Strong Red Band Research Articles

Preparation and optical properties of sulfur-doped silicon oxide microbelts and microrods

Amorphous S-doped and non-doped silicon oxide (SiO 2 ) one-dimensional structures with various morphologies are synthesized on Si substrates by vapor deposition with Ag 2 S as the precursor in a horizontal tube furnace. Curved microwires, grass-like microwires, S-doped microbelts, and straight S-doped microrods are obtained at the downstream of the furnace with different deposition temperatures in sequence. The microwires and microbelts are formed by the direct vapor-solid mechanism. The morphologies of microwires are largely determined by the inherent isotropy of their amorphous structure and the competitive growth in vapor phase. The microbelts are formed by the lateral growth of small microwires and the doped S played a critical role in their formation. However, the Ag–Si–S–O nanoparticles located at the growth ends suggests that the formation of S-doped SiO 2 microrods should be controlled by the vapor-liquid-solid mechanism. Both curved and grass-like microwires have similar photoluminescence behavior with strong blue/green/yellow bands and weak violent/red bands. However, S-doped microbelts exhibit strong violet/blue bands and relative strong a red band, and S-doped microrods exhibit low violet/blue bands and a strong red band. The obvious shifts in the intensities and wavelengths of the violet/blue/yellow bands are attributed to the morphology/size effects of microwires and microbelts, while the improved red-light emission is assigned to the doped S in microbelts and microrods. • S-doped SiO 2 nanobelts and nanorods are synthesized by vapor deposition. • S-doped SiO 2 nanobelts and nanorods are twist-free and straight. • Doped S determines the formation and morphology of the nanobelts. • Doped S can tune the optical properties of the nanobelts and nanorods.

Evaluating Street Lighting Quality in Residential Areas by Combining Remote Sensing Tools and a Survey on Pedestrians’ Perceptions of Safety and Visual Comfort

The perceived quality of street lighting influences pedestrians’ perceptions of safety and visual comfort, as well as outdoors activities at night. This study explores the association between street lighting attributes, such as illuminance and wavelength, and pedestrians’ feeling of safety (FoS) and perceived lighting quality (PLQ) in eight residential districts in Dalian, China. To achieve this goal, we combine remote sensing technology with ground investigation. The ground research includes physical measurements of lighting attributes, such as intensity, color temperature, and glare, as well as survey evaluations of pedestrians’ perceptions of safety and visual comfort. We also analyze the influence of several environmental factors, such as traffic volumes and vegetation, while accounting for personal characteristics of the observers, such as gender and age. Findings from the remote sensing reveal that Dalian’s residential districts differ substantially by their nighttime light emissions, with high concentration of strong red band (i.e., long wavelength) emissions occurring in Zhongshan and Jinzhou, and strong blue band (i.e., short wavelength) emissions found in central Zhongshan. Results from the ground surveys further indicate that a satisfactory level of FoS reaches at the illumination levels of 5–17 lx, and that people feel safer if nighttime light is warm and uniform. From a multiple regression analysis, it is also found that illuminance and uniformity are the main factors affecting PLQ under conditions of low or high illuminance, while glare and color temperature play a more significant role under high illuminance. In addition, a satisfactory level of PLQ is found at illuminance levels of 25–35 lx and light color temperature of 4000 K–5500 K.

Structural and Enhanced Optical Properties of Stabilized γ‒Bi2O3 Nanoparticles: Effect of Oxygen Ion Vacancies.

We report the synthesis of room temperature (RT) stabilized γ–Bi2O3 nanoparticles (NPs) at the expense of metallic Bi NPs through annealing in an ambient atmosphere. RT stability of the metastable γ–Bi2O3 NPs is confirmed using synchrotron radiation powder X-ray diffraction and Raman spectroscopy. γ–Bi2O3 NPs exhibited a strong red-band emission peaking at ~701 nm, covering 81% integrated intensity of photoluminescence spectra. Our findings suggest that the RT stabilization and enhanced red-band emission of γ‒Bi2O3 is mediated by excess oxygen ion vacancies generated at the octahedral O(2) sites during the annealing process.

Molecular cytogenetic characterization and phylogenetic analysis of four Miscanthus species (Poaceae).

