Study of Laser-Induced Multi-Exciton Generation and Dynamics by Multi-Photon Absorption in CdSe Quantum Dots.

Multi-exciton generation by multi-photon absorption under low-energy photons can be thought a reasonable method to reduce the risk of optical damage, especially in photoelectric quantum dot (QD) devices. The lifetime of the multi-exciton state plays a key role in the utilization of photon-induced carriers, which depends on the dynamics of the exciton generation process in materials. In this paper, the exciton generation dynamics of the photon absorption under low-frequency light in CdSe QDs are successfully detected and studied by the temporal resolution transient absorption (TA) spectroscopy method. Since the cooling time of hot excitons extends while the rate of auger recombination is accelerated when incident energy is increased, the filling time of defect states is irregular, and exciton generation experiences a transition from single-photon absorption to multi-photon absorption. This result shows how to change the excitation. Optical parameters can prolong the lifetime of excitons, thus fully extracting excitons and improving the photoelectric conversion efficiency of QD optoelectronic devices, which provides theoretical and experimental support for the development of QD optoelectronic devices.

Surface Vertical Multi-Emission Laser with Distributed Bragg Reflector Feedback from CsPbI3 Quantum Dots.

Quantum dots (QDs) laser has become an important way to solve micro-application problems in many fields. However, single wavelength distributed Bragg reflector (DBR) has many limitations in practical applications, such as signal transmission. How to realize multiwavelength DBR lasing output simply is a challenge. To achieve a stable multi-wavelength quantum dots laser in the near-infrared region, the perovskite CsPbI3 QDs laser with DBR structure is developed in this paper. A tetragonal crystal structure with complete bonding information and no defect is explained by X-ray diffractions (XRD) and Raman spectrum. The cross-section morphology of the DBR laser and the surface morphology of QDs is measured by scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. An elliptical light propagation field and a double wavelength laser radiation are obtained from the finite-difference time-domain (FDTD) simulation. The output of the three wavelength lasers at 770 nm, 823 nm, and 873 nm is measured. The emission time of a DBR laser is about 2 h, and the average fluorescence quantum yield is 60%. The cavity length selection and energy level model are put in place to clearly see the working mechanism. All the results suggest that an effective and stable CsPbI3 quantum dots DBR laser is realized.

CdTe quantum dot-based self-supporting films with enhanced stability for flexible light-emitting devices.

The enhancement of photoluminescence (PL) stability of colloidal quantum dots (CQDs) is of great significance in light-emitting devices. In this work, the PL stability of CdTe CQDs under time storage, strong light irradiation, acid and alkali corrosion and low temperature freezing is analyzed, and the PL quenching mechanism in a harsh environment is analyzed. Furthermore, the PL stability is extremely improved by core-shell coating, film deposition and polymer encapsulation. This solves the problem of rapid dropping of the PL intensity at the initial illumination stage and improves the corrosion resistance in an acidic environment and long-term storage stability of film devices. CQD polymer films have an interesting phenomenon of fluorescence enhancement under illumination due to the light-soaking effect. Biocompatible coating and encapsulation materials expand the application of CQD devices in the field of biological tissue imaging and sensing. Through the PL regulation of CQD solutions and the simple superposition of self-supporting films, a panchromatic light-emitting device with broadband adjustable chromaticity is realized. The solid-state stable whispering-gallery-mode (WGM) laser is realized by monodisperse SiO2 microspheres embedded in the film. This work is of great significance for the application of CQDs in flexible light-emitting devices.

Ultrasimple and Ultrafast Method of Optical Modulation by Perovskite Quantum Dot Attachment to a Graphene Surface.

