Room Temperature Visible Photoluminescence Research Articles

Controlled and environmentally friendly hydrothermal synthesis of nano-V4O9 plate-like for photocatalytic degradation of methyl orange under solar irradiation

Nano-V4O9 plate-like morphology has been synthesized by hydrothermal treatment using vanadium oxide (V2O5) as vanadium source and 3-amino-1-propanol (H2N–(CH2)3–OH) as reducing and structure-directing agent, for the first time. The structural and morphological properties of the nano-V4O9 were investigated by X-ray diffraction (XRD), infrared spectroscopy and scanning electron microscopy (SEM). XRD study demonstrated the existence of orthorhombic structure V4O9 with high crystallinity. SEM micrographs revealed that the particles have a plate-like morphology with uniform size distribution whose thickness is on the order of 46 nm. The formation mechanism of V4O9 nanoplates has also been proposed. Optical properties of the as-synthesized samples were investigated by UV–visible diffuse reflection spectroscopy and room temperature photoluminescence. This study shows that when the hydrothermal treatment was carried out for 96 h, the band gap can be estimated at 3.832 eV. The photoactivity of V4O9 nanoplates was evaluated in the degradation of methyl orange under solar irradiation.

Optical Properties of Hydrothermally Grown ZnO Nanoflowers

Abstract: A simple hydrothermal method has been successfully employed to synthesize flower-like ZnO nanostructure. X-ray diffraction data confirm the formation of ZnO with a Wurtzite structure. FESEM images show the flower-like morphology of the synthesized nanostructures. The energy dispersive X-ray spectroscopic analysis confirms the stoichiometric composition.. X-ray fluorescence spectrum shows no impurity element in the synthesized ZnO. The synthesized ZnO exhibits low absorption in the visible region of wavelength. Band gap enhancement was also observed owing to the quantum confinement effect. The synthesized ZnO nanoflowers exhibit strong room-temperature photoluminescence with a broad emission peak at 429 nm arising due to the recombination of electrons at zinc interstitials and holes in the valence band. This defect-related photoluminescence is very important in the context of understanding the defect dynamics in ZnO. Background: Zinc oxide (ZnO) is a well-known multifunctional material possessing unique structural, electrical, and optical properties that are very useful in various device applications. Being a high and direct band gap semiconductor, it is potentially being used in various UV light sources and detectors fabrication. However, the emission and absorption properties strongly depend on the size of the ZnO nanoparticles which in turn depends on the morphology of the nanostructure. Therefore, it is very much important to understand the structure-property relationship for a predictable device performance. Objectives: Our objective of this work is to synthesize flower-like ZnO nanostructures using a simple hydrothermal method. The flower-like ZnO morphology offers a large surface area that will be very suitable for designing gas and chemical sensor devices. Another objective of this work is to study the crystallography of ZnO. Next, the optical properties (emission and absorption) have been investigated to understand the defect-related photoluminescence mechanism. Method: A simple hydrothermal method has been deployed to synthesize flower-like ZnO nanostructures. A chloride decomposition scheme has been used to produce zinc hydroxide ions that will produce ZnO nuclide. At the onset of saturation, ZnO nanocrystals start to grow. The entire reaction was performed inside a Teflon cell stainless steel autoclave. The autoclave was placed in a horizontal tube furnace and maintained at 150 °C for 2 hr. resulting in the formation of white powder-like material. Results: The X-ray diffraction data confirm the formation of polycrystalline ZnO having a Wurtzite structure. Flower-like morphology was clearly observed in FESEM images. The EDS data confirm the composition of ZnO with proper stoichiometry. Gibb’s free energy calculation favors the reaction under the experimental condition. The absorption spectrum was used to calculate the band gap of the synthesized ZnO nanoflowers. The Tauc plot revealed the band gap of the synthesized ZnO to be~ 3.69 eV. This enhancement of band gap compared to bulk ZnO occurs due to the quantum confinement effect. The synthesized ZnO nanoflowers exhibit broad photoluminescence peaked at 429 nm owing to the presence of interstitial zinc. Conclusion: A hydrothermal method has been successfully used to synthesize well-crystalline ZnO nanoflowers of proper stoichiometry. The flower-like nanostructure exhibits band gap enhancement due to the quantum confinement effect. Room temperature visible photoluminescence was observed from the ZnO nanoflowers with a board emission peak at 429 nm. This emission arises due to the presence of deep-level zinc interstitial states. This finding will be very useful in understanding the role of defects in the visible emission from ZnO nanostructures.