Chromosomes of four Miscanthus (Andersson, 1855) species including M. sinensis (Andersson, 1855), M. floridulus (Schumann & Lauterb, 1901), M. sacchariflorus (Hackel, 1882) and M. lutarioriparius (Chen & Renvoize, 2005) were analyzed using sequentially combined PI and DAPI (CPD) staining and fluorescence in situ hybridization (FISH) with 45S rDNA probe. To elucidate the phylogenetic relationship among the four Miscanthus species, the homology of repetitive sequences among the four species was analyzed by comparative genomic in situ hybridization (cGISH). Subsequently four Miscanthus species were clustered based on the internal transcribed spacer (ITS) of 45S rDNA. Molecular cytogenetic karyotypes of the four Miscanthus species were established for the first time using chromosome measurements, fluorochrome bands and 45S rDNA FISH signals, which will provide a cytogenetic tool for the identification of these four species. All the four have the karyotype formula of Miscanthus species, which is 2n = 2x = 38 = 34m(2SAT) + 4sm, and one pair of 45S rDNA sites. The latter were shown as strong red bands by CPD staining. A non-rDNA CPD band emerged in M. floridulus and some blue DAPI bands appeared in M. sinensis and M. floridulus. The hybridization signals of M. floridulus genomic DNA to the chromosomes of M. sinensis and M. lutarioriparius genomic DNA to the chromosomes of M. sacchariflorus were stronger and more evenly distributed than other combinations. Molecular phylogenetic trees showed that M. sinensis and M. floridulus were closest relatives, and M. sacchariflorus and M. lutarioriparius were also closely related. These findings were consistent with the phylogenetic relationships inferred from the cGISH patterns.

Bright red upconversion luminescence from Er3+ and Yb3+ co-doped ZnO-TiO2 composite phosphor powder

Abstract ZnO-TiO2 composites co-doped with Er3+ and Yb3+ ions were successfully synthesized by powder-solution mixing method and their upconversion (UC) luminescence was evaluated. The effect of firing temperature, ZnO/TiO2 mixing ratio, and dopant concentration ranges on structural and UC luminescence properties was investigated. The crystal structure of the product was studied and calculated in detail by means of X-ray diffraction (XRD). Also, the site preference of Er3+ and Yb3+ ions in the host material was considered and analyzed based on XRD results and UC luminescence characteristics. Brightest UC luminescence was observed in the ZnO-TiO2:Er3+,Yb3+ phosphor fired at 1300 °C in which the system consisted of mixed phases; Zn2TiO4, TiO2, RE2Ti2O7 and RE2TiO5 (RE = Er3+ and/or Yb3+). Under the excitation of a 980 nm laser, the two emission bands were detected in the UC emission spectrum, weak green band centered at 544 and 559 nm, and strong red band centered at 657 and 675 nm wavelengths in accordance with 2H11/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ ion, respectively. The simple chemical formula equations, for explaining the site preference of Er3+ and Yb3+ ions in host crystal matrix, were generated by considering the Zn2TiO4 crystal structure, its crystal properties, and the effect of Er3+ and Yb3+ ions to the host crystal matrix. The UC emission intensity of the products was changed by varying ZnO/TiO2 mixing ratios, and Er3+ and Yb3+ concentrations. The best suitable condition for emitting the brightest UC emission was 1ZnO:1TiO2 doped with 3 mol% Er3+, 9 mol% Yb3+ fired at 1300 °C for 1 h.

Switching green to red emission in tridoped ZrO2:Yb3+–Er3+–Bi3+ nanocrystals

Tridoped ZrO2:Yb3+–Er3+–Bi3+ nanophosphor was synthesized by hydrothermal process and demonstrated the possibility of switching from a strong green–yellow broadband signal to red emission due to Bi3+ and Er3+ ion by changing excitation from 350nm to 970nm, respectively. The green–yellow band is associated to the transition 3P1→1S0 and was overlapped with the green band associated to the transition 2H11/2+4S3/2→4I15/2 of Er3+ as a result of the energy transfer from Bi3+ to Er3+. The strong red band is associated to 4F9/2→4I15/2 transition of Er3+ and enhanced by a factor of 3 as a result of the forward and backward energy transfer process (Er3+→Bi3+→Er3+). This sink effect where electrons can be stored temporally and released back can be useful to enhance the emitted signal of other lanthanides.

Effects of organic moieties on the photoluminescence spectra of perovskite-type tin bromide based compounds

The photoluminescence (PL) and optical absorption (OA) spectra of some compounds of the type (SC)SnBr3, (BC)2SnBr4, and (SC)(BC)2Sn2Br7 (where SC is CH3NH3+ or Cs+; BC is C4H9NH3+,CH3C6H4CH2NH3+,C12H25NH3+,C18H37NH3+ and 1-naphthylmethyl ammonium group), in the forms of thin deposits on several substrates, are investigated. Generally, using the 350nm as excitation line, the obtained PL spectra of compounds of the type (BC)2SnBr4 with short alkyl chain-length in the alkyl ammonium moiety, show broad and strong bands. For example, the PL spectra of compound (C4H9NH3)2SnBr4 exhibit a weak band at ca 475nm, attributed to free-excitons and a broad and strong band at ca 570 nm, attributed to radiative decay of self-trapped excitons in the inorganic moiety. This is a bright yellow-orange emission, which can be seen by naked eye, even at room temperature. In the case of the compounds with long alkyl chain-length in the alkyl ammonium moiety, the PL spectra are dominated by an excitonic band, which occurs close to the corresponding fundamental OA edge. The PL spectrum of (1-naphthylmethyl ammonium)2SnBr4 shows the strong red band with main maxima at ca 603 and 642nm, arising from tetramers of naphthyl moieties. Also, the PL spectra of the compounds of the type (SC)SnBr3 and (SC)(BC)2Sn2Br7, after grinding, show strong bands at 600–620nm.