Optical modulation is the process of modifying the structure and elemental composition of materials so that the main optical parameters, including amplitude, frequency, and phase, are changed. Currently, much research attention has been directed toward ultrafast dynamics, but the process of modulation is often complex. To simplify the optical modulation process and improve the optical properties of perovskites for semiconductor quantum dot (QD) lasers, the process and physical mechanism underlying graphene QD ultrafast modulation of the optical properties of perovskite CsPbBr3 QDs were investigated. The typical cubic structure and square shape of CsPbBr3 QDs were characterized by transmission electron microscopy and X-ray diffraction, respectively. A luminescent peak centered near 540 nm and Stokes shift of 21.34 nm of CsPbBr3 QDs without graphene QDs were measured by absorption and photoluminescence spectroscopy. A maximum modulation shift of 133 nm and a modulation depth of 900% were achieved in CsPbBr3 with graphene. The results indicated that graphene QDs had the best modulation effect on perovskites when the drop volume was 0.05 mL. The process of ultrafast optical modulation via graphene QDs occurring within 1 ps was confirmed by the transient absorption spectrum. The modulation mechanism of graphene to perovskites is presented for guidance. This paper can be used as a reference for the optical modulation of perovskite materials.

Polarization Maintaining Fiber Temperature and Stress Gradient Sensitization Sensor Based on Semiconductor-Metal-Polymer Three-Layer Film Coating.

Increasing sensitivity, measuring points, and stability have always been the pursuit of sensors. ZnSe9:CO1 and Ag composite nano films were coated on polarization maintaining fiber (PMF). Then, the coated PMF was nested in capillary and hose which was encapsulated with polydimethylsiloxane (PDMS) and epoxy resin. The integrated capillary sensor and thermoplastic hose sensor were prepared. The gradient sensitization of various measurement parameters such as temperature, stress, and micro bending is realized. The temperature sensitivity is 1.49 nm/°C, the micro bending sensitivity is 1.72 nm/102 g, and the stress sensitivity is 6.27 nm/mε. The sensors maintain good linearity and instantaneous response while having high sensitivity. By adjusting the length of PMF, the number of troughs is increased in the same band range, and different troughs have different sensitivities, which solves the inherent problem of cross sensitivity and realizes multiparameter measurement. Capillary sensors are used for remote safe real-time monitoring of mechanical overheating, and hose sensors are used for real-time monitoring of bridge load and human joint bending. This work is of great significance to the extension of the application range of optical fiber sensor.

Cancer photothermal therapy based on near infrared fluorescent CdSeTe/ZnS quantum dots.

Micro targeted therapy for cancer has become a hot topic in recent years because of its advantages of little damage to the human body and early treatment of cancer. Therefore, accurate, rapid treatment methods and biofriendly exogenous substances are extremely important. CdTeSe/ZnS core-shell quantum dots (QDs) have great potential in biomedical imaging and biological ablation therapy due to their advantages of near-infrared radiation, aqueous synthesis and bio-friendliness. In this paper, CdTeSe/ZnS core-shell QDs were prepared by aqueous synthesis, and have near infrared output and excellent photothermal properties. A blue laser was used as the irradiation source and QD fluorescence imaging can accurately calibrate the treatment area. Under the photothermal and photodynamic effects of QDs, apoptosis of hepatoma cells Huh7 was induced, which provides a new micro-nano technology and biofriendly exogenous substances for cancer treatment.

Micro-Structure Changes Caused by Thermal Evolution in Chalcogenide GexAsySe1-x-y Thin Films by In Situ Measurements.

To understand the effects of thermal annealing on the structure of GexAsySe1-x-y thin films, the thermal evolution of these films was measured by the in situ X-ray diffraction (XRD) at different temperature (773 K or 1073 K) in a vacuum (10-1 Pa) environment. The entire process of crystallization can be observed by using in situ XRD, which is from the appearance of a crystal structure to melting liquid-state and ultimately to the disappearance of the amorphous structure. In the crystallized process, the corresponding state-transition temperatures Tx (the onset crystallization temperature), Tl (the transition temperature from glassy-state to liquid-state), Tp (peak crystallization temperature) are linear with MCN (Mean Coordination Number). In order to obtain information about changes in the amorphous structural origin of the anneal-induced material, the samples were analyzed by in situ Raman spectroscopy. Analysis of the results through decomposing the Raman spectra into different structural units showed that the Ge-Ge, As-As, or Se-Se homopolar bonds as the nonequilibrium minority carriers could be found in films. It suggests that the formation of these bonds cannot be completely suppressed in any case, as one falls and another rises.

