Abstract: In this review, the major achievements and research and development (R&D) trends from the last decade in the field of single crystal scintillator materials are described. Two material families are included, namely, those of halide and oxide compounds. In most cases, the host crystals are doped with Ce3+, Pr3+ or Eu2+ rare earth ions. Their spin- and parity-allowed 5d–4f transitions enable a rapid scintillation response, on the order of tens to hundreds of nanoseconds. Technological recipes, extended characterization by means of optical and magnetic spectroscopies, and theoretical studies are described. The latter provide further support to experimental results and provide a better understanding of the host electronic band structure, energy levels of specific defects, and the emission centers themselves. Applications in medical imaging and dosimetry, security measures, high-energy physics and the high-tech industry, in which X(γ)-rays or particle beams are used and monitored, are recognized as the main driving factor for R&D activities in this field.

Abstract: A metamaterial thermal emitter for highly efficient radiative cooling is demonstrated. The emitter selectively radiates within the atmospheric transparency window and minimizes absorption of atmospheric radiation outside the transparency window. Exploiting its intriguing radiative properties, the emitter has the ability to deliver a remarkably high cooling power of more than 100 W m−2 and to cool down 12 °C below the ambient temperature.

Abstract: Upconversion of low-energy photons into high-energy photons increases the efficiency of photovoltaic devices by converting photons with energies below the absorption threshold of the solar cell into photons that can be utilized. In this review, an overview is provided of quantitative studies of the upconversion quantum yield of upconverter materials, and of the achieved efficiency enhancements in upconverting solar cell devices. Different materials and devices are compared based on well-defined figures-of-merit and the challenges to their accurate measurement are discussed. Internal upconversion quantum yields above 13% have been reported both for Er3+-based materials as well as for organic upconverters, using irradiance values below 0.4 W cm−2. On the upconverting solar cell device level, relative enhancements of the solar cells' short-circuit currents by up to 0.55% have been achieved. These values document progress by orders of magnitude achieved in the last years. However, they also show that the field of upconversion needs further development to become a relevant technology option in photovoltaics. Different options regarding how upconversion performance can be increased further in the future are outlined.

Abstract: First reported by Farnum as much as 40 years ago, diketopyrrolopyrroles (2,5-dihydropyrrolo[4,3-c]pyrrolo-1,4-diones) are currently one of the most widely used dyes, with applications that span high-quality pigments, field-effect transistors, bulk-heterojunction solar cells, dye-sensitized solar cells, and fluorescence imaging. Due to the breadth of their utility, there have been several focused reviews on this topic since 1988. Considering the growing importance of these dyes, this review describes the overall progress made in four decades in both synthesis and the elucidation of their reactivity, and offers a critical comparison of various methods reported in the literature. The relationship between their structure and optical properties is also reviewed in detail. The extension of diketopyrrolopyrroles' chromophore leads to a significant change in both linear and nonlinear optical properties. A very strong bathochromic shift in the absorption and an increase in the two-photon absorption cross-section are typical for these analogues. Straightforward synthesis combined with good stability and a near-unity fluorescence quantum yield ensures that diketopyrrolopyrroles will continue to attract attention for years to come. The goal of this review is to systematize knowledge on these dyes, enabling their use in more real-world applications.

Abstract: Microlasers have experienced tremendous development in the past decade and become an essential part in laser evolution, as miniature lasers provide strong optical confinement and feature greatly enhanced light–matter interactions. Among all the configurations, whispering gallery mode (WGM) microcavities and microlasers exhibit outstanding optical performances with high quality factors and small mode volumes, thus ensuring low lasing thresholds. In addition, some unique properties inherent to WGM cavities, like bi-directional propagation and an evanescent field that spans several hundred nanometers across the boundary, can be exploited for novel applications. Therefore, designing and engineering innovative WGM microcavities and microlasers has attracted increasing research interest. The fundamentals and characteristics of WGM are introduced here, and then the developments and current status of WGM microcavities and microlasers are reviewed in terms of the evolution of fabrication techniques and built-up materials. In particular, the melting of glassy materials in early studies, top-down and bottom-up approaches with semiconductors, coating structures, as well as flexible, soft microresonators in recent years are presented. Finally, the application prospects of microlasers including the wavelength manipulation, sensing and microresonator coupling, are discussed.