Effect of Yb3+ on the Structural and Visible to Near-Infrared Wavelength Photoluminescence Properties in Sm3+-Yb3+-Codoped Barium Fluorotellurite Glasses.

We report on the Sm3+ and Sm3+:Yb3+-doped barium fluorotellurite glasses prepared using the conventional melting and quenching method. The spectroscopic characterisations were investigated with Raman and FTIR to evaluate the glasses’ structural and hydroxyl (-OH) content. The Raman analysis revealed a structural modification in the glass network upon adding and increasing the Yb3+ concentration from a TeO3 trigonal pyramid to a TeO4 trigonal bi-pyramid polyhedral. At the same time, the FTIR measurements showed the existence of -OH groups in the glass. Thus, under the current experimental conditions and nominal composition, the -OH group contents are too large to enable an effective removal. The near-infrared region of the absorption spectra is employed to determine the nephelauxetic ratio and bonding parameters. The average nephelauxetic ratio decreases, and the bonding parameter increases with the increasing Yb3+ content in the glasses. A room temperature visible and near-infrared photoluminescence ranging from 500 to 1500 nm in wavelength and decay properties were investigated for glasses doped with Sm3+ and Sm3+-Yb3+ by exciting them with 450 and 980 nm laser sources. Exciting the Sm3+- and Sm3+-Yb3+-doped glasses by 450 nm excitation reveals a new series of photoluminescence emissions at 1200, 1293, and 1418 nm, corresponding to the 6F11/2 state to the 6HJ (J = 7/2, 9/2, 11/2) transitions. Under the 976 nm laser excitation, a broad photoluminescence emission from 980 to 1200 nm was detected. A decay lifetime decreased from ~244 to ~43 μs by increasing the Yb3+ content, ascribing to concentration quenching and the OH content.

Highly enhanced ultraviolet to visible room temperature photoluminescence emission ratio in Al implanted ZnO nanorods

We present here a comprehensive study on the effect of Al ion implantation on the room temperature (RT) photoluminescence (PL) emission properties of aqueous chemically grown vertically-aligned ZnO nanorods (NRs) implanted with 100 keV Al ions of various doses varying from 1 × 1013 ions/cm2 to 1 × 1016 ions/cm2 followed by annealing at 450 °C in an inert ambient. As compared to the pristine sample, an unprecedented enhancement (1.4 times) in the ratio of the intensities of the near band edge, INBE (ultraviolet) to the defect level, IDL (visible) emissions has been observed for the ZnO NRs implanted with a 5 × 1013 ions/cm2 dose of Al ions. Though the ratio INBE/IDL is decreased with an increase in the Al dose beyond 5 × 1013 ions/cm2, it is still higher than the pristine sample up to a Al dose of 1 × 1015 ions/cm2. Finally, a 0.87 times drop in the ratio is observed for the highest dose (1 × 1016 ions/cm2) Al implanted sample. Detailed analyses of the RT PL results show that excitons bound to neutral Al donor for lower and non-radiative surface defects related recombination centers for higher doses are responsible respectively for highly enhanced and reduced PL emissions in Al implanted ZnO NRs.

