Shuai Ye

Enhanced photoluminescence of CsPbBr3@Ag hybrid perovskite quantum dots

CsPbBr3@Ag hybrid nanocrystals are synthesized for the first time by reacting CsPbBr3 nanocrystals with AgX (X = Cl, Br, or I) powders in hexane. The morphologies of the hybrid nanocrystals showed that 2–5 nm Ag nanoparticles were nucleated randomly outside the CsPbBr3 nanocrystals, which indicated that Ag+ ions released by AgX powders could be reduced to Ag0 by surfactant ligands of CsPbBr3 nanocrystals and aggregated to Ag nanoparticles. Significant enhancement of the photoluminescence intensity of CsPbBr3@Ag hybrid nanocrystals was observed compared with that of pure CsPbBr3 nanocrystals under the excitation of 400 nm light, which was mainly attributed to the enhanced absorbance of ultraviolet or blue light by the Ag induced plasmonic near-field effect. Numerical simulations showed that CsPbBr3@Ag hybrid nanocrystals provided intense local field amplification at the perimeter of Ag nanoparticles. However, Ag adhesion can also cause the deteriorating surface quality of CsPbBr3 nanocrystals, and in turn reduce photoluminescence quantum yield. Therefore, Ag adhesion has two completely different influences on the photoluminescence of hybrid perovskite quantum dots. To achieve an enhanced photoluminescence, we have to optimize CsPbClxBr3−x@Ag hybrid nanocrystals so that the effect of plasmonic resonance enhancement occupied a significantly advantageous position. The surface trap states served as a nonradiative relaxation pathway for the photogenerated charge carriers and decreased the emission quantum yield of the hybrid nanocrystals. This suggests that a potential issue concerning the performance of CsPbBr3@Ag hybrid nanocrystals was a trade-off between enhanced light absorbance of CsPbBr3@Ag hybrid nanocrystals and reduced photoluminescence due to energy transfer from CsPbBr3 nanocrystals to Ag nanoparticles. This simple method to construct CsPbBr3@Ag hybrid nanocrystals offers new opportunities to enhance optical properties and expand the application of perovskite quantum dots for light emitting diodes and other optoelectronic devices.

Characteristic Analysis of Low-Threshold Plasmonic Lasers Using Ag Nanoparticles With Various Shapes Using Photochemical Synthesis

The characteristics of plasmonic lasers using Ag nanoparticles (AgNPs) with various shapes as cores and gain material doped dielectric medium as shell are analyzed using the finite-element method. We can synthesize spherical, decahedral, flaky hexagonal, and flaky triangular AgNPs in a photochemical process, which induce local surface plasmon resonances at different wavelengths. We analyzed the absorption and scattering characteristics of these AgNPs coated with gain material doped dielectric medium with a given gain coefficient as plasmonic lasers. Numerical results show that compared to conventional spherical AgNPs, AgNPs with sharp corners provide a much lower threshold for plasmonic laser applications. Flaky triangular AgNP is the optimum choice as a resonant core for plasmonic lasers, with the lowest threshold (0.0116) and a relatively narrow linewidth (~0.111 nm). Then, we analyzed the influence of structural parameters on lasing performance using a flaky triangular AgNP as the core of the core-shell plasmonic laser. Changing the size of the core, the thickness of the shell, the refractive index of the dielectric medium, or the radius of the rounded corner for AgNPs regulate the resonant wavelength. Using smaller flaky triangular AgNP as the core and gain material doped silica, refractive index 1.5, as the shell reduced the threshold of the plasmonic laser. In addition, a thermal analysis was also carried out to study the effect of enhanced local fields on the performance of the plasmonic lasers.

Ultrahigh Enhancement Factor by Using a Silver Nanoshell With a Gain Core Above a Silver Substrate for Surface-Enhanced Raman Scattering at the Single-Molecule Level

Single-molecule surface-enhanced Raman scattering (SERS) has been extensively studied over the past decade. In this paper, we propose a novel method to obtain ultrahigh enhancement of local electric fields by using a silver nanoshell with a gain core above a silver substrate. Numerical results show that an ultrahigh enhancement factor of the local electric field on the order of 105-106 and a SERS enhancement factor on the order of 1020-1025 can be obtained with the present system. The SERS enhancement factor is five orders of magnitude greater than the highest theoretical value reported for SERS applications at the single-molecule level. In addition, we use the finite-element method to analyze in detail the influences of the gain coefficient of the gain core and the other structure parameters on the enhancement factor.