Abstract: A facile solvothermal route to synthesize S,N co-doped graphene quantum dots (S,N-GQDs) with unique optical properties is demonstrated. Three absorption bands are observed at 338, 467, and 557 nm, which is different from any previous reports. The photoluminescent spectra display emissions in three primary colors that are independent of the excitation wavelength, within the excitation wavelength ranges of 340–420 nm, 460–540 nm, and 560–620 nm. The PL excitation spectra indicate that each emission is related to a single excitation band. It is proposed that three independent luminescent centers coexist in S,N-GQDs because the doping with S and N may change the chemical environment of the GQDs. However, energy-transfer processes usually do not occur among the independent luminescent centers under different wavelength light excitation. Heteroatom-doping of GQDs provides an attractive means of effectively tuning their optical properties for the purpose of exploiting new applications in visible-light photocatalytic and bioimaging. S,N-GQDs/TiO2 composites exhibit better hydrogen production activities under visible light (λ > 420 nm) than commercial TiO2 (P25), owing to the presence of characteristic absorption bands in the visible region. Furthermore, the S,N-GQDs have a pronounced biocompatibility and bioimaging ability under long-wavelengths excitation for live A549 cells.

Abstract: Photonic spin Hall effect (PSHE; i.e., spin-polarized photons can be laterally separated in transportation) gains increasing attention from both science and technology, but available mechanisms either require bulky systems or exhibit very low efficiencies. Here it is demonstrated that a giant PSHE with ≈100% efficiency can be realized at certain meta-surfaces with deep-subwavelength thicknesses. Based on rigorous Jones matrix analysis, a general criterion to design meta-surfaces that can realize 100%-efficiency PSHE is established. The criterion is approachable from two distinct routes at general frequencies. As a demonstration, two microwave meta-surfaces are fabricated and then experimentally characterized, both showing ≈90% efficiencies for the PSHE. The findings here pave the way for many exciting applications based on high-efficiency manipulations of photon spins, with a polarization detector experimentally demonstrated here as an example.

Abstract: Dr. A. Benayas, Prof. F. Vetrone Institut National de la Recherche Scientifi que Centre – Energie Materiaux et Telecommunications 1650, Boul. Lionel Boulet Varennes , QC J3X 1S2 , Canada E-mail: [email protected] B. del Rosal, A. Perez-Delgado, Dr. D. Jaque Fluorescence Imaging GroupDepartamento de Fisica de Materiales Facultad de Ciencias, Universidad Autonoma de Madrid Campus de Cantoblanco Madrid 28049 , Spain Dr. K. Santacruz-Gomez Departamento de Fisica, Universidad de Sonora Rosales y Blvd. Luis Encinas s/n CP 8300 , Hermosillo , Sonora , Mexico Dr. D. Jaque IRYCIS, Instituto Ramon y Cajal de Investigacion Sanitaria. Hospital Ramon y Cajal, 28034 Madrid, Spain Dr. G. A. Hirata Centro de Nanociencias y Nanotecnologia Universidad Nacional Autonoma de Mexico Ensenada , Baja California C.P. 22860 , Mexico

Abstract: Nanoplasmonics is a rapidly growing field of research that opens up multiple opportunities toward practical applications. The understanding of the extreme confinement of light at the nanoscale has facilitated the development of a wide range of interesting materials for many different fields. Nanoparticles of noble metals, such as gold or silver, present unique optical properties that may end up making a large impact on our daily lives. Modern biomedical techniques can successfully treat cancer via plasmon-mediated photothermal therapy, in which metal nanoprobes act as intense heaters to kill cancer cells. Moreover, our society is also seeing an increasing interest in the development of alternative (green) energy sources, where plasmonic nanostructures are also considered to provide an advantage, e.g., improving the performance and feasibility of photovoltaic devices. In this progress report, relevant advances and applications of plasmonic nanoparticles, from energy to health, are discussed, and their potential implications in future society are highlighted.

