Increase In Photoluminescence Intensity Research Articles

Porous Quaternary Al0.1In0.1Ga0.8N Film Formation via Photoelectrochemical Etching in HF:C2H5OH Electrolyte

Pore formation in AlInGaN films using photoelectrochemical etching in different volume ratios of hydrofluoric acid:ethanol solution (1:1, 1:2, 1:3, and 1:4) has been investigated structurally, morphologically, and optically. A significant increase in root mean square roughness and photoluminescence intensity in AlInGaN film etched in 1:1 solution has yielded the highest pore density and the largest average pore size in the film. Moreover, the acquisition of the lowest total dislocation density as well as the largest in‐plane biaxial stress relaxation in the film suggested potential use of the porous film as a template to grow subsequent layers for development of light‐emitting diodes.

InGaN nanowires with high InN molar fraction: growth, structural and optical properties

The structural and optical properties of axial GaN/InGaN/GaN nanowire heterostructures with high InN molar fractions grown by molecular beam epitaxy have been studied at the nanoscale by a combination of electron microscopy, extended x-ray absorption fine structure and nano-cathodoluminescence techniques. InN molar fractions up to 50% have been successfully incorporated without extended defects, as evidence of nanowire potentialities for practical device realisation in such a composition range. Taking advantage of the N-polarity of the self-nucleated GaN NWs grown by molecular beam epitaxy on Si(111), the N-polar InGaN stability temperature diagram has been experimentally determined and found to extend to a higher temperature than its metal-polar counterpart. Furthermore, annealing of GaN-capped InGaN NWs up to 800 °C has been found to result in a 20 times increase of photoluminescence intensity, which is assigned to point defect curing.

Relationship between structural and optical properties of colloidal Cd x Zn 1 − x S quantum dots in gelatin

Aqueous synthesis of mixed cadmium and zinc sulfides colloidal quantum dots (QDs) has been successfully realized. Colloidal CdxZn1−xS QDs are formed in a cubic crystal lattice with particle size of ∼2 nm. The blueshift of optical absorption spectra from 420 to 295 nm and recombination photoluminescence from 646 to 483 nm with increasing zinc content in QDs was observed. Optimum photoluminescence intensity occurs for QDs with Cd0.3Zn0.7S composition. With increasing zinc content up to Cd0.3Zn0.7S, luminescence intensity increases and decreases when zinc content is larger than 0.7. The increase in photoluminescence intensity is explained by the increase in the number of point defects, such as complexes of interstitial metal atoms–metal vacancies [Mei−VMe]. Such complexes occur due to displacement of the metal atom at the center of the elementary tetrahedron due to substitution of one of the four sulfur atoms by an impurity atom, such as an oxygen atom.

Efficient Synthesis of Highly Photoluminescent Short Dendritic CdSeS/ZnS Quantum Dots for Biolabeling.

A convenient and efficient approach is reported to synthesize CdSeS with low-cost and low-toxic materials. The influence of the Se/S ratio and reaction time on the photoluminescent properties of CdSeS QDs is investigated through researching the temporal evolution of the absorption and the emission. Following, the high photoluminescent short dendritic green-emitting CdSeS/ZnS QDs are prepared using the method inspired by the successive ion layer adsorption and reaction procedure, which are composed of a CdSeS core and ZnS branches. Transmission electronic microscopy and X-ray diffraction show that the CdSeS/ZnS QDs is in a cubic zinc blende structure. The photoluminescence intensity increase significantly when the ZnS branches form as a result of the charge carriers being confined in the core. The photoluminescence quantum yield of the obtained CdSeS/ZnS core-shell QDs can be up to 90%, which is much higher than that of initial CdSeS QDs (39%). In addition, CdSeS/ZnS QDs have good photoluminescence intensity after they are transferred from organic solvent into aqueous media through ligand replacement using mercaptoacetic acid. Afterwards, the E. Coli O-157 are not only successfully conjugated with CdSeS/ZnS QDs but also present clear images under UV irradiation.

Role of C-N Configurations in the Photoluminescence of Graphene Quantum Dots Synthesized by a Hydrothermal Route.