Physical, structural, optical and photons attenuation attributes of lithium-magnesium-borate glasses: Role of Tm2O3 doping

Room temperature visible photoluminescence from rare earth ions doped in glasses became prospective for eye safe laser and sensor applications. Driven by this idea, glass system with nominal composition of 20Li2O–(70-x)B2O3–10MgO–xTm2O3 (where 0 ≤ x ≤ 1) were synthesized via a melt-quenching technique. As-quenched samples were analyzed using various analytical tools at room temperature. XRD patterns of as-quenched samples confirmed their amorphous nature and FTIR spectra revealed the existence of BO3 and BO4 structural units. Achieved glasses were transparent and thermally stable (verified by DTA curves). UV–vis-NIR spectra of glasses disclosed four significant absorption bands at round 791, 683, 466 and 355 nm which were assigned to the transitions from ground level of 3H6 to respective 3H4, 3F3, 1G4 and 1D2 excited levels of Tm3+ ions. Photoluminescence emission spectra (at an excitation wavelength of 473 nm) of prepared glasses displayed three characteristic peaks positioned at 476, 650 and 783 nm corresponding to 1G4→3H6, 1G4→3F4 and 3H4→3H6 transitions from Tm3+ ions. Also, the photon shielding properties for the LMB glasses with different Tm2O3 content were studies using the well known program (XCOM). The mass attenuation coefficients showed an increase behavior as the Tm2O3 concentration rise. Overall, the properties of LMB glasses were discerned to be sensitive to the Tm2O3 concentration variation. It was concluded that the proposed glass compositions may be useful for solid state lasers and telecommunications applications.

Investigation of Nanostructure and Optical Properties of Flexible AZO Thin Films at Different Powers of RF Magnetron Sputtering

In this study Al-doped Zinc Oxide (AZO) thin films were successfully deposited on the flexible Polymethyl methacrylate (PMMA) substrate by RF magnetron sputtering. The effects of RF power on the crystal structure, morphology, thickness and optical properties of AZO thin films have been investigated. The AZO thin films were analyzed using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), DEKTAK 3 profilometer, UV–Visible spectroscopy and room temperature photoluminescence (PL) spectroscopy. The XRD patterns show that increase of RF power leads to increase in the predominant direction along (100) and crystal plane of hexagonal ZnO. Moreover, the transmittance of thin films decreased from 76% to 61% and optical bang gap varied among 3.34[Formula: see text]eV to 3.22[Formula: see text]eV with increasing RF power. The PL spectra show excellent light-emitting characteristics: 375[Formula: see text]nm, 428[Formula: see text]nm, 467[Formula: see text]nm and 505[Formula: see text]nm. The results indicate that the peak intensity increases with increasing RF power from 80[Formula: see text]W to 180[Formula: see text]W.

Cu-doping and annealing effect on the optical properties and enhanced photocatalytic activity of ZnO nanoparticles

Hexagonal wurtzite structure of Cu-doped ZnO nanoparticles with an optical band-gap of ∼3.48 eV has been synthesized through a co-precipitation method at room temperature followed by annealing at 600 °C for 3 h. Structural, morphological and optical studies are performed for different concentrations of Cu-doped ZnO and annealed ZnO nanoparticles. Crystallite size, lattice parameters, unit cell volume, bond length and Young's modulus are calculated and compared. Morphology and average particle size of the samples have been characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The favorable band-gap reduction and defect states for photocatalytic activity are demonstrated from UV–Visible absorption spectroscopy and room temperature photoluminescence (PL) spectroscopy data. The photocatalytic degradation efficiency of the prepared nanoparticles towards the toxic methylene blue (MB) dye has been successfully investigated under white light irradiation.

