All-inorganic perovskite nanocrystal scintillators

a, In bulk inorganic materials, X-ray photons absorbed by the lattice atoms can generate hot charge carriers, followed by exciton thermalization and subsequent transport to defect sites or activator centres (‘traps’), where radiative emission occurs. VB, valence band; CB, conduction band; V_k, self-trapped hole; F, Farbe centre; ν_exc, photon frequency during excitonic luminescence; ν_A, photon frequency during activator (A) luminescence. b, Scintillation properties of CsPbBr₃ QDs and commercial bulk inorganic materials under X-ray excitation. The full-width at half-maximum (FWHM) represents the spectral width of the scintillation spectra of the crystal. The insets show photographs of the corresponding samples acquired under X-ray excitation. BGO, Bi₄Ge₃O₁₂.

a, TEM images of the as-prepared cubic-phased nanocrystals (left) and the corresponding size distribution of the nanocrystals (right). The samples are CsPbCl₃, CsPb(Cl/Br)₃, CsPbBr₃, CsPb(Br/I)₃ and CsPbI₃ nanocrystals (from top to bottom). Insets are images of perovskite nanocrystals dispersed in cyclohexane, recorded under 365-nm ultraviolet light excitation. b, Powder X-ray diffraction patterns for typical ternary and mixed-halide CsPbX₃ (X = Cl, Br or I) nanocrystals. All peaks are indexed in accordance with the cubic-phased CsPbBr₃ structure (Joint Committee on Powder Diffraction Standards file (PDF) number 54-0752). c, d, Dark-field scanning transmission electron micrographs (STEM; JEM-F200HR) of CsPbBr₃ nanocrystals. e, Elemental mapping of Br, Pb and Cs for the nanocrystals, obtained from the area marked by the rectangular box in d using energy-dispersive X-ray spectroscopy. f, Atomically resolved dark-field STEM image of a single CsPbBr₃ nanocrystal, showing Cs and Pb lattice atoms. g, Energy-dispersive X-ray spectrum of the as-prepared CsPbBr₃ perovskite nanocrystals, confirming the stoichiometric composition of the CsPbBr₃ nanocrystals. We note that strong Cu signals come from the TEM copper grid.

a, Demonstration of X-ray-induced luminescence modulation using CsPbX₃ QDs of different compositions (X = Cl, Br or I). b, Multicolour X-ray scintillation from CsPb(Cl/Br)₃, CsPbBr₃ and CsPb(Br/I)₃ nanocrystals cast on a PDMS substrate. The X-ray dose rate is 278 μGy s⁻¹. c, Typical photographs of radioluminescence from CsPb(Cl/Br)₃, CsPbBr₃ and CsPb(Br/I)₃ QDs under X-ray excitation. d, e, Multicolour visualization of as-developed perovskite QD scintillators using X-rays (d) and the corresponding bright-field image (e).

a–c, Radioluminescence spectra of carbon dots (a), CdTe QDs (b) and CsPbBr₃ nanocrystals (NCs; c) under X-ray excitation at 5.0 μGy s⁻¹ and 278 μGy s⁻¹. d, Comparison of radioluminescence intensity for the as-prepared carbon dots, CdTe QDs and CsPbBr₃ nanocrystals under 278 μGy s⁻¹ X-ray excitation. e, Scintillation performance and maximal K-edge energy of lead halide perovskite nanocrystals, carbon dots and CdTe QDs.

a–c, Radioluminescence spectra of bulk single-crystal CH₃NH₃PbBr₃ (a) and CsPbBr₃ (b) and of CsPbBr₃ nanocrystals (c) under X-ray excitation at 5.0 μGy s⁻¹ and 278 μGy s⁻¹. The insets are photographs of CsPbBr₃ bulk single crystal (b) and nanocrystal powders (c) taken under ambient light (top) and X-ray illumination (bottom). The X-ray dose used for the experiments was 278 μGy s⁻¹. d, Comparison of radioluminescence intensity for three types of perovskite material under 278 μGy s⁻¹ X-ray excitation. e, PLQY and exciton binding energy of perovskite materials at 300 K^31,37. We note that the thermal energy at 300 K is k_BT ≈ 25 meV. Nanocrystalline perovskites are highly luminescent materials, whereas bulk perovskite crystals are most suitable for the generation of free charge carriers owing to their low exciton binding energy.

a, Temperature-dependent scintillation spectra of the CsPbBr₃ nanocrystals at 77–300 K under X-ray illumination at 50 μGy s⁻¹. b, Arrhenius plot of the X-ray-induced luminescence intensities of the CsPbBr₃ nanocrystals at 532 nm. c, Experimental setup for the synchrotron-radiation-induced radioluminescence measurements at the X-ray beamline of the Shanghai Synchrotron Radiation Facility (SSRF). The X-ray energy is 10–38 keV. d, The electronic edge energies for Pb L, Cs K and Br K.

