Aqueous Sulfur Passivation of N-Type GaSb Substrates Studied by Photoluminescence Spectroscopy

In this work the influence of aqueous sulfur passivation on the surface of n-type (100) GaSb single crystals has been studied through low-temperature photoluminescence (PL) characterization. The samples were passivated at different times using aqueous solutions of sodium sulfide. PL spectroscopy was used to determinate the optimum time of sulfur passivation, through the measurement of the PL intensity for the different passivation times. For the samples measured, the PL spectra show the presence of two emission bands, whose intensity and energy position change for the different passivation times of the GaSb samples. According to the PL results, a passivation surface treatment of 6 min shows the highest PL intensity spectrum.

Tip-enhanced photoluminescence spectroscopy of monolayer MoS_2

Probing the optical properties of molybdenum disulfide(MoS_2) is vital to its application in plasmon-enhanced spectroscopy, catalysts, sensing, and optoelectronic devices. In this paper, we theoretically studied the Raman and fluorescence properties of monolayer MoS_2 using tip-enhanced spectroscopy(TES). In the strong-coupling TES system, the Raman and fluorescence enhancement factors can be turned to as high as 4.5 × 10~8 and 3.3 × 10~3,respectively, by optimizing the tip–MoS_2-film distance. Our theoretical results not only help to deeply understand the TES properties of monolayer MoS_2, but also provide better guidance on the applications of the novel two-dimensional material.

Confocal photoluminescence characterization of silicon-vacancy color centers in 4H-SiC fabricated by a femtosecond laser

Silicon-vacancy(VSi)centers in silicon carbide(SiC)are expected to serve as solid qubits,which can be used in quantum computing and sensing.As a new controllable color center fabrication method,femtosecond(fs)laserwriting has been gradually applied in the preparation of VSi in SiC.In this study,4H-SiCwas directlywritten by an fs laser and characterized at 293 K by atomic force microscopy,confocal photoluminescence(PL),and Raman spectroscopy.PL signals of VSi were found and analyzed using 785 nm laser excitation by means of depth profiling and two-dimensional mapping.The influence of machining parameters on the VSi formation was analyzed,and the three-dimensional distribution of VSi defects in the fs laser writing of 4H-SiC was established.

On the origin of carrier localization in AlInAsSb digital alloy

We compared the photoluminescence(PL)properties of Al In As Sb digital alloy samples with different periods grown on Ga Sb(001)substrates by molecular beam epitaxy.Temperature-dependent S-shape behavior is observed and explained using a thermally activated redistribution model within a Gaussian distribution of localized states.There are two different mechanisms for the origin of the PL intensity quenching for the Al In As Sb digital alloy.The high-temperature activation energy E_(1)is positively correlated with the interface thickness,whereas the low-temperature activation energy E_(2)is negatively correlated with the interface thickness.A quantitative high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)study shows that the interface quality improves as the interface thickness increases.Our results confirm that E_(1)comes from carrier trapping at a state in the In Sb interface layer,while E_(2)originates from the exciton binding energy due to the roughness of the Al As interface layer.

Mg-doped ZnO radial spherical structures via chemical vapor deposition

Mg-doped ZnO radial spherical structures with nanorods grown on both sides of the spherical shell were successfully prepared via chemical vapor deposition （CVD） of Zn and Mg powders in the absence of a catalyst. The structures associated with different growth temperatures （700, 800, and 850°C） were monitored by scanning electron microscopy （SEM）, and the result shows that the length of the nanorods increase progressively with the growth temperature increasing. X-ray diffraction （XRD） shows that the as-obtained samples can be indexed to high crystallinity with wurtzite structure. The growth of the nanostructures mainly depends on the formation of sphere-like Mg-doped Zn droplets before adding oxygen. Photoluminescence （PL） spectra that show a 39 meV blue shift indicates that the band gap becomes large, because Mg substitutes Zn in the lattice.

Hydrothermal Synthesis,Crystal Structure and Fluorescence Spectrum Studies of a Novel Supramolecular Compound {[2-(2-Pyridyl)benzimidazoleH_2]_2·[BiCl_6]·Cl}

A novel supramolecular compound,{[2-（2-pyridyl）benzimidazoleH2]2·[BiCl6]·Cl},was synthesized by the hydrothermal reaction of o-phenylenediamine and α-pyridinecarboxylic acid with BiCl3 in 6.0 mol·L-1 HCl solution,and characterized by elemental analysis,IR,X-ray single-crystal diffraction and photoluminescence spectroscopy.The crystal （C24H22N6Cl7Bi,Mr= 851.61） belongs to the triclinic system,space group P1 with a =7.2887（18）,b =9.548（2）,c= 12.469（3）,α=85.306（4）,β=82.814（4）,γ=71.349（4）°,Z=1,V=814.9（3）3,Dc=1.735 g/cm3,μ（MoKα）=6.007 mm-1,F（000）=410,R=0.0307 and wR=0.0787.The bismuth ion and six chlorine ions construct a distorted octahedral configuration.The three-dimensional supramolecular network is built from electrostatic attractions,hydrogen bonds and π-π interaction between the BiCl6 anion,Cl anion and [2-（2-pyridyl）benzimidazoleH2] cation.The photoluminescence spectroscopy study shows that the title compound has a blue fluorescent emission at 450 nm in the solid state.