Abstract: The gyroid is a continuous and triply periodic cubic morphology which possesses a constant mean curvature surface across a range of volumetric fill fractions. Found in a variety of natural and synthetic systems which form through self-assembly, from butterfly wing scales to block copolymers, the gyroid also exhibits an inherent chirality not observed in any other similar morphologies. These unique geometrical properties impart to gyroid structured materials a host of interesting optical properties. Depending on the length scale on which the constituent materials are organised, these properties arise from starkly different physical mechanisms (such as a complete photonic bandgap for photonic crystals and a greatly depressed plasma frequency for optical metamaterials). This article reviews the theoretical predictions and experimental observations of the optical properties of two fundamental classes of gyroid structured materials: photonic crystals (wavelength scale) and metamaterials (sub-wavelength scale).

Abstract: Gold nanobipyramids (NBPs) and nanorods (NRs) are two common types of elongated colloidal plasmonic metal nanocrystals, with their longitudinal plasmon wavelengths synthetically tunable over a wide spectral range. Au NBPs have sharper tips and narrower shape and size distributions than Au NRs. However, the number percentages of Au NBPs have been limited below ≈60%. Herein, a method for producing Au NBPs with number percentages approaching 100% and longitudinal plasmon resonance wavelengths synthetically tuned from ≈700 to ≈1200 nm is reported. This method relies on a stepwise combination of seed-mediated growth, Ag overgrowth, depletion force-induced self-separation, and final chemical etching of Ag. The obtained Au NBPs have the same shapes and sizes as the directly grown ones. Systematic comparisons of the plasmonic properties between the purified Au NBP and high-yield single-crystalline Au NR samples show unambiguously that Au NBPs are superior to Au NRs in terms of the plasmon peak width, refractive index sensitivity, figure of merit, two-photon photoluminescence, and surface-enhanced Raman scattering.

Abstract: As a fundamental optical device, a lens lies in the heart of many important applications in various scientifi c communities such as physics, optics, biology, medicine, and security. People have been fascinated by using different technologies to develop lenses with unusual features, such as ultrathin metalenses based on metasurface [ 27,28,39,40 ] and multifoci diffractive lenses [ 41,42 ] based on diffraction optics. A multifoci diffractive lens allows a single incident beam to focus at different positions along the longitudinal axis or along the transverse direction, which has been widely used in imaging systems, detectors, optical data storage, laser printing and optical freespace communications. [ 41–44 ] However, all the polarization states of the focal points are the same as that of the incident light. Moreover, the traditional method to design and fabricate such a lens is based on diffractive optics, thus the thickness is much larger than the wavelength of light. While there has been great progress in the miniaturization of optical lenses by using metasurfaces, much attention has been paid to constructing a lens with a single focal point by using different geometry structures such as V-shape, [ 22,23,45,46 ] nanorods, [ 27,32,36 ] and nanoslits. [ 47 ] Although the work on metasurface lenses is in its infancy, it offers in the long run major opportunities if multifunction nanostructured lenses can be experimentally realized in ultrathin and fl at confi gurations. Here, we apply the concept of controllable interfacial phase discontinuity to realize an ultrathin fl at metasurface lens with multiple focal points along the longitudinal direction. Unlike the traditional multifoci diffractive lenses, the position and the polarization of the focal points can be controlled by changing the helicity of the incident light. Furthermore, the developed devices are ultrathin (40 nm) and planar, which can facilitate the system integration. Figure 1 shows the schematic of the plasmonic metasurface lens. It consists of nanorods with spatially varying orientation in three different regions marked by I, II, and III, as shown in Figure 1 a. The radius of region I (R-I) is r 1 , and the inner radius and outer radius of region II (R-II) are r 1 and r 2 . r 2 and r 3 are the inner radius and outer radius of region III (R-III). The relationship among r 1 , r 2 , and r 3 is governed by

