In Vivo NIR-II Fluorescence Lifetime Imaging of Whole-Body Vascular Using High Quantum Yield Lanthanide-Doped Nanoparticles.

Second near infrared (NIR-II, 1000-1700 nm) fluorescence lifetime imaging is a powerful tool for biosensing, anti-counterfeiting, and multiplex imaging. However, the low photoluminescence quantum yield (PLQY) of fluorescence probes in NIR-II region limits its data collecting efficiency and accuracy, especially in multiplex molecular imaging in vivo. To solve this problem, lanthanide-doped nanoparticles (NPs) ß-NaErF4 : 2%Ce@NaYbF4 @NaYF4 with high PLQY and tunable PL lifetime through multi-ion doping and core-shell structural design, are presented. The obtained internal PLQY can reach up to 50.1% in cyclohexane and 9.2% in water under excitation at 980 nm. Inspired by the above results, a fast NIR-II fluorescence lifetime imaging of whole-body vascular in mice is successfully performed by using the homebuilt fluorescence lifetime imaging system, which reveals a murine abdominal capillary network with low background. A further demonstration of fluorescence lifetime multiplex imaging is carried out in molecular imaging of atherosclerosis cells and different organs in vivo through NPs conjugating with specific peptides and different injection modalities, respectively. These results demonstrate that the high PLQY NPs combined with the homebuilt fluorescence lifetime imaging system can realize a fast and high signal-to-noise fluorescence lifetime imaging; thus, opening a road for multiplex molecular imaging of atherosclerosis.

Sharp angular and unidirectional filter based on accidental degeneracy between two twisted Weyl semimetal-based defect modes in a one-dimensional photonic crystal.

To address the challenges associated with the realization of optical non-reciprocity and enhance the efficiency of GaAs solar cells, among other systems, in this study, we investigated defect-mode interactions in a one-dimensional photonic crystal containing two Weyl semimetal-based defect layers. Moreover, two non-reciprocal defect modes were observed, namely, when defects are identical and nearby. Increasing the defect distance weakened the defect-mode interactions, thus causing the modes to gradually move closer and then degenerate into one mode. It should be noted that by changing the optical thickness of one of the defect layers, the mode was found to degrade to two non-reciprocal dots with different frequencies and angles. This phenomenon can be attributed to an accidental degeneracy of two defect modes with dispersion curves that intersect in the forward and backward directions, respectively. Moreover, by twisting Weyl semimetal layers, the accidental degeneracy occurred only in the backward direction, thus resulting in a sharp angular and unidirectional filter.

Dual-directional group delays during optical topological transitions in black phosphorus-based asymmetric hyperbolic metamaterials.

We theoretically study the optical properties of TM waves when their magnetic field direction is perpendicular to the armchair and zigzag optical axes of black phosphorus, respectively. It is found that hyperbolic dispersion and elliptic dispersion coexist in periodically arranged black phosphorus multilayers. Interestingly, by tilting the symmetric multilayers to be asymmetric, the elliptical part of the original two dispersions disappears as the wavelength increases. As such only the hyperbolic dispersion remains, showing an optical topological transition. In the region of the topological transition, a large transmitted group delay (3ps) and a reflected group delay (0.2ps) of the TM waves occurs simultaneously. The corresponding group velocities are slowed down to approximately c/1000 and c/100 (c is the speed of light in a vacuum), respectively. This dual-directional group delays significantly increase the wave-matter interaction so that nonreciprocal perfect absorptions can be realized in the mid-infrared band. Such asymmetrical black phosphorus hyperbolic metamaterials can be applied to the directional, tunable, and nonreciprocal perfect absorbers and also to devices based on strong wave-matter interactions.

A Novel Loop Closure Detection Approach Using Simplified Structure for Low-Cost LiDAR.

Reducing the cumulative error is a crucial task in simultaneous localization and mapping (SLAM). Usually, Loop Closure Detection (LCD) is exploited to accomplish this work for SLAM and robot navigation. With a fast and accurate loop detection, it can significantly improve global localization stability and reduce mapping errors. However, the LCD task based on point cloud still has some problems, such as over-reliance on high-resolution sensors, and poor detection efficiency and accuracy. Therefore, in this paper, we propose a novel and fast global LCD method using a low-cost 16 beam Lidar based on "Simplified Structure". Firstly, we extract the "Simplified Structure" from the indoor point cloud, classify them into two levels, and manage the "Simplified Structure" hierarchically according to its structure salience. The "Simplified Structure" has simple feature geometry and can be exploited to capture the indoor stable structures. Secondly, we analyze the point cloud registration suitability with a pre-match, and present a hierarchical matching strategy with multiple geometric constraints in Euclidean Space to match two scans. Finally, we construct a multi-state loop evaluation model for a multi-level structure to determine whether the two candidate scans are a loop. In fact, our method also provides a transformation for point cloud registration with "Simplified Structure" when a loop is detected successfully. Experiments are carried out on three types of indoor environment. A 16 beam Lidar is used to collect data. The experimental results demonstrate that our method can detect global loop closures efficiently and accurately. The average global LCD precision, accuracy and negative are approximately 0.90, 0.96, and 0.97, respectively.

