Results Of Photoluminescence Measurements Research Articles

Dilute GaAs1−xBix epilayers with different bismuth concentrations grown by Molecular Beam Epitaxy: A promising candidate for gamma radiation sensor applications

Radiation interaction studies are very important for exploring the technological applications of new materials in radiation environments. This work reports the effect of gamma radiation dose on the structural and optical properties of dilute GaAs1−xBix epitaxial layers grown with different Bismuth contents by MBE on (100) GaAs substrates. The influence of radiation has been studied by X-Ray Diffraction (XRD), Raman spectroscopy, and photoluminescence (PL) measurements. The samples were also characterized by Scanning Transmission Electron Microscopy (STEM) and Scanning Electron Microscopy (SEM. Gamma radiation (γ-) was found to influence the optical properties of GaAs1−xBix epitaxial layers. From Raman measurements it was found that the concentration of holes increased when the samples were irradiated. This result is in good agreement with photoluminescence results, which showed that the intensity of the main peak increases after irradiation, indicating that the optical properties have improved for all samples. Furthermore, the XRD data revealed that for irradiated GaAs1−xBix samples, the crystallographic quality of the samples was slightly changed after irradiation. This result is consistent with the results of photoluminescence measurements, which demonstrated that the GaAs1−xBix samples exposed to 50 kGy dose showed an increase in photoluminescence and full width at half maximum for all irradiated samples.

Structural and optical analyses for InGaN-based red micro-LED

This study presents a comprehensive analysis of the structural and optical properties of an InGaN-based red micro-LED with a high density of V-shaped pits, offering insights for enhancing emission efficiency. The presence of V-shaped pits is considered advantageous in reducing non-radiative recombination. Furthermore, to systematically investigate the properties of localized states, we conducted temperature-dependent photoluminescence (PL). The results of PL measurements indicate that deep localization in the red double quantum wells can limit carrier escape and improve radiation efficiency. Through a detailed analysis of these results, we extensively investigated the direct impact of epitaxial growth on the efficiency of InGaN red micro-LEDs, thereby laying the foundation for improving efficiency in InGaN-based red micro-LEDs.

High-Quality GaN Films Grown on AlN/Sapphires for Power Electronic Device Applications

High quality GaN films have been successfully grown on multi-AlN/sapphire templates by metal organic chemical vapor deposition system. The Hall mobility and the carrier concentration of 720 cm2/Vs and 6.7x1016 cm-3 at 300K, respectively, along with low dislocation density of 4.1x109 cm-2 have been achieved. The X-ray rocking curve full-width at half-maximum were 160 and 290 arcsec for (0004) and (20-24) reflection planes also obtained, respectively. Besides that, the atomic force microscopy images showed smooth surface morphology and a higher intensity near the band edge was also observed by photoluminescence measurement result.

Growth of High-Quality GaN Films on Multi-AlN/Sapphire Templates By MOCVD

GaN is an attractive material for the applications in visible and ultraviolet optoelectronics, high power, high temperature and high frequency devices. Sapphire substrates have been widely used for the growth of GaN films. However, it is difficult to grow high quality GaN films because of lattice constant and thermal expansion coefficient between GaN and sapphire substrate. In this paper, we report on the high quality GaN films have been successfully grown on multi-AlN/sapphire templates by metal organic chemical vapor deposition system. The Hall mobility and the carrier concentration of 801 cm2/Vs and 7.9x1016 cm-3 at 300K, respectively, along with low dislocation density of 4.5x107 cm-2 have been achieved. The X-ray rocking curve full-width at half-maximum were 51 and 211 arcsec for (0004) and (20-24) reflection planes also obtained, respectively. Besides that the atomic force microscopy images showed smooth surface morphology and a higher intensity near the band edge was also observed by photoluminescence measurement result.

A fundamental study of photoluminescence modulation from DNA-wrapped single-walled carbon nanotubes.

In this study, we investigated the interaction of base sequence-assigned single-stranded DNA (ssDNA) molecules with the surfaces of single-walled carbon nanotube (SWNT)-thymine (T30)/cytosine (C30) hybrids (T30/C30-SWNT), by measuring the modulation of near-infrared (NIR) photoluminescence (PL). Significant PL shifts were observed when T30/C30-SWNTs were reacted with 30-mers of adenine (A30)/guanine (G30). In contrast, when non-complementary ssDNA was used, no significant energy shift was observed in the PL modulation except when T30-SWNTs were reacted with G30. Furthermore, atomic force microscopy (AFM) measurements revealed that the average heights of the T30-SWNTs and C30-SWNTs, after reaction with A30 were 2±0.6 and 1.1±0.3nm, respectively. This result was in good agreement with the results of PL measurements. Our data reveal that DNA hybridization could be detected by measuring PL from SWNTs, without the use of fluorescent molecules. This leads to the possibility of developing nanotube-based photoelectric conversion or optical switch devices driven by organic molecules.

