Synthesis and photoluminescence of ZnS : Cu nanoparticles

The room-temperature photoluminescence (PL) of copper doped zinc sulfide (ZnS:Cu) nanoparticles were investigated. These ZnS:Cu nanoparticles were synthesized by a facile wet chemical method, with the copper concentration varying from 0 to 2 mol%. By Gaussian fitting, the PL spectrum of the undoped ZnS nanoparticles was deconvoluted into two blue luminescence peaks (centered at 411 nm and 455 nm, respectively), which both can be attributed to the recombination of the defect sates of ZnS. But for the doped samples, a third peak at about 500 nm was also identified. This green luminescence originates from the recombination between the shallow donor level (sulfur vacancy) and the t(2) level of Cu2+. With the increase of the CU2+ concentration, the green emission peak is systematically shifted to longer wavelength. In addition, it was found that the overall photoluminescence intensity is decreased at the Cu2+ concentration of 2%. The concentration quenching of the luminescence may be caused by the formation of CuS compound. (c) 2005 Elsevier B.V. All rights reserved.

Photoluminescence from C+ ion-implanted and electrochemical etched Si layers

The microstructural and optical analysis of Si layers emitting blue luminescence at about 431 nm is reported. These structures have been synthesized by C+ ion implantation and high-temperature annealing in hydrogen atmosphere and electrochemical etching sequentially. With the increasing etching time, the intensity of the blue peak increases at first, decreases then and is substituted by a new red peak at 716 nm at last, which shows characteristics of the emission of porous silicon. C=O compounds are induced during C+ implantation and nanometer silicon with embedded structure is formed during annealing, which contributes to the blue emission. The possible mechanism of photoluminescence is presented. (c) 2005 Elsevier B.V. All rights reserved.

Pressure dependence of the near-band-edge photoluminescence from ZnO microrods at low temperature

The temperature and pressure dependences of band-edge photo luminescence from ZnO microrods have been investigated. The energy separation between the free exciton (FX) and its first order phonon replica (FX-1LO) decreases at a rate of k(B)T with increasing temperature. The intensity ratio of the FX-1LO to the bound exciton (BX) emission is found to decrease slightly with increasing pressure. All of the exciton emission peaks show a blue shift with increasing pressure. The pressure coefficient of the FX transition, longitudinal optical (LO) phonon energy, and binding energy of BX are estimated to be 21.4, 0.5, and 0.9 meV/GPa, respectively. (c) 2006 Elsevier Ltd. All rights reserved.

Tunable spin transport in magnetic-electric superlattice

We study the spin-dependent electron transport in a special magnetic-electric superlattice periodically modulated by parallel ferromagnetic metal stripes and Schottky normal-metal stripes. The results show that, the spin-polarized current can be well controllable by modulating the magnetic strength of the ferromagnetic stripes or the voltage applied to the Schottky normal-metal stripes. It is obvious that, to the system of the magnetic superlattice, the polarized current can be enhanced by the magnetic strength of ferromagnetic stripes. Nevertheless, it is found that, for the magnetic-electric superlattice, the polarized current can also be remarkably advanced by the voltage applied to the Schottky normal-metal stripes. These results may indicate a useable approach for tunable spintronic devices. (c) 2006 Elsevier B.V. All rights reserved.

Tunable Fano resonance in photonic crystal slabs

A three dimensional analysis of a special class of anisotropic materials is presented. We introduce an extension of the Scattering Matrix Method (SMM) to investigate the behavior of anisotropic Photonic Crystal Slabs (PhCS) subject to external radiation. We show how the Fano effect can play a fundamental role in the realization of tunable optical devices. Moreover, we show how to utilize electron injection, electric field and temperature as parameters to control the Fano resonance shift in both isotropic and anisotropic materials as Si and Potassium Titanium Oxide Phosphate (KTP). We will see that because Fano modes are sensitive and controllable, a broad range of applications can be considered. (c) 2006 Optical Society of America

