Excellent Optical Quality Research Articles

Radiative recombination mechanisms in individual wurtzite ZnSe nanowires with a defect-free single-crystalline microstructure

Photoluminescence (PL) spectroscopy performed on arrays of semiconductor nanowires (NWs) suffers from ensemble broadening of PL lines, and fails to separate the PL from NWs of different crystal structures in the ensemble. Even the results on PL from single NWs are not devoid of ambiguity. This is because the influence of structural defects in NWs, such as stacking faults, twin boundaries and dislocations, on their optical spectra cannot be accounted for since the structural characteristics of the same NW remain largely unknown. We performed low-temperature PL spectroscopy on individual wurtzite (WZ) ZnSe NWs, and confirmed a homogeneous single-crystalline microstructure without any extended defects in these NWs, thus excluding any role of structural imperfections in their optical spectra. The luminescence is shown to be dominated solely by native point defects, while no role of extrinsic impurities was found. The radiative recombination is shown to originate from excitons bound to vacancies of Zn (VZn), VZn-complexes, and their phonon replicas. The binding energies of the acceptor-bound excitons, ionization energies of the acceptors, and average number of phonons emitted for shallow donor-VZn acceptor pair related transition were determined. Distinct from previous studies on PL from arrays of ZnSe NWs, this work provides an unambiguous interpretation of the PL spectra and assignment of PL peaks to WZ ZnSe. Narrow excitonic emission of linewidths 2.9 meV indicate excellent optical quality of WZ ZnSe NWs.

Silk fibroin biopolymer films as efficient hosts for DFB laser operation

Biopolymer hosts can be successfully used for the fabrication of multifunctional photonic devices due to their good optical properties, biocompatibility, remarkable mechanical properties and a wealth of chemical functionalization. Particularly, the silk fibroin (SF) biopolymer presents a wide range of suitable properties for photonic applications that were not fully exploited. In the present work, we demonstrate the operation of a distributed feedback (DFB) laser based on SF films doped with Rhodamine 6G (Rh6G) dye and films containing Rh6G and silica or silver nanoparticles. The SF grating structures were fabricated using a commercial blank digital versatile disc (DVD) as the template. The addition of silica or silver nanoparticles to the SF film led to enhanced emission due to the multiple scattering of light by the silica nanoparticles and a reduction of the emission linewidth. The laser wavelength was centered between ≈560 and ≈575 nm corresponding to the fourth-order diffraction of a 750 nm period of the SF grating. The results show that regenerated SF films are promising matrices for DFB lasers because of the excellent optical quality and large potential for biomedicine regarding biocompatibility and benign processing conditions.

Underwater Radiance Distributions Measured with Miniaturized Multispectral Radiance Cameras

AbstractMiniaturized radiance cameras measuring underwater multispectral radiances in all directions at high-radiometric accuracy (CE600) are presented. The camera design is described, as well as the main steps of its optical and radiometric characterization and calibration. The results show the excellent optical quality of the specifically designed fish-eye objective. They also show the low noise and excellent linearity of the complementary metal oxide semiconductor (CMOS) detector array that is used. Initial results obtained in various oceanic environments demonstrate the potential of this instrument to provide new measurements of the underwater radiance distribution from the sea surface to dimly lit layers at depth. Excellent agreement is obtained between nadir radiances measured with the camera and commercial radiometers. Comparison of the upwelling radiance distributions measured with the CE600 and those obtained with another radiance camera also shows a very close agreement. The CE600 measurements allow all apparent optical properties (AOPs) to be determined from integration of the radiance distributions and inherent optical properties (IOPs) to be determined from inversion of the AOPs. This possibility represents a significant advance for marine optics by tying all optical properties to the radiometric standard and avoiding the deployment of complex instrument packages to collect AOPs and IOPs simultaneously (except when it comes to partitioning IOPs into their component parts).

