves the existence of an effective energy transfer channel from the host to the Mn²⁺ ions. The crystal structure of the Mn²⁺:PEA₂CdCl₄ crystal remains unchanged after exposure to air for 2 months. This study uses Mn²⁺ doping to optimize the material, change the mechanism of energy transfer, improve the quantum efficiency, and achieve luminescence modulation, which provides a reference for improving the luminescence performance.

2. Materials and Methods

2-Phenylethylamine hydrochloride ((C₆H₅NH₂)CH₂CH₃·HCl, 98%), manganese chloride tetrahydrate (MnCl₂·4H₂O, 99.9%) and anhydrous cadmium chloride (CdCl₂, 99%) were purchased from Macklin Inc. (Shanghai, China). Hydrochloric acid (HCl, AR, 37%) was purchased from Aladdin Scientific Inc. (Shanghai, China). All of these chemical agents were used as received without further purification. Firstly, a certain concentration of Mn²⁺ ion doped precursor solution was prepared. Mn²⁺ precursor solution with a molar concentration of 0.1 mmol/mL was obtained by dissolving 1 mmol MnCl₂·4H₂O in 10 mL HCl. Subsequently, 0.5 mmol 2-phenylethylamine hydrochloride, 0.25 mmol total metal salts (a mixture of CdCl₂ and varying volumes of Mn²⁺ precursor solution while maintaining the total Cd²⁺+Mn²⁺ content at 0.25 mmol), and 3 mL HCl were loaded into a 25 mL polytetrafluoroethylene-lined autoclave, which was then sealed in a stainless steel reactor. The reaction proceeded at 180 °C for 150 min followed by natural cooling to room temperature. The products were collected by centrifugation and washed with absolute ethanol, ultimately yielding PEA₂CdCl₄ single crystals with varying Mn²⁺ doping concentrations.

3. Discussion

A series of x% Mn-doped PEA₂CdCl₄ (x = 0–20) hybrid metal halides were prepared by the hydrothermal method. As shown in Figure 1a, the crystal structure of the single-layer R-P phase metal halide PEA₂CdCl₄ is orthorhombic, and the space group is Pbca [23]. In this structure, each Cd atom is coordinated with six Cl atoms to form a [CdCl₆]⁴⁻ octahedron. As depicted in Figure 1b, along the c-axis, the inorganic sublattice [CdCl₆]⁴⁻ in the compound exhibits angular sharing, and the average bond lengths of Cd₁–Cl₁, Cd₁–Cl₂ and Cd₁–Cl₃ are 2.6497 Å, 2.6513 Å and 2.5550 Å, respectively. The axial compression of [CdCl₆]⁴⁻ octahedron leads to its distortion (Figure S1). The degree of octahedral distortion can be quantified using the formula [24,25,26,27]

. $${\lambda }_{\mathrm{oct}}={\displaystyle \frac{1}{6}}{\sum }_{\mathrm{i}=0}^6{[{\displaystyle \frac{d_{\mathrm{i}}-d_0}{d_0}}]}^2$$

(1)

where d_i is the Cd-Cl bond length, and d₀ is the average bond length of Cd–Cl in [CdCl₆]²⁻ octahedron. The result is λ_oct = 2.96 × 10⁻⁴. The organic cation PEA⁺ occupies the corner-sharing octahedral gap and the two cations between the layers are bound to each other by van der Waals forces. The organic bimolecular layer and the inorganic layer are alternately arranged to form a two-dimensional structure, and the crystal layer spacing is 19.204 Å. In addition, Figure 1e illustrates the powder XRD spectra of x% Mn²⁺:PEA₂CdCl₄ (x = 0–30) samples. The XRD pattern of the undoped sample (x = 0) matches well with the standard card of PEA₂CdCl₄, indicating that the sample has no excess impurity phase and exhibits good phase purity. The XRD patterns of different concentrations of Mn²⁺ ions showed that a series of doped samples were successfully synthesized, and the doping of Mn²⁺ did not change the structure of PEA₂CdCl₄. The amplification diagram on the right side shows that Mn²⁺ doping has a slight shift on the XRD diffraction peak, which is due to the different ionic radius of Mn²⁺ and Cd²⁺. Figure 1f shows the photo of x% Mn²⁺:PEA₂CdCl₄ (x = 0–30) excited by natural light and ultraviolet light (254 nm). The samples appear as white flakes under natural light irradiation, and under ultraviolet light excitation, there is almost no emission from the undoped samples. However, the Mn²⁺-doped PEA₂CdCl₄ exhibit bright red emission, which is spin-forbidden [26,28,29].