Abstract: 779 wileyonlinelibrary.com C O M M U N IC A IO N In this article, we introduce a metasurface-based broadband fl at-lens array functioning in the terahertz regime. Being functional devices consisted of a number of regularly arranged lenslets, lens arrays not only possess superior focusing and imaging functionalities but also have many intriguing characteristics beyond what a single lens would approach. Lens arrays have been widely used in photography, communications, and photomemory. For instance, ideal wavefront measurement method can be achieved by combining lens array with Hartmann-Shack sensor at visible light frequencies. [ 31 ] Besides, they are widely used in digital cameras to increase the fi lling factor of the detector array. In the terahertz regime, the lens array is one of the key components in terahertz cameras and terahertz communication systems. Generally, by employing a terahertz detector behind each lenslet, the lens array enables multipixel receiving. Moreover, lens arrays with tunable focal length have potential applications in 2D and 3D switchable displays and tunable photonic devices. However, conventional fabrication approaches including direct laser writing in photoresist [ 32 ] and silicon machining technique [ 33 ] are complex and very costly due to requiring interconnections, storage systems, and photovoltaic photography. There is a strong demand for a low-cost, broadband, and fl exible terahertz lens array for various applications of terahertz technology. Here, by adopting the C-shape split-ring resonators (CSRRs) with phase discontinuities, we proposed a metasurface-based terahertz fl at-lens array. We experimentally examined and explored the unique characteristics of the fl atlens array by using near-fi eld scanning terahertz microscopy (NSTM). We show that the proposed fl at-lens array is fl exible, robust, and broadband. Compared to the lens arrays developed with conventional approaches, the metasurface-based lens array is much thinner and lighter, more fl exible, and has broader numerical aperture (NA) variation range. The proposed metasurface-based fl at-lens array paves a novel way to planar terahertz device designs and may have important applications in terahertz imaging and communications. To realize the focusing functionality using metasurfaces, it is crucial to achieve a group of unit elements that enable abrupt phase shift covering a 2π range and a nearly constant transmission amplitude simultaneously. Ultrathin fl at lenses based on metasurfaces have already been demonstrated using 2D V-shaped or rotated bar antennas. [ 20–23 ] Here, the CSRR which reveals strong response to the terahertz radiation is designed as the basic unit structures, [ 34 ] as shown in Figure 1 a. The symmetry lines of the CSRRs are oriented ±45° with respect to the x -axis. Due to structure symmetry, when the incidence polarization is along the x -axis, it partially converts into the y -polarized component in the resonance frequencies range. This feature essentially lies on the superposition of different resonance A Broadband Metasurface-Based Terahertz Flat-Lens Array

