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We report a controlled emission of Ce3+ ions inside single Yttrium Aluminum Garnet Y3Al5O12 (YAG:Ce3+) nanocrystals with a diameter of 22±10 nm as a result of a coupling of a surface plasmon mode propagating along single gold nanowire (NW). From the photoluminescence images, the intensity for single YAG:Ce3+ nanocrystals in the proximity of the single gold NW increases by a factor of two in comparison with that without the NW. Also, we observe a maximum of 3.8-fold emission rate enhancements for the single nanocrystal close to the single gold NW. The emission rate enhancements of YAG:Ce3+ nanocrystals are two folds the enhancements of 100-nm fluorescent nanospheres. This value is in agreement with the calculation of a combination from the analytical scattering model and boundary element method. We also confirm that the small size light sources are more efficient for the emission rate enhancements. Thus, the controlled emission of small YAG:Ce3+ nanocrystals with the perfect photostabilities will pave the way for the ultimate efficient nanoscale light sources. [ABSTRACT FROM AUTHOR]

Heterostructure is playing a crucial role in current optoelectronic applications. Realizing the heterostructure in a recently exciting semiconductor material: hybrid halide perovskite crystals, has been a long-sought goal in the field. Here, we demonstrate modulation-doped layer growth on large hybrid halide perovskite crystals. We show that the well known problem of halide ion inter-diffusion can be controlled by (1) using low halide composition gradient and (2) adjusting solution concentrations just above the critical supersaturation, in the solvothermal liquid-phase growth process. In comparison to a few seconds dipping time previously reported for the ion-exchange processes, our layer growth time could be conveniently extended up to 80 minutes to grow a uniform and controllable layer, with a very thin inter-diffusion region. The growth of the CH3NH3PbBr3 layer on top of the CH3NH3Pb(Br0.85Cl0.15)3 bulk substrate is studied for different growth times to obtain up to a 30 μm layer thickness. The ion diffusion profile and layer thickness are verified, respectively, by cross-sectional characterization using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS). Electron back-scattering diffraction (EBSD) suggests a similar crystallographic orientation for both substrate and grown layers. Our diffusion model illustrates the halide ion concentration at the interface, correlating with the EDS mapping results. Optical imaging and photoluminescence (PL) characterization confirm the quality and bandgap of the grown layers. Especially, the growth process is further extended for two consecutive layers to create a double heterostructure for the first time with a large perovskite crystal. Our low cost process could pave the way for many optoelectronic applications such as color tunable light emitting diodes or photodetectors developed with perovskite crystals. [ABSTRACT FROM AUTHOR]

Spontaneous emission of PbS quantum dots (QDs) in different photonic nanostructures has been studied. We use the temperature-dependent exciton photoluminescence and the classic dipole near interface models to understand the spontaneous emission control at various temperatures. Then, we demonstrate that the enhancement and the inhibition of PbS QDs due to the local density of states (LDOS) inside nanostructures are more efficient at temperature as low as 77 K than the inhibition at 300 K. Largest emission rate enhancement at 77 K of 1.67 ± 0.10 and inhibition factors at 100 K of 2.27 ± 0.15 are reported for the gold (Au) planar mirror and silicon (Si) two-dimensional photonic crystal bandgap, respectively. We attribute those enhancement and inhibition to the large quantum yields Q e at low temperatures, which is much larger than that at 300 K. These results are relevant for application and optimization of PbS QDs in nanophotonics at telecommunication wavelength. [ABSTRACT FROM AUTHOR]

Subwavelength semiconductor nanowires have recently attracted interest for photonic applications because they possess various unique optical properties and offer great potential for miniaturizing devices. However, realizing tight light confinement or efficient coupling with photonic circuits is not straightforward and remains a challenge. Here we show that a high-Q nanocavity can be created by placing a single III-V semiconductor nanowire with a diameter of under 100 nm in a grooved waveguide in a Si photonic crystal, by means of nanoprobe manipulation. We observe very fast spontaneous emission (91 ps) from nanowires accelerated by the strong Purcell enhancement in nanocavities, which proves that very strong light confinement can be achieved. Furthermore, this system enables us to move the nanocavity anywhere along the waveguide. This configuration provides a significant degree of flexibility in integrated photonics and permits the addition and displacement of various functionalities of III-V nanocavity devices in Si photonic circuits. [ABSTRACT FROM AUTHOR]