Characteristic analysis of broadband plasmonic emitting devices based on transformation optics

The crescent nanostructure with gain medium inside is theoretically studied to analyze the characteristic of plasmonic emitting with wide bandwidth. An accurate analytical model is built based on the transformation optics. In this model, the poles of the electrostatic potential function are in the second and the fourth quadrant of the complex plane if the imaginary part of the relative permittivity of the gain medium is larger than the loss compensation threshold, and then the extinction cross section is to be negative by integrating the electrostatic potential over the half complex plane via an inverse Fourier transform. The positive extinction cross section corresponds to absorption, and the negative corresponds to emission. The proposed analytical model agrees well with the numerical simulation results based on the finite element method, to give a physical insight into the loss compensation property of the plasmonic nanostuctures. Results show that the negative extinction cross section is realizable by introducing the gain medium into a plasmonic crescent nanowire, which is equivalent to an emitting device with wide bandwidth.

Controllable emission bands and morphologies of high-quality CsPbX 3 perovskite nanocrystals prepared in octane

Halide perovskite (CsPbX3, X = Cl, Br, or I) quantum dots have received increasing attention as novel colloidal nanocrystals (NCs). Accurate control of emission bands and NC morphologies are vital prerequisites for most CsPbX3 NC practical applications. Therefore, a facile method of synthesizing CsPbX3 (X = Cl, Br, or I) NCs in the nonpolar solvent octane was developed. The process was conducted in air at ∼ 90 °C to synthesize high-quality CsPbX3 NCs showing 12–44 nm wide emission and high photoluminescence quantum yield, exceeding 90%. An in situ anion-exchange method was developed to tune CsPbX3 NC photoluminescence emission, using PbX2 dissolved in octane as the halide source. NC morphology was controlled by dissolving specific metal–organic salts in the precursor solution prior to nucleation, and nanocubes, nanodots, nanosheets, nanoplatelets, nanorods, and nanowires were obtained following the same general method providing a facile, versatile route to controlling CsPbX3 NC emission bands and morphologies, which will broaden the range of CsPbX3 NC practical applications.

Analysis of halide composition in CsPb(Br/Cl)3 nanocrystals with trace amounts of samples using laser induced breakdown spectroscopy

It is essential to determine the elemental composition of doped functional materials, particularly for nanometer scale semiconductors, to guide synthesis and interpret physical phenomena. This study applied laser induced breakdown spectroscopy (LIBS) for elemental analysis of halides in perovskite type quantum dots, i.e., CsPbX3 nanocrystals (NCs). The optimum LIBS delay time and laser energy were experimentally determined, and small quantities of CsPbX3 NCs (μg) with different Cl/Br ratios and different photoluminescence (PL) properties were measured. Coefficients to correlate weight and LIBS emission intensity ratios for Cl and Br were experimentally determined from CuBr2/CaCl2 mixtures. The measured Cl/Br weight ratios correspond to NC PL emission wavelengths and the supplied amount of PbCl2 precursor. The proposed LIBS approach showed better sensitivity and stability than electron dispersive spectroscopy. Ideal detection accuracy and precision could be realized using LIBS, requiring only trace amounts of NC samples and simple pretreatment processes, with NC integrity retained until the test.

Low-Saturation-Intensity, High-Photostability, and High-Resolution STED Nanoscopy Assisted by CsPbBr3 Quantum Dots