Abstract: 1537 wileyonlinelibrary.com C O M M U N IC A IO N linewidth accompanied with an extremely small resonance intensity. Typically, in most of the Fano resonant plasmonic and metamaterial systems, the quality factor declines exponentially with the increase in the resonance intensity. Thus, it becomes very important to investigate the tradeoff between the quality factor and the intensity of Fano resonances. Terahertz is a perfect regime to study this tradeoff behavior due to the ease of fabrication and the precise control that could be exercised in designing metamaterial samples with extremely small variation in the geometry of the chosen meta-atoms. Terahertz split-ring resonators (SRRs) with dual split capacitive gaps that consist of two unequal metallic wires form an asymmetric resonator that have been demonstrated in the recent past to be excellent candidates in exciting the Fano resonance with ultrahigh quality factor ( Q factor). [ 2,5 ] Such a high Q factor design can overcome the radiative loss to a large extent due to the strong confi nement of photons in the resonators. [ 25 ] The Fano resonances have also been demonstrated to be potential candidates for designing ultrasensitive sensors. [ 4,26 ] Strong confi nement of energy in such systems occur due to the antiparallel oscillating currents in the metasurface array that minimizes the radiative losses if arranged in a large periodic lattice. Therefore, weak coupling of the current mode to the free space occurs at Fano resonance once the intrinsic symmetry of the unit cell is broken, which actually breaks the resonance equilibrium in the adjacent arms. Such a weak free space coupling enables long decay time and has been argued to be an excellent cavity to realize metasurfacebased fl at lasing spaser. [ 27 ] However, the ultrahigh Q factor is obtained at the expense of the Fano resonance intensity which makes it challenging to effi ciently harness this low-loss resonance feature at subwavelength scales. The high Q resonance at low intensities also presents the diffi culty in measuring the Fano resonance with low resolution and low signal-to-noise ratio systems. Therefore, it is extremely important to excite a rather high Q resonance that has strong intensity in the transmission spectra in order to exploit these resonances for several photonic applications. In this work, we address the problem of optimizing the Q factor and the resonance intensity of the Fano resonances by probing the Figure of Merit (FoM) that we defi ne here as the product of quality factor and the resonance intensity. In order to thoroughly study the factors that determine the behavior of Fano resonances, we investigated the infl uence of structural confi guration on Fano resonance with geometrically symmetric and asymmetric SRRs through detailed experiments and simulations. The asymmetry parameter in the Fano resonator is defi ned as 1 2 1 2 100% l l l l α = − + × , where l 1 and l 2 are the length of the two wires (see the Supporting Information) that form the resonator. The length difference between the adjacent wires, l 1 – l 2 Fano Resonances in Terahertz Metasurfaces: A Figure of Merit Optimization

Abstract: Achieving an efficient spectral tuning in liquid-crystal (LC)-loaded active photonic metamaterials has so far remained a challenge due to strong surface anchoring of LC molecules. This paper reports on a novel approach in the development of hybrid metamaterials that enables to overcome this problem and engage for the first time in-plane switching of liquid-crystal molecules on the nanoscale. Combined with the usual volume switching, it unlocks the full potential of the liquid crystals as a functional component of active metamaterial hybrids operating at optical frequencies. As a result, the resonant response of an active metasurface can now be controlled both in terms of its magnitude and wavelength with the spectral tunability approaching the theoretical limit of 9%. This mechanism of two-way active switching of the hybrid metamaterial is also confirmed theoretically by simulating the distribution of the LC director around the metamaterial fabric.

Abstract: The efficient generation of white light by phosphor-converted LEDs (pcLEDs) suffers from a trade-off between high color rendition, low correlated color temperatures, and luminous efficacy. While this is partially an inherent problem, it is also caused by the spectral efficiency of the materials used. The particular challenges for materials research lie, amongst the demanding general requirements, in finding very narrow-band or line-emitting materials: excitable with blue light, emitting in the near red. A way to design Mn(IV) activated line emitters is proposed, and methods for high-throughput combinatorial syntheses are specified.

Abstract: In order to increase the response speed of the InSe-based photodetector with high photoresponsivity, graphene is used as the transparent electrodes to modify the difference of the work function between the electrodes and the InSe. As expected, the response speed of InSe/graphene photodetectors is down to 120 μs, which is about 40 times faster than that of an InSe/metal device. It can also be tuned by the back-gate voltage from 310 μs down to 100 μs. With the high response speed, the photoresponsivity can reach as high as 60 A W−1 simultaneously. Meanwhile the InSe/graphene photodetectors possess a broad spectral range at 400–1000 nm. The design of 2D crystal/graphene electrical contacts can be important for high-performance optoelectronic devices.