Energy Transfer and Electron Transfer in Composite System of Carbon Quantum Dots/Rhodamine B Molecules

In this work, we investigated the energy transfer (EnT) and electron transfer (ET) processes as well as their relationship in the carbon quantum dots/rhodamine B (CQDs/RhB) including o-CQDs/Rh B and m-CQDs/RhB systems by using photoluminescence spectroscopy in combination with steady-state and transient absorption spectroscopy. We found that the ET process is negligible in the o-CQDs/RhB system with an EnT efficiency as high as 73.2%,while it becomes pronounced in the m-CQDs/RhB system whose EnT efficiency is lower than 33.5%. Such an interplay of En T and ET processes revealed in the prototypical composite system consisting of carbon quantum dots and dye molecules would provide helpful insights for applications of relevance to exciton quenching.

Photoluminescence and Raman Spectroscopy Study on Color Centers of Helium Ion-Implanted 4H-SiC

Color centers in silicon carbide(SiC)are promising candidates for quantum technologies.However,the richness of the polytype and defect configuration of SiC makes the accurate control of the types and position of defects in SiC still challenging.In this study,helium ion-implanted 4H-SiC was characterized by atomic force microscopy(AFM),confocal photoluminescence(PL),and confocal Raman spectroscopy at room temperature.PL signals of silicon vacancy were found and analyzed using 638-nm and 785-nm laser excitation by means of depth profiling and SWIFT mapping.Lattice defects(C-C bond)were detected by continuous laser excitation at 532 nm and 638 nm,respectively.PL/Raman depth profiling was helpful in revealing the three-dimensional distribution of produced defects.Differences in the depth profiling results and SRIM simulation results were explained by considering the depth resolution of the confocal measurement setup,helium bubbles,as well as swelling.

Ce-Co-doped BiFeO_3 multiferroic for optoelectronic and photovoltaic applications

The Ce-Co-doped BiFeO3 multiferroic, Bi（1-x）Ce）xFe（1-x）CoxO3（x = 0.00, 0.01, 0.03, and 0.05）, has been prepared by a sol-gel auto-combustion method and analyzed through Raman spectroscopy, photoluminescence, and UV-visible spectroscopy. We have observed an anomalous intensity of the second-order Raman mode at - 1260 cm^-1 in pure BFO and suppressed intensity in doped samples, which indicates the presence of spin two-phonon coupling in these samples.The photoluminescence spectra show reduction in the intensity of emission with the increasing dopant concentration, which indicates the high charge separation efficiency. A sharp absorption with three charge transfer（C-T） and two d-d transitions are shown by UV-visible spectra in the visible region. The band gap of BiFeO3（BFO） is decreasing with increasing dopant concentrations and the materials are suitable for photovoltaic applications.

Universal,predominant exciton transfer in perovskite nanocrystal solids

Perovskite nanocrystal(PNC)solids are promising materials for optoelectronic applications.Recent studies have shown that exciton diffusion in PNC solids occurs via alternate exciton hopping(EH)and photon recycling(PR).The energy disorder induced by the size distribution is a common factor in PNC solids,and the impact of this energy disorder on the exciton diffusion remains unclear.Here,we investigated the exciton diffusion in CsPbBr3 NC solids with a Gaussian size distribution of 11.2±6.8 nm via steady and time-resolved photoluminescence(PL)spectroscopy with multiple detection bands in transmission mode.Our results indicated that exciton diffusion was controlled by a downhill transfer among the different energy sites through the disordered energy landscape,as confirmed by the accompanying low-temperature PL analysis.A detailed examination revealed that the acceptor distribution in tandem with the reabsorption coefficient determined the contribution of EH and PR to exciton transfer between different energy sites.Consequently,the exciton diffusion mechanism varied in PNC solids of different thicknesses:in a thin solid with a thickness of several hundred nanometers,the exciton transfer was dominated by efficient EH and PR from the high-energy sites to the lower-energy sites;in a few-micrometer-thick solid,transfer from the medium-energy sites toward the lower-energy sites also became prominent and occurred mainly through PR.These findings enhance the understanding of the vital role that the acceptor distribution plays in the exciton diffusion process in PNC solids,providing important insights for optoelectronic applications based on PNC solids.Our work also exploits the use of commonly available tools for in-depth exciton diffusion studies,which reveals the interior diffusion information that is usually hidden in surface sensitive PL imaging methods.