Enhancement of photoluminescence intensity of GaInNAs/GaAs quantum wells by two-step rapid thermal annealing

We investigate the effect of rapid thermal annealing on InGaNAs/GaAs quantum wells. At optimized annealing temperatures and times, the greatest enhancement of the photoluminescence intensity is obtained by a special two-step annealing process. To identify the mechanism affecting the material quality during the rapid thermal annealing, differential temperature analysis is applied, and temperature- and power-dependent photoluminescence is carried out on the samples annealed under different conditions. Our experiment reveals that some composition redistribution or other related ordering process may occur in the quantum-well layer during annealing. Annealing at a lower temperature for a long time primarily can remove defects and dislocations while annealing at a higher temperature for a short time primarily homogenizes the composition in the quantum wells.

Synthesis and photoluminescence properties of vertically aligned ZnO nanorod-nanowall junction arrays on a ZnO-coated silicon substrate

Arrays of vertically well-aligned ZnO nanorod-nanowall junctions have been synthesized on an undoped ZnO-coated silicon substrate by a carbothermal reduction and vapour phase transport method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that the nanostructures are well-oriented with the c-axis perpendicular to the substrate. The room temperature photoluminescence (PL) spectrum of the as-prepared ZnO nanostructure reveals a dominant near-band-edge (NBE) emission peak and a weak deep level (DL) emission, which demonstrates its good optical properties. Temperature-dependent PL spectra show that both the intensity of NBE and DL emissions increased with decreasing temperature. The NBE emission at 3.27 eV is identified to originate from the radiative free exciton recombination. The possible growth mechanism of ZnO nanorod-nanowall junctions is also proposed.

Near infrared photoluminescence from Yb,Al Co-implanted SiO2 films on silicon

Intense room-temperature near infrared (NIR) photoluminescence (980 nm and 1032 nm) is observed from Yb,Al co-implanted SiO2 films on silicon. The optical transitions occur between the F-2(5/2) and F-2(7/2) levels of Yb3+ in SiO2. The additional Al-implantation into SiO2 films can effectively improve the concentration quenching effect of Yb3+ in SiO2. Photoluminescence exitation sprectroscopy shows that the NIR photoluminescence is due to the non-radiative energy transfer from Al-implantation-induced non-bridging oxygen hole defects in SiO2 to Yb3+ in the Yb-related luminescent complexes. It is believed that the defect-mediated luminscence of rare-earth ions in SiO2 is very effective.

Effect of substrate temperature on the growth and photoluminescence properties of vertically aligned ZnO nanostructures

Vertically well-aligned ZnO nanoridge, nanorod, nanorod-nanowall junction, and nanotip arrays have been successfully synthesized on Si (100) substrates using a pulsed laser deposition prepared ZnO film as seed layer by thermal evaporation method. Experimental results illustrated that the growth of different morphologies of ZnO nanostructures was strongly dependent upon substrate temperature. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies showed that the ZnO nanostructures were single crystals with a wurtzite structure. Compared with those of the other nanostructures, the photoluminescence (PL) spectrum of nanorod-nanowall junctions showed the largest intensity ratio of ultraviolet (UV) to yellow-green emission and the smallest full-width at half-maximum (FWHM) of the UV peak, reflecting the high optical quality and nearly defect free of crystal structure. The vertical alignment of the nanowire array on the substrate is attributed to the epitaxial growth of the nanostructures from the ZnO buffer layer. The growth mechanism was also discussed in detail. (c) 2006 Elsevier B.V. All rights reserved.

Anti-Stokes photoluminescence in ZnO microcrystal

Low temperature (10 K) strong anti-Stokes photoluminescence (ASPL) of ZnO microcrystal excited by low power cw 532 nm laser is reported here. Energy upconversion of 1.1 eV is obtained in our experiment with no conventional nonlinear effect. Through the study of the normal photoluminescence and temperature dependence of ASPL we conclude that the green band luminescence in ZnO is related to deep donor to valance band transition. Using the two-step two-photon absorption model, we provide a plausible mechanism leading to the ASPL phenomenon in our experiment. (c) 2006 American Institute of Physics.

