Facile synthesis and photoluminescent properties of redispersible CeF3, CeF3 : Tb3+, and CeF3 : Tb3+/LaF3 (core/shell) nanoparticles

CeF3, CeF3:Tb3+, and CeF3:Tb3+/LaF3 (core/shell) nanoparticles were prepared by the polyol method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), UV-vis absorption spectra, photoluminescence (PL) spectra, and lifetimes. The results of XRD indicate that the obtained CeF3, CeF3:Tb3+, and CeF3:Tb3+/LaF3 (core/shell) nanoparticles crystallized well at 200 degrees C in diethylene glycol (DEG) with a hexagonal structure. The TEM images illustrate that the CeF3 and CeF3:Tb3+ nanoparticles are spherical with a mean diameter of 7 nm. The growth of the LaF3 shell around the CeF3:Tb3+ core nanoparticles resulted in an increase of the average size (11 nm) of the nanopaticles as well as in a broadening of their size distribution. These nanocrystals can be well-dispersed in ethanol to form clear colloidal solutions. The colloidal solutions of CeF3 and CeF3:Tb3+ show the characteristic emission of Ce3+ 5d-4f (320 nm) and Tb3+ D-5(4)-F-7(J) (J = 6-3, with D-5(4)-F-7(5) green emission at 542 nm as the strongest one) transitions, respectively. The emission intensity and lifetime of the CeF3:Tb3+/LaF3 (core/shell) nanoparticles increased with respect to those of CeF3:Tb3+ core particles.

Well-organized structures of ZnS semiconductor nanocrystals using amphiphilic triblock copolymer aggregates as templates

Ring- and rod-shaped P4VP-b-PS-b-P4VP ( PS, polystyrene; P4VP, poly( 4-vinylpyridine)) triblock copolymer aggregates are used as templates to synthesize ZnS nanocrystals. Herein, PVP serves as both a stabilizing agent and a structure- directing agent. The resulting ZnS nanocrystals could be aligned along the corona of the copolymer aggregates in near-perfect structures through control of both the molar ratio of Zn2+ to P4VP and the reaction time. The diameter of the as-synthesized ZnS layer on the surface of polymer template is approximate 2 - 3 nm. High-resolution transmission electron microscopy images reveal that the ZnS particles are single crystal in a zinc blende structure. This method provides a simple, reproducible route at room temperature to prepare assembled hybrid polymer - semiconductor nanocrystal nanocomposites.

Luminescent CdSe and CdSe/CdS core-shell nanocrystals synthesized via a combination of solvothermal and two-phase thermal routes

A new solvothermal route has been developed for synthesizing the size-controlled CdSe nanocrystals with relatively narrow size distribution, and the photoluminescence (PL) quantum yields (QYs) of the nanocrystals can reach 5-10%. Then the obtained CdSe nanocrystals served as cores to prepare the core/shell CdSe/CdS nanocrystals via a two-phase thermal approach, which exhibited much higher PL QYs (up to 18-40%) than the CdSe core nanocrystals. The nanocrystal samples were characterized by ultraviolet-visible (UV-vis) absorption spectra, PL spectra, wide-angle Xray diffraction (WAXD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM).

Fabrication and excitation-power-density-dependent micro-photoluminescence of hexagonal nanopillars with a single InGaAs/GaAs quantum well

Hexagonal nanopillars with a single InGaAs/GaAs quantum well (QW) were fabricated on a GaAs (111) B substrate by selective-area metal-organic vapor phase epitaxy. The standard deviations in diameter and height of the nanopillars are about 2% and 5%, respectively. Zincblende structure and rotation twins were identified in both the GaAs and the InGaAs layers by electron diffraction. The excitation-power-density-dependent micro-photoluminescence (mu-PL) of the nanopillars was measured at 4.2, 50, 100 and 150 K. It was shown that, with increasing excitation power density, the mu-PL peak's positions shift to a higher energy, and their intensity and width increase, which were rationalized using a model that includes the effects of piezoelectricity, photon-screening and band-filling. It was also revealed that the rotation twins significantly reduce the diffusion length of the carriers in the nanopillars, compared to that in the regular semiconductors.

Low threshold current density 1.3 mu m metamorphic InGaAs/GaAs quantum well laser diodes

Very low threshold current density InGaAs/ GaAs quantum well laser diodes grown by molecular beam epitaxy on InGaAs metamorphic buffers are reported. The lasing wavelength of the ridge waveguide laser diode with cavity length of 1200 mm is centred at 1337.2 nm; the threshold current density is 205 A/cm(2) at room temperature under continuous-wave operation.

High responsivity resonant-cavity-enhanced InGaAs/GaAs quantum-dot photodetector for wavelength of similar to 1 mu m at room temperature

The characteristics of a resonant cavity-enhanced InGaAs/GaAs quantum-dot n-i-n photodiode with only a bottom distributed Bragg reflector used as the cavity mirror, are reported. To suppress the dark current, an AlAs layer is inserted into the device structure as the blocking layer. It turns out that the structure still possesses the resonant coupling nature, and makes Rabi splitting discernible in the photoluminescence spectra. The measured responsivity spectrum of the photocurrent shows a peak at lambda = 1030 nm, and increases rapidly as the bias voltage increases. A peak responsivity of 0.75 A/W, or equivalently an external quantum efficiency of 90.3%, is obtained at V-bias = -1.4 V.

Magneto - Transport of electron symmetric and antisymmrtric states in highly doped InGaAs/InAlAs single quantum well

Beating patterns in longitudinal resistance caused by the symmetric and antisymmetric states were observed in a heavily doped InGaAs/InAlAs quantum well by using variable temperature Hall measurement. The energy gap of symmetric and antisymmetric states is estimated to be 4meV from the analysis of beating node positions. In addition, the temperature dependences of the subband electron mobility and concentration were also studied from the mobility spectrum and multicarrier fitting procedure.