Influence of annealing temperature on morphological, optical and UV detection properties of ZnO nanowires grown by chemical bath deposition

Chemical solution deposition is a low-temperature method with possibly the lowest-cost for growing zinc oxide (ZnO) nanowires (NWs) on an amorphous glass substrate. A ZnO seed layer is needed to initialize the uniform growth of oriented nanowires. In the present work, we deposited the seed layer onto the glass substrate using radio frequency magnetron sputtering system. The ZnO NWs were fabricated on the seeded substrate by immersing them in a chemical bath containing zinc nitrate and hexamethylenetetramine (HTMA) aqueous solution. Several properties of as-grown ZnO NWs and annealed ZnO NWs at different temperatures in pure oxygen atmosphere were investigated. Well-defined ZnO nanowires almost perpendicular to substrate surface were observed through field emission scanning electron microscopy micrographs. X-ray diffraction measurements showed that all ZnO samples possessed a typical wurtzite structure with high crystallinity and no other impurity phases. The results of UV–Visible spectroscopy and room temperature photoluminescence implied that increasing the annealing temperature could have a significant influence on the performance of samples. The ZnO-based interdigitated metal–semiconductor–metal (MSM) was produced using the thermal evaporation of silver contacts. The results of current–voltage and transient response measurements demonstrate that despite using the low-cost thin film techniques, high responsivity was obtained.

Photoacidic and Photobasic Behavior of Transition Metal Compounds with Carboxylic Acid Group(s).

Excited state proton transfer studies of six Ru polypyridyl compounds with carboxylic acid/carboxylate group(s) revealed that some were photoacids and some were photobases. The compounds [Ru(II)(btfmb)2(LL)](2+), [Ru(II)(dtb)2(LL)](2+), and [Ru(II)(bpy)2(LL)](2+), where bpy is 2,2'-bipyridine, btfmb is 4,4'-(CF3)2-bpy, and dtb is 4,4'-((CH3)3C)2-bpy, and LL is either dcb = 4,4'-(CO2H)2-bpy or mcb = 4-(CO2H),4'-(CO2Et)-2,2'-bpy, were synthesized and characterized. The compounds exhibited intense metal-to-ligand charge-transfer (MLCT) absorption bands in the visible region and room temperature photoluminescence (PL) with long τ > 100 ns excited state lifetimes. The mcb compounds had very similar ground state pKa's of 2.31 ± 0.07, and their characterization enabled accurate determination of the two pKa values for the commonly utilized dcb ligand, pKa1 = 2.1 ± 0.1 and pKa2 = 3.0 ± 0.2. Compounds with the btfmb ligand were photoacidic, and the other compounds were photobasic. Transient absorption spectra indicated that btfmb compounds displayed a [Ru(III)(btfmb(-))L2](2+)* localized excited state and a [Ru(III)(dcb(-))L2](2+)* formulation for all the other excited states. Time dependent PL spectral shifts provided the first kinetic data for excited state proton transfer in a transition metal compound. PL titrations, thermochemical cycles, and kinetic analysis (for the mcb compounds) provided self-consistent pKa* values. The ability to make a single ionizable group photobasic or photoacidic through ligand design was unprecedented and was understood based on the orientation of the lowest-lying MLCT excited state dipole relative to the ligand that contained the carboxylic acid group(s).

Tetragonal pencil-like VO2(R) as electrode materials for high-performance redox activities

Pencil-like tetragonal vanadium dioxide has been synthesized via one-step hydrothermal treatment. The compounds were analyzed through X-ray powder diffraction; scanning electron microscope and X-ray photoelectron spectroscopy (XPS). The optical properties of the as-synthesized material were studied by UV–visible diffuse reflection spectroscopy and room temperature photoluminescence. Thin films of VO2(R) deposited on ITO substrates were electrochemically characterized by cyclic voltammetry (CV). The voltammograms show a reversible redox behavior with a doping/dedoping process corresponding to reversible cation intercalation/de-intercalation into the crystal lattice of the pencil. This process is easier in propylene carbonate than in aqueous solvent. It is also easier for the small Li+ cation than larger ones, Na+ and K+. This is attributed to a probable presence of one tunnel cavities in the structure of VO2(R). The good electrochemical property of the VO2(R) is attributed to its unique ultralong nanopencils structure with a good structural stability.