High-performance photorefractive polymer composites based on poly(9-vinyl-3-carbazolcarboxyaldehyde diphenylhydrazone)

Photorefractivity is based on the combined effects of photoconductivity and electro-optic property. Under the illumination of non-uniform light formed by the interference of two coherent laser beams, a spatially oscillating space charge field is formed arising from the generation and the redistribution of photo-induced charges. The refractive index of material is subsequently modulated via an electro-optic effect. The photorefractive materials have potentials applications in the fields such as dynamic holography, 3D display, 3D printer, reversible data storage and information processing. In 1994, remarkable improvement in the performance of PR polymeric material was obtained by using the photoconductive polymer poly(N-vinylcarbazole) (PVK). PVK/2,5DMNPAA/ECZ/TNF=34:50:15:1 wt% composite, showed a large gain coefficient of 220 cm and a diffraction efficiency of nearly 100% at the applied electric field of 90 V/ μm. Many studies have been done since Meerholz and coworkers proposed high-performance photorefractive (PR) polymeric composite. Despite this progress, the search for new photorefractive materials are still required for their widespread utilization in information technologies. In a previous paper, we reported on the synthesis and characterization of a photoconducting poly(siloxane) having pendant diphenylhydrazone. This composite shows a high diffraction efficiency of 81% at an electric field of 40 V/μm. Poly[4-(diphenyl-hydrazonomethyl)-phenyl]-[3-(methoxydimethyl-silanyl)-propyl]-methyl-amine (PSX-HZ) system have advantages including excellent optical quality, long shelf lifetime, the large birefringence, and high diffraction efficiency at low electric field. Despite the various advantages, the PSX-HZ system has suffered from relatively slow PR response time. To solve this problem, we applied the polyvinyl-backbone containing the hole transport moiety that is 9-vinyl-3-carbazolcarboxyaldehyde diphenylhydrazone (CPH). Hydrazone based on aromatic amines and arylaldehyde hydrazone are widely studied as organic hole transport materials due to enhanced hole mobility. Carbazole-containg hydrazone especially, exhibit relatively high hole mobility. We expect the realization of large photoconductivity of new polymer. The chemical structures investigated are shown in Figure 1, although the details of the synthesis and photophysical properties will be published elsewhere. The composition our samples was PVCPH/DB-IP-DC/ BBP/PCBM (54:30:15:1 wt%)-C1 and PVCPH/PDCST/BBP/ PCBM (54:30:15:1 wt%)-C2. Where poly(9-vinyl-3-carbazolcarboxyaldehyde diphenylhydrazone) (PVCPH) are photoconducting material, 2-{3-[(E)-2-(dibutylamino) ethen-1yl]-5,5-dimethylcyclohex-2-enylidene}malononitrile (DBIP-DC) and 2-(4-piperidinobenzylidene)malononitrile (PDCST) are nonlinear optical chromophore, butyl benzyl phthalate (BBP, Tokyo Kasei Kogyo Co.) is plasticizer, phenyl-C61butyric acid methyl ester (PCBM, Solenne Co.) is photosensitizer. The device was prepared by sandwiching the softened composite between two indium tin oxide (ITO) coated glass plates.

Film based on Y2O3:Eu3 + (5 mol% of Eu3 +) for flat panel display

This paper reports on Y2O3:Eu3+ containing 1mol% of Ag0 nanoparticle films recovered with a SiO2 layer by using glass foil as a substrate for a possible optical display device application. The obtained film showed an intense emission at 612nm due to the Eu3+5D0→7F2 hypersensitive transition, a high transmittance in that emission range, an excellent optical quality, and a high absorption only below 300nm. Moreover, despite the presence of the SiO2 layer used to improve the phosphor adhesion on Corning® foil substrates, the intensity ratios between the emissions assigned to Eu3+5D0→7F2 (dipole electric transition) and 5D0→7F1 (dipole magnetic transition) were not affected by it. The x and y coordinate values found in the 1931 Commission Internationale de l'Eclairage Chromaticity Diagram for this film reveal that it has a suitable pure red color emission for optical displays devices.