Spectroscopy of Protonated Tetraphenylporphyrins with Amino/Carbomethoxy Substituents: Hyperporphyrin Effects and Evidence for a Monoprotonated Porphyrin

Spectrophotometric titrations for a full series of para-amino/carbomethoxy-substituted tetraphenylporphyrins were carried out using methanesulfonic acid in DMSO to study the hyperporphyrin effect across different substitution patterns. The series included zero, one, two (cis and trans), three, and four amino groups, with the remaining para substituents carbomethoxy groups. With increasing numbers of aminophenyl groups, the relative basicity increased and the hyperporphyrin effect increased, marked by a strong red band and a split Soret band. The cis diamino derivative showed a stronger hyperporphyrin effect compared to the trans isomer, which can be explained based on simple resonance forms. For the monoamino derivative, an initial increase in the Soret band upon acid titration along with well-defined isosbestic points provided evidence for a monoprotonated porphyrin, distinct from the diprotonated and triprotonated states. The relative stability of this unusual intermediate is proposed to be due to charge delocalization of the first cation to the single amino group and destabilization of the second protonation by the electron-withdrawing carbomethoxy substituents.

Avoiding trap states in poly(n-vinylcarbazole) thin films

Optical properties of poly(n-vinylcarbazole) (PVK) thin films are revisited. Steady-state emission spectra put in evidence a strong red band whose intensity increases with decreasing temperature when the solid state PVK film is excited by a continuous 375nm laser line. This red band is assigned to the emission from PVK aggregate states which act as trap states for the monomeric PVK triplet high energy (blue) excitons. At the same low temperatures, these trap states can be avoided when the excitation of the PVK film is made by a 355nm pulsed laser line with 10Hz repetition rate. The red band was also observed to compete with the emission of guest poly(3-octadecylthiophene) (PODT) molecules in a PVK/PODT sequential bilayer structure. Different optical geometries enabled us to show that the exciton energy transfer effect from PVK donor to PODT acceptor states dominates the scenario in the bilayer structure, suppressing almost completely the trap state emissions.

Non-linear photoluminescence from purified aqueous PbS nanocrystals

A simple and effective method for purifying photoluminescent water-soluble surface passivated PbS nanocrystals has been developed. Centrifuging at high speeds removes PbS nanocrystals that exhibit strong red band edge photoluminescence from an original solution containing multiple nanocrystalline species with broad photoluminescence spectra. The ability to purify the PbS nanocrystals allowed two-photon photoluminescence spectroscopy to be performed on water-soluble PbS nanocrystals and be attributed to band edge recombination.

The synthesis of one-dimensional controllable ZnO microrods

Various morphology ZnO submicrorods and microrods have been fabricated onto glass substrates through chemical solution growth by the source of zinc acetate (Zn(CH3COO)2.2H2O) and hexamethylene tetraamine ((CH2)6N4). We discuss the influence of PH and the concentration of the solution on the shapes of the as-synthesized ZnO samples. And analyse the growth mechanism. The regular hexagonal ZnO rods align has been made by control of a certain concentration and proper PH. The hexagonal ZnO columns mainly grew in the [002] direction. X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) are used to characterize the structure, the morphology and optical property of the samples. The photoluminescence spectrum of hexagonal ZnO columns shows that there are a broad strong red band (650nm) and a broad band in short wavelength which are two overlapped emission bands with the peaks at about 380nm and 430nm.The UV emission (~387nm) comes from recombination of free excitons. The blue emission with peak at 430nm is assigned for the recombination from an electron at interstitial Zn to a hole in VB. The red emission at 650nm is ascribed to the recombination from an electron at Vo2+ to a hole in VB.

Copper‐Activated Zinc Sulfide Phosphors with Yellow and Red Emission

Hexagonal, phosphors prepared with 0.05 to 1 per cent Cu are characterized by a yellow‐red luminescent emission obtained with ultraviolet, cathode ray, x‐ray, and electroluminescent excitation as well as with infrared stimulation. Peaked at 6500 Å, the emission is shown to consist of two bands, a strong red band at 6700 Å and a weaker yellow band at 5800 Å. The intensity of the yellow band declines toward zero at −196°C, while the red band increases in intensity and moves toward longer wave lengths. With electroluminescent excitation, the yellow‐red emission persists without changing to blue over the frequency range of 60 to 15000 cps.Washed with solution to remove excess free copper sulfide, the phosphors retain only a certain percentage of the amount of Cu originally added. The amount of retained Cu is one or two orders of magnitude larger than in conventional phosphors, indicating a limit of solubility near 0.3 per cent Cu. The incorporation of Cu into the lattice must be explained without benefit of charge compensating ions. To account for the double band emission and the infrared stimulability, the presence of two species of Cu atoms may be assumed.