To further verify the doping effect of Mn²⁺, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used to analyze the morphology, element distribution, and valence state of the doped samples. As shown in Figure S2a, SEM images reveal that the Mn²⁺:PEA₂CdCl₄ crystal has a lamellar structure and good crystallinity. Meanwhile, the energy dispersive spectroscopy (EDS) analysis (Figure S2b–d) also confirms the presence of N, Cd, Mn and Cl, and the elements are evenly distributed. This further supports the phase purity of the PEA₂CdCl₄ and the successful doping of Mn²⁺ ions. Subsequently, XPS was used to analyze the elemental valence state and chemical composition of the samples. The XPS spectrum of Figure S3a also shows the presence of N, Cd, Mn and Cl elements. The high-resolution XPS spectrum shown in Figure S3b reveals distinct characteristic peaks at 199 and 198 eV, which belong to 2p_3/2 of Cl, respectively. The characteristic peaks at 412.5 eV and 405.5 eV in Figure S3c correspond to the 3d_3/2 and 3d_5/2 orbitals of Cd, respectively. In summary, the elemental compositions of the samples and their valence states were determined. Both Mn²⁺ and Cd²⁺ are present in the +2 valence. The similar valence state and ionic radius also indicate that the addition of Mn²⁺ ions preferentially replaces the sites of Cd²⁺. The above results show that the element distribution of Mn²⁺:PEA₂CdCl₄ synthesized by the hydrothermal method is uniform and has high phase purity.

It is well known that Mn²⁺ ions, as transition metals with d electrons, significantly improve the optical properties of metal halides by doping the crystal lattice. As shown in Figure 1f, the undoped sample exhibits almost no emission under 254 nm excitation. In contrast, after doping with Mn²⁺ ions, the crystal shows obvious red emission. To further investigate the luminescence properties, absorption, photoluminescence excitation (PLE) spectra, photoluminescence (PL) spectra and PL decay curves were performed. Figure 2d illustrates the absorption spectra of the samples doped with different concentrations of Mn²⁺. Compared with the sample with x = 0, the absorption band edge shows a slight red shift with the increase in Mn²⁺ doping concentration. A smaller absorption band edge also indicates a larger band gap value. The band gap of x% Mn²⁺:PEA₂CdCl₄ (x = 0, 15, 30) was calculated by the Kubelka–Munk (K-M) Equation (2),

$${\left[F\left(R_{\infty }\right)h\nu \right]}^n=A(h\nu -E_g)$$

(2)

where F(R_∞) is the Kubelka–Munk (K–M) function, hυ is the photon energy, A is the scaling constant, and E_g is the band gap. For direct semiconductors, n = 2 is used to calculate the undoped PEA₂CdCl₄ and Mn²⁺ doped samples. As shown in Figure S4, the band gap of undoped PEA₂CdCl₄ is 4.44 eV, while the band gaps of 15% and 30% Mn²⁺:PEA₂CdCl₄ are 4.37 eV and 4.30 eV, respectively. The band gap decreases with an increasing Mn²⁺ doping concentration, which is consistent with its absorption spectra.