a, The Brillouin zone of the cubic-phased crystal lattice in CsPbBr₃, calculated using relativistic corrections. Γ, M, R and X denote high-symmetry points within the reciprocal space (blue). b, c, Calculated electron density associated with the valence band (b) and the conduction band (c) of the cubic CsPbBr₃. We note that the halide ions contribute to the changes of the bandgap in the perovskite nanocrystal through the influence of the valence orbitals. Cs, purple; Pb, grey; Br, orange; electron orbital, blue; hole orbital, green. d–g, Localized electronic and hole levels for V_Br and V_Pb at different charge states. h, i, Schematic diagram of energy transfer for radioluminescence induced by intrinsic lattice defects and the quenching effect caused by evident ion movement (Cs⁺). \({{\rm{V}}}_{{\rm{P}}{\rm{b}}}^{\delta -}\) denotes a Pb vacancy with small (|δ| < 1) charge transfer. j, Thermodynamic transition levels of the perovskite nanocrystal. E_c, maximum valence band energy; E_v, minimum conduction band energy.

a, Simplified model of CsPbBr₃ structure composed of 293 atoms with a particle size of 12.06 Å. b, Calculated orbital contour plots of a CsPbBr₃ nanocrystal, showing the HOMO (blue), LUMO (green) and SVIC trapping (red) states. The SVIC states are formed owing to unsaturated p orbitals of surface Br sites. c, PDOS of the CsPbBr₃ QD. The SVIC state is located near the Fermi level (E_F). d, The relative energy of the SVIC state to the valence band (VB) maximum as a function of inter-particle distance, d. The red line is calculated by fitting with the Gaussian distribution function. The top inset shows the simulation model used to calculate the energy evolution of the CsPbBr₃ nanocrystal as a function of particle distance. CB, conduction band.

a, Absorption spectra of CsPbBr₃ nanocrystals dispersed in cyclohexane at different concentrations. b, Absorption as a function of concentration for CsPbBr₃ nanocrystals. The molar extinction coefficient, ε, was determined by applying the Beer–Lambert law A = εcL, where A is the absorbance, c is the molar concentration (mol l⁻¹) and L is the optical path length (1 cm) through the sample. The absorption cross-section, σ, was determined by ε = N_Aσ/(1,000 × ln10), where N_A is Avogadro’s number. c, Photoluminescence (PL) lifetime of a single CsPbBr₃ perovskite nanocrystal. d, Second-order correlation function, g²(τ), of the nanocrystal. The value g²(0) = 0.16 confirms the single-quantum-emitter nature of the photon emission. e, Fluorescence intermittency trace recorded for a single CsPbBr₃ perovskite nanocrystal. The recorded photoluminescence intensity reaches more than 2,000 counts per 20-ms bin.

a, Normalized radioluminescence intensity of CsPbBr₃ nanocrystals of different thickness under X-ray excitation at a voltage of 50 kV. b, Normalized radioluminescence intensity as a function of perovskite nanocrystal film thickness. c, X-ray output spectra recorded at 10, 20, 30, 40 and 50 kV. d, Kinetic measurement of radioluminescence intensity at 532 nm in response to an X-ray dose rate of 0.013–278 μGy s⁻¹. e, Emission spectra of CsPbBr₃ nanocrystal scintillator in response to an X-ray dose rate of 0.013–278 μGy s⁻¹. f, Radioluminescence (RL) intensity as a function of the X-ray dose rate shown in e.

a–d, A flexible flat cable (a) and needle-implanted pork tissue (b) were imaged with bright-field and X-ray imaging (c, d). We note that the CsPbBr₃ nanocrystal scintillator platform shown in Fig. 3d was used for the X-ray phase contrast imaging. In both cases, the X-ray images clearly reveal the presence of metallic wires embedded in the cable and pork tissue. e, Synthesis of CsPbBr₃/SiO₂ core-shell nanoparticles with a hydrophobic surface for protection against moisture. RT, room temperature. f, TEM image of the as-prepared CsPbBr₃/SiO₂ nanoparticles. g, Multicolour luminescence spectra of the perovskite nanocrystals under X-ray irradiation at a voltage of 50 kV. The materials’ compositions are CsPbBr₃, CsPbBr_1.5I_1.5 and CsPbBr_1.2I_1.8 for green (G), orange (O) and red (R) emissions, respectively. We note that the risk of lead toxicity must be considered during experimentation. h, Bright-field and multicolour luminescent in vivo imaging in mice under X-ray excitation at a voltage of 50 kV. The X-ray-induced luminescence was recorded by a charge-coupled-device camera equipped with three optical filters at 530 nm, 630 nm and 670 nm.