Active optics methods for exoplanet direct imaging

Context. The next generation of exoplanet hunters will be targeting hot Jupiter-like exoplanets orbiting around nearby stars through direct imaging. The high contrast needed for such planet finders requires optical surfaces free of high spatial frequency ripples that might remain in the post-coronagraphic image as quasi-static speckles. Aims. We report results on the manufacturing of three supersmooth aspherical mirrors for the ESO/VLT-SPHERE instrument. The excellent optical quality obtained will allow the future planet hunter to increase the level of achievable contrast by a strong reduction of the noise level and residual quasi-static speckles on the image plane. Methods. The stress polishing method used on these mirrors is well suited to superpolishing aspheric components for astronomy. The main advantage of this technique is the very high optical quality obtained either on the form errors or on the high spatial frequency errors. Furthermore, the roughness can be decreased to a few angstroms, thanks to the classical polishing with a large pitch tool.Results. Interferograms obtained during polishing and in the final stage show the supersmooth quality of each mirror. Errors in the high spatial frequency range are lower than 4 nm rms WF, thereby avoiding the degradation of the post-coronagraphic image. A comparison of the power spectral density (PSD) obtained by stress polishing and the PSD of the VLT-UT3 primary mirror demonstrates that the contrast capabilities will not be limited by the aspherical mirrors.

Growth of High Quality ZnO Nanowires on Graphene

We report growth of the ZnO nanowires on graphene/SiO2/Si substrates using a chemical vapor deposition method. The length of nanowires varies from 1 microm to 10 microm with increasing the growth time from 30 min to 90 min. X-ray diffraction and high-resolution transmission electron microscopy investigations predict the high structural quality of the c-axis grown single crystalline ZnO nanowires. Temperature dependent photoluminescence spectra from the nanowires reveal excellent optical quality and excitonic behavior in the single crystalline ZnO nanowires. A well-resolved free exciton emission at 3.375 eV, indicates high crystalline quality nanowires and a strong PL peak at 3.370 eV is assigned to neutral-donor bound excitons (D0X).

Novel horseshoe-shaped ZnO nanorods and their optical properties

Large areas of ZnO horseshoe-shaped nanorods have been fabricated vertically on MgO-coated Si (111) substrates by chemical vapor deposition method. The well-aligned nanorod arrays were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscope (HRTEM), energy-dispersive X-ray spectroscopy (EDS), and photoluminescence spectroscopy (PL). The results show that the nanorods are perfect single crystals with hexagonal wurzite structure along the [0001] growth direction. The nanorods have regular horseshoe shape, and the diameter of the rods rang 70–99nm while the length is about 600nm. The PL spectrum exhibits a strong peak at 500.8nm and two relatively weak emission bands centered at 387.7nm and 648.6nm, which indicates that the ZnO arrays are of excellent optical quality.

Disposable roll-to-roll hot embossed electrophoresis chip for detection of antibiotic resistance genemecA in bacteria

We present a high-throughput roll-to-roll (R2R) manufacturing process for foil-based polymethyl methacrylate (PMMA) chips of excellent optical quality. These disposable, R2R hot embossed microfluidic chips are used for the identification of the antibiotic resistance gene mecA in Staphylococcus epidermidis. R2R hot embossing is an emerging manufacturing technology for polymer microfluidic devices. It is based on continuous feeding of a thermoplastic foil through a pressurized area between a heated embossing cylinder and a blank counter cylinder. Although mass fabrication of foil-based microfluidic chips and their use for biological applications were foreseen already some years ago, no such studies have been published previously.

Distribution of Neodymium and properties of Nd:YAG crystal by horizontal directional solidification

Nd 3+-doped Y 3Al 5O 12 single crystal has been grown by the horizontal directional solidification (HDS) method. The crystal structure was determined by X-ray diffraction analysis, and the relatively small FWHM of the [111] symmetric rocking curve demonstrated the good crystallinity of the crystal. The distribution of Nd 3+ ions was studied by the inductively coupled plasma atomic emission spectrometry (ICP-AES) method and the segregation coefficient was 0.234. The Nd 3+ions distribution along the [111] growth axis well agreed with the general distribution equation: C s = C m K 0 ( 1 − g ) K 0 − 1 , and the concentration of Nd 3+ ions along the thickness and width direction (perpendicular to [111] growth axis) was near unity. The absorption and emission spectroscopy results indicated that the crystal had excellent laser optical quality for InGaAs diode-laser pumping.

