Strong Visible Emission Research Articles

Luminescence characterization of Sm3+-doped sodium potassium borate glasses for laser application

Sodium potassium borate glasses doped with different concentrations of Sm3+ ions (NKBSm) were prepared using a normal melt quench technique. Optical absorption, excitation, emission and emission decay measurements were performed to understand visible luminescence and lasing potentialities of the prepared glasses. The bonding parameters (δ) have been estimated from the absorption spectra to know about the bonding nature between Sm3+ ions and nearby ligands. The Judd–Ofelt (J–O) intensity parameters (Ωλ, λ = 2, 4, and 6), acquired from the experimental oscillator strengths of the absorption spectral features were used to estimate different radiative properties of the fluorescent transitions, 4G5/2→6HJ, J=5/2, 7/2, 9/2 and 11/2, of Sm3+ ions in NKBSm glasses to get knowledge about the potentiality of these materials as visible lasers. The asymmetric ratios (O/R) were calculated to know the local disorder of Sm3+ ions in the glass network. The experimental lifetimes (τexp) for 4G5/2 emission state were found to be decreasing with increasing Sm3+ ion concentration owing to energy transfer. The quantum efficiency (η) of NKBSm10 glass has been measured by coupling the experimental lifetime (τexp), measured from the decay profiles with radiative lifetimes (τR), obtained from J-O theory. The strong visible emission, large stimulated emission cross-section (σe), high branching ratios (βR) and good quantum efficiency (η) were observed for the most intense transition 4G5/2 → 6H7/2 (orange) in NKBSm10 glass, indicating the suitability of this glass for the development of laser and photonic devices operating in visible region.

Photoluminescence enhancement and morphological properties of nanoporous anodic alumina prepared in oxalic acid with varying time and temperature

We report on the photoluminescence (PL) enhancement and morphological properties of highly ordered Nanoporous anodic alumina (NAA) fabricated by two-step anodization for 2–10 h at 5 °C and 25 °C anodization temperatures. Structural features and pore arrangements of NAA were characterized. Pore-properties such as pore-diameter, porosity and growth rate showed an increase with rising in temperature whereas pore-wall thickness and barrier layer thickness decreased, however, interpore distance and pore density were not affected. Two-dimensional fast Fourier Transform (FFT) analysis was used to study the pore arrangement. The average pore regularity ratio was higher at 5 °C. The Photoluminescence (PL) spectra of NAA samples exhibited a strong visible blue emission at room temperature. The broad PL peak was deconvoluted into two Gaussian sub-bands attributed to luminescent F+ and F centers. Experimental results showed that NAA prepared at elevated temperature showed PL enhancement by about 3.6–4.8 fold due to the increased anodizing current which leads to the increased density of F centers compared to F+ centers.

Magnetic-luminescent cerium-doped gadolinium aluminum garnet nanoparticles for simultaneous imaging and photodynamic therapy of cancer cells

Nanoparticle (NP) and photosensitizer (PS) conjugates capable of X-ray photodynamic therapy (X-PDT) are a research focus due to their potential applications in cancer treatment. Combined with X-PDT, appropriate imaging properties of the nanocomposite will make it suitable for theranostics of deep lying tumors. In this work, we describe the development of magnetic-luminescent Gd2.98Ce0.02Al5O12 nanoparticles (GAG) coated with mesoporous silica (mSiO2) and loaded with rose bengal (RB) to yield a nanocomposite GAG@mSiO2@RB capable of X-PDT. GAG nanoparticles were synthesized using the sol-gel method. The synthesized GAG nanoparticles showed a strong visible yellow emission with a quantum yield of ∼32%. Moreover, the broad emission spectra of GAG nanoparticles centered at 585 nm showed a good overlap with the absorption of RB. Upon irradiation with X-rays (55 KV), the GAG@mSiO2@RB nanocomposite produced significantly higher singlet oxygen compared with RB alone, as confirmed by the 1,2-diphenylisobenzofuran (DPBF) assay. The developed GAG@mSiO2@RB nanocomposite significantly reduced the viability of human breast cancer (MDA-MB-231) cells upon irradiation with blue light (λ = 470 nm). The calculated LC50 of GAG@mSiO2@RB nanocomposites were 26.69, 11.2, and 6.56 µg/mL at a dose of ∼0.16, 0.33 and 0.5 J/cm2, respectively. Moreover, the nanocomposite showed paramagnetic properties with high magnetic mass susceptibility which are useful for high contrast T1 weighted magnetic resonance imaging (MRI). Together with X-PDT, the paramagnetic properties of the proposed GAG@mSiO2@RB nanocomposite system are promising for their future application in simultaneous detection and treatment of deep-lying tumors.