Strong visible light emission from silicon-oxycarbide nanowire arrays prepared by electron beam lithography and reactive ion etching

Abstract

Phycosynthesis of silver nanoparticles and photocatalytic degradation of methyl orange dye using silver (Ag) nanoparticles synthesized from Hypnea musciformis (Wulfen) J.V. Lamouroux

In the present investigation, simple and eco-friendly chemical reaction for the synthesis reported on biological synthesis of nano-sized silver and biosynthesis of silver nanoparticles using Hypnea musciformis at room temperature along with photocatalytic degradation of methyl orange dye. The nanoparticles of silver were formed by the reduction of silver nitrate to aqueous silver metal ions during exposure to the extract of red alga H. musciformis. The optical properties of the obtained silver nanoparticles were characterized by applying UV–visible absorption and room temperature photoluminescence. The X-ray diffraction results revealed that the synthesized silver nanoparticles were in the cubic phase. The existence of functional groups was identified using Fourier transform infrared spectroscopy. The morphology and size of the synthesized particles were studied with atomic force microscope measurements. Photocatalytic degradation of methyl orange was measured spectrophotometrically by using silver as nanocatalyst under visible light illumination. The results revealed that biosynthesized silver nanoparticles using H. musciformis was found to be impressive in degrading methyl orange.

Effect of pH on the growth of zinc oxide nanorods using Citrus aurantifolia extracts

The effect of pH during sol–gel synthesis of ZnO nanorods using Citrus aurantifolia juice extracts has been investigated. Zinc nitrate solutions and C. aurantifolia fruit extracts mixtures were heated at 90°C at pH of 5, 7 and 9. Solid reaction products were annealed in air at 300°C yielding nanorods with diameters of about 100nm for all samples. XRD analysis showed pure hexagonal wurtzite ZnO structure. Room temperature visible photoluminescence spectroscopy revealed emissions which were attributed to the common defects states associated with ZnO. Nanorods growth in acidic solution was found to be inhibited compared to nanorods from neutral and alkaline solutions. This was due to preferential erosion of ZnO (0001) face in acidic solution and the enhanced growth in neutral and alkaline solutions which favored the formation of Zn(OH)2 which is an intermediate molecule in the reaction to form ZnO.

Light-Emitting Characterization of Vacuum Plasma Sprayed Silicon Coatings

In the present work, the light-emitting property of silicon coating was explored and the related morphologies and chemical structure of silicon coating were characterized. Silicon coating was prepared by vacuum plasma spray technique and chemically treated by HNO3/HF vapor. The coatings before and after the vapor etching were characterized by field emission scanning electron microscopy and micro-raman spectroscopy. The photoluminescence spectra of the silicon coatings treated with different time were examined. It is found that pores of micrometer and microcracks formed on the surface of silicon coatings after the treatment. The treated silicon coatings exhibited room temperature visible photoluminescence with emission wavelength around 650 nm after excitation. The results of micro-raman measurement proved that there were polysilane and oxygen related functional groups appeared on the coating surface after the vapor treatment, which was supposed to be responsible for the photoluminescent phenomena.

The room temperature visible photoluminescence in g- As2S3 and Ge-based glasses

Фотолюмінесцентне випромінювання, що спостерігалося зі сколу стекол на основі GeS 2 при старінні, віднесено до окисної фази, що утворилася на поверхні стекол під час тривалого зберігання зразків на повітрі. Усі ФЛ максимуми пов'язані з центрами GeО x ,зникли з фотолюмінесцентного спектру, коли фотолюмінесцентний спектр був знятий зі свіжесколотої поверхні з об'ємного скла g-GeS 2 (T 3 V 2 ).

Biosynthesis of silver nanoparticles from the marine seaweed Sargassum wightii and their antibacterial activity against some human pathogens

In this paper, we have reported on biological synthesis of nano-sized silver and its antibacterial activity against human pathogens. The nanoparticles of silver were formed by the reduction of silver nitrate to aqueous silver metal ions during exposure to the extract of marine seaweed Sargassum wightii. The optical properties of the obtained silver nanoparticles were characterized using UV–visible absorption and room temperature photoluminescence. The X-ray diffraction results reveal that the synthesized silver nanoparticles are in the cubic phase. The existence of functional groups was identified using Fourier transform infrared spectroscopy. The morphology and size of the synthesized particles were studied with atomic force microscope and high-resolution transmission electron microscope measurements. The synthesized nanoparticles have an effective antibacterial activity against S. aureus, K. pneumoniae, and S. typhi.

