Multiphoton upconversion and non-resonant optical nonlinearity in perovskite quantum dot doped glasses.

By incorporating the CsPbBr3 quantum dots (QDs) into a glass host, we report for the first time, to our knowledge, the measurement of non-resonant optical nonlinearity and multiphoton upconversion (UC) processes for this QD-in-glass composite. We observe up to four-photon stable UC photoluminescence under excitation by infrared femtosecond pulses, low optical limiting thresholds, and high nonlinear optical absorption coefficients close to those of colloid processed metal halide perovskite (MHP) QDs. Combined with high robustness against air and moisture, the monolithic inorganic glass with incorporated MHP QDs could be a better platform for exploiting strong light-matter interaction for MHPs.

An electrostatic energy-based charge model for molecular dynamics simulation.

The interactions of the polar chemical bonds such as C=O and N-H with an external electric field were investigated, and a linear relationship between the QM/MM interaction energies and the electric field along the chemical bond is established in the range of weak to intermediate electrical fields. The linear relationship indicates that the electrostatic interactions of a polar group with its surroundings can be described by a simple model of a dipole with constant moment under the action of an electric field. This relationship is employed to develop a general approach to generating an electrostatic energy-based charge (EEC) model for molecules containing single or multiple polar chemical bonds. Benchmark test studies of this model were carried out for (CH3)2-CO and N-methyl acetamide in explicit water, and the result shows that the EEC model gives more accurate electrostatic energies than those given by the widely used charge model based on fitting to the electrostatic potential (ESP) in direct comparison to the energies computed by the QM/MM method. The MD simulations of the electric field at the active site of ketosteroid isomerase based on EEC demonstrated that EEC gave a better representation of the electrostatic interaction in the hydrogen-bonding environment than the Amber14SB force field by comparison with experiment. The current study suggests that EEC should be better suited for molecular dynamics study of molecular systems with polar chemical bonds such as biomolecules than the widely used ESP or RESP (restrained ESP) charge models.

Enhanced luminescence of CsPbBr3 perovskite quantum-dot-doped borosilicate glasses with Ag nanoparticles.

Ag nanoparticles (NPs) and CsPbBr3 perovskite quantum dots (QDs) are precipitated in a borosilicate glass by the conventional melt-quenching method, which has outstanding stability benefited from the amorphous oxide matrix. X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electronic microscopy results show that part of Ag+ ions replace Pb2+ ions in the CsPbBr3 QDs, and the other Ag+ ions convert into Ag NPs. The presence of these Ag-species results in enhanced photoluminescence total intensity by 5 times for the CsPbBr3 QD-doped glasses, explained by the accelerated growth of QDs and the Ag NPs-induced plasmonic near-field effect.

Photoluminescence enhancement in wide spectral range excitation in CsPbBr3 nanocrystal/Ag nanostructure via surface plasmon coupling.

This work demonstrates the surface plasmon (SP)-exciton coupling effect on the photoluminescence (PL) enhancement in CsPbBr3 nanocrystal (NC) at PMMA/Ag nanostructure (NS) in wide spectral range excitation. The spectra dependent time resolved PL measurement reveals that the emission photons are from the recombination of localized excitons and the PL enhancement can be attributed to the near-field effect, which is also supported by evidence that the enhancements are nearly the same in the whole excitation wavelength from 200 nm to 900 nm. The non-spectral dependence of the enhancement factor suggests that there is the same dynamic process of hot electrons in CsPbBr3 NC in multiphoton excitation. The hot electrons will relax into localized exciton states, and the electric field generated by SPs will enhance the radiative recombination of excitons. This work will have benefits for revealing dynamics of hot electron relaxing and interactions in multi-photon absorption, as well as the inner mechanism of SP coupling effects.

Enhanced photoluminescence properties of bismuth sulfide nanocrystals with core-shell Ag@SiO2.

A novel self-assembled hybrid nanocompound consisting of bismuth sulfide nanocrystals (Bi2S3 NCs) and Ag@SiO2 nanoparticles (NPs) is used to study the enhancement of photoluminescence by localized surface plasmon resonance (LSPR). Ag@SiO2 core-shell NPs were prepared by deposition of silica onto the surface of Ag NPs through the sol-gel method and followed by surface modification via 3-aminopropyltriethoxysilane for the coming conjugation with Bi2S3 NCs. We propose the photoluminescence enhancement by the LSPR effect through adjusting the thickness of silica shell and the Ag@SiO2 NP concentration. By modulating the thickness of the silica shell and the concentration of Ag NPs, the maximum enhancement of a 5.7 fold can be reached with the thickness of an SiO2 shell at 22.5 nm. A clear red shift of the emission peaks in the Bi2S3 NCs-Ag@SiO2 NPs hybrid structures is observed. Such a metal-enhanced Bi2S3 quantum dot (QD) fluorescence system may have promising applications in optoelectronic device.

PbSe Quantum Dot Doped Mode-Locked Fiber Laser.

Herein, a PbSe quantum dot-doped-mode-locked fiber laser is experimentally demonstrated. A PbSe quantum dot-doped fiber is prepared using a melting method and induced as a gain medium in our mode-locked fiber laser. By increasing the pump power, a stable pulse train is obtained with a pulse duration of 36 ps, a pulse repetition rate of 4.5 MHz, an average laser power of 9.8 mW, and a central wavelength of 1214.5 nm. The pulse duration can be changed by adjusting the PC or increasing the pump power. The maximum laser power obtained was 42.7 mW under the pump power of 800 mW. Our results prove that a quantum dot-doped-mode-locked fiber laser is achievable, which provides a new scheme to solve wavelength problem of rare-earth-doped mode-locked fiber lasers.

Boosting Continuous-Wave Laser-Driven Nonlinear Photothermal White Light Generation by Nanoscale Porosity.

The irradiation of an optically absorptive medium by a continuous-wave (CW) near-infrared (NIR) laser can result in a spectral continuum emission covering both the visible and NIR regions, which is attractive for applications as continuum light sources in diverse fields. It is shown here that this NIR-laser-driven light emission can be effectively modulated with nanoscale architecture in the medium. By using porous silica as the model matrix and Yb3+ ions as the photothermally active centers, up to 100 folds increment in NIR-laser-induced emission intensity and dramatic decrease in threshold excitation density are demonstrated. It is observed that the emission intensity exhibits a strong nonlinear dependence on the power of the NIR excitation laser, featuring clear excitation power thresholds. Based on combined numerical simulation and spectral and temperature measurements, the improved broadband emission and photothermal nonlinearity are interpreted by enhanced optical energy localization around the laser spot that results in boosting the photon-to-photon conversion efficiency. The use of the nonlinear photothermal emission process as a broadband NIR light source, which could be exploited for applications including NIR spectroscopy, imaging, and sensing, is further demonstrated as a proof-of-concept.