Preparation and performance of CdS-hyperbranched poly(arylene ether ketone) nanocomposite materials

ABSTRACTA new kind of CdS-hyperbranched poly (arylene ether ketone) (HP-PAEK) nanocomposite was prepared in dimethylformamide solution by carboxylic-functionalised HP-PAEK as surface modifier without ligand exchange. The CdS/HP-PAEK nanocomposites were characterised through ultraviolet–visible and photoluminescence spectroscopy. The experimental results of photoluminescence measurement showed that the nanocomposites had obvious luminescence properties. The formation and size of CdS quantum dots were determined by Fourier transform infrared spectroscopy and transmission electron microscopy. The thermal properties of CdS/HP-PAEK nanocomposites were analysed by differential scanning calorimetry and thermogravimetric analysis. Owing to the introduction of CdS nanoparticles, the nanocomposites exhibited excellent heat resistance and higher fluorescent quantum efficiency.

In-situ template synthesis of a polymer/nanoparticles nanohybrid using hyperbranched poly(aryl ether ketone)

Nanostructured ZnS/hyperbranched poly(aryl ether ketone) (ZnS/HPAEK) hybrid material was synthesized by a facile hydrothermal reaction of HPAEK–Zn(Ac)2⋅2H2O in DMF. ZnS nanoparticles were prepared by heterogeneous stirring of carboxylic-functionalized hyperbranched poly(aryl ether ketone) (PCA-HPAEK)–Zn(Ac)2⋅2H2O in DMF with DMF solution of thiourea. The obtained nanocomposites were characterized using various techniques such as Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM), UV–Vis spectroscopy and photoluminescence. FTIR and HRTEM studies confirmed the formation of ZnS QDs with small particle size. And the results of photoluminescence measurement showed that the nanocomposites exhibited distinct luminescence properties. Differential scanning calorimetry and thermogravimetric analysis studies indicated that the nanocomposites exhibited excellent heat resistance. In general, a new ZnS/PCA-HPAEK nanohybrid was synthesized without ligand exchange, and had good optical properties and excellent heat resistance.

C and O doped BN nanoflake and nanowire hybrid structures for tuneable photoluminescence

Abstract C and O doped BN nanoflakes and hybrid nanoflake-nanowire structures were synthesized in N2+H2 environment using plasma-enhanced hot filament chemical vapour deposition with solid B4C as boron and carbon precursor. Structure and chemical composition of the C and O doped BN nanoflakes and hybrid nanoflake-nanowire hybrid structures were systemically studied using advanced characterization instruments including high resolution transmission electron microscope, micro-Raman spectroscope, Fourier transform infrared spectroscope, X-ray diffractometer, field emission scanning electron microscope, and X-ray photoelectron spectroscope. The obtained results evidence that the C and O doped BN nanowires nucleate and grow directly on the tops of C and O doped BN nanoflakes due to the presence of dangling bonds on the surfaces of tips of C and O doped BN nanoflakes, which were formed by the ion bombardment in plasma. The photoluminescence (PL) properties of C and O doped BN nanoflakes and C and O doped BN nanoflake-nanowire hybrid structures were studied at room temperature using a micro-Raman system with the 325 nm line of He-Cd laser as the excitation source. The results of PL measurements indicate that the PL properties of C and O doped BN nanoflake-nanowire hybrid structures significantly change with the length of C and O doped BN nanostructures due to the interface zones caused by the nanowire length. Thus, the PL properties can be efficiently tuned by the length of nanowires. These achievements can contribute to the synthesis of novel BN-based hybrid nanostructures and the development of the next generation BN-based optoelectronic nanodevices.

Silica Encapsulation of SrAl<sub>2</sub>O<sub>4</sub>:Eu<sup>2+</sup>, Dy<sup>3+</sup> Phosphors by Sol-Gel Method

SrAl2O4:Eu2+,Dy3+ phosphors were synthesized under different temperature by high temperature solid phase method. Encapsulation modification of SrAl2O4:Eu2+,Dy3+ by using SiO2glycol were made over chemically unstable against water. Photoluminescence measurement result shows that when the sintering temperature is 1300 °C, the initial afterglow brightness of SrAl2O4:Eu2+,Dy3+ is up to the highest, 12101 mcd/m2. FTIR results showed that new IR peaks at 1085 cm−1 due to the vibration of Si-O-Si and at 931cm−1 due to the vibration of Si-O-Al appeared after silica encapsulation. This verified that the silica encapsulation is not only a physical absorption process but also involving chemical bonding process. Both phosphors before and after encapsulation have same emission peak at 510 nm. A dense layer of silica formed on phosphor surface has the highest water-resistance after being encapsulated for 2h under the condition of pH 4 and encapsulation amount 10:1. The pH value of aqueous solution contained phosphor was steadily 8, and the initial afterglow brightness decreased only by 9%, that is, from 12101 to 11011 mcd/m2.