Abstract: Among the inorganic phosphors used in advanced solid-state lighting technologies, nitridosilicates have drawn significant attention because of their superior photoluminescence properties with high efficiency and high thermal stabilities. However, the synthesis of nitride phosphors usually requires strict processing conditions and a long processing time, leading to very high manufacturing costs. Herein, a novel orthosilicate green phosphor, Ba9Lu2Si6O24:Ce3+, is synthesized via a simple solid-state reaction. The photoluminescence characterization identifies a main peak at 400 nm in the excitation spectrum, making it viable for near-UV LED excitation. This phosphor exhibits a broad emission band with a width of nearly 120 nm, peaking at 490 nm. By optimizing the Ce3+ concentration, an internal quantum efficiency (QE) as high as 82% can be achieved, which is equivalent to that of most nitride phosphors. Furthermore, nearly 94% of the room-temperature internal QE is still maintained at 160 degrees C, which is superior to that of most nitride phosphors. The excellent thermal stability and luminescent properties show this compound to be a promising candidate as a green phosphor for near-UV-based white LEDs.

Abstract: In this paper, we present a highly broadband (from visible to infrared) photodetector based on chemical vapor deposition (CVD) graphene–silicon heterostructure, together to be operated in photoconductor mode. This device shows very high responsivity (>10 4 A W −1 ) at wavelength of 632 nm, where light absorption relies on silicon. More importantly, even in the infrared region (1550 nm), where light absorption only depends on the graphene, the responsivity of our detector can be as high as 0.23 A W −1 , which is much higher those by pure monolayer graphene-based devices without optically assisted structure in this spectral region. [ 13,15,24 ] The signifi cant response is mainly due to the fact that the built-in fi eld in heterostructure can effectively prolong the ultrashort lifetime of photon-induced carriers. Besides, we also fi nd three dynamic processes in the transient response: photo-induced carriers sweeping into graphene by the built-in fi eld, electrons in the depletion region diffusion back to graphene, and photo-induced carriers in the bulk silicon diffusion to graphene. Due to the fi rst mechanism, the response time of our detector is less than 3 μs, which has not been reported among graphene photoconductor/ phototransistors. [ 1 ]

Abstract: Photodetectors play key roles in many applications such as remote sensing, night vision, reconnaissance, medical imaging, thermal imaging, and chemical detection. Several properties such as performance, reliability, ease of integration, cost, weight, and form factor are all important in determining the attributes of photodetectors for particular applications. While a number of materials have been used over the past several decades to address photo­detection needs across the electromagnetic spectrum, the advent of nanomaterials opens new possibilities for photodetectors. In particular, carbon-based nanomaterials such as carbon nanotubes (CNTs) and graphene possess unique properties that have recently been explored for photodetectors. Here, the status of the field is reviewed, presenting a broad coverage of the different types of photodetectors that have been realized with CNTs, placing particular emphasis on the types of mechanisms that govern their operation. A comparative summary is presented of the main performance metrics for such detectors, and an outlook for performance improvements.

Abstract: Metallic helical metamaterials give rise to broadband and scalable chiro-optical effects orders of magnitude higher than found in nature. While arrays of gold helices have been suggested as compact circular polarizers, where a large difference of the diagonal elements of the Jones transmission matrix is desired, chiral metamaterials can also be designed to exhibit strong circular-polarization conversions. Here, a novel helical metamaterial design, exhibiting asymmetric, broadband circular-polarization conversion, is introduced. The metamaterial is composed of unit cells with a single helix that changes its handedness halfway along the helix axis. Based on numerical calculations, an intuitive model explaining the principle of operation is given. Furthermore, a novel fabrication approach employing STED-inspired direct laser writing in combination with electrochemical deposition of gold is presented. The experimental data show circular-polarization conversion of up to 75% for an unmatched bandwidth of one octave, in very good agreement with theory.