Evidence of a strong electron–hole separation effect in ZnO@TiO2 core/shell nanowires

In this work, a strong electron-hole separation effect in ZnO@TiO2 core/shell nanowire arrays was investigated. On the surface of well-aligned ZnO nanowires, a high-quality TiO2 shell was grown in a range of thicknesses through the deposition of TiO2 nanoparticles on ZnO nanowire arrays by pulsed laser deposition (PLD). In the photoluminescence (PL) spectra of the ZnO@TiO2 core/shell nanowires, a strong and broad visible emission band from 450 to 650 nm appears, which is related to surface defects; meanwhile, the ultraviolet (UV) emission due to exciton recombination simultaneously disappears. These changes in the PL spectra originate from a highly efficient electron-hole separation effect. This work presents evidence of this strong electron-hole separation effect in these ZnO@TiO2 core/shell nanowire arrays, which makes them promising candidates for use in optoelectronic devices for dye-sensitized solar cells and ultraviolet photodetectors.

Photoluminescence and stress-luminescence of non-piezoelectric ZnS:Cu amorphous materials

In this work, the non-piezoelectric ZnS:Cu amorphous powder was sintered at 1100 °C. The dominant photoluminescent emission peak at ∼484 nm can be found upon a ∼365 nm light excitation. An obvious stress-luminescence of ZnS:Cu, appearing reproducibly strong visible emission under mechanical pulse load, is found. The stress-luminescence mechanism of the non-piezoelectric ZnS:Cu amorphous powder may be attributed to the internal energy change under the mechanical pulse load.

Synthesis and characterization of hybrid Ag-ZnO nanocomposite for the application of sensor selectivity

Facile, rapid, and environmentally benign hybrid Ag-ZnO nanocomposites were synthesized by two steps from green synthesis approach at room temperature. The absence of an impurity peak in X-ray diffraction (XRD) pattern confirmed the formation of polycrystalline nanocomposite material. An additional peak (111) of Ag was detected along with ZnO crystalline wurtzite structure. The surface area electron diffraction (SAED) pattern further confirmed the crystallinity of nanocomposites. The compositional analysis of hybrid Ag-ZnO was determined by EDS-mapping and confirmed the presence of Zn, O and Ag in the composite. The room-temperature photoluminescence (PL) spectra of hybrid Ag-ZnO depict a weak ultraviolet (UV) emission at 385 nm, and the strong visible emission at ∼600 nm, while increasing the Ag concentration in to ZnO matrix, the UV peak was completely disappeared and major visible peak was moved to ∼500 nm indicated to the best optimal detection peak for sensors. The fluorescence spectra were measured with respect to Ag concentrations of Ag-ZnO nanocomposite at room temperature to investigate the functionality and the selectivity of nanomaterials. This work opens a notable way to fabricate Ag-ZnO nanohybrids, and makes a significant contribution to the fluorescence based sensor applications.

Enhancement of visible luminescence and photocatalytic activity of ZnO thin films via Cu doping

Highly transparent Cu doped ZnO thin films were deposited on glass substrates by spray pyrolysis technique. Crystallinity of the films improved at lower doping concentrations due to the easy fitting of Cu dopants in the Zn Lattice sites and preferred highly textured growth along the (002) plane. Higher doping concentration deteriorated the crystallinity and the optical transmission followed the similar trend. EDX spectra analysis confirmed the incorporation of Cu in the doped films. Optical energy gap red-shifted with the addition of Cu contents due to the exchange interactions and difference in iconicity of Zn and Cu. Cu doped films exhibited strong visible emission due to the modulation of the band structure and subsequently new levels acting as emission centres will be formed in the forbidden gap of ZnO. Moreover, the addition of Cu dopants increases the concentration of zinc interstitials as well as zinc and oxygen vacancies which cause more intense emission in the visible region. Cu doped films exhibited excellent photocatalytic activity due to the efficient trapping of photo-generated electrons thereby suppressing the electron-hole recombination and higher doping level slightly decreased the degradation efficiency because excess dopants may act as recombination centres.