Graphene quantum dots (GQDs) containing N atoms were successfully synthesized using a facile, inexpensive, and environmentally friendly hydrothermal reaction of urea and citric acid, and the effect of the GQDs’ C–N configurations on their photoluminescence (PL) properties were investigated. High-resolution transmission electron microscopy (HR-TEM) images confirmed that the dots were spherical, with an average diameter of 2.17 nm. X-ray photoelectron spectroscopy (XPS) analysis indicated that the C–N configurations of the GQDs substantially affected their PL intensity. Increased PL intensity was obtained in areas with greater percentages of pyridinic-N and lower percentages of pyrrolic-N. This enhanced PL was attributed to delocalized π electrons from pyridinic-N contributing to the C system of the GQDs. On the basis of energy electron loss spectroscopy (EELS) and UV-Vis spectroscopy analyses, we propose a PL mechanism for hydrothermally synthesized GQDs.

Influence of pluronic P123 in modifying the morphological and optical properties of PbS nanocomposite

Pluronic (P123) capped lead sulphide (PbS) nanoparticles were synthesized for the first time by simple wet chemical method. Series of experiments were conducted by changing the concentration of P123 to establish the most suitable conditions for obtaining different morphologies of PbS nanoparticles. The synthesized product has been characterized by powder X-ray diffraction (XRD), UV–Vis spectrophotometry, scanning electron microscopy (SEM), transmission electron Microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and photoluminescence studies. The particle size observed from XRD analysis is around 44–3 nm. Significant “blue shift” from bulk material was observed on the PbS nanoparticles using UV–Vis spectra. A sevenfold increase in photoluminescence intensity has been observed from PbS nanoparticles after surface passivation by P123 agent.

Simultaneous coupling of surface plasmon resonance and photonic bandgap to InGaAs quantum well emission

A photonic bandgap structure was created on the 100 nm thick GaAs barrier layer with Au nanodisks deposited inside the holes. To mitigate the nonradiative surface recombination of GaAs, the Au nanodisks were formed on top of a 15 nm SiO2 deposited in the holes. A maximum 7.6-fold increase in photoluminescence intensity was obtained at the etch depth of 80 nm. In this configuration, the Au nanodisk is separated from the quantum well by 20 nm of GaAs and 15 nm of SiO2. The experimental result was verified by the simulation based on this structure. There was a good agreement between experiments with simulation results.

Photoluminescence characterisations of a dynamic aging process of organic-inorganic CH3NH3PbBr3 perovskite.

After unprecedented development of organic-inorganic lead halide perovskite solar cells over the past few years, one of the biggest barriers towards their commercialization is the stability of the perovskite material. It is thus important to understand the interaction between the perovskite material and oxygen and/or humidity and the associated degradation process in order to improve device and encapsulation design for better durability. Here we characterize the dynamic aging process in vapour-assisted deposited (VASP) CH3NH3PbBr3 perovskite thin films using advanced optical techniques, such as time-resolved photoluminescence and fluorescence lifetime imaging microscopy (FLIM). Our investigation reveals that the perovskite grains grow spontaneously and the larger grains are formed at room temperature in the presence of moisture and oxygen. This crystallization process leads to a higher density of defects and a shorter carrier lifetime, specifically in the larger grains. Excitation-intensity-dependent steady-state photoluminescence shows both N2 stored and aged perovskite exhibit a super-linear increase of photoluminescence intensity with increasing excitation intensity; and the larger slope in aged sample suggests a larger density of defects is generated, consistent with time-resolved PL measurements.

Effect of hydrogen passivation on the photoluminescence of Tb ions in silicon rich silicon oxide films

In this work, silicon-rich silicon oxide films containing terbium were prepared by means of plasma enhanced chemical vapor deposition. The influence of hydrogen passivation on defects-mediated non-radiative recombination of excited Tb3+ ions was investigated by photoluminescence, photoluminescence excitation, and photoluminescence decay measurements. Passivation was found to have no effect on shape and spectral position of the excitation spectra. In contrast, a gradual increase in photoluminescence intensity and photoluminescence decay time was observed upon passivation for the main 5D4-7F5 transition of Tb3+ ions. This observation was attributed to passivation of non-radiative recombination defects centers with hydrogen. It was found that the number of emitted photons increases upon passivation as a result of two effects: (1) longer Tb3+ lifetime in the 5D4 excited state and (2) optical activation of new Tb3+ emitters. The obtained results were discussed and compared with other experimental reports.