Abstract: In this progress report the development of three-dimensional μ-printing and its impact as an enabling technology onto different scientific fields is reviewed. Driven by direct laser writing via two-photon absorption, the technology has reached a level of maturity and ease of application such that 3D printing on the micrometer scale can now be considered. While the underlying technology is still developing towards higher resolution and increasing speed of fabrication, the last five years have seen new fields rising that were obviously enabled by 3D μ-printing. Among the recent technological developments discussed in this progress report are the fields of super-resolution lithography and spatial light modulator-based lithography. Novel fields relying on these technological advances like aperiodic photonic structures, mechanical metamaterials, and structures for biological studies will be reviewed. A glimpse into developing research directions will also be provided.

Abstract: The rapid ascent of nanoscience has garnered significant attention in recent years. Much of the interest generated has dealt with the integration of nanoparticles in various applications ranging from automotive and textiles to bioimaging and nanomedicine. In order for the realization of this potential, their synthesis and chemistry need to be thoroughly understood. One particularly interesting class of nanoparticles comprises a lanthanide-doped inorganic matrix. Due to their physicochemical and optical properties, these lanthanide-doped nanoparticles are undergoing widespread investigation in many fields, particularly for in vitro and in vivo imaging, as well as theranostics. They offer significant advantages in biological applications, particularly the extension of the system applicability to deep tissue regions of the body, a reduced scattering of the excitation wavelength, reduction of autofluorescence, and decrease in thermal loading and photodamage to the system under study. Specifically, lanthanide-doped fluoride hosts are being propelled to the forefront of the current research efforts as they offer several advantages relative to other studied upconverting host materials. This review will take an in-depth look at lanthanide-doped upconverting fluoride nanoparticles with a particular emphasis on the synthesis, nucleation, and growth mechanisms and, finally, the potential to tailor particle properties.

Abstract: The persistent and near-infrared photostimulated optical properties of CaS nanoparticles and CaS:Eu2+ and CaS:Eu2+,Dy3+ nanophosphors are presented. Proposed mechanisms are elucidated for both phenomena by carrying out wavelength-resolved, thermally stimulated luminescence (TSL) and photostimulated luminescence (PSL) measurements. After UV (254 nm) irradiation, blue persistent and near-infrared photostimulated luminescence is obtained due to the presence of intrinsic defects in CaS nanoparticles. By introducing Eu2+ as a dopant, the formation of shallow traps below the conduction band is observed and red persistent and near-infrared PSL is obtained. Dy3+ is added as a codopant to create shallow and near-infrared photostimulated deeper traps, lengthening the strong red persistent luminescence to 5 h and PSL time to 18 min.

Abstract: better organic photodetector performance could be achieved if a low dark current density and a high EQE can be reached at the same time. In this paper, we present the fabrication and characterization of an all polymer photodetector sensing from 300 nm to 1000 nm with a calculated peak detectivity greater than 1.0 × 10 13 Jones in the NIR region, on the basis of the shot noise limit. The device also shows a respectable EQE of 27.7% at a wavelength of 850 nm under −0.5 V bias. Importantly, the dark current density is as extremely low as 0.64 nA cm −2 , which should be the best result among all wide spectrum response organic photodetectors reported so far. It can be seen that introducing a thin cross-linkable hole transporting/electron blocking layer greatly reduces the dark current density, while simultaneously preserving the photoresponse. A low-bandgap diketopyrrolopyrrole (DPP)-based polymer poly(diketopyrrolopyrrole-terthiophene) (PDPP3T), as shown in Figure 1 a, is utilized as the donor material, which has proven to be a promising candidate for organic fi eld-effect transistors (OFETs) and organic solar cells. [ 21–24 ] This polymer possesses a narrow-bandgap of 1.3 eV and nearly balanced hole and electron mobilities of 0.04 and 0.01 cm 2 V −1 s −1 . [ 21 ] As shown, it is able to cover the UV/visible/NIR spectral region and outputs a high photoresponse when incorporated with a (6,6)-phenylC71-butyric acid methyl ester (PC 71 BM) acceptor. Poly[ N , N ′-bis(4-butylphenyl)N , N ′-bis(phenyl)-benzidine] (poly-TPD) is an effi cient hole transport material with a hole mobility of about 2.0 × 10 −3 cm 2 V −1 s −1 and has been widely used in polymer/quantum dot light emitting diodes as hole transporting layer due to its resistance to nonpolar organic solvents, such as toluene and p-xylene. [ 25–27 ] As reported, polyTPD is also cross-linkable under 254 nm UV light exposure, [ 28 ]

