Red Shift In Photoluminescence Spectra Research Articles

The Investigation of Porous Al<sub>X</sub>Ga<sub>1-X</sub>N Layers on Si (111) Substrate with GaN/AlN as Buffer Layer

High quality undoped AlxGa1-xN with high Ga composition was grown on Si (111) substrate, using GaN/AlN as the buffer layer, by plasma-assisted molecular beam epitaxy (PAMBE). The present work reports on the photoluminescence (PL) studies of porous AlxGa1-xN prepared by ultraviolet (UV) assisted electrochemical etching in a solution of 2 % concentration of KOH electrolyte under illumination of an UV lamp with 500 W power for 30 min. The optical properties of porous AlxGa1-xN sample was compared to the corresponding as-grown GaN. PL studies suggested that the porosity was capable of improving the lattice mismatch induced strain. Porosity induced PL intensity enhancement was found in nanoporous sample. The resulting nanoporous AlxGa1-xN display red-shifted PL spectra compared to the as-grown AlxGa1-xN. Appearance of the red-shifted emission is correlated with the development of highly anisotropic structures in the morphology.

Synthesis, characterization and optical properties of distyrylanthracene-based polymers

Distyryl- and nitrodistyrylanthracene-based polymers (P1 and P2, respectively) have been synthesized and characterized. The polymers are fully soluble in common organic solvents and have number-average molecular weights of 18 570 and 23 480 g mol−1 for P1 and P2, respectively. The optical properties of the polymers were investigated by UV-visible absorption and photoluminescence spectroscopies. The optical gaps were estimated from the absorption-onsets of the polymer films; their values were 2.79, 2.75 eV for P1 and P2, respectively. A blue photoluminescence was observed in dilute solution. In solid thin film, Π–Π interactions influence the optical properties, and red-shifted photoluminescence spectra were obtained; a green emission (573 nm) for P1 and an orange one (605 nm) for P2 were observed. The HOMO and LUMO levels were estimated using cyclic voltammetry analysis. Single-layer devices of the indium-tin oxide/polymer/aluminum configuration were fabricated and showed relatively low turn-on voltages (5.14 V for P1 and 5.00 V for P2).

Synthesis and characterization of new anthracene‐based semiconducting polyethers

AbstractNew anthracene‐based polyethers, anthracene/bisphenol A (An–BPA) and anthracene/fluorinated bisphenol A (An–BPAF), were synthesized and characterized. An–BPA and An–BPAF were fully soluble in common organic solvents and had number‐average molecular weights of 2580 and 3240, respectively. The optical properties of the polymers were investigated with ultraviolet–visible absorption and photoluminescence spectroscopy. Blue photoluminescence was observed in dilute solutions. In solid thin films, π–π interactions influenced the optical properties, and redshifted photoluminescence spectra were obtained; a green emission (504 nm) for An–BPAF and a green‐yellow emission (563 nm) for An–BPA were found. By cyclic voltammetry, the electrochemical band gap was estimated to be 2.72 and 3.05 eV for An–BPA and An–BPAF, respectively. Single‐layer diode devices of an indium tin oxide/polyether/aluminum configuration were fabricated and showed relatively low turn‐on voltages (3.5 V for An–BPA and 3.7 V for An–BPAF). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Facile pyrolytic synthesis of silicon nanowires

One-dimensional nanostructures such as silicon nanowires (SiNW) are attractive candidates for low power density electronic and optoelectronic devices including sensors. A new simple method for SiNW bulk synthesis [1,2] is demonstrated in this work, which is inexpensive and uses low toxicity materials, thereby offering a safe, energy efficient and green approach. The method uses low flammability liquid phenylsilanes, offering a safer avenue for SiNW growth compared with using silane gas. A novel, duo-chamber glass vessel is used to create a low-pressure environment where SiNWs are grown through vapor–liquid–solid mechanism using gold nanoparticles as a catalyst. The catalyst decomposes silicon precursor vapors of diphenylsilane and triphenylsilane and precipitates single crystal SiNWs, which appear to grow parallel to the substrate surface. This opens up possibilities for synthesizing nano-junctions amongst wires which is important for the grid architecture of nanoelectronics proposed by Likharev [3]. Even bulk synthesis of SiNW is feasible using sacrificial substrates such as CaCO 3 that can be dissolved post-synthesis. Furthermore, by dissolving appropriate dopants in liquid diphenylsilane, a controlled doping of the nanowires is realized without the use of toxic gases and expensive mass flow controllers. Upon boron doping, we observe a characteristic red shift in photoluminescence spectra. In summary, an inexpensive and versatile method for SiNW is presented that makes these exotic materials available to any lab at low cost.

Photoluminescence and laser properties of mesostructured SBA-15 monolith doped with coumarin 151

Large, flawless and transparent silica monoliths were prepared at room temperature by solvent evaporation method and loaded with dye. The composites containing dye molecules were characterized by X-ray diffraction, transmission electron microscopy, Uv–vis and photoluminescence spectra. A red-shift in photoluminescence spectrum was observed from the composite monolith compared with that of laser dye in C2H5OH solution. The property of laser narrowing has been shown when the composites are pumped at p = 355 nm by nitrogen laser.