Investigation of Electrodeposited and Solution Grown ZnO Nanorod Based UV Photodetector

In this work solution growth technique as well as electrodepostion technique was employed to directly grow ZnO nanorod arrays on the p-GaN layer for fabricating n-ZnO nanorod/ p-GaN heterojunction diodes. Microstructure and room temperature photoluminescence (PL) measurement confirmed the growth of ZnO nanorod arrays with near perfect microstructure, stoichiometry and excellent optical quality. Current-voltage (I-V) measurements showed the formation of diode structure with a typical diode characteristic having a turn on voltage of 2.5V and 6.4V respectively, for solution grown and electrodeposited ZnO nanorod based p-n diode. A low resistive ITO coated glass was used to make contact with the top nanorod arrays and spectral response of the p-n diode was investigated. UV response particularly from solution grown ZnO nanorod based p-n diode was very promising.

Flame spray synthesis of Lu 2O 3 nanoparticles

We have used a Flame Spray Pyrolysis (FSP) technique to synthesize lutetium oxide (Lu 2O 3) nanoparticles from lutetium nitrate. Optical quality transparent ceramics were prepared via hot pressing of the Lu 2O 3 nanoparticles formed using the FSP technique. We present data demonstrating that the FSP system can be used to control the material phase of the nanoparticles by changing the O 2 dispersion gas flow rate. Different O 2 dispersion gas flow rates affect the particle residence time in the flame resulting in the formation of different nanoparticulate phases. Our work has led to the synthesis of a metastable phase of Lu 2O 3 which has never been reported using the FSP technique. Significantly, the presence of the metastable phase enables the ceramic powders to be hot pressed at lower temperatures resulting in smaller grain sizes, resulting in excellent optical quality Lu 2O 3 windows.

Effect of RF power and sputtering pressure on the structural and optical properties of TiO 2 thin films prepared by RF magnetron sputtering

TiO 2 thin films were deposited onto quartz substrates by RF magnetron sputtering. The samples deposited at various RF powers and sputtering pressures and post annealed at 873 K, were characterized using X-ray diffraction (XRD), micro Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV–vis spectroscopy and photoluminescence (PL) spectroscopy. XRD spectrum indicates that the films are amorphous-like in nature. But micro-Raman analysis shows the presence of anatase phase in all the samples. At low sputtering pressure, increase in RF power favors the formation of rutile phase. Presence of oxygen defects, which can contribute to PL emission is evident in the XPS studies. Surface morphology is much affected by changes in sputtering pressure which is evident in the SEM images. A decrease in optical band gap from 3.65 to 3.58 eV is observed with increase in RF power whereas increase in sputtering pressure results in an increase in optical band gap from 3.58 to 3.75 eV. The blue shift of absorption edge in all the samples compared to that of solid anatase is attributed to quantum size effect. The very low value of extinction coefficient in the range 0.0544–0.1049 indicates the excellent optical quality of the samples. PL spectra of the films showed emissions in the UV and visible regions.

In-situ preparation of high optical quality ZnO nanoparticles in nanofibrous PVA matrix

Fabrication of ultraviolet light emitting devices using ZnO nanostructures is still difficult due to the high cost synthesis for high quality ZnO. It is important to suppress the visible emission. In this paper, we report the effective low cost in-situ preparation of high quality monodispersed and non-agglomerate ZnO nanoparticles in nanofibrous PVA matrix derived from electrospinning method. The final product was investigated by SEM, EDAX, XRD, FTIR, TEM, and SAED. The XRD analysis proved the successful preparation of ZnO with wurtzite hexagonal phase. FTIR spectroscopic measurements showed the interaction between ZnO and PVA. The purity of the sample was studied using PL. The result showed that the obtained sample exhibits intense ultraviolet emissions at 369 nm while the absence of deep level emission confirms the high quality sample. PVA matrix and electrospinning method are found to have a vital role to the preparation of defect free ZnO. Experimental results have proven that the prepared ZnO by this method have excellent optical quality.