The luminescence properties of Mn²⁺:PEA₂CdCl₄ were further investigated by monitoring the optical behaviors, such as PL, PLE, and PL decay curves. As shown in Figure 2a, the performance of Mn²⁺ ions with different doping concentrations in the PLE spectra showed a consistent trend with the corresponding absorption spectra. The five excitation peaks in the PLE spectra are located at 269, 291, 329, 356 and 418 nm, which correspond to ⁶A₁(S)→⁴A₂(F), ⁶A₁(S)→⁴T₁(F), ⁶A₁(S)→⁴E(D), ⁶A₁(S)→⁴T₂(D) and ⁶A₁(S)→⁴A₁, ⁴E₁(G) of Mn²⁺, respectively [30]. At the same time, with the increase in Mn²⁺ ion doping, the absorption at 269 nm is enhanced, which further confirms that it comes from the absorption of Mn²⁺ ions. As shown in Figure 1f and Figure 2b, the undoped sample does not radiate outward under ultraviolet excitation. After the introduction of Mn²⁺, the sample exhibits a narrow-band emission at 616 nm under 269 nm, and its FWHM is about 78 nm. This indicates that the emission comes from the ⁴T₁→⁶A₁(S) transition of Mn²⁺ ions [31], and the emission intensity reaches the peak value when the doping concentration reaches 15%. Simultaneously, the PL intensity of Mn²⁺:PEA₂CdCl₄ decreases rapidly at a high doping concentration (after doping concentration exceeds 15%), which is attributed to the concentration quenching effect after Mn²⁺ doping (Figure S5) [32]. Additionally, as shown in Figure S6, the peak position of x% Mn²⁺:PEA₂CdCl₄ does not shift at different excitations and different Mn²⁺ ion doping concentrations (x = 5–30), which further confirms that the orange-red emission arises from the d-d transition of the Mn²⁺ ion spin-forbidden. There is only a single luminescent center. After that, PL attenuation monitoring was performed on samples with different doping concentrations to further exclude the possibility of other emission sources. The PL decay curves of 5–30% Mn²⁺: PEA₂CdCl₄ can be fitted by use of the formulas [33]

$$I_{\left(t\right)}=I_0+A_1\mathit{exp}\left(t/{\tau }_1\right)+A_2\mathit{exp}\left(t/{\tau }_2\right)+A_{3}exp\left(t/{\tau }_3\right)$$

(3)

$${\tau }_{ave}=(A_1{\tau }_1^2+A_2{\tau }_2^2+A_3{\tau }_3^2)/(A_1{\tau }_1+A_2{\tau }_2+A_3{\tau }_3)$$

(4)

where I_(t) is the intensity of the PL at the time of t, I₍₀₎ is the initial intensity, A₁, A₂, and A₃ are constants, and τ₁, τ₂, and τ₃ are the decay times of the corresponding exponential components. The average lifetimes after fitting were 62.15 μs, 1.01 ms, 2.11 ms, 2.01 ms, and 57.5 μs, respectively. Under 269 nm, the PL decay lifetime shows a consistent trend with the emission spectrum (Figure 2c), and the long lifetime (in milliseconds) also confirms that the red narrow-band emission originates from the spin-forbidden transition of Mn²⁺ ions. When the doping concentration exceeds the optimal doping concentration of Mn²⁺ ions (15%), the lifetime also decreases with the increase in doping concentration. Further optical performance tests show that under 254 nm excitation, compound 1 achieves a photoluminescence quantum yield (PLQY) of 90.85% (Figure S7), indicating its great potential for optoelectronic applications.

To explore the optical behavior of the material at different temperatures, we monitored the temperature-dependent PL spectra of 15%Mn²⁺:PEA₂CdCl₄. Different from the previously studied process of Sb³⁺ ion doping with ns² electrons, Mn²⁺ exhibits different optical behaviors. Figure 3a,b illustrate the temperature-dependent PL spectra and corresponding pseudo-color maps in the temperature range of 100 K to 360 K. From these figures, it can be observed that the PL peak position consistently exhibits a blue shift with increasing temperature, while its intensity first increases and then decreases. As the temperature increases, the intensity of the crystal field due to lattice expansion decreases, which causes the blue shift of the peak position. We can fit the dependence of FWHM on temperature using Formula (5) [33],

$${FWHM}_{\left(T\right)}=2.36\sqrt{S}{\hslash \omega }_{phonon}\sqrt{coth{\displaystyle \frac{{\hslash \omega }_{phonon}}{2K_{B}T}}}$$