Surface/interface engineering of methylammonium lead bromide (MAPbBr3) single crystals (SCs) is crucial for carrier generation/recombination, separation, and transportation, thereby enabling superior optoelectronics. Herein, a surface‐engineered crystallization technique is presented in which a thin polycrystalline MAPbBr3 layer is in situ grown on the surface of bulk mm‐sized MAPbBr3 SCs. The growth direction and the atomic distribution of both the polycrystalline surface layer and the single crystalline core have been analyzed by damage‐free atomic‐resolution transmission electron microscopy (TEM). The polycrystalline nature of the crystals gives rise to bright green emission under UV light. Scanning probe microscopy results show that the current at the emissive MAPbBr3 film/MAPbBr3 SC surface is five times higher than that at a non‐emissive surface when illuminated. Lateral photodetectors based on MAPbBr3 film/MAPbBr3 SCs can achieve excellent detectivities (≈1013 Jones) and high photoresponsivities (≈20 A W−1). Furthermore, a semiconductor‐based fluorescence quick response (FQR) code is patterned on the same bright green‐emitting surface of the MAPbBr3 film/MAPbBr3 SC using a picosecond laser pulse, with a scalability of 3 × 3 mm2. An FQR code integrated with a photodetector may serve as a potential double security tag in bank cards, passports, door security, etc. [ABSTRACT FROM AUTHOR]

[Display omitted] Tricobalt tetroxide (Co 3 O 4) has been developed as a promising photocatalyst material for various applications. Several reports have been published on the self-modification of Co 3 O 4 to achieve optimal photocatalytic performance. The pristine Co 3 O 4 alone is inadequate for photocatalysis due to the rapid recombination process of photogenerated (PG) charge carriers. The modification of Co 3 O 4 can be extended through the introduction of doping elements, incorporation of supporting materials, surface functionalization, metal loading, and combination with other photocatalysts. The addition of doping elements and support materials may enhance the photocatalysis process, although these modifications have a slight effect on decreasing the recombination process of PG charge carriers. On the other hand, combining Co 3 O 4 with other semiconductors results in a different PG charge carrier mechanism, leading to a decrease in the recombination process and an increase in photocatalytic activity. Therefore, this work discusses recent modifications of Co 3 O 4 and their effects on its photocatalytic performance. Additionally, the modification effects, such as enhanced surface area, generation of oxygen vacancies, tuning the band gap, and formation of heterojunctions, are reviewed to demonstrate the feasibility of separating PG charge carriers. Finally, the formation and mechanism of these modification effects are also reviewed based on theoretical and experimental approaches to validate their formation and the transfer process of charge carriers. [ABSTRACT FROM AUTHOR]

We investigate the influence of multiple excitons on the photon emission properties of a quantum dot (QD)-cavity system via the master equation for the density matrix. We show that in the intermediate to strong coupling regimes, the multiple excitons lead to the suppressed QD emissions as well as the absence of anti-crossing near zero detuning, arising from the interaction between the multiple excitons and cavity. Furthermore, we analyze the role of the cavity-biexciton detuning in the photon emission properties of cavity and exciton through the second-order correlation function. The small cavity-biexciton detuning yields the significant Purcell effect and the high probability of single photon emissions. The proposed model offers the fundamental approach in developing efficient single-photon emitting devices. [ABSTRACT FROM AUTHOR]

Fast hybrid organic–inorganic two-dimensional (2D) perovskite scintillators with high light yield are measured for their scintillating properties. With a light yield of 17 300 ± 2140 photons/MeV, undoped PEA2PbBr4 crystals already exhibit 100 ± 4 ps coincidence time resolution (CTR) at 511 keV excitation. However, Li-doped PEA2PbBr4 crystals have improved the light yield to 21 400 ± 2140 photons/MeV and showed sub-100 ps CTR. Such CTR values and low-cost manufacturing processes make these 2D perovskite scintillators as promising competitors for commercial lanthanide scintillators in time-of-flight positron emission tomography and for fast timing detectors. [ABSTRACT FROM AUTHOR]

[Display omitted] • A non-noble-metal based novel SERS substrate-porous carbon film/WO 3-x nanosheets was developed; • Detection limit of 10-7 M with the Raman enhancement factor of 106 was achieved on the optical substrate. • A deep leaning method was used to accurately analyze the Raman spectra of flavonoids of quercetin, 3-hydroxyflavone and flavone. • Quercetin can be accurately detected by the fully convolutional network, and lowest detectable concentration of 10-5 M was achieved. The Surface-enhanced Raman scattering (SERS) is an attractive optical detecting method with high sensitivity and detectivity, however challenges on large-area signal uniformity and complex spectra analysis methods always retards its wide application. Herein, a highly sensitive and uniform SERS detection strategy supported by porous carbon film/WO 3-x nanosheets (PorC/WO 3-x) based noble-metal-free SERS substrate and deep learning algorithm are reported. Experimentally, the PorC/WO 3-x substrate was prepared by high-temperature annealing the PorC/WO 3 films under the argon atmosphere. The defect density of the WO 3 was controlled by tuning the reducing reaction time during the annealing process. The SERS performance was evaluated by using R6G as the Raman reporter, it showed that the SERS intensity obtained on the substrate with the optimal annealing time of 3 h was about 8 times as high as that obtained on the PorC/WO 3 substrate without annealing treatment. And detection limit of 10-7 M and Raman enhancement factor of 106 could be achieved. Moreover, the above optimal SERS substrate was utilized to detect flavonoids of quercetin, 3-hydroxyflavone and flavone, and a deep learning algorithms was incorporated to identify the quercetin. It revealed that quercetin can be accurately detected within the above flavonoids, and lowest detectable concentration of 10-5 M can be achieved. [ABSTRACT FROM AUTHOR]