Porous ZnAl2O4 spinel nanorods doped with Eu3+: synthesis and photoluminescence

Eu3+-doped zinc aluminate (ZnAl2O4) nanorods with a spinel structure were successfully synthesized via an annealing transformation of layered precursors obtained by a homogeneous coprecipitation method combined with surfactant assembly. These spinel nanorods, which consist of much finer nanofibres together with large quantities of irregular mesopores and which possess a large surface area of 93.2 m(2) g(-1) and a relatively narrow pore size distribution in the range of 6 - 20 nm, are an ideal optical host for Eu3+ luminescent centres. In this nanostructure, rather disordered surroundings induce the typical electric-dipole emission (D-5(0) --> F-7(2)) of Eu3+ to predominate and broaden.

Photoluminescence from the nitrogen-perturbed above-bandgap states in dilute GaAs1-xNx alloys: A microphotoluminescence study

Using microphotoluminescence (mu-PL), in dilute N GaAs1-xNx alloys, we observe a PL band far above the bandgap E-0 with its peak energy following the so-called E+ transition, but with contribution from perturbed GaAs host states in a broad spectral range (> 100 meV). This finding is in sharp contrast to the general understanding that E+ is associated with a well-defined conduction band level (either L-1c or N-x). Beyond this insight regarding the strong perturbation of the GaAs band structure caused by N incorporation, we demonstrate that a small amount of isoelectronic doping in conjunction with mu-PL allows direct observation of above-bandgap transitions that are not usually accessible by PL.

Anomalous temperature dependence of photoluminescence peak energy in InAs/InAlAs/InP quantum dots

We have observed an unusual temperature sensitivity of the photoluminescence (PL) peak energy for InAs quantum dots grown on InAs quantum wires (QDOWs) on InP substrate. The net temperature shift of PL wavelength of the QDOWs ranges from 0.8 to -4. angstrom/degrees C depending upon the Si doping concentration in the samples. This unusual temperature behavior can be mainly ascribed to the stress amplification in the QDOWs when the thermal strain is transferred from the surrounding InAs wires. This offers an opportunity for realizing quantum dot laser devices with a temperature insensitive lasing wavelength. (c) 2006 Elsevier Ltd. All rights reserved.

Influence of the cavity on the low-temperature photoluminescence of SiGe/Si multiquantum wells grown on a silicon-on-insulator substrate

The influences of the cavity on the low-temperature photoluminescence of Si0.59Ge0.41/Si multiquantum wells grown on silicon-on-insulator substrates are discussed. The positions of the modulated photoluminescence (PL) peaks not only relate to the nature of SiGe/Si multiquantum wells, but also relate to the characteristic of the cavity. With increasing temperature, a redshift of the modulated PL peak originating from the thermo-optical effect of the cavity is observed.

Enhancement of 1.53 mu m photoluminescence from spin-coated Er-Si-O (Er2SiO5) crystalline films by nitrogen plasma treatment

Er-Si-O (Er2SiO5) crystalline films are fabricated by the spin-coating and subsequent annealing process. The fraction of erbium is estimated to be 21.5 at% based on Rutherford backscattering measurement. X-ray diffraction pattern indicates that the Er-Si-O films are similar to Er2SiO5 compound in the crystal structure. The fine structure of room-temperature photoluminescence of Er3+-related transitions suggests that Er has a local environment similar to the Er-O-6 octahedron. Our preliminary results show that the intensity of 1.53 mu m emission is enhanced by a factor of seven after nitrogen plasma treatment by NH3 gas with subsequent post-annealing. The full-width at half-maximum of 1.53 pm emission peak increases from 7.5 to 12.9 nm compared with that of the untreated one. Nitrogen plasma treatment is assumed to tailor Er3+ local environment, increasing the oscillator strength of transitions and thus the excitation/emission cross-section. (c) 2005 Elsevier B.V. All rights reserved.