Highly efficient eco-friendly X-ray scintillators based on an organic manganese halide

Scintillators convert ionizing radiation into visible photons and are crucial for radiation detection across monitoring, security, space exploration, and medical imaging. Existing scintillators face limitations, including challenging growth conditions and hygroscopicity for inorganic crystals, anisotropic scintillation in organic crystals, and low light yields in plastics. Lead halide perovskites (e.g., CsPbBr3, MAPbBr3) have shown promise for direct X-ray imaging and scintillation, but lead toxicity limits their commercial applicability, motivating exploration of lead-free metal halide perovskites and hybrids. Prior advances include double perovskite Cs2AgBiBr6 single-crystal detectors and low-dimensional metal halide hybrids (e.g., Bmpip2SnBr4, Rb2CuX3) for scintillation. Eco-friendly organic Mn(II) halide hybrids are known for strong photoluminescence spanning green to red from well-understood Mn2+ d–d transitions in tetrahedral or octahedral fields, and have been used in LEDs, vapochromic sensors, and solvent sensing. However, scintillators based on organic Mn(II) halide hybrids had not been reported. Here, the authors demonstrate high-performance, eco-friendly X-ray scintillators based on a zero-dimensional (0D) phosphonium Mn(II) bromide hybrid, (C38H34P2)MnBr4, prepared via a facile room-temperature solution method to inch-scale single crystals, exhibiting bright green emission (517 nm, PLQE ~95%) and excellent scintillation properties (exceptional linearity, high light yield, low detection limit) enabling high-resolution X-ray imaging.

• Lead halide perovskites (CsPbBr3, MAPbBr3) have enabled sensitive direct X-ray detection and scintillation but pose toxicity concerns (Nature 2017; Nat. Photonics 2015–2017; ACS/Nano-Micro Lett.).
• Lead-free alternatives and low-dimensional hybrids have emerged: Cs2AgBiBr6 single crystals for X-ray detection with low detection limits, and low-dimensional hybrids like Bmpip2SnBr4 and Rb2CuX3 (X = Cl, Br) as scintillators showing promising light yields and sensitivity.
• Organic Mn(II) halide hybrids exhibit strong PL based on Mn2+ d–d transitions: tetrahedral coordination yields green emission, octahedral yields red. Demonstrated applications include LEDs with ~10% EQE using (PPh4)2MnBr4 and DBFDPO-MnBr2, vapochromism (MnBr2(dppeO)2), and solvent sensing ((C9NH20)2MnBr4). Prior to this work, their use as X-ray scintillators had not been explored.
• Recent lead-free copper halides (e.g., Cs3Cu2I5, Rb2CuBr3) demonstrate high light yields and stability, offering benchmarks for comparison in eco-friendly scintillators.

Synthesis and crystal growth:

• 0D (C38H34P2)MnBr4 single crystals obtained via solvent diffusion: diethyl ether diffused into a dichloromethane (DCM) precursor containing ethylenebis(triphenylphosphonium bromide) (C38H34P2Br2) and MnBr2 in a 1:1 molar ratio. Crystallization at room temperature over 3 days yields pale green block crystals (>1 inch) with ~89% yield.
• Preparative details: MnBr2 (429.5 mg, 2.0 mmol) and ethylenebis(triphenylphosphonium bromide) (1.424 g, 2.0 mmol) dissolved in 10 mL DCM, filtered into a 20 mL vial; placed inside a 100 mL vial containing 60 mL diethyl ether; sealed and left undisturbed for 3 days.

Structural and thermal characterization:

• Single-crystal X-ray diffraction (SCXRD): Rigaku XtaLAB Synergy-S diffractometer with HyPix-6000HE HPC detector, dual Mo/Cu microfocus sources. Structure: monoclinic, 0D molecular structure with isolated MnBr4 tetrahedra surrounded by C38H34P22+ cations; average Mn–Br bond length 2.51 Å; bond angle 108.48°.
• Powder X-ray diffraction (PXRD): Panalytical X'PERT Pro (Cu Kα, 40 kV, 40 mA, X'Celerator RTMS), 2θ = 5–40°, step 0.02°, RT. PXRD matches simulated patterns from SCXRD, confirming phase purity.
• Thermal analysis: TGA/DSC on TA Instruments Q600, N2 flow 100 mL min−1, heating 25–700 °C at 5 °C min−1. No weight loss before 310 °C (high stability); DSC endotherm at 295 °C indicates melting point and phase stability below this temperature.

Optical characterization:

• UV–vis absorption: Cary 5000 UV-Vis-NIR; observed intense band ~285 nm and peaks at 360 and 450 nm.
• Steady-state PL: Edinburgh Instruments FS5; bright green emission at 517 nm (FWHM 51 nm).
• Photoluminescence quantum efficiency (PLQE): Hamamatsu Quantaurus-QY (C11347-11) with xenon lamp, integrating sphere, CCD; PLQE ~95% using provided equation and calibration.
• Time-resolved PL: Edinburgh FLS920 with TCSPC to 10,000 counts; single-exponential decay, lifetime 318 μs (R2 = 0.999).
• Moisture stability: PL intensity monitored over 1 month in ambient air; unchanged.

Scintillation characterization:

• Radioluminescence (RL) spectra and intensity vs dose: FS5 with X-ray source (Amptek Mini-X, Au target, max 4 W). Ce:LuAG used as reference (similar emission ~520 nm) to minimize detector spectral response differences.
• Dose-response: RL measured across dose rates 36.7 nGy s−1 to 89.4 μGy s−1, linearity assessed; detection limit determined at SNR = 3.
• Light yield estimation: Relative to Ce:LuAG (25,000 ph MeV−1) using corrected response amplitudes and spectral corrections for Hamamatsu R928 PMT per provided equation.
• Radiation stability: Continuous X-ray irradiation at 89.4 μGy s−1 for 4 h; RL monitored for degradation.
• Afterglow: Sample excited 20 s by xenon lamp; afterglow recorded by Hamamatsu R928 PMT at 10 ms intervals; time to decay to background evaluated.