(5)

Here, the phonon frequency is the phonon frequency, S is the Huang–Rhys factor, and K_B is the Boltzmann constant. The fitted value of the Huang–Rhys factor S is about 29.37 (Figure 3e). As a parameter describing electron–phonon interaction, S is closely related to the Jahn–Teller distortion. The larger S value indicates that there is a strong electron–phonon coupling in Mn²⁺:PEA₂CdCl₄. In addition, the electron–phonon coupling energy Γ_op is obtained by fitting the FWHM with 1/T using the Formula (6) [34]

$$\Gamma \left(T\right)={\Gamma }_0+{\Gamma }_{\mathrm{o}\mathrm{p}}/(e^{\hslash {\omega }_{op}/K_{B}T}-1)$$

(6)

Γ₀ and Γ(T) are the intrinsic half-peak widths at 0 and T K, respectively. Γ_(op) is the electron–phonon coupling energy, ℏω_op is the phonon energy and K_B is a Boltzmann constant. The fitted Γ_op value is about 152.42 meV (Figure 3c).

Meanwhile, the FWHM increases continuously with increasing temperature, which is mainly attributed to the diffusion of more excited state electrons into the vibrational energy level caused by the temperature increase, which in turn leads to the radiative transition to the ground state. It is worth noting that the PL intensity increases with the increase in temperature in the range of 100–260 K (Figure S8). This is due to the temperature dependence of the PL of Mn²⁺ ions from the vibrational activation of the radiative d-d transition [19,35]. In this process, the sensitization of the d-d transition of Mn²⁺ ions is gradually activated by lattice vibration heat, and the increase in emission intensity can be observed. As shown in Figure 3a, it decreases with the increase in temperature in the range of 280–360 K. This is due to the rise in non-radiative complexation due to electron–phonon coupling and defects with increasing temperature. Then, the thermal activation energy (∆E_a) required for the exciton to transfer from the host to the Mn²⁺-doped ion is estimated using Formula (7):

$$I_{Mn}\left(T\right)=I_0\ast e^{{-∆E}_a/K_{B}T}$$

(7)

K_B is the Boltzmann constant, I₀ is the initial strength and I_Mn(T) is the integrated PL intensity at different temperatures (100–260 K). In the range of 100–260 K, the thermal activation energy ΔE_a of Mn²⁺:PEA₂CdCl₄ is about 10.38 meV, derived by fitting the dependence of PL intensity on the reciprocal of temperature [36,37]. Such a small potential barrier is also the reason why excitons can be effectively transferred to Mn²⁺ ions, resulting in the maximum PL intensity. Therefore, further heating (i.e., from 260 to 360 K) will reduce the intensity of PL. As shown in Figure 3f, the PL decay curves at different temperatures were monitored to gain a deeper understanding of this unusual phenomenon. The PL decay at different temperatures shows a similar trend to its PL. The results show that the doping of Mn²⁺ ions further opens the channel of energy radiation. After the material is excited by light, the electrons transition from the ground state to the unstable excited state, and then the excitons transfer from the host to the dopant Mn²⁺ downward radiative transition (Figure 2e).