ZnO nanoswords and nanopills: Hydrothermal synthesis, characterization and optical properties

Abstract Nanostructured hexagonal zinc oxide pills and swords-like were hydrothermally synthesized using zinc sulfate heptahydrate (ZnSO4·7H2O) as an inorganic precursor and adipic acid (HOOC(CH2)4COOH) as a structure-directing agent. The structure, the crystallinity, the morphology and the composition of the materials were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). XRD study demonstrated the existence of wrutzite ZnO of high degree of crystallinity with crystallite size in the range of 70–80 nm. The optical properties of the as-synthesized ZnO were investigated by UV–visible absorption and room temperature photoluminescence (RTPL). The band gap for ZnO nanswords and nanopills was found to be 3.25 and 3.27 eV, respectively.

Ultrahigh throughput plasma processing of free standing silicon nanocrystals with lognormal size distribution

We demonstrate a method for synthesizing free standing silicon nanocrystals in an argon/silane gas mixture by using a remote expanding thermal plasma. Transmission electron microscopy and Raman spectroscopy measurements reveal that the distribution has a bimodal shape consisting of two distinct groups of small and large silicon nanocrystals with sizes in the range 2–10 nm and 50–120 nm, respectively. We also observe that both size distributions are lognormal which is linked with the growth time and transport of nanocrystals in the plasma. Average size control is achieved by tuning the silane flow injected into the vessel. Analyses on morphological features show that nanocrystals are monocrystalline and spherically shaped. These results imply that formation of silicon nanocrystals is based on nucleation, i.e., these large nanocrystals are not the result of coalescence of small nanocrystals. Photoluminescence measurements show that silicon nanocrystals exhibit a broad emission in the visible region peaked at 725 nm. Nanocrystals are produced with ultrahigh throughput of about 100 mg/min and have state of the art properties, such as controlled size distribution, easy handling, and room temperature visible photoluminescence.

Synthesis and characterization of nano ZnO rods via microwave assisted chemical precipitation method

A microwave assisted chemical precipitation method has been employed for the synthesis of nano zinc oxide rods by reacting zinc nitrate and potassium hydroxide. The amount of potassium hydroxide was adjusted for three different pHs to achieve ZnO nano rods with varying aspect ratio. The mechanism of growth of nano rods is explained briefly. The average crystallite size of the as synthesized samples was analyzed by means of powder XRD pattern and estimated to vary from 25.6nm to 43.1nm. The existence of rods was confirmed using scanning electron microscopy (SEM). The samples were also analyzed using FT-IR. The optical properties of the samples were also studied by means of UV–visible spectra and Room Temperature Photo Luminescence studies. The band gap of the samples was determined from the DRS spectrum. A strong near band emission peaks due to surface defects are observed in the PL spectrum.

Enhanced formation of Ge nanocrystals in Ge : SiO2 layers by swift heavy ions

In this paper we report the ability of swift heavy Xe ions with an energy of 480 MeV and a fluence of 1012 cm−2 to enhance the formation of Ge nanocrystals within SiO2 layers with variable Ge contents. These Ge-SiO2 films were fabricated by the co-sputtering of Ge and quartz sources which followed various annealing procedures. In particular, we found that the irradiation of the Ge : SiO2 films with subsequent annealing at 500 °C leads to the formation of a high concentration of nanocrystals (NCs) with a size of 2–5 nm, whereas without irradiation only amorphous inclusions were observed. This effect, as evidenced by Raman spectra, is enhanced by pre-irradiation at 550 °C and post-irradiation annealing at 600 °C, which also leads to the observation of room temperature visible photoluminescence.