Photodegradation behavior of ZnO nanorods on various types of organic dyes

In this paper, the effectiveness of ZnO nanorods in degrading various types of organic dyes under UV irradiation was studied. ZnO nanorods were synthesized by solution precipitation method using zinc nitrate tetrahydrate and hexamethylenetetramine as precursors. The nanorods were hexagonal wurtzite ZnO as shown in XRD analysis. The sample displayed strong UV absorption attributed to its wide energy bandgap, i.e. 3.37 eV. The room temperature PL spectrum showed low UV emission with relatively strong visible emission, indicating the presence of large amount of defects in the ZnO nanorods. Three organic dyes, i.e. RhB, MB and MO, were degraded by ZnO nanorods via cycloreversion. The removal efficiencies of ZnO nanorods were 99.3, 96.6 and 74.1% for RhB, MB and MO dyes, respectively after 30 min of UV light (λ = 352 nm) irradiation. The photodegradation of RhB, MB and MO by ZnO nanorods followed the pseudo first-order kinetic reaction. It was proposed that the variation of photodegradation efficiencies by ZnO nanorods was due to the different types of bonding in various organic dyes.

Influence of pH on hydrothermally derived ZnO nanostructures

Zinc oxide (ZnO) nanostructures with numerous morphology was prepared by using hydrothermal method. The effect of pH on structural, optical and photocatalytic activity of ZnO was investigated systematically. The prepared ZnO samples were characterized by various characterization techniques. The X-ray diffraction study revealed that the crystalline hexagonal phase of ZnO nanostructures was observed. Scanning electron microscopic observations revealed that the variation of pH significantly alters the morphology of the grown ZnO nanostructures. The UV–vis spectrum shows an optical bandgap was not significantly influenced by pH of reactant solution. Photoluminescence studies at room temperature for different pH values revealed a weak band edge emission altogether with strong defect-related visible emission peaks. Photocatalytic activity of methylene blue (MB) under visible light illumination was studied. Maximum degradation of 99% was observed in 100 min for ZnO nanostructure prepared at pH 11.

Highly Efficient Visible Blue-Emitting Black Phosphorus Quantum Dot: Mussel-Inspired Surface Functionalization for Bioapplications.

The preparation of blue-emitting black phosphorus quantum dots (BPQDs) is based on the liquid-phase exfoliation of bulk BP. We report the synthesis of soluble BPQDs showing a strong visible blue-light emission. Highly fluorescent (photoluminescence quantum yield of ≈5% with the maximum emission (λmax) at ≈437 nm) and dispersible BPQDs in various organic solvents are first prepared by simple ultrasonication of BP crystals in chloroform in the ambient atmosphere. Furthermore, simple mussel-inspired surface functionalization of BPQDs with catechol-grafted poly(ethylene glycol) in basic buffer afforded water-soluble blue-emitting BPQDs showing long-term fluorescence stability, very low cytotoxicity, and excellent fluorescence live cell imaging capability.

Electrical properties and aquatic ecotoxicity effects of ZnS nanocrystals

A new synthesis method of ZnS colloidal nanocrystals is presented in this work, and this novel approach allows one to produce Zinc sulfide nanocrystals owing to a modified polyol process that makes use of 1.3-propanediol as a solvent. The structure and morphology of the nanoparticles were characterized by high-resolution transmission electron microscopy, transmission electron microscopy, X-ray diffraction and spectroscopy photoluminescence. The results showed that quasi-spherical ZnS nanocrystals with sizes in the range 3–5 nm were formed. Their morphology, size and colloidal stability are driven by the polyol solvent. Under UV excitation, a strong visible PL emission, due to the radiative recombinations of the electron–hole pairs photo-generated in the ZnS nanoparticles, was observed. In order to study the environmental risk of ZnS, mussels Mytilus galloprovincialis were exposed to ZnS C1 $$=$$ 0.1 mg/L, ZnS C2 $$=$$ 1 mg/L and ZnS C3 $$=$$ 10 mg/L. Superoxide dismutase, catalase activities and protein thiols density were determined in the gill of treated and untreated mussels. No significant effects were detected in the gills of exposed mussels after 14 days of exposure compared to control. Optical property of the new nanomaterial, together with the easy synthesis process, makes the ZnS nanocrystals a promising candidate for applications optoelectronics and photocatalyst. The frequency-dependent impedance and AC conductivity have been investigated in this context. Impedance and modulus plane plots from 10 to $$10^{7}$$ Hz show the presence of bulk and grain boundary phases in ZnS at each measurement temperature from 125 to $$225\,^{\circ }\hbox {C}$$ . The activation energy was calculated from the temperature variation of DC conductivity. Studies of frequency and temperature dependence of electrical data of the compound suggest that conduction process in the material is thermally activated. Environmental risk assessment results constitute a scientific support for considering the use of this nonmaterial on various applications after further complementary studies in order to ensure the safety of these NPs.