Renewed interest has brought significant attention to tune coherently the electronic and optical properties of hybrid organic–inorganic perovskites (HOIPs) in recent years. Tailoring the intimate structure–property relationship is a primary target toward the advancement of light-harvesting technologies. These constructive progresses are expected to promote staggering endeavors within the solar cells community that needs to be revisited. Several considerations and strategies are introduced mainly to illustrate the importance of structural stability, interfacial alignment, and photo-generated carriers extraction across the perovskite heterostructures. Here, we review recent strides of such vast compelling diversity in order to shed some light on the interplay of the interfacial chemistry, photophysics, and light-emitting properties of HOIPs via molecular engineering or doping approach. In addition, we outline several fundamental knowledge processes across the role of charge transfer, charge carrier extraction, passivation agent, bandgap, and emission tunability at two-dimensional (2D) level of HOIPs/molecule heterointerfaces. An extensive range of the relevant work is illustrated to embrace new research directions for employing organic molecules as targeted active layer in perovskite-based devices. Ultimately, we address important insights related to the physical phenomena at the active molecules/perovskites interfaces that deserve careful considerations. This review specifically outlines a comprehensive overview of surface-based interactions that fundamentally challenges the delicate balance between organic materials and perovskites, which promotes bright future of desired practical applications. [ABSTRACT FROM AUTHOR]

Exosome is a recently emerging cancer-associated biomarker for early diagnostic and prognostic owing to their noninvasive, intrinsic stability, and representativeness of primitive cell state. However, the development of convenient and quantitative methods for exosome analysis remains technically challenging. Here, we proposed a cost-effective assay for the direct capture and rapid monitoring of exosomes utilizing the multifunctional surface enhanced Raman scattering (SERS) substrate, which consisted of Cu 2 O–CuO nanowires prepared by a simple thermo-oxidative growth method and subsequently sputtered with Ag NPs. This reticulate substrate made up of interlaced one-dimensional nanowires that highly favored for exosome recognition and collection. Particularly, the electromagnetic hotspots with high density were uniformly distributed on the nanowires due to uniform physical deposition, facilitating robust SERS property with an enhancement factor (EF) of 3.3 × 108 and signal reproducibility with a relative standard deviation (RSD) of 13%. In addition, the presence of Cu 2 O–CuO heterojunction enabled further elevation of the SERS performance attributed to the effective charge transfer, triggering a significant chemical enhancement effect. Finally, clinical validation with the serum specimens of prostate cancer patients indicated that the proposed immunosensor possessed great potential for application in rapid cancer screening and diagnosis. [ABSTRACT FROM AUTHOR]

In the past decades, perovskite-based materials have demonstrated excellent performances in a wide range of applications, including chemosensing. Owing to their unique structure-property relationship, chemosensing applications have become a point of interest that intrigued researchers from various backgrounds. Recently, several studies have reported the application of perovskite in chemosensing using various methods and analytes. However, the development for stable, sensitive, and selective chemosensors requires multiple approaches and considerations. In this review, the recent progress on perovskite-based chemosensor is summarized, with regards to different sensing mechanisms and target analytes subject to detection. Several aspects and fundamental factors affecting the chemosensor designs are also briefly discussed. In addition to the type of perovskites (including oxide, all inorganic halide, and hybrid organic-inorganic halide perovskites), perovskite design should also consider the structural dimensionality as an important factor that influenced the chemical and physical properties of the materials. We describe the upcoming challenges and limitations that could potentially be encountered in the development of perovskite chemosensors to provide some potential solutions and outlook. The future prospect of perovskite-based chemosensors is expected to rise due to continued interests and attention, which might pave the way for the advancement of innovative sensing technology. [Display omitted] • Chemosensor applications using perovskite materials is still at the early stage. • Designs for the future applications show many potential aspects. • Stability of perovskites remain the primary concern as sensors for analytes. • Dimensionality and nanostructures increase sensitivity and selectivity of sensors. • Enhancements for the sensing signals from low concentration analytes are needed. [ABSTRACT FROM AUTHOR]