Improvement of the performance of dye-sensitized solar cells using Sn-doped ZnO nanoparticles

Sn-doped and undoped ZnO nanoparticles were synthesized by hydrothermal method and their performance as the photoanode of dye-sensitized solar cells (DSSCs) was investigated. Energy dispersive X-ray spectroscopy and X-ray diffraction showed that the Sn had been doped into the ZnO lattice. A red shift of photoluminescence spectra which was induced by Sn doping was observed. The photocurrent density–voltage curves of DSSCs indicated that the efficiency was increased by as high as 140% on bare-FTO substrate and 105% on ZnO compact layer/FTO substrate via Sn doping. Also the effect of the ZnO compact layer was discussed by both of Sn-doped or undoped DSSCs.

Optical property of silicon quantum dots embedded in silicon nitride by thermal annealing

We present the effects on the thermal annealing of silicon quantum dots (Si QDs) embedded in silicon nitride. The improved photoluminescence (PL) intensities and the red-shifted PL spectra were obtained with annealing treatment in the range of 700 to 1000 °C. The shifts of PL spectra were attributed to the increase in the size of Si QDs. The improvement of the PL intensities was also attributed to the reduction of point defects at Si QD/silicon nitride interface and in the silicon nitride due to hydrogen passivation effects.

InGaN nanorod arrays grown by molecular beam epitaxy: Growth mechanism structural and optical properties

Vertically c-axis-aligned InGaN nanorod arrays were synthesized on c-plane sapphire substrates by radio-frequency molecular beam epitaxy. In situ reflection high-energy electron diffraction was used to monitor the growth process. X-ray diffraction, transmission electron microscopy, field-emission scanning electron microscope, and photoluminescence were used to investigate the structural and optical properties of the nanorods. The growth mechanism was studied and a growth model was proposed based on the experimental data. A red shift of photoluminescence spectrum of InGaN nanorods with increasing growth time was found and attributed to the partial release of stress in the InGaN nanorods.

Preparation of the stimuli-responsive ZnS/PNIPAM hollow spheres

Novel quantum dots ZnS/poly(N-isopropylacrylamide) (PNIPAM) hybrid hollow spheres were obtained by localizing free radical polymerization of NIPAM and crosslinker (MBA) at the peripheral of PCL nanoparticles, followed by biodegradation of PCL with an enzyme of the Lipase PS. The formation of ZnS/PNIPAM hollow spherical structures and the thermo-sensitive reversible properties was systematically investigated by transmission electron microscopy (TEM) and dynamic light scattering (DLS), respectively. The ZnS/PNIPAM hollow spheres possess the photoluminescence properties and a swelling and de-swelling at about 32°C, which agrees well with the slight red shift in photoluminescence spectra.

Near-field detected photoluminescence spectra of CdS0.65Se0.35 nanoribbon at room temperature

Ternary alloy CdS0.65Se0.35 nanoribbons were successfully grown by a one-step thermal evaporation. The nanoribbons obtained have high-quality single-crystalline nature. To understand the whole picture of waveguide behavior in CdS0.65Se0.35 nanoribbons, we quantitatively studied the guided photoluminescence (PL) through individual CdS0.65Se0.35 nanoribbon by using scanning near-field optical microscopy (SNOM) at room temperature. The results show significant sustained red shift of PL spectra of the CdS0.65Se0.35 nanoribbons optical waveguide with the increase of the light propagation distance. According to our analysis, the red shift is attributed to the absorption of band-tail of states in nanoribbons. This finding may be extended to other ternary nanosyotems and be useful for fabricating new subwavelength photonic components.

Effect of Hydrostatic Pressure on Photoluminescence Spectra from Structures with Si Nanocrystals Fabricated in SiO2Matrix

The effect of hydrostatic pressure applied at high temperature on photoluminescence of Si-implanted SiO 2 films was studied. A blue-shift of PL spectrum from the SiO 2 films implanted with Si + ions to total dose of 1.2× 10 1 7 cm - 2 with an increase in hydrostatic pressure was observed. For the films implanted with Si + ions to a total dose of 4.8 x 10 1 6 cm - 2 high temperature annealing under high hydrostatic pressure (12 kbar) causes a red-shift of photoluminescence spectrum. The red photoluminescence bands are attributed to Si nanocrystals while the blue ones are related to Si nanocrystals of reduced size or chains of silicon atoms or ≡Si-Si≡ defects. A decrease in size of Si nanocluster size occurs in result of the pressure-induced decrease in the diffusion of silicon atoms.

Low energy excitation of photoluminescence in a-Si:H : Temperature and intensity effects

Photoluminescence (PL) spectra from both glow discharge and sputtered a-Si:H are reported, excited with photons of energies between 2.4eV and 1.55eV. Low energy excitation produces a red shifted PL spectrum, which responds quite differently to changes of temperature compared with PL excited by above-gap photons. With rising temperature, the peak moves more slowly to lower energies, the efficiency falls less rapidly, and the kinetics are bimolecular even at the lowest excitation intensities. We compare two possible models to explain these effects, one based on a thermalisation gap and the other on two centre emission.