Synthesis of Nd:YAG Powders by the Co-Precipitation Method

Yttrium Aluminum Garnet (Nd:YAG) transparent ceramic doped with Nd have predominantly chemical stability, excellent optical quality and high temperature stability, it is becomeing a substitute for single crystal, had already become new generation laser material, have important strategic sense in the laser and the superelevation powders laser system. Al(NO3)3·9H2O, Y2O3, Nd2O3,(NH4)2SO4 and NH4HCO3 are raw material, TEOS is additive and ethylene glycol(EG). Nd:YAG precursor powders witch is Homogeneously dispersed, little agglomerated, pure YAG phase, different Nd3+ doped density were prepared by the co-precipitation method. The Nd:YAG ceramic powders were characterized by TG-DTA, XRD, FT-IR.

GaAs nanoneedles grown on sapphire

Heterogeneous integration of dissimilar single crystals is of intense research interests. Lattice mismatch has been the most challenging bottleneck which limits the growth of sufficient active volume for functional devices. Here, we report self-assembled, catalyst-free, single crystalline GaAs nanoneedles grown on sapphire substrates with 46% lattice mismatch. The GaAs nanoneedles have a 2–3 nm tip, single wurtzite phase, excellent optical quality, and dimensions scalable with growth time. The needles have the same sharp, hexagonal pyramid shape from ∼100 nm (1.5 min growth) to ∼9 μm length (3 h growth).

Stacked GaAs quantum dots fabricated by refilling of self-organized nanoholes: opticalproperties and post-growth annealing

We study the photoluminescence and impact of post-growth annealing of stacked,strain-free GaAs quantum dots fabricated by refilling of self-organized nanoholes usingmolecular beam epitaxy. Temperature- and power-dependent photoluminescence studiesreveal an excellent optical quality of the quantum-dot stack. After high-temperaturepost-growth annealing only slight blueshifts and an increase in full width at half-maximumof the photoluminescence peak are observed, indicating very high-temperature stability andcrystalline quality of the stacked GaAs quantum-dot structure.

Photoluminescence Properties of Non-Tapered InN Nanorods Grown by Plasma-Assisted Metalorganic Chemical Vapor Phase Deposition

We have successfully grown non-tapered InN nanorods on Si substrate using an RF plasma assisted metalorganic chemical vapor deposition technique. Employment of 50 W nitrogen plasma reduces the optimal growth temperature to 500 degrees C. In order to study the temperature dependent bandgap and thermal quenching mechanism in relation to the localized states, photoluminescence measurement over a temperature range from 7 to 160 K are conducted. The photoluminescence at 7 K shows a strong near-band-emission energy of 0.682 eV with a narrow band width of 0.027 eV, which reveals excellent optical and structural qualities of the InN nanorods.

Electroluminescence from Solution Grown n-ZnO Nanorod/p-GaN-Heterostructured Light Emitting Diodes

To fabricate n-ZnO nanorod/p-GaN-heterostructured light emitting diodes, well-aligned ZnO nanorod arrays were synthesized on metallorganic chemical vapor deposited p-GaN layers on sapphire substrates using low temperature and low cost solution growth techniques. Current–voltage measurements showed the formation of a diode structure with a typical diode characteristic having a turn-on voltage of 4.8 V. Microstructure and room-temperature photoluminescence measurements confirmed the growth of ZnO nanorod arrays with a near-perfect microstructure, stoichiometry, and excellent optical quality. Room-temperature electroluminescence in the blue-violet region with a peak wavelength of was observed under a forward bias. No defect-related emission was observed in the deep visible region.

Low density MOVPE grown InGaAs QDs exhibiting ultra-narrow single excitonlinewidths

Low density (∼107 cm − 2), small sized InGaAs quantum dots were grown on a GaAs substrate by metal–organicvapor-phase epitaxy and a special annealing technique. The structural quantumdot properties and the influence of the annealing technique was investigated byatomic force microscope measurements. High-resolution micro-photoluminescencespectra reveal narrow photoluminescence lines, with linewidths down to 11 µeV and fine structuresplittings of 25 µeV. Highsignal to noise ratios (∼140) and a nearly background free autocorrelation measurement indicate an excellent opticalquality and single photon emission behavior. Furthermore, time resolved measurementsreveal excitonic decay times typically in the range between 800 and 2300 ps and biexcitonicdecay times around 300 ps.