Abstract: Realizing laterally continuous ultra-thin gold films on transparent substrates is a challenge of significant technological importance. In the present work, formation of ultra-thin gold films on fused silica is studied, demonstrating how suppression of island formation and reduction of plasmonic absorption can be achieved by treating substrates with (3-mercaptopropyl) trimethoxysilane prior to deposition. Void-free films with deposition thickness as low as 5.4 nm are realized and remain structurally stable at room temperature. Based on detailed structural analysis of the films by specular and diffuse X-ray reflectivity measurements, it is shown that optical transmission properties of continuous ultra-thin films can be accounted for using the bulk dielectric function of gold. However, it is important to take into account the non-abrupt transition zone between the metal and the surrounding dielectrics, which extends through several lattice constants for the laterally continuous ultra-thin films (film thickness below 10 nm). This results in a significant reduction of optical transmission, as compared to the case of abrupt interfaces. These findings imply that the atomic-scale interface structure plays an important role when continuous ultra-thin films are considered, e.g., as semi-transparent electrical contacts, since optical transmission deviates significantly from the theoretical predictions for ideal films.

Abstract: Tuning the luminescence of phosphors is extremely important in controlling and processing light for active components of light sources, optical sensing, display devices, and biomedicine So far, conventional chemical approaches have routinely been employed to modify the luminescence during the phosphor's synthesis It is interesting to broaden the modulation of luminescence by physical methods, such as electric field, magnetic field, mechanical stress, temperature, photons, ionizing radiation, and so on Since some physical methods may provide unusual routes to tune the luminescence in in-situ, real-time, dynamical and reversible manners, it should be beneficial for our understanding the fundamentals of luminescence and widespread applications in a variety of advanced optical materials and devices In this review, a unified picture and primary physical strategies used for tuning the luminescence are provided An attempt is made to review recent advances of tuning the luminescence in a wide range of phosphors, including metal-ion-doped compounds, semiconductors, 2D layered nanomaterials, and stimuli-responsive organic phosphors Lastly, some potential directions of challenging issues in this exciting field are suggested

Abstract: In order to develop organic light-emitting diodes with improved optical properties, a series of phosphorescent complexes exhibiting narrow-band emission spectra are prepared and color tuned to emit efficiently across the whole visible spectrum through a judicious molecular design. Devices employing a green narrow-band phosphorescent emitter are fabricated and demonstrate an internal quantum efficiency of close to unity and impressive device operational lifetimes, estimate at over 70 000 h at a practical luminance of 100 cd m-2. Additionally, a deep blue narrow-band emitter is incorporated into a device setting that demonstrates a peak external quantum efficiency of 17.6% and CIE coordinates of (0.14, 0.09).

Abstract: Black phosphorus (BP), a two-dimensional (2D) material, has a direct bandgap that can be tuned by changing the layers and applied strain, which fills the lacuna left by graphene topological insulators and transition-metal dichalcogenides. Theoretically, the direct and tunable bandgap should enable broadband applications for optoelectronics with high efficiencies in the spectral range from the visible to the mid-infrared. Here, a BP broadband optical modulator is experimentally constructed and passively modulated lasers at 639 nm (red), 1.06 μm (near-infrared), and 2.1 μm (mid-infrared) are realized by using a BP optical modulator as the saturable absorber in bulk lasers. The obtained results provide a promising alternative for rare broadband optical modulators and broaden the application range of BP in photonics.