The electronic structure and optical band gap of the samples can be explained and predicted by density functional theory (DFT). We calculated the electronic band structure and projected density of states (PDOS) to investigate the influence of Mn²⁺ ion doping on the electronic properties and optical band gap. As shown in Figure 4a, the undoped PEA₂CdCl₄ exhibits an indirect band gap of 3.67 eV, so the downward transition radiation process is dipole-forbidden. The doped sample is based on the structure of the undoped sample, with Mn²⁺ replacing Cd²⁺, and the doping concentration is 15%. The optical band gap is reduced to 2.56 eV after doping with Mn²⁺. The discrepancy between the calculated and experimental values can be attributed to the tendency of standard DFT calculations to underestimate the band gap of materials, often resulting in values that are lower than the actual measurements. This phenomenon has been well-documented in the context of organic–inorganic hybrid metal halides. Furthermore, the computed results provide a deeper understanding of the electronic structure. It is well known that the doping of Mn²⁺ will disturb the electronic composition of the host near the optical band gap, mainly due to the introduction of Mn²⁺ into the intermediate energy levels. The PDOS, valence band maximum (CBM) and conduction band minimum (VBM) shown in Figure 4b reveal that the VBM and CBM of undoped PEA₂CdCl₄ are composed of Cd and Cl, which are confined to [CdCl₄]²⁻. In contrast, as shown in Figure 4c,d, the CBM and VBM of Mn:PEA₂CdCl₄ are composed of Mn and Cl, respectively.

Stability and Applications

As shown in Figure 5a, the X-ray diffraction (XRD) patterns of Mn²⁺:PEA₂CdCl₄ after two months of exposure to air closely match those of freshly synthesized samples, indicating excellent phase stability with no formation of secondary phases. Simultaneously, we monitored the PL spectra of the samples after exposure to air, as shown in Figure 5b. The PL intensity can be maintained at 74% of the freshly prepared sample. Additionally, Figure 5c shows the LED based on 15%Mn²⁺:PEA₂CdCl₄ powder to study its potential utility in practical applications. The illustrations depict the LED at a driving voltage of 3.5 V, producing a stable bright orange light with CIE coordinates of (0.332, 0.199). At different driving currents (60–100 mA), the LED spectrum also shows high color stability (Figure 5d). These results show that Mn²⁺:PEA₂CdCl₄ can withstand the heat brought by the operation of the device and has good luminescence stability, making it very suitable for use in solid-state lighting and backlight displays. To further explore the material’s applicability, we mixed 15%Mn²⁺:PEA₂CdCl₄ powder with polydimethylsiloxane (PDMS) to create a flexible film, as shown in Figure 5e. We used different narrow-band pass filters (allowing > 620 nm pass, 520–590 nm pass and 420–480 nm pass, respectively) to extract information in the RGB channels. The results yield customized color outputs, demonstrating significant potential for application in the intelligent era. The prepared flexible film exhibits a high degree of flexibility without compromising its luminous efficiency. In addition to polymerization with PDMS, we further prepared highly transparent films by mixing 15% Mn²⁺:PEA₂CdCl₄ powder with polymethyl methacrylate (PMMA) (Figure 5f) and demonstrated X-ray imaging using the system shown in Figure 5g. As illustrated in Figure 5h, the 15% Mn²⁺:PEA₂CdCl₄@PMMA film enabled the clear imaging of small metal pendants, with leaf contours smaller than 1 mm distinctly visible. Furthermore, the 15% Mn²⁺:PEA₂CdCl₄ film also exhibited an excellent detection capability for the spring inside the capsule. These results highlight the great potential use of 15% Mn²⁺:PEA₂CdCl₄ as an X-ray scintillator for X-ray imaging applications. Overall, these findings contribute to the development of smart luminescent materials, and highlight their potential in various practical applications.

4. Conclusions

In summary, we have designed and synthesized a novel Mn²⁺-doped two-dimensional hybrid metal halide, PEA₂CdCl₄, which exhibits intense orange-red emission with an almost 100% PLQY. Experimental and theoretical analyses indicate that this high-efficiency luminescence can be attributed to the effective energy transfer between the host and Mn²⁺, followed by the ⁴T₁-⁶A₁ transition in Mn²⁺. Furthermore, we fabricated LEDs based on Mn²⁺:PEA₂CdCl₄ powders and flexible X-ray scintillator films, both of which demonstrated excellent optoelectronic performance, highlighting the broad application potential of Mn²⁺:PEA₂CdCl₄ in the field of optoelectronics.