Synthetic CT generation from CBCT based on structural constraint cycle-EEM-GAN.

Objective. Cone beam CT (CBCT) typically has severe image artifacts and inaccurate HU values, which limits its application in radiation medicines. Scholars have proposed the use of cycle consistent generative adversarial network (Cycle-GAN) to address these issues. However, the generation quality of Cycle-GAN needs to be improved. This issue is exacerbated by the inherent size discrepancies between pelvic CT scans from different patients, as well as varying slice positions within the same patient, which introduce a scaling problem during training.Approach. We introduced the Enhanced Edge and Mask (EEM) approach in our structural constraint Cycle-EEM-GAN. This approach is designed to not only solve the scaling problem but also significantly improve the generation quality of the synthetic CT images. Then data from sixty pelvic patients were used to investigate the generation of synthetic CT (sCT) from CBCT.Main results.The mean absolute error (MAE), the root mean square error (RMSE), the peak signal to noise ratio (PSNR), the structural similarity index (SSIM), and spatial nonuniformity (SNU) are used to assess the quality of the sCT generated from CBCT. Compared with CBCT images, the MAE improved from 53.09 to 37.74, RMSE from 185.22 to 146.63, SNU from 0.38 to 0.35, PSNR from 24.68 to 32.33, SSIM from 0.624 to 0.981. Also, the Cycle-EEM-GAN outperformed Cycle-GAN in terms of visual evaluation and loss.Significance.Cycle-EEM-GAN has improved the quality of CBCT images, making the structural details clear while prevents image scaling during the generation process, so that further promotes the application of CBCT in radiotherapy.

[Breast cancer subtypes based on ER/PR and Her2 expression: comparison of MR imaging features].

OBJECTIVE: To evaluate the magnetic resonance (MR) imaging findings of breast cancer subtypes based on the profiles of ER/PR and Her2. METHODS: A retrospective study was conducted for 267 breast cancer subjects between February 2007 and January 2011. Clinicopathologic features and MR imaging findings of four subtypes were compared. The Chi-square (χ(2)) test, Fisher's exact test and χ(2) section method were employed for categorical variables. RESULTS: MR imaging findings:Patients with segment or linear enhancement type accounted for 25.6% in ER/PR(+), Her2(+) subtype group and 36.1% in ER/PR(-), Her2(+) subtype, no significant difference existed between them (χ(2) = 1.112, P = 0.641). But they were significantly higher than ER/PR(+), Her2(-) subtype group and ER/PR(-), Her2(-) subtype group (χ(2) = 32.793, P < 0.001; χ(2) = 14.565, P < 0.001). ER/PR(-), Her2(-) subtype patients accounted for 14.6% of the total breast cancer patients (39/267). Subjects with ER/PR(-), Her2(-) subtype were more likely to present unifocal (91.7%, 33/36) and mass type lesion (92.3%, 36/39). The mass type lesions in ER/PR(-), Her2(-) subtype group were more likely to showed smooth margin [58.3% (21/36), P < 0.001], very high intratumoral signal and peripheral hyperintense pattern on fat suppression T2-weighted imaging (P < 0.001) and early rim enhancement [81.5% (29/36), P < 0.001]. No significantly difference of four subtypes were found on number of mass, mass shape and pattern at dynamic enhancement imaging (χ(2) = 1.413, P = 0.713; χ(2) = 8.423, P = 0.204; χ(2) = 4.657, P = 0.540). CONCLUSION: Segment or linear enhancement type is characterized by MR imaging. Early rim enhanced mass is ER/PR(-), Her2(-) breast cancer. The most important characteristics of MR imaging include a smooth edge of breast mass, very high intratumoral signal on fat suppression T2-weighted imaging and peripheral hyperintense pattern.

Suppression of Photoinduced Phase Segregation in Mixed-Halide Perovskite Nanocrystals for Stable Light-Emitting Diodes.

Halide segregation is a critical bottleneck that hampers the application of mixed-halide perovskite nanocrystals (NCs) in both electroluminescent and down-conversion red-light-emitting diodes. Herein, we report a strategy that combines precursor and surface engineering to obtain pure-red-emitting (peaked at 624 nm) NCs with a photoluminescence quantum yield of up to 92% and strongly suppresses the halide segregation of mixed-halide NCs under light irradiation. Red-light-emitting diodes (LED) using these mixed-halide NCs as phosphors exhibit color-stable emission with a negligible peak shift and spectral broadening during operation over 240 min. By contrast, a dramatic peak shift and spectral broadening were observed after 10 min of operation in LEDs based on mixed-halide NCs synthesized by a traditional method. Our strategy is critical to achieving photo- and band-gap-stable mixed-halide perovskite NCs for a variety of optoelectronic applications such as micro-LEDs.

