A novel strategy for boosting the photoluminescence quantum efficiency of CdSe nanocrystals at room temperature

Highly luminescent colloidal nanocrystals have wide applications in bioimaging and various optoelectronic devices.Herein we report a facile and mild procedure by combining S2-treatment and binary ligand passivation,which can efficiently enhance the luminescent property of CdSe nanocrystals at room temperature.The photoluminescence quantum yield of as-treated CdSe nanocrystals exhibits drastic enhancement(e.g.,188 times for CdSe nanorods)after this dual-passivation treatment.The methodology proposed here can be applied to various CdSe nanocrystals,regardless of their sizes,shapes,and crystal structures.

Growth Kinetics of Nanocrystals and Nanorods by Employing Small-angle X-ray Scattering (SAXS) and Other Techniques

In this article, we report the results of our detailed investigations of the growth kinetics of zero-dimensional nanocrystals as well as one-dimensional nanorods by the combined use of small angel X-ray scattering （SAXS）, transmission electron microscopy （TEM） along with other physical techniques. The study includes growth kinetics of gold nanocrystals formed by the reduction of HAuCl4 by tetrakis（hydroxymethyl） phosphonium chloride in aqueous solution, of CdSe nanocrystals formed by the reaction of cadmium stearate and selenium under solvothermal conditions, and of ZnO nanorods formed by the reaction of zinc acetate with sodium hydroxide under solvothermal conditions in the absence and presence of capping agents. The growth of gold nanocrystals does not follow the diffusion-limited Ostwald ripening, and instead follows a Sigmoidal rate curve. The heat change associated with the growth determined by isothermal titration calorimetry is about 10 kcal·mol^-1 per I nm increase in the diameter of the nanocrystals. In the case of CdSe nanocrystals also, the growth mechanism deviates from diffusion-limited growth and follows a combined model containing both diffusion and surface reaction terms. Our study of the growth kinetics of uncapped and poly（vinyl pyrollidone） （PVP）-capped ZnO nanorods has yielded interesting insights. We observe small nanocrystals next to the ZnO nanorods after a lapse of time in addition to periodic focusing and defocusing of the width of the length distribution. These observations lend support to the diffusion-limited growth model for the growth of uncapped ZnO nanorods. Accordingly, the time dependence on the length of uncapped nanorods follows the L3 law as required for diffusion-limited Ostwald ripening. The PVP-capped nanorods, however, show a time dependence, which is best described by a combination of diffusion （L^3） and surface reaction （L^2） terms.

Power-Dependent Luminescence of CdSe/ZnS Nanocrystal Assembled Layer-by-Layer on a Silver Nanorod Array

We investigate the power-dependent luminescence of CdSe/ZnS semiconductor quantum dots closely packed layer- by-layer in the proximity of a silver nanorod array cavity. It is found that the emission peak shifts significantly to the longer wavelengths as the excitation power increases, especially when the longitudinal surface plasmon resonance of the Ag nanorod array cavity is adjusted to be close to the emission wavelength. The equivalent gain varies with the coating layer of CdSe/ZnS semiconductor quantum dots and the excitation power is also studied to explain this interesting spectrum-shifting effect. These findings could find applications in the dynamic information processing of active plasmonic and photonic nanodevices.

Colloidal semiconductor nanocrystals for light emission and photonic integration

Solution-processed colloidal semiconductor nanocrystals(NCs)have become attractive materials for the development of optoelectronic and photonic devices due to their inexpensive synthesis and excellent optical properties.Recently,CdSe NCs with different dimensions and structures have achieved significant progress in photonic integrated circuits(PICs),including light generation(laser),guiding(waveguide),modulation,and detection on a chip.This article summarizes the development of CdSe NCs–based lasers and discusses the challenges and opportunities for the application of CdSe NCs in PICs.Firstly,an overview of the optical properties of CdSe-based NCs with different dimensions is presented,with emphasis on the amplified stimulated emission and laser properties.Then,the nanophotonic devices and PICs based on CdSe NCs are introduced and discussed.Finally,the prospects for PICs are addressed.

Laser-annealing-made amplified spontaneous emission of "giant" CdSe/CdS core/shell nanocrystals transferred from bulk-like shell to quantum-confined core

'Giant' Cd Se/Cd S core/shell nanocrystals(NCs) were synthesized with thick Cd S shell(15 monolayers), and the x-ray diffraction(XRD) measurement indicates there is a zinc blende phase in the thick Cd S shell, whereas it transformed into wurtzite phase under 5 min radiation with a 400 nm, 594 μJ∕cm2femtosecond(fs) laser beam.The evolution of the NCs’ spontaneous emission under the fs laser radiation was recorded with a Hamamatsu streak camera. The as-synthesized NCs exhibit an amplified spontaneous emission(ASE) at 530 nm, which comes from a bulk-like Cd S shell due to the interfacial potential barrier, which could slow down the relaxation of holes from the shell to the core. After being annealed by an fs laser, the ASE of the g-NCs is transferred from a bulk-like Cd S shell to a quantum-confined Cd Se core because the phase transformation determined with the XRD measurement could remove the interfacial barrier. Besides the ASE at 643 nm, two shorter-wavelength ASE peaks at 589 and 541 nm, corresponding to optical transitions of the second(1P) and third(1D) electron quantization shells of the Cd Se core, also appear, thus indicating that Auger recombination is effectively suppressed.