Nanolasers Incorporating CoxGa0.6-xZnSe0.4 Nanoparticle Arrays with Wavelength Tunability at Room Temperature.

Semiconductor nanolaser has important research value and wide applications in many fields. However, it is still a challenge to obtain a nanolaser with tunability and high intensity at the nanoscale. Here, we report on lasers with two modes of emission wavelengths operating in near-infrared of nanohole filled with CoxGa0.6-xZnSe0.4 nanoparticle arrays at room temperature. The nanohole arrays are drawn on the photoresist by using the method of three-beam laser interferometric etching. Graphene with graphite which is coated on nanohole arrays is conducted by pulsed laser deposition (PLD) to construct the cavity. The CoxGa0.6-xZnSe0.4 nanoparticles are filled into the nanohole acting laser gain medium via the magnetic traction nanofilling technology. The results show that the laser at 868 and 903 nm is radiated, which can be tuned by changing the concentration and position of the filled nanoparticles in terms of wavelength and intensity. The nanolasers based on this approach represent an advantageous alternative to other design and fabrication methods. This nanoparticle nanolasers can be used in a micronano light source of an intelligent photonic chip.

Sensitivity enhancement through overlapping simultaneously excited Fano resonance modes of metallic-photonic-crystal sensors.

We investigated enhancement of sensitivity of sensors based on metallic photonic crystals through tuning the thickness of the waveguide layer by pulsed laser deposition. Thicker waveguides made of InGaZnO allow double resonance of Fano coupling modes due to plasmonic-photonic interactions. Tuning the angle of incidence enables overlap between these doubly resonant modes, which induces much enlarged and spectrally narrowed sensor signals, leading to significantly enhanced sensitivity of the sensor device. The thickness of the waveguide layer is found to be a crucial structural parameter to improve sensitivity of the MPC sensors.

Soft plasmons with stretchable spectroscopic response based on thermally patterned gold nanoparticles.

Flexible photonic crystals are attractive devices owing to their multifold tunable parameters additionally introduced by soft substrates or by nanostructured, nano-doped, or nano-embedded soft matters. This not only extends significantly the intrinsic functions of photonic crystals, but also facilitates easy integration of the photonic crystal device into various optoelectronic and sensing systems. So far, flexible metallic photonic structures have been constructed on micrometer scales with complex fabrication procedures. Much simpler and more reproducible methods are expected to achieve such metamaterials in large scales and at low costs. In address to these challenges, we developed a straightforward approach to create soft plasmonic photonic crystals consisting of gold nanolines arranged on stretchable substrates with nanoscale periods, centimeter-scale areas, and high reproducibility using annealed gold nanoparticle colloids.

Random laser based on waveguided plasmonic gain channels.

A waveguide-plasmonic scheme is constructed by coating the matrix of randomly distributed gold nanoisland structures with a layer of dye-doped polymer, which provides strong feedback or gain channels for the emission from the dye molecules and enables successful running of a random laser. Excellent overlap of the plasmonic resonance of the gold nanoislands with the photoluminescence spectrum of the dye molecules and the strong confinement mechanism provided by the active waveguide layer are the key essentials for the narrow-band and low-threshold operation of this random laser. This kind of feedback configuration potentially enables directional output from such random lasers. The flexible solution-processable fabrication of the plasmonic gold nanostructures not only enables easy realization of such a random laser but also provides mechanisms for the tuning and multicolor operation of the laser emission.

InGaZnO semiconductor thin film fabricated using pulsed laser deposition.

The InGaZnO thin films are fabricated on the quartz glass using pulsed laser deposition (PLD), where the target is prepared by mixing the Ga(2)O(3), In(2)O(3), and ZnO powders at a mol ratio of 1:1:8 before the solid-state reactions in a tube furnace at the atmospheric pressure. The product thin films were characterized comprehensively by X-ray diffraction, atomic force microscopy, Hall-effect investigation, and X-ray photoelectron spectroscopy. Thus, we demonstrate semiconductor thin-film materials with high smoothness, high transmittance in visible region, and excellent electrical properties.