Kinetics of self-induced nucleation and optical properties of GaN nanowires grown by plasma-assisted molecular beam epitaxy on amorphous AlxOy

Nucleation kinetics of GaN nanowires (NWs) by molecular beam epitaxy on amorphous AlxOy buffers deposited at low temperature by atomic layer deposition is analyzed. We found that the growth processes on a-AlxOy are very similar to those observed on standard Si(111) substrates, although the presence of the buffer significantly enhances nucleation rate of GaN NWs, which we attribute to a microstructure of the buffer. The nucleation rate was studied vs. the growth temperature in the range of 720–790 °C, which allowed determination of nucleation energy of the NWs on a-AlxOy equal to 6 eV. This value is smaller than 10.2 eV we found under the same conditions on nitridized Si(111) substrates. Optical properties of GaN NWs on a-AlxOy are analyzed as a function of the growth temperature and compared with those on Si(111) substrates. A significant increase of photoluminescence intensity and much longer PL decay times, close to those on silicon substrates, are found for NWs grown at the highest temperature proving their high quality. The samples grown at high temperature have very narrow PL lines. This allowed observation that positions of donor-bound exciton PL line in the NWs grown on a-AlxOy are regularly lower than in samples grown directly on silicon suggesting that oxygen, instead of silicon, is the dominant donor. Moreover, PL spectra suggest that total concentration of donors in GaN NWs grown on a-AlxOy is lower than in those grown under similar conditions on bare Si. This shows that the a-AlxOy buffer efficiently acts as a barrier preventing uptake of silicon from the substrate to GaN.

Coupling Behaviors of Surface Plasmon Polariton and Localized Surface Plasmon with an InGaN/GaN Quantum Well

Surface plasmon (SP) coupling behaviors of an InGaN/GaN quantum well (QW) with surface plasmon polariton (SPP) induced on a smooth Ag-film/GaN interface and localized surface plasmon (LSP) induced on randomly distributed surface Ag nanoparticles (NPs) are compared based on temperature-dependent, excitation power-dependent, and time-resolved photoluminescence (PL) measurements. By comparing the variations of PL excitation power-dependent emission at 10 and 300 K, the contribution of SP coupling to the increase of PL intensity can be differentiated from that of PL excitation-intensity increase at the QW due to the enhanced reflection at the Ag/GaN interface. The observed stronger SP coupling effect through SPP, when compared with that through LSP, is attributed to its larger available SP state number per unit area for coupling with the QW. Although the SP coupling strength through LSP on the surface Ag NPs is weakly dependent on PL excitation power, that through SPP at the smooth Ag-film/GaN interface increases significantly with PL excitation power. Such different behavior is due to the abundant SPP states available for coupling with the QW of a higher carrier density. It can also be attributed to the spectral blueshift of QW emission through the screening of the quantum-confined Stark effect and the band filling effect for QW coupling with SPP of a higher density of state.

Photophysical properties of phosphorescent elastomeric composite nanofibers

Phosphorescent elastomeric nanofibers were successfully prepared via electrospinning technique. Thermoplastic polyurethane (TPU) was used as carrier polymer, where copper doped zinc sulfide (ZnS:Cu) phosphorescent nanoparticles were incorporated at 0.5–2.0% concentrations. Scanning electron microscopy (SEM) analysis showed that particles were mostly embedded within TPU nanofibers. Average diameter of the neat TPU nanofibers was found to be around 246 ± 100 nm, which nearly doubled for 2.0% ZnS:Cu/TPU nanofibers. Optical properties of the nanofibers were analyzed via fluorescent spectrofluorophotometer. Fluorescence emission maximums around 460, 490, 515 and 530 nm were assigned to TPU, whereas phosphorescent emission obtained at wavelength 515 nm was due to ZnS:Cu particles. Elastomeric nanofibers might be stretched up to 30% of their initial length without deforming web structure, which is thought to be important for practical textile applications. Interestingly stretching up to 20% resulted with increase in photoluminescence (PL) lifetime and intensity which might be due to lesser shielding by carrier polymer.

