The rising demand for radiation detection materials in many applications has led to extensive research on scintillators. The ability of a scintillator to absorb high-energy (kiloelectronvolt-scale) X-ray photons and convert the absorbed energy into low-energy visible photons is critical for applications in radiation exposure monitoring, security inspection, X-ray astronomy and medical radiography. However, conventional scintillators are generally synthesized by crystallization at a high temperature and their radioluminescence is difficult to tune across the visible spectrum. Here we describe experimental investigations of a series of all-inorganic perovskite nanocrystals comprising caesium and lead atoms and their response to X-ray irradiation. These nanocrystal scintillators exhibit strong X-ray absorption and intense radioluminescence at visible wavelengths. Unlike bulk inorganic scintillators, these perovskite nanomaterials are solution-processable at a relatively low temperature and can generate X-ray-induced emissions that are easily tunable across the visible spectrum by tailoring the anionic component of colloidal precursors during their synthesis. These features allow the fabrication of flexible and highly sensitive X-ray detectors with a detection limit of 13 nanograys per second, which is about 400 times lower than typical medical imaging doses. We show that these colour-tunable perovskite nanocrystal scintillators can provide a convenient visualization tool for X-ray radiography, as the associated image can be directly recorded by standard digital cameras. We also demonstrate their direct integration with commercial flat-panel imagers and their utility in examining electronic circuit boards under low-dose X-ray illumination.

Optical characteristics of luminescent materials, such as emission profile and lifetime, play an important role in their applications in optical data storage, document security, diagnostics, and therapeutics. Lanthanide-doped upconversion nanoparticles are particularly suitable for such applications due to their inherent optical properties, including large anti-Stokes shift, distinguishable spectroscopic fingerprint, and long luminescence lifetime. However, conventional upconversion nanoparticles have a limited capacity for information storage or complexity to prevent counterfeiting. Here, we demonstrate that integration of long-lived Mn2+ upconversion emission and relatively short-lived lanthanide upconversion emission in a particulate platform allows the generation of binary temporal codes for efficient data encoding. Precise control of the particle’s structure allows the excitation feasible both under 980 and 808 nm irradiation. We find that the as-prepared Mn2+-doped nanoparticles are especially useful for multilevel anti-counterfeiting with high-throughput rate of authentication and without the need for complex time-gated decoding instrumentation.

A new class of lanthanide-doped upconversion nanoparticles are presented that are without Yb or Nd sensitizers in the host lattice. In erbium-enriched core-shell NaErF :Tm (0.5 mol %)@NaYF nanoparticles, a high degree of energy migration between Er ions occurs to suppress the effect of concentration quenching upon surface coating. Unlike the conventional Yb -Er system, the Er ion can serve as both the sensitizer and activator to enable an effective upconversion process. Importantly, an appropriate doping of Tm has been demonstrated to further enhance upconversion luminescence through energy trapping. This endows the resultant nanoparticles with bright red (about 700-fold enhancement) and near-infrared luminescence that is achievable under multiple excitation wavelengths. This is a fundamental new pathway to mitigate the concentration quenching effect, thus offering a convenient method for red-emitting upconversion nanoprobes for biological applications.

Highly uniform core/double-shell-structured β-NaYF4:Er(3+),Yb(3+)@SiO2@TiO2 hexagonal sub-microprisms are prepared and employed in dye-sensitized solar cells (DSCs) internally. This work paves a facile way to enable the most-efficient upconversion material (β-NaYF4:Er(3+),Yb(3+)) to be used as scattering and upconversion centers in the photoelectrode of a DSC.

2Methylammonium lead trihalide perovskites (MAPbX 3 , X: Cl, Br or I) feature fascinating chemical and physical properties, including tunable bandgap, large light absorption coefficient in the UV-Vis spectral region, long carrier diffusion length, and solution processability. [1][2][3][4][5] As such, this class of materials has been intensively exploited for developing optoelectronic devices such as solar cells, light-emitting diodes, photodetectors, and phototransistors. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Thus far, solution processing is the most widely used technique to synthesize perovskite films due to its low cost and simplicity. Furthermore, a recent transient THz spectroscopy study showed that bi-molecular recombination rates are much lower than the fundamental Langevin limit in such perovskite films, leading to high carrier mobilities.[3]However, solution-processed pristine polycrystalline films still suffer from structural imperfections such as grain boundaries, trapping defects and drifting cations. [21,22] Perovskite single crystals have shown exceptionally good structural and physical properties, [23][24][25] but their bulk form impedes practical device applications. In order to improve the performance of perovskite-based devices, particularly photodetectors, a few works have been devoted to interfacing perovskite films with other functional materials. [18,26] In fact, such an interfacebased approach has been applied to a wide range of optoelectronic devices in achieving optimal performance because of the synergistic effect of individual building blocks. [27][28][29][30][31][32] Inspired by the extraordinary physical properties of semiconducting single-walled carbon nanotubes (CNTs), [33][34][35][36][37] particularly their ultrahigh charge carrier mobility, we reasoned that marrying halide perovskites with CNTs in composite films could be a viable approach toward high-performance optoelectronics. However, CNTs tend to aggregate into bundles due to the strong intra-tube van der Waals attraction, which is a severe obstacle for its integration with other materials through solution processing.[38] Surprisingly, we found that the perovskite precursor in N,N-dimethylformamide (DMF) solution is an excellent stabilizer for the homogeneous dispersion of semiconducting CNTs with a (7,6) chirality. This composite Submitted to 3 material combines the light-absorbing characteristics of perovskites with the high-mobility property of semiconducting CNTs.Our design principle for the CH 3 NH 3 PbI 3−x Cl x /CNTs composites is illustrated in Figure 1a.On light illumination, an efficient transfer of the photo-excited holes from the perovskite matrix to semiconducting CNTs is likely to occur, resulting in a significant reduction in charge recombination and hence enhanced carrier transport. The CNTs were characterized by transmission electron microscopy (TEM, Figure S1) and Raman spectroscopy (see Figure S2), and they are approximately 0.5-2 µm in length and 1.2-1.4 nm in diameter. Subsequently, w...