Hexagonal boron nitride (hBN) has become a prominent material for nanophotonic and quantum technology studies. Its wide bandgap can accommodate room temperature radiative optical transitions originating from defect states in different atomic structures. Here, we report the engineering of visible defects in chemical vapor deposited monolayer hBN irradiated by femtosecond pulses (0.1–0.5 W) at room temperature. Photoluminescence and transient photoluminescence measurements reveal the presence of a sharp emission at 630 nm with a time constant of approximately 3 ns randomly distributed around the irradiated region. We imaged the distribution of the photogenerated electrons by time-resolved photoemission electron microscopy in the picosecond and nanosecond timescales with 100 nm spatial resolution. We determined the precise location of the defects within the region of interest corresponding to an optical transition between 1.95 eV and 3.90 eV above the valence band maximum of hBN, ascribed to NBVN color centers. [ABSTRACT FROM AUTHOR]

Hybrid organic–inorganic perovskite (HOIP) photovoltaics have emerged as a promising new technology for the next generation of photovoltaics since their first development 10 years ago, and show a high-power conversion efficiency (PCE) of about 29.3%. The power-conversion efficiency of these perovskite photovoltaics depends on the base materials used in their development, and methylammonium lead iodide is generally used as the main component. Perovskite materials have been further explored to increase their efficiency, as they are cheaper and easier to fabricate than silicon photovoltaics, which will lead to better commercialization. Even with these advantages, perovskite photovoltaics have a few drawbacks, such as their stability when in contact with heat and humidity, which pales in comparison to the 25-year stability of silicon, even with improvements are made when exploring new materials. To expand the benefits and address the drawbacks of perovskite photovoltaics, perovskite–silicon tandem photovoltaics have been suggested as a solution in the commercialization of perovskite photovoltaics. This tandem photovoltaic results in an increased PCE value by presenting a better total absorption wavelength for both perovskite and silicon photovoltaics. In this work, we summarized the advances in HOIP photovoltaics in the contact of new material developments, enhanced device fabrication, and innovative approaches to the commercialization of large-scale devices. [ABSTRACT FROM AUTHOR]

It is well understood that nonlinear optical (NLO) phenomena are deeply related to the material's symmetry. Mathematically, the material symmetry can be described in terms of the nonzero parameters in the nonlinear susceptibility tensors. Generally, more complex structures involve more nonzero parameters in the tensor. The number of parameters increases rapidly if higher NLO orders are considered, complicating the physical analysis. Conventionally, these parameters are obtained via abstract symmetry analysis, e.g., group theory (GT). This work presents a novel theoretical analysis to approach the nonlinear tensor using the simplified bond hyperpolarizability model (SBHM) and compare it with GT. Our analysis is based on a light–matter interaction classical phenomenological physical framework. Rather than just looking at the symmetry of the crystal, the model applies physical considerations requiring fewer independent parameters in the tensor than GT. Such a simplification significantly improves the determination of the surface–bulk SHG contribution factors, which cannot be extracted from the experiment alone. We also show for the case of perovskite that the SHG contribution can be addressed solely from their surface dipoles with only one independent component in the tensor. Therefore, this work may open the path for a similar analysis in other complicated semiconductor surfaces and structures in the future, with potential applications to nanoscale surface characterization and real-time surface deposition monitoring. [ABSTRACT FROM AUTHOR]

Strong interactions between surface plasmons in ultracompact nanocavities and excitons in 2D materials have attracted wide interests for its prospective realization of polariton devices at room temperature. Here, a continuous transition from weak coupling to strong coupling between excitons in molybdenum disulfide (MoS2) monolayer and highly localized plasmons in ultracompact nanoantenna is proposed. The nanoantenna is assembled by a silver nanocube positioned over a gold film and separated by a dielectric spacer layer. A 1570‐fold enhancement in the photoluminescence is observed at weak coupling regime in hybrid nanocavities with thick spacer layers. The interaction between excitons and plasmons is then directly prompted to strong coupling regime by shrinking down the thickness of spacer layer. Room temperature formation of polaritons with Rabi splitting up to 190 meV is observed with a fair polariton loss around 165 meV. Numerical calculations quantify the relation between coupling strength, local density of states, and spacer thickness, and reveal the transition between weak coupling and strong coupling in nanocavities. The findings in this work offer a guideline for feasible designs of plasmon–exciton interaction systems with gap plasmonic cavities. [ABSTRACT FROM AUTHOR]