Scintillator screens and imaging:

• Rigid screen: Hand-ground (C38H34P2)MnBr4 powders (<3 μm particles by FEI Nova NanoSEM 400) filled into PXRD holder.
• Flexible screens: Powders blended with two-part PDMS EI-1184 at 40 wt% loading; cast in PTFE mold; cured at 100 °C for 30 min; cooled to yield flat films (4.5 × 5.8 cm2). Flexibility tested (bending, stretching) and uniform emission under UV assessed.
• Imaging setup: Home-built system (Supplementary Fig. 9) with target objects (speaker chip 9 × 6 mm, wrench) placed between X-ray source and scintillator screen; images captured with Nikon D90 digital camera. Spatial resolution obtained by fitting point spread function with Gaussian; FWHM taken as resolution.

• Material and structure: 0D organic manganese(II) halide (C38H34P2)MnBr4 forms inch-scale single crystals via facile room-temperature solvent diffusion. Monoclinic crystal with isolated MnBr4 tetrahedra; robust thermal stability (no TGA weight loss before 310 °C; DSC endotherm at 295 °C).
• Photophysics: Strong green emission at 517 nm with FWHM 51 nm; near-unity PLQE ~95%; single-exponential lifetime 318 μs (R2 = 0.999). Absorption features at ~285 nm (intense), 360 nm, and 450 nm corresponding to A1→4G and A1→4D transitions of tetrahedral Mn2+. Moisture-stable PL over 1 month.
• Scintillation performance:
  • RL spectrum identical to PL; RL intensity >3× that of Ce:LuAG under identical X-ray dose rate.
  • Linear dose-response from 36.7 nGy s−1 to 89.4 μGy s−1 for both single crystals and flexible films.
  • Detection limit: 72.8 nGy s−1 (SNR = 3) for single crystals; 461.1 nGy s−1 for PDMS composite films.
  • Light yield: ~79,800 photon MeV−1 (derived from 3.2× Ce:LuAG with 25,000 photon MeV−1) for crystals; 66,256 photon MeV−1 for flexible films.
  • Stability: Little-to-no RL degradation after 4 h continuous X-ray at 89.4 μGy s−1.
  • Afterglow: Emission decays to background within 10 ms after excitation ceases, enabling high-contrast imaging.
• Imaging:
  • Clear X-ray images of a speaker chip showing internal components; spatial resolution 0.322 mm (FWHM).
  • Flexible PDMS-based screens provide distinct contrast images for a wrench and a speaker chip with good resolution.
• Benchmarking and eco-friendliness:
  • Light yield comparable to lead-free Cs3Cu2I5 (79,279 ph MeV−1) and Rb2CuBr3 (91,056 ph MeV−1), exceeding Rb2CuCl3 (16,600), CsPbBr3 nanocrystals (21,000), and commercial CsI:Tl (54,000) and CdWO4 (28,000).
  • Toxicity considerations indicate (C38H34P2)MnBr4 is significantly less toxic (Mn2+ is less hazardous) than many lead-, thallium-, cesium-, copper-, or gadolinium-containing scintillators.

The study addresses the need for low-cost, high-performance, and environmentally friendly X-ray scintillators by employing a 0D organic Mn(II) halide hybrid, (C38H34P2)MnBr4. The isolated MnBr4 tetrahedra confer strong, efficient green emission via Mn2+ d–d transitions and minimize self-absorption. The material exhibits outstanding scintillation metrics—linear dose response over several orders of magnitude, low detection limit (72.8 nGy s−1), and high light yield (~79,800 photon MeV−1)—surpassing many commercial scintillators and comparable to the best lead-free halides. Stability under continuous irradiation and fast afterglow decay (to background within 10 ms) enable high-contrast, high-resolution imaging demonstrated on electronic components. The facile, room-temperature synthesis to large single crystals and the successful fabrication of flexible PDMS-based screens extend applicability to portable and flexible imaging platforms. Collectively, these results validate organic Mn(II) halide hybrids as a viable, eco-friendly class of scintillators for practical X-ray imaging and detection.

A 0D organic manganese(II) bromide hybrid, (C38H34P2)MnBr4, was synthesized via a simple room-temperature solution growth method to inch-scale single crystals. The material shows near-unity PLQE (~95%), robust thermal and moisture stability, and state-of-the-art scintillation performance—excellent linearity, high light yield (~79,800 photon MeV−1), and low detection limit (72.8 nGy s−1). High-resolution X-ray imaging was achieved with both rigid powder screens and large-area flexible PDMS composites. The combination of low cost, eco-friendliness, facile processing, and superior performance positions (C38H34P2)MnBr4 as a promising scintillator for commercial applications. This work opens avenues to explore additional low-cost, high-performance, environmentally benign hybrid materials for radiation scintillation.

• Flexible PDMS composite screens exhibit reduced light yield (66,256 photon MeV−1) and higher detection limit (461.1 nGy s−1) compared to single crystals, likely due to lower active material loading, potential non-uniform particle distribution, and PDMS attenuation effects.
• Light yield was derived relative to a Ce:LuAG reference using detector response corrections rather than via absolute photon counting, introducing dependence on calibration accuracy.
• Long-term radiation hardness was assessed over 4 hours; extended lifetime and high-dose endurance studies are not reported.
• Spatial resolution was demonstrated at ~0.322 mm with the home-built setup; performance with clinical imaging systems and under varying geometries/thicknesses was not explored.