LUMINESCENCE INVESTIGATION OF POWDER ZNO NANOPARTICLES DOPED WITH SM AND LI IONS PREPARED BY COPRECIPITATION METHOD

The present study focuses on the structural and optical properties of ZnO doped with Sm and Li at very dilute concentrations, with compounds Zn1-x-ySmxLiyO (x = 0, 0.03 and y =0, 0.01, 0.03, 0.05). These compounds have been synthesized by a chemical coprecipitation method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman microscopy. The XRD pattern of all the samples showed ZnO hexagonal wurtzite structure, sharp and intense peaks with small change in lattice parameters due to doping in ZnO, indicating the substitution of Sm and Li ions for Zn sites. For Raman spectra, the strongest peak centered at about 435-437 cm-1 can be observed in all the samples, and the intensity of this peak decreases with Sm doping and increases with Li doping. The optical properties of the samples were systematically studied by ultraviolet-visible spectroscopy (UV-V) and photoluminescence (PL) spectroscopy. The maximum absorption of ZnO and Zn0.97Sm0.03O samples appears around 370 and 374 nm respectively near the absorption edge. Doping with Li affects the absorption edge and make it shift toward ultra violet and that the absorption increase with increasing Li content. The PL spectra show a broad and strong visible emission at 564 nm emission covering a large part of the visible region indicating the presence of intrinsic defects like vacancies.

Phosphorous doped graphitic-C3N4 hierarchical architecture for hydrogen production from water under visible light

Enriched macro/mesoporous graphitic-C3N4 (g-C3N4) micro-rods (CNRs) are prepared by direct calcination of reflux treated ethylene diphosphonic acid-melamine complex fiber network. The optimized phosphorous doped CNRs (P-CNRs) exhibit a high hydrogen-evolution rate of 4960 μmol h−1 g−1 (5.5 times that of pristine g-C3N4) with a remarkable recycling stability. The significantly enhanced performance is found to be attributed to the intentionally designed morphology and electronic properties of P-CNRs. This distinctive hierarchical architecture of CNRs enhances the light scattering, and provides a high specific surface area and thus more catalytically active sites. The P doping of g-C3N4 greatly increases the visible light absorption, narrows the band gap. It also results in a boost in the density state of the conduction band as revealed by the electron paramagnetic resonance (EPR) spectra. The strong visible light emission quenching, observed from the photoluminescence of P-CNRs and photocurrent measurements, implies an enhanced charge transfer/separation process. This work presents a very simple and direct method of designing and developing high-performance visible light driven catalysts for hydrogen production.

Near-infrared downconversion luminescence of SrMoO4:Tm3+,Yb3+ phosphors

Tm3+ and Yb3+ codoped SrMoO4 phosphors were synthesized by the high-temperature solid-state reaction method. The structure, ultraviolet-visible diffuse reflectance spectra, photoluminescence, decay properties and theoretical energy transfer efficiency of the phosphors were investigated in detail. The electronic structure and band gap of SrMoO4 were estimated by density functional theory (DFT) calculation. The XRD results show that all the prepared phosphors can be readily indexed to scheelite-type structure. The strong visible emission around 473nm from Tm3+ (1G4→3H6) and near-infrared (NIR) emission around 998nm from Yb3+ (2F5/2→2F7/2) of the SrMoO4:Tm3+,Yb3+ phosphors were observed under 283nm excitation. The dependence of the visible and NIR emissions on Yb3+ concentration have also been investigated. The quenching concentration of Yb3+ ions approaches 10mol%. In addition, the energy transfer processes and possible transfer routes were proposed.