Long-Lived Dark Exciton Emission in Mn-Doped CsPbCl3 Perovskite Nanocrystals.

The unusual temperature dependence of exciton emission decay in CsPbX3 perovskite nanocrystals (NCs) attracts considerable attention. Upon cooling, extremely short (sub-ns) lifetimes were observed and were explained by an inverted bright-dark state splitting. Here, we report temperature-dependent exciton lifetimes for CsPbCl3 NCs doped with 0-41% Mn2+. The exciton emission lifetime increases upon cooling from 300 to 75 K. Upon further cooling, a strong and fast sub-ns decay component develops. However, the decay is strongly biexponential and also a weak, slow decay component is observed with a ∼40-50 ns lifetime below 20 K. The slow component has a ∼5-10 times stronger relative intensity in Mn-doped NCs compared to that in undoped CsPbCl3 NCs. The temperature dependence of the slow component resembles that of CdSe and PbSe quantum dots with an activation energy of ∼19 meV for the dark-bright state splitting. Based on our observations, we propose an alternative explanation for the short, sub-ns exciton decay time in CsPbX3 NCs. Slow bright-dark state relaxation at cryogenic temperatures gives rise to almost exclusively bright state emission. Incorporation of Mn2+ or high magnetic fields enhances the bright-dark state relaxation and allows for the observation of the long-lived dark state emission at cryogenic temperatures.

Tuning Exciton-Mn2+ Energy Transfer in Mixed Halide Perovskite Nanocrystals.

Doping nanocrystals (NCs) with luminescent activators provides additional color tunability for these highly efficient luminescent materials. In CsPbCl3 perovskite NCs the exciton-to-activator energy transfer (ET) has been observed to be less efficient than in II-VI semiconductor NCs. Here we investigate the evolution of the exciton-to-Mn2+ ET efficiency as a function of composition (Br/Cl ratio) and temperature in CsPbCl3-x Br x :Mn2+ NCs. The results show a strong dependence of the transfer efficiency on Br- content. An initial fast increase in the relative Mn2+ emission intensity with increasing Br- content is followed by a decrease for higher Br- contents. The results are explained by a reduced exciton decay rate and faster exciton-to-Mn2+ ET upon Br- substitution. Further addition of Br- and narrowing of the host bandgap make back-transfer from Mn2+ to the CsPbCl3-x Br x host possible and lead to a reduction in Mn2+ emission. Temperature-dependent measurements provide support for the role of back-transfer as the highest Mn2+-to-exciton emission intensity ratio is reached at higher Br- content at 4.2 K where thermally activated back-transfer is suppressed. With the present results it is possible to pinpoint the position of the Mn2+ excited state relative to the CsPbCl3-x Br x host band states and predict the temperature- and composition-dependent optical properties of Mn2+-doped halide perovskite NCs.

Efficient and Stable Luminescence from Mn2+ in Core and Core-Isocrystalline Shell CsPbCl3 Perovskite Nanocrystals.

There has been a growing interest in applying CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) for optoelectronic application. However, research on doping of this new class of promising NCs with optically active and/or magnetic transition metal ions is still limited. Here we report a facile room temperature method for Mn2+ doping into CsPbCl3 NCs. By addition of a small amount of concentrated HCl acid to a clear solution containing Mn2+, Cs+, and Pb2+ precursors, Mn2+-doped CsPbCl3 NCs with strong orange luminescence of Mn2+ at ∼600 nm are obtained. Mn2+-doped CsPbCl3 NCs show the characteristic cubic phase structure very similar to the undoped counterpart, indicating that the nucleation and growth mechanism are not significantly modified for the doping concentrations realized (0.1 at. % - 2.1 at. %). To enhance the Mn2+ emission intensity and to improve the stability of the doped NCs, isocrystalline shell growth was applied. Growth of an undoped CsPbCl3 shell greatly enhanced the emission intensity of Mn2+ and resulted in lengthening the radiative lifetime of the Mn2+ emission to 1.4 ms. The core-shell NCs also show superior thermal stability and no thermal degradation up to at least 110 °C, which is important in applications.

Design of omnidirectional and multiple channeled filters using one-dimensional photonic crystals containing a defect layer with a negative refractive index.

The band structures of one-dimensional photonic crystals containing a defect layer with a negative refractive index are studied, showing that the defect modes possess three types of dispersion: positive, zero, and negative types. Based on these three types of dispersion, practical designs for large incident angle filters without polarization effect and for narrow frequency and sharp angular filters are suggested. Moreover, the splitting of one degenerate defect mode into multiple defect modes is observed in the band gap when the parameters of the defect layer vary. This mode splitting phenomenon can be used to design multiple channeled filters or filters with a rectangular profile. The dispersion multiplicity of the defect modes can be understood by an approximate formula, and the critical condition for the defect mode splitting is also analyzed. Based on these analyses, practical optimization design of omnidirectional filter is also suggested.