Synthesis of CdTe Quantum Dots with Tunable Photoluminescence Using Tellurium Dioxide as Tellurium Source

A simple and convenient method has been developed for synthesis of water-soluble CdTe quantum dots （QDs） under ambient atmospheric conditions. In contrast to the traditional aqueous synthesis, green to red emitting CdTe QDs were prepared by using TeO2 to replace Te or AIzTe3 as tellurium source in this method. The influences of ex- perimental variables, including pH value, 3-mercaptopropionic acid （MPA）/Cd and Te/Cd molar ratios, on the emis- sion peak and photoluminescence （PL） quantum yield （QY） of the obtained CdTe QDs have been systematically investigated. Experimental results indicate that green to red emitting CdTe QDs with a maximum photolumines- cence quantum yield of 35.4% can be prepared at pH 11.3 and rt（Cd） ： n（Te） ： n（MPA）= 1 ： 0.1 ： 1.7.

Silicon Vacancy Color Centers in 6H-SiC Fabricated by Femtosecond Laser Direct Writing

As a single photon source,silicon vacancy(V_(Si))centers in wide bandgap semiconductor silicon carbide(SiC)are expected to be used in quantum technology as spin qubits to participate in quantum sensing and quantum computing.Simultaneously,the new direct femtosecond(fs)laser writing technology has been successfully applied to preparing V_(Si)s in SiC.In this study,6H-SiC,which has been less studied,was used as the processed material.V_(Si) center arrays were formed on the 6H-SiC surface using a 1030-nm-wavelength fs pulsed laser.The surface was characterized by white light microscopy,atomic force microscopy,and confocal photoluminescence(PL)/Raman spectrometry.The effect of fs laser energy,vector polarization,pulse number,and repetition rate on 6H-SiC V_(Si) defect preparation was analyzed by measuring the V_(Si) PL signal at 785-nm laser excitation.The results show that fs laser energy and pulse number greatly influence the preparation of the color center,which plays a key role in optimizing the yield of V_(Si)s prepared by fs laser nanomachining.

Preparation and characterization of CeO_2 doped ZnO nano-tubes fluorescent composite

ZnO nanotubes were hydrothermally synthesized and the ZNTs/CeO2 fluorescent composite were prepared by introducing nano CeO2 particles into ZnO nano-tubes via a chemical solution adsorption and annealing process. The samples were characterized by X-ray diffraction, scanning electron microscopy, Fourier transformation infrared spectroscopy and room temperature photoluminescence measurement. Due to the interaction between Ce4+ and the surface atoms of ZnO2 nano-tubes, a photoluminescence enhancement was obser...

Synthesis and electroluminescence properties of tris-[5-choloro-8-hydroxyquinoline]aluminum Al(5-Clq)_3

A new electroluminescent material tris- [5-choloro-8-hydroxyquinoline] aluminum has been synthesized and characterized. Solution of this material AI（5-Clq）3 in toluene showed absorption maxima at 385 nm which was attributed to the moderate energy （π-π＊） transitions of the aromatic rings. The photoluminescence spectrum of AI（5-Clq）3 in toluene solution showed a peak at 522 nm. This material shows thermal stability up to 400 ℃. The structure of the device is ITO/0.4 wt%F4-TCNQ doped α-NPD （35 nm） / AI（5-Clq）3 （30 nm） / BCP （6 nm）/ Alq3 （30 nm） / LiF （1 nm） / A1 （150 nm）. This device exhibited a luminescence peak at 585 nm （CIE coordinates, x = 0.39, y = 0.50）. The maximum luminescence of the device was 920 Cd/m2 at 25 V. The maximum current efficiency of OLED was 0.27 Cd/A at 20 V and maximum power efficiency was 0.04 lm/W at 18 V.

Synthesis and electroluminescence characterization of a new aluminum complex, [8- hydroxyquinoline] bis [2, 2＇bipyridine] aluminum Al(Bpy)2q

We have synthesized and characterized a new electroluminescent material, [8-hydroxyquinoline] bis[2,2＇bipyridine] aluminum. A solution of this material Al（Bpy）2q in toluene showed absorption maxima at 380 nm,which was attributed to the moderate energy（ π–π＊） transitions of the aromatic rings. The photoluminescence spectrum of Al（Bpy）_2q in the toluene solution showed a peak at 518 nm. This material shows thermal stability up to300 ℃. The structure of the device is ITO/F4-TCNQ（1 nm）/α-NPD（35 nm）/Al（Bpy）2q（35 nm）/ BCP（6 nm）/Alq3（28 nm）/Li F（1 nm）/Al（150 nm）. This device exhibited a luminescence peak at 515 nm（CIE coordinates, xD0.32,yD0.49）. The maximum luminescence of the device was 214 cd/m^2 at 21 V. The maximum current efficiency of OLED was 0.12 cd/A at 13 V and the maximum power efficiency was 0.03 lm/W at 10 V.