The Photoluminescence Enhancement and Stability of Porous Silicon by Cathodic Reduction and Acid Treatment

Porous silicon (PSi) was fabricated by using electrochemical anodic etching method. Then acid treatment and cathode reduction treatment were employed to improve the luminescence properties and stability of PSi material. Photoluminescence (PL) measurements and scanning electron microscope (SEM) were used to observe the luminescence properties and microstructure of samples, respectively. The results of PL measurements showed that the PL intensity and the stability of luminescence of samples after cathodic reduction and acid treatment were significantly improved. The SEM images showed that the porosity of PSi may be increased through the cathodic reduction treated.

Influences of post-heat treatment on microstructures, optical and magnetic properties of unintentionally doped GaN epilayers implanted with Mn ions

In this study, GaN:Mn thin films are fabricated by implementing Mn ions into the undoped GaN material. The effects of annealing temperature on microstructures, optical and magnetic properties of the thin films are investigated. The Raman spectra measured from Mn-implanted GaN samples at different annealing temperatures show that new phonon modes, which are related to macroscopic disorder or vacancy-related defects caused by Mn-ion implantation and the local vibrational mode of Mn atoms in the (Ga, Mn)N, are created. The results of photoluminescence measurement show that new peaks appear at 2.16, 2.53, and 2.92 eV. Among these, the new emission around 2.16 eV, besides some contributions from optical transitions from the conduction band or shallow donor to a deep acceptor, cannot exclude the contribution from optical transitions of free electrons in the conduction band to Mn acceptor level. The Hall test shows that the annealed samples are of n type. Ferromagnetism is observed in the Mn doped GaN thin film at 300 K and found to be sensitive to the density of holes that mediate the Mn-Mn magnetic exchange interaction in this Mn-related impurity band.

Indium doping induced modification of the structural, optical and electrical properties of nanocrystalline CdSe thin films

Nanocrystalline thin films of CdSe:In 1% and CdSe:In 5% are prepared by thermal evaporation using the Inert Gas Condensation method. The effects of different doping concentrations of In have been investigated. X-ray diffraction, optical absorption, Photoluminescence (PL) and electrical techniques are used to characterize the films. X-ray diffraction measurements indicate that the nc-CdSe:In 1% and nc-CdSe:In 5% thin films possess hexagonal structure. The crystallinity of the films and the grain size decreases as the In doping concentration increases. The results of PL measurements indicate that the PL intensity decreases as the In doping concentration increases. The optical band gap values increase as the In doping concentration increases. The dc electrical conductivity increases from undoped nc-CdSe to nc-CdSe:In 1% and decreases for nc-CdSe:In 5%. The density of the states near Fermi level N(EF), degree of disorder (To), hopping distance (R) and hopping energy (W) near the Fermi level are calculated using dc conductivity measurements at low temperatures. The effect of In doping concentration on these parameters is discussed. Hall measurements are performed on nc-CdSe, nc-CdSe:In 1% and nc-CdSe:In 5% to calculate the carrier concentration, carrier type and mobility of charge carriers.

A steady blue-emitting CdS nanocrystals-polystyrene composites

CdS nanocrystals with narrow size distribution were synthesized in an organic solution and transparent CdS nanocrystals/polystyrene composite films were fabricated. Transmission electron microscopy, energy dispersive X-ray spectroscopy, photoluminescence and Raman spectra were adopted to investigate these samples. The result of photoluminescence measurement shows that the composite films exhibit distinct luminescence properties of more stable emission and a narrower full-width at half-maximum than that of CdS nanocrystals in solution. Detailed analysis of the Raman spectra has enabled us to identify the origin of the optimized optoelectronic properties of the CdS nanocrystals-polystyrene composites films.

Electrical and optical properties of CdHgTe films grown by molecular-beam epitaxy on silicon substrates

The electrical and optical properties of epitaxial CdHgTe films grown on silicon substrates by molecular-beam epitaxy have been studied. The results of photoluminescence measurements are indicative of the high structural perfection of the films, and Hall data combined with low-energy ion treatment point to a low concentration of residual donors (∼5 × 1014 cm−3). Acceptor states supposedly related to the capture of impurities at structural defects typical of strongly lattice-mismatched heteroepitaxial structures are found in the films.

