Low-cost X-ray detectors with high performance, durability, and flexibility, are required for a wide range of applications in several fields, such as medical (diagnostic radiology, imaging, etc.), nondestructive testing (radioscopic inspections, radiography testing, etc.), security and defence (baggage/body scanning systems, paper mail, etc.), nuclear and radiation industries (nuclear power plants, research reactors, users of nuclear gauges, etc.), and research and development. [1] X-ray detection using semiconductors, based on the direct generation of electrical signals by X-rays (i.e., direct scheme), offers better spatial resolution and a simpler route than indirect schemes, in which X-rays are converted into photons by scintillating phosphors before detection by photodiode arrays. [2] Currently, the conventional materials used for direct conversion of X-rays include stabilized amorphous Se (α-Se), PbI 2 , HgI 2 , CdTe, and CdZnTe. [3] Metal halide perovskites represent a family of the most promising materials for fascinating photovoltaic and photodetector applications due to their unique optoelectronic properties and much needed simple and low-cost fabrication process. The high atomic number (Z) of their constituents and significantly higher carrier mobility also make perovskite semiconductors suitable for the detection of ionizing radiation. By taking advantage of that, the direct detection of soft-X-ray-induced photocurrent is demonstrated in both rigid and flexible detectors based on all-inorganic halide perovskite quantum dots (QDs) synthesized via a solution process. Utilizing a synchrotron soft-X-ray beamline, high sensitivities of up to 1450 µC Gy air −1 cm −2 are achieved under an X-ray dose rate of 0.0172 mGy air s −1 with only 0.1 V bias voltage, which is about 70-fold more sensitive than conventional α-Se devices. Furthermore, the perovskite film is printed homogeneously on various substrates by the inexpensive inkjet printing method to demonstrate large-scale fabrication of arrays of multichannel detectors. These results suggest that the perovskite QDs are ideal candidates for the detection of soft X-rays and for large-area flat or flexible panels with tremendous application potential in multidimensional and different architectures imaging technologies.

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It is highly desirable and a great challenge for red light emission of carbon dots under long wavelength excitation. Here, we developed a facile route to synthesize carbon dots with red emission due to the doping effect of S and N elements, borrowing from the concept of the semiconductor. The maximum emission locates at 594 nm under 560 nm excitation. The absolute photoluminescence (PL) quantum yield (QY) is as high as 29% and 22% in ethanol and water, respectively. XPS and FTIR spectra illustrated that there exist -SCN and -COOH groups on the surface of the carbon dots. They endow the carbon dots with high sensitivity for ion detection of Fe. The quenched PL emission of Fe-S,N-CDs can be recovered by adding ascorbic acid to release the -COOH and -SCN group due to Fe formation in the presence of ascorbic acid. High PL QY of red emission is beneficial to application in bioimaging. Doxorubicin was loaded onto carbon dots through π-π stacking to form a theranostic agent. When the CD-Dox was injected into the tumor site, a strong PL emission was observed. The PL intensity indicates the concentration of the theranostic agent. After 7 times injection, both the tumor size and weight clearly decrease. The results demonstrate that the S,N-CDs are a potentially excellent bioimaging component in the theranostic field.

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We consider theoretically the spaser excited electrically via a nanowire with ballistic quantum conductance. We show that in the extreme quantum regime, i.e., for a single conductance-quantum nanowire, the spaser with the core made of common plasmonic metals, such as silver and gold, is fundamentally possible. For ballistic nanowires with multiple-quanta or non-quantized conductance, the performance of the spaser is enhanced in comparison with the extreme quantum limit. The electrically-pumped spaser is promising as an optical source, nanoamplifier, and digital logic device for optoelectronic information processing with speed ∼ 100 GHz to ∼ 100 THz. Active or gain nanoplasmonics was introduced [1] by spaser (surface plasmon amplification by stimulated emission of radiation). The spaser is a nanoscale quantum generator and ultrafast nanoamplifier of coherent localized optical fields [1][2][3][4][5]. The spaser is a nanosystem constituted by a plasmonic metal and a gain medium. The spaser is based on compensation of optical losses in metals by gain in the active medium (nanoshell) overlapping with the surface plasmon (SP) eigenmodes of the metal plasmonic nanosystem. There are many experimentally observed and investigated spasers where the gain medium consisted of dye molecules [6][7][8], unstructured semiconductor nanostructures and nanoparticles [9][10][11][12][13][14][15][16][17][18], or quantum-confined semiconductor heterostructures: quantum dots (QDs) [19,20], quantum wires (QWs), or quantum wells [21].Classified by mode confinement, there are the spasers with one-dimensional [9,11,13], two-dimensional [10], or three-dimensional (3d) confinement [6,7,18]. The spasers can also be classified by the spasing-eigenmode type, which can be either localized surface plasmons (SPs) [6,7,14,18], or surface plasmon polaritons (SPPs) [22,23] as in the rest of the cases. Among the observed spasers, most are with optical pumping, including all the spasers with the strong 3d confinement [6,7,14,18]. Only few SPP spasers, whose confinement and losses are not strong, are with electric pumping [9,11,13].There have been doubts expressed in the literature regarding viability of the nanospaser with the strong 3d confinement [24], especially with electrical pumping [25]. In a direct contrast, the possibility of the optically pumped strongly 3d-confined spaser has been both theoretically shown [1,3,26,27] and experimentally demonstrated [6,7,14,18]. Here we theoretically establish that the electrically-pumped spaser is fundamentally possible. A principal difference of our theory from the previous works [24,25] is that we consider ballistic, quantum electron transport instead of classical, dissipative one. Another important difference is that the contradicting theoretical work [24,25] on spasers (sometimes also called plasmonic nanolasers) has ignored distinction between the threshold condition of spasing and the condition of developed spasing with N n ∼ 1 quanta (SPs) per generating mode. While for macroscopic lasers with enormousl...

2D materials show wide-ranging physical properties with their electronic bandgaps varying from zero to several electronvolts, offering a rich platform to explore novel electronic and optoelectronic functions. Notably, atomically thin 2D materials are well suited for integration in optoelectronic circuits, because of their ultrathin body, strong light-matter interactions, and compatibility with the current silicon photonic technology. In this paper, an overview of the state of the art of using 2D materials in optoelectronic devices and integration is provided. The optoelectronic properties of 2D materials and their typical electronic and optoelectronic applications including light sources, optical modulators, photodetectors, field-effect transistors, and logic circuits are summarized. The device configurations, operation mechanisms, and device figures-of-merit are introduced and discussed. By discussing the recent advances, future trends, and existing challenges of 2D materials and their optoelectronic devices, this review has provided an insight into the perspectives of 2D materials for optoelectronic integration and may guide the development of this field within the research community.