Enhanced near infrared emission in water-soluble NdF_3 nanocrystals by Ba^(2+) doping

A simple and efficient method for the synthesis of water-soluble NdF3 and NdF3：Ba^2＋ nanocrystals under hydrothermal conditions is established. The method involves the coating of the nanocrystals with a layer of hydrophilic polymer polyvinylpyrrolidone （PVP）. The as-prepared products are characterized by powder X-ray diffraction, field emission scanning electronic microscopy, Fourier transform infrared spectroscopy, and photoluminescence spectroscopy. The PVP coating transforms the nanocrystals into a biocompatible material and improves the fluorescence intensity of NdF3 in the near infrared （NIR） region. The morphology of the nanoparticles changes, whereas the fluorescence intensity of NdF3 in the NIR region increases when a small amount of Ba^2＋ is doped into the NdF3/PVP nanoparticles.

Effect of Preparation Conditions on the Crystallinity of Chemically Synthesized BCNO Nanophosphor

The carbon based boron oxynitride （BCNO） phosphor was synthesized by solid state reaction between boric acid （H3BO3） and melamine （C3H6N6） in the molar ratios of 1：1 and 2：1 respectively at different temperatures up to 1400℃. The composition with molar ratios 1：1 of starting materials is found to be highly crystalline with an average particle size of 38 nm and the lattice constants a=b=0.251 nm and c=0.666 nm. The solid state reaction of boric acid and melamine in the composition 2：1 leads to the formation of compound in the semi-crystalline state under the same conditions of preparation, but its phase cannot be recognised. The X-ray diffraction （XRD） spectra, transmission electron microscopy （TEM） and scanning electron microscopy （SEM） images of BCNO compound confirm the phase, nanometre size and shape respectively of synthesized material. The photoluminescence （PL） spectra of the synthesized BCNO products reveals that the electronic structure of BCNO compound can be controlled by changing the molar ratios of starting materials and heating temperatures. These synthesized compounds are very interesting and important candidate materials for light emitter.

Luminescent polymer electrolytes based on chitosan and containing europium triflate

Solid polymer electrolytes based on chitosan and europium triflate were prepared by solvent casting and characterized by X-ray diffraction, scanning electron microscopy （SEM）, atomic force microscopy （AFM）, and photoluminescence spectroscopy. The X-ray diffraction exhibited that the samples were essentially amorphous with organized regions over the whole range of the salt content studied. The AFM analysis demonstrated that the smoother sample had roughness of 4.39 nm. Surface visualization through SEM revealed good homogeneity without any phase separation for more conductive samples and the less conductive showed some im- perfections on the surface. The emission and excitation spectra displayed the characteristic bands of Eu（CF3SO3）3 in addition to broad bands corresponding to the polymer host. The excited state 5D0 lifetime values ranged from 0.29-0.37 ms for the studied samples.

Fabrication of single-crystalline ZnSe multipod-based structures

ZnSe multipod-based structures,including tetrapod-like microrods,long microwires,and short nanorods,are selectively prepared by atmospheric pressure thermal evaporation of ZnSe nanoparticles without using any catalyst.The morphologies could be well controlled by simply adjusting the deposition position.The phase structures,morphologies,and optical properties of the products are investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM),high-resolution transmission electron microscopy(TEM),and photoluminescence(PL) spectroscopy.A vapor-liquid mechanism is proposed for the formation of ZnSe multipod-based structures.The presented route is expected to be applied to the synthesis of other Ⅱ-Ⅵ groups or other group's semiconductor materials with controllable morphologies.

Optical and electrical properties of blue-light polyfluorence/porous silicon composites

Optical and electrical properties of composites formed by mixing porous silicon （PS） and poly （9, 9- diocty-2, 7-fluorene- co-4, 4＇-butoxydiphenyl） （PFP） have been studied by Fourier transform-infrared spectroscopy （FT-IR）, scanning electron microscopy （SEM） and photoluminescence （PL） spectroscopy. The optical spectra show that porous silicon is incorporated into the polymer without significant change in the polymer properties. The FT-IR spectroscopy has detected the existence of specific interactions, which may be attributed to non-conjugated alkoxy segment. By fitting the current-voltage （/-V） curve of PFP/PS structure with the modified standard ecluation, the n factor and I0 are cletermined