Stimulated emission depletion (STED) nanoscopy is one of the most promising super-resolution imaging techniques for microstructure imaging. Commercial CdSe@ZnS quantum dots are used as STED probes and ≈50 nm lateral resolution is obtained. Compared with other quantum dots, perovskite CsPbBr3 nanoparticles (NPs) possess higher photoluminescence quantum yield and larger absorption cross-section, making them a more effective probe for STED nanoscopy. In this study, CsPbBr3 NPs are used as probes for STED nanoscopy imaging. The fluorescence intensity of the CsPbBr3 sample is hardly weakened at all after 200 min irradiation with a 39.8 mW depletion laser, indicating excellent photobleaching resistance of the CsPbBr3 NPs. The saturation intensity of the CsPbBr3 NPs is extremely low and estimated to be only 0.4 mW (0.126 MW cm-2 ). Finally, an ultrahigh lateral resolution of 20.6 nm is obtained for a single nanoparticle under 27.5 mW STED laser irradiation in CsPbBr3 -based STED nanoscopy imaging, which is a tenfold improvement compared with confocal microscopy. Because of its high fluorescence stability and ultrahigh resolution under lower depletion power, CsPbBr3 -assisted STED nanoscopy has great potential to investigate microstructures that require super-resolution and long-term imaging.

Semimetal-Semiconductor Transitions for Monolayer Antimonene Nanosheets and Their Application in Perovskite Solar Cells

Antimonene-based 2D materials are attracting increasing research interest due to their superior physicochemical properties and promising applications in next-generation electronics and optoelectronics devices. However, the semiconductor properties of antimonene are still at the theoretical simulation stage and are not experimentally verified, significantly restricting its applications in specific areas. In this study, the semiconductor properties of monolayer antimonene nanosheets are experimentally verified. It is found that the obtained semiconductive antimonene nanosheets (SANs) exhibit indirect bandgap properties, with photoluminescence (PL) bandgap at about 2.33 eV and PL lifetime of 4.3 ns. Moreover, the obtained SANs are ideal for the hole extraction layer in planar inverted perovskite solar cells (PVSCs) and significantly enhance the device performance due to fast hole extraction and efficient hole transfer at the perovskite/hole transport layer interface. Overall, these findings look promising for the future prospects of antimonene in electronics and optoelectronics.

Core-shell structured NaMnF3: Yb, Er nanoparticles for bioimaging applications

NaMnF3: Yb,Er upconversion nanoparticles (UCNPs) have received considerable attention due to their single-band emission. In this paper, a modified thermal decomposition method to synthesize single or core/shell structured lanthanide-doped NaMnF3 nanoparticles is proposed. The NaMnF3: 20% Yb3+, 2% Er3+ nanoparticles displayed pure red emission under 980 nm laser excitation, and the emission intensity could be significantly enhanced by coating a NaMnF3 or NaMnF3: 20% Yb3+ shell layer on their surfaces. Moreover, NaMnF3: 20% Yb3+, 2% Er3+ nanoparticles shelled with NaMnF3: 20% Nd3+ or NaMnF3: 20% Yb3+, 20% Nd3+ were synthesized for the first time, and displayed pure red emission when excited by an 808 nm laser. The core/shell structured NaMnF3: Yb/Er@NaMnF3: Yb or NaMnF3: Yb/Er@NaMnF3: Yb/Nd nanoparticles were applied to bioimaging. The NaMnF3 based UCNPs exhibited good photostability and biocompatibility in HeLa cells. The obtained images indicated that the UCNPs could mainly exist in the cytoplasmic regions in the cells. Besides, images from the same region exposed to laser irradiations at 808 nm and 980 nm were found to be comparable. This result indicated that, for NaMnF3: 20% Yb3+, 2% Er3+@NaMnF3: 20% Yb3+, 20% Nd3+ nanoparticles, laser excitation at 808 nm was as efficient as that at 980 nm for bioimaging.

A facile method to prepare NaMn3F10:Yb,Er//m upconversion nanoparticles with single band (Conference Presentation)

Here, we reported a novel and facile thermal decomposited method to prepare NaMnF3 :Yb,Er/Tm upconversion nanoparticles (UCNPs). In this method, Rare earth acetate and manganese(II) 2,4-pentanedionato were used as raw material. The as-synthesized NaMnF3 :Yb,Er/Tm nanoparticles were monodispersed, uniform and their sizes were both smaller than 10 nm. The NaMnF3 :Yb,Er and NaMnF3 :Yb,Tm nanoparticles radiated intense pure red emission and near-infared emission under the excitation of 980 nm laser. Then, the core/shell structured NaMnF3 :Yb,Er/Tm@NaMnF3 nanoparticles were prepared to enhance the UC emission effectively.