Selective H2S sensing characteristics of hydrothermally grown ZnO-nanowires network tailored by ultrathin CuO layers

Random networks of ZnO nanowires (ZnO-NWs) have been fabricated on the Si/SiO2 substrates by hydrothermal process using ZnO-nanoparticles as seed. The ZnO-NWs networks have been modified by depositing ultrathin CuO layers (nominal thickness: 10nm) using thermal evaporation of Cu followed by oxygen annealing at 600°C. The results of photoluminescence measurements on ZnO-NWs and CuO:ZnO-NWs networks suggest formation of a p–n junction between p-CuO and n-type ZnO. The gas sensing characteristics of both ZnO-NWs and CuO:ZnO-NWs networks have been investigated. It has been demonstrated that CuO:ZnO-NWs network has selective response toward H2S with a sensitivity of ∼40 (for 10ppm) at an operating temperature of 200°C. A sensing mechanism based on the destruction of p–n junctions due to the formation of metallic CuS (product of chemical reaction between CuO and H2S) has been proposed.

In Situ: 2-D Inorganic Layer Lead-MOF Built from [(μ 4-O)Pb4] Core

In situ lead-MOF derived from 2-Methyl-3-acetylnaphtho[2,3-b]furan-4,9-dione (MAFD), [Pb7O2(OH)2(1,2-BDC)4(H2O)] 1, 1,2-BDC = C6H4(COOH)2, phthalic acid, has been synthesized and characterized by elemental analysis, IR, TG-DTA, powder X-ray diffraction (XRD) and single crystal X-ray diffraction. Compound 1 possesses 2-D inorganic layer structure built from rare tetranuclear unit [(μ4-O)Pb4]. In 1, both crystallographic distinct Pb(1) and Pb(4) ions adopt six-coordination geometry, and the other two crystallographic distinct Pb(2) and Pb(3) ions display eight-coordination geometry under the condition of Pb–O bond length extended to 3.10 A. A 3-D supramolecular network is also formed by hydrogen bonds (C–H···O). Result of photoluminescence measurement indicates an emission band at 385 nm (λexcitation = 209 nm).

Temperature Dependent Luminescence Spectra of Synthetic and Natural Alexandrite (BeAl<sub>2</sub>O<sub>4</sub>:Cr<sup>3+</sup>)

Results of photoluminescence measurements for natural and synthetic alexandrite (BeAl2O4:Cr3+) are presented, where the samples are excited by the 488 nm line of an Ar+ laser, at different temperatures. The main issue is the analysis of the Cr3+ transition in the chrysoberyl matrix (BeAl2O4), with major technological application as active media for laser action. Results indicate anomalous behavior of Cr33+ transition depending on the measurement temperature. A simple model to explain the phenomena is suggested.

Lasing from InGaP quantum dots in a spin-coated flexible microcavity

We report the realization of a mechanically flexible microcavity laser emitting at 657 nm using spin coating. These optically pumped vertical cavity surface emitting lasers use InGaP colloidal quantum dots as the active medium and alternating polymer layers of different refractive indices as the Bragg mirrors. Results of photoluminescence measurements indicating enhancement in spontaneous emission are presented. We also demonstrate the possibility of peeling the device off the substrate yielding a flexible structure that can conform to any shape and whose emission spectra can be mechanically tuned. This new class of hybrid lasers combines advantages of organic and inorganic materials.

Improved a-plane GaN quality grown with flow modulation epitaxy and epitaxial lateral overgrowth on r-plane sapphire substrate

The authors demonstrate superior crystal quality of a-plane GaN grown on r-plane sapphire substrate based on the flow modulation epitaxy (FME) technique, in which the Ga atom supply is alternatively switched on and off with continuous nitrogen supply. With the FME technique, a high growth rate of 2.3μm∕h can still be achieved. With or without epitaxial lateral overgrowth (ELOG), either c- or m-mosaic condition is significantly improved in the samples of using FME. With ELOG, the surface roughness can be reduced from 1.58to0.647nm in an area of 10×10μm2 microns by using the FME technique. Based on the results of photoluminescence measurement, one can also conclude the better optical property of the FME-grown a-plane GaN thin films. Besides, it is shown that tensile strain is more relaxed in the FME samples.

Coalescence overgrowth of GaN nano-columns with metalorganic chemical vapordeposition

The authors demonstrate the coalescence overgrowth of GaN nano-columns on a (111) Sisubstrate with metalorganic chemical vapor deposition to show high-quality opticalproperties in the overgrown film. Plan-view scanning electron microscopy (SEM) showscoalesced surface morphology, although hexagonal structures are still visible in the images.The cross-section cathodoluminescence (CL) image shows more efficient emission in theovergrowth layer than from the nano-column layer. The plan-view CL image demonstratesthat the emitted light is mainly from the hexagonal structures. The photoluminescencemeasurement result indicates that the emission efficiency of the overgrown layer is evenhigher than that of an undoped GaN thin film of high quality. The presence of hexagonalstructures correlates to surface roughness values in the range of several nanometres.