Effect of annealing in the Sb and In distribution of type II GaAsSb-capped InAs quantum dots

Type II emission optoelectronic devices using GaAsSb strain reduction layers (SRL) over InAs quantum dots (QDs) have aroused great interest. Recent studies have demonstrated an extraordinary increase in photoluminescence (PL) intensity maintaining type II emission after a rapid thermal anneal (RTA), but with an undesirable blueshift. In this work, we have characterized the effect of RTA on InAs/GaAs QDs embedded in a SRL of GaAsSb by transmission electron microscopy (TEM) and finite element simulations. We find that annealing alters both the distribution of Sb in the SRL as well as the exchange of cations (In and Ga) between the QDs and the SRL. First, annealing causes modifications in the capping layer, reducing its thickness but maintaining the maximum Sb content and improving its homogeneity. In addition, the formation of Sb-rich clusters with loop dislocations is noticed, which seems not to be an impediment for an increased PL intensity. Second, RTA produces flatter QDs with larger base diameter and induces a more homogeneous QD height distribution. The Sb is accumulated over the QDs and the RTA enlarges the Sb-rich region, but the Sb contents are very similar. This fact leaves the type II alignment without major changes. Atomic-scale strain analysis of the nanostructures reveal a strong intermixing of In/Ga between the QDs and the capping layer, which is the main responsible mechanism of the PL blueshift. The improvement of the crystalline quality of the capping layer together with higher homogeneity QD sizes could be the origin of the enhancement of the PL emission.

The effect of the sulfide passivation on the luminescence of microdisk mesas with quantum wells and quantum dots

Sulphide passivation was used for reducing the surface recombination velocity of microdisk mesas based on (AlGaIn)As/GaAs heterostructures with active region formed either by ten GaAs/AlAs quantum wells or by 1 layer of InAs/In0.15Ga0.85As quantum dots. It was demonstrated that the sulfide passivation results in substantial increase of photoluminescence intensity in all types of the mesa-structures studied.

Synthesis and luminescence study of BaZrO3:Eu3+ phosphor

The phosphor of BaZrO3 doped with different concentration of Eu3+ ions (0.1, 0.5, 1 mol%) was prepared by solid–state reaction method. The prepared samples were characterized by X-ray diffraction (XRD), photoluminescence (PL) and thermoluminescence (TL) techniques. Analysis of XRD data shows the formation of perovskite structure of prepared phosphor. The room temperature excitation spectra vary with the Eu3+ concentration and consist of an intense charge transfer band and weak f–f transitions. The PL emission spectra, excited at 254 nm, consist of 4f–4f emission transitions from the 5D0 excited level of the Eu3+ ions to the 7FJ (J = 0–3) levels. The dependence of luminescence intensity on the Eu3+ concentration in BaZrO3:Eu3+ was studied. The present phosphor can act as single host for intense red emission for display devices application. Commission internationale de I'Eclairage techniques gives information about correlated color temperature and prominent emissions in PL emission spectra. Detail process and possible mechanism for PL and TL are studied and discussed in this paper. For the variable concentration of Eu3+ ions on PL studies shows the PL intensity increase with increasing the concentration of dopant. In TL glow curve the optimized concentration in 1 mol% for UV irradiated sample. The kinetic parameters were calculated by computerized glow curve deconvolution (CGCD) technique.

Quantum Confined Intense Red Luminescence from Large Area Monolithic Arrays of Mesoporous and Nanocrystal-Decorated Silicon Nanowires for Luminescent Devices

We report intense red luminescence from mesoporous n+-Si(100) nanowires (NWs) and nanocrystal-decorated p-Si NWs fabricated using electroless metal assisted chemical (MAC) etching. n+-Si NWs are composed of a labyrinthine network of silicon nanocrystals in a random mesoporous structure. p-type Si(100) NWs exhibit solid core structure, with a surface roughness that contains surface-bound nanocrystals. Both mesoporous n+-Si NWs and rough, solid p-Si NWs exhibit red luminescence at ∼1.7 and ∼1.8 eV, respectively. Time-resolved photoluminescence (PL) measurements indicated long (tens of μs) radiative recombination lifetimes. The red luminescence is visible with the naked eye and the red light is most intense from mesoporous n+-Si NWs, which exhibit a red-shift in the emission maximum to 1.76 eV at 100 K. The red PL from monolithic arrays of p-type NWs with nanocrystal-decorated rough surfaces is comparatively weak, but originates from the surface bound nanocrystals. Significant PL intensity increase is found during excitation for mesoporous NWs. X-ray photoelectron spectroscopy identifies a stoichiometric SiO2 on the rough p-Si NWs with a SiOx species at the NW surface. No distinct oxide is found on the mesoporous NWs. The analysis confirms that long life-time PL emission arises from quantum confinement from internal nanoscale crystallites, and oxidized surface-bound crystallites, on n+- and p-Si NWs respectively.

