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Porous silicon light-emitting diodes were found to emit strong line-shaped ultraviolet under a forward bias driving voltage of about 20 volts. The intensity was sufficiently strong to pump an organic crystal, Tb-dipicolinic acid, producing clear Tb 4f intra-shell transition photoluminescence spectrum. The current-voltage characteristics of the devices also showed negative differential resistance, which was frequency dependent. In addition, purging of the device with various gases could quench the electroluminescence but the intensity recovered partially after each purging, but with no change in emission spectrum. Both results indicate the transport was influenced strongly by local space charge. From the results, the electroluminescence mechanism is tentatively attributed to core recombination in the porous layer, and the spectral characteristics is due to the microcavity effect between the top Au contact and silicon substrate. The present study shows that porous silicon has the potential as UV source in optoelectronics applications.
We have carried out an investigation of the electro-chemical doping (ECD) of porous silicon (PS) with rare earth elements, especially Er was chosen for the main doping element in our work. Under certain conditions, after doping a blue shift was shown in the visible range photoluminescence (PL), and enhancement of PL intensity was observed. We address this that the impurity states in forbidden gap increase the optical probability of trapping carriers and the optical transition probability. Moreover, in the Infrared (IR) range, luminescence is observed around 1.54μm at room temperature and is assigned to the optical transitions from intra-4f energy levels of Er3+. X-ray Photo-electronic Spectroscopy (XPS) showed that at least 3 atomic percen of the rare earth element has been incorporated into porous silicon layer. In conclusion, by choosing suitable electrolyte, we successfully doped rare earth elements into porous silicon by electro-chemical method.
The electron emission switching property of the multilayer structures, which constitute of nitrogen doped tetrahedral amorphous carbon (n+-ta-C) film and intrinsic ta-C layer fabricated by the filtered cathodic vacuum arc (FCVA) technique has been investigated. Low voltage DC bias (9V) was applied between the top and bottom layers in conjunction with the conventional electric field applied between the cathode and anode. It has been demonstrated that by varying the low DC bias polarity, the on-set electric field for the electron emission can be varied by ∼ ±6 V/μm compared to the unbiased situation. A possible mechanism for the multilayer field emission and the switching property is proposed.
Olivine (LiFePO4)-carbon nanofibre composites were synthesized through a combination of electrospinning and solvothermal methods. Morphology, distribution and crystal structure of these composites were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Electrochemical properties of synthesized LiFePO4-carbon fibre composite cathodes have been studied in litium ion coin cells by means of galvanostatic cycling and cyclic voltammetry. As compared to pristine LiFePO4, there was significant improvement in the specific capacity (˜25% at 0.1C rate) of LiFePO4 - ECNF owing to the improved conductivity.
Photonic microcavity promises to be one of the photonic devices that can have immediate applications such as super bright LED and low threshold laser. Most photonic crystal structures currently used on microcavity are cubic or hexagonal, whose folding symmetry is no greater than 6. In this work, we fabricated 2-D photonic microcavity with Penrose quasicrystal pattern and measured the angular resolved transmission and photoluminescence spectra of the microcacity. From the experimental result it is found that isotropic photonic band gap exists in the microcavity with the Penrose quasicrystal pattern.
In this work, we fabricated near-infrared emitting MOLEDs with two organic layers. The hole transporting layer was N, N′ – di(naphthalene-1-yl) - N,N′- diphenylbenzidine (NPB), while tris(8-hydroxyquinoline) aluminum (Alq) was the emissive and electron transporting layer. The bilayer structure was sandwiched between two silver mirrors. In order to investigate the influence of cavity Q-factor to the emission spectra, devices with different thickness of bottom mirror (anode) were fabricated. The influence of the choice of the bottom mirror (anode) was also investigated, and the devices with copper anode were also fabricated. The devices were characterized by angular dependent electroluminescence, photoluminescence, and transmittance measurements. Possible origins of the observed phenomena are discussed.
A hexagonal lattice photonic crystal was fabricated inside the metallic microcavity. And a thin film of Alq3 was incorporated inside the textured cavity as an active medium. The microcavity is designed such that the modified photonic modes due to the textured structure can couple to the excited electronic states of Alq3. This leads to changes in the emission characteristics of Alq3. From the angle-resolved transmission (ARTR) results, the photonic bandgap was observed at all angles from normal incident to 60°. The presence of surface plasmon (SP) was observed in both TM and TE modes of the transmission. Compare to the bulk Alq3 photoluminescence spectrum, significant modification of the photoluminescence (PL) spectrum was observed in the angle-resolved photoluminescence (ARPL). The photoluminescence spectra showed clear suppression in luminescence intensity for the range inside the photonic bandgap. We use decouple approximation for the standing wave modes and derive the photonic waveguide characteristics for two-dimensional textured metallic microcavities. The theoretical result is in good agreement to the experimental result.
(1) To present a rare case of stridor secondary to prolonged laryngospasm in a patient with Parkinson's disease, and (2) to review the literature on stridor in Parkinson's disease.
We report a 73-year-old Parkinson's disease patient who developed acute stridor due to prolonged laryngospasm triggered by overspill of excessive secretions. The literature was reviewed, following a Medline search using the keywords ‘Parkinson's disease’ and ‘stridor’ or ‘airway obstruction’ or ‘laryngospasm’ or ‘laryngeal dystonia’ or ‘bilateral vocal cord palsy’.
Only 12 previously reported cases of stridor in Parkinson's disease patients were identified. Causes included bilateral vocal fold palsy (eight cases), laryngospasm (five), and dystonia of the jaw and neck muscles (two). The mechanism of laryngospasm in our patient was similar to ‘dry drowning’, and has not previously been described.
Laryngospasm can be triggered in Parkinson's disease by excessive secretions entering the larynx. The mechanism is similar to ‘dry drowning’. Treatment focuses on reducing secretions. The use of botulinum toxin to reduce spasm is inappropriate in this situation. This case emphasises the importance of recognising different causes of stridor in Parkinson's disease patients, as this affects management.
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