Investigation of temperature-dependent photoluminescence in multi-quantum wells.

Photoluminescence (PL) is a nondestructive and powerful method to investigate carrier recombination and transport characteristics in semiconductor materials. In this study, the temperature dependences of photoluminescence of GaAs-AlxGa1-xAs multi-quantum wells samples with and without p-n junction were measured under both resonant and non-resonant excitation modes. An obvious increase of photoluminescence(PL) intensity as the rising of temperature in low temperature range (T < 50 K), is observed only for GaAs-AlxGa1-xAs quantum wells sample with p-n junction under non-resonant excitation. The origin of the anomalous increase of integrated PL intensity proved to be associated with the enhancement of carrier drifting because of the increase of carrier mobility in the temperature range from 15 K to 100 K. For non-resonant excitation, carriers supplied from the barriers will influence the temperature dependence of integrated PL intensity of quantum wells, which makes the traditional methods to acquire photoluminescence characters from the temperature dependence of integrated PL intensity unavailable. For resonant excitation, carriers are generated only in the wells and the temperature dependence of integrated PL intensity is very suitable to analysis the photoluminescence characters of quantum wells.

Synthesis, optical and surface morphological properties of polyethylene glycol capped lead sulphide nanoparticles

The polyethylene glycol (PEG) capped lead sulphide (PbS) nanoparticles were successfully synthesized by simple wet chemical method. The synthesized product has been characterized by powder X-ray diffraction (XRD), UV–vis spectrophotometry, FTIR spectroscopy, transmission electron microscopy and photoluminescence studies. The size of the PEG capped PbS nanoparticles was determined from XRD and it is found that the size of the particles of the order of 43–4 nm. Significant “blue shift” from bulk material was observed on the PbS nanoparticles using UV–Vis and photoluminescence spectrum. A eightfold increase in photoluminescence intensity is reached at 6 g PEG addition.

Preparation and luminescence properties of Tb3+ activated microcrystalline ZrO2 green emitting phosphor for solid state lighting

The purpose of the present study is to develop an understanding of photoluminescence properties of Tb3+ activated ZrO2 green emitting phosphor which have served as efficient promising phosphor for solid state lighting. The phase formation, structure and morphology were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The photoluminescence properties were measured using Shimadzu RF 5301 at room temperature. Photoluminescence excitation spectrum measurements of ZrO2:Tb3+ show this phosphor may be efficiently excited by the UV–vis light region 300–400nm, i.e. 379nm and it exhibited strong green emission (545nm) emission corresponding to 5D4–7F5 transition of Tb3+. The incorporation of Tb3+ ions into ZrO2 lattice could induce a remarkable increase of photoluminescence intensity so the dependence of the emission intensity on the Tb3+ concentration for the host was also been studied. CIE chromaticity coordinates determined with the help of emission spectra of the prepared phosphor. TL glow curve can be analyzed for the determination of trapping parameter such as activation energy, order of kinetics and frequency factor. The strong and color-uniform fluorescence images of the Tb3+ activated samples confirmed the potential applications of the phosphors in solid state lighting.

Simultaneous ligand and cation exchange in PbSe/CdSe nanocrystal films

Trap states formed at the surface of colloidal semiconductor nanocrystals can have deleterious impact on performance in emerging optoelectronic applications. To mitigate surface traps in nanocrystal thin films we investigated simultaneous surface passivation and ligand exchange for PbSe nanocrystal films via treatment with a cadmium acetate solution. We show that a kinetically limited surface cation exchange produces a thin CdxPb1−xSe shell that effectively passivates the nanocrystal surface as confirmed by increased photoluminescence intensity and photoluminescence lifetime. Ligand exchange to acetate ligands is confirmed via Fourier transform infrared spectroscopy and grazing incidence small angle X-ray scattering. We studied the impact of the cadmium acetate treatment on interparticle coupling and found that the reduced interparticle spacing and limited shell thickness leads to increased Förster resonant energy transfer in nanocrystal films. Simultaneous cation/ligand exchange enables the production of heterostructured nanocrystal films with properties like Quasi-Type II nanocrystals synthesized in solution.