Encapsulation of TOPO stabilized NaYF4:Er3+,Yb3+ nanoparticles in biocompatible nanocarriers: Synthesis, optical properties and colloidal stability

The emulsification process leading to up-converting NaYF4:Er3+,Yb3+ NPs encapsulation, was performed using a modified water/oil/water double emulsion evaporation method, where poly(lactic-co-glycolic acid) was used as biocompatible polymer. Span 80 and Cremophor A25 were applied as non-ionic surfactants and dichloromethane as oily phase. The use of trioctylphosphine oxide ligands for the synthesis of up-converting NaYF4:Er3+,Yb3+ NPs allowed to obtain spherical particles with sizes below 10nm, what further facilitated the efficient encapsulation process. Those newly designed nanosystems were subjected to analysis of their morphology, colloidal stability and optical properties by: dynamic light scattering, ζ-potential, atomic force microscopy, transmission electron microscopy and measuring the up-conversion emission spectra of free and loaded NaYF4:Er3+,Yb3+ NPs. The encapsulated NaYF4:Er3+,Yb3+ NPs showed increased colloidal stability for a long period of 60 days of storage in different conditions. Simultaneously, the encapsulation process did not significantly influenced their optical properties and strong visible emission could be observed upon nearinfrared excitation.

The effect of structural and optical properties on the photocatalytic efficiency of Zinc Sulphide nanoparticles obtained by hydro/solvothermal decomposition of Zinc N,N-diethyldithiocarbamate

Cubic and hexagonal zinc sulphide nanoparticles were prepared by hydro/solvothermal decomposition of Zinc N,N-diethyldithiocarbamate by using different experimental conditions such as pH values, solvents and the presence of a particle stabilizer, sodium polyacrylate. The effect of these different experimental conditions on the microstructure and photocatalytical efficiency of ZnS was investigated in this work. Microstructural parameters, such as, apparent mean crystal size, microstrain and crystal size distribution were determined by analysis of experimental X-ray diffraction. Apparent mean crystal sizes were in the range of 6.5–44nm and the lattice microstrain varied from 0.24% to 0%. Dimethylformamide showed to be more suitable than water to form small particles with a very narrow size distribution. The obtained optical band gaps and Urbach energies were in range of 3.32–3.60eV and 0.09–0.15eV, respectively. Photoluminescence spectra showed strong visible light emissions (green, blue and white) associated to the electronic levels introduced by the presence of superficial defects. The photocatalytic efficiency of these samples was investigated towards methylene blue degradation and a correlation between this efficiency and the PL intensity was observed. This correlation was associated to the formation of surface active centres at catalyst surfaces and the local potential fluctuations of valence and conduction bands.

Multi-color fluorescent carbon dots for wavelength-selective and ultrasensitive Cu2+ sensing

Water dispersible carbon dots with multi-color visible luminescence were fabricated by a facile solvothermal route using citric acid/urea as carbon/nitrogen sources and dimethylformamide as solvent. Importantly, the intense long-wavelength red emission from carbon dots was selectively quenched upon the addition of Cu2+ ions, making them promising application as Cu2+ sensing material. There was no significant interference by other metal ions for Cu2+ detecting and the detection limit reached as low as 40 nM. Such sensing ability was almost reversible without any remarkable effect on sensitivity after introducing strong Cu2+ chelator ethylenediaminetetraacetic acid. It is expected that the investigated carbon dots with strong visible absorption and red emission as well as ultrasensitive Cu2+ sensing may find practical applications in biodetecting and bioimaging.

Improved light emission from n-ZnO/p-Si heterojunction with HfO2 as an electron blocking layer

Light-emitting diodes (LEDs) based on ZnO were fabricated on a p-Si substrate by using a pulsed laser deposition system. Significant electroluminescence (EL) improvement was demonstrated with the insertion of an HfO2 electron blocking layer (EBL) in n-ZnO/p-Si heterojunctions. Distinct near-band-edge emission at around 392nm accompanying by a broadly strong visible emission was achieved when a proper thickness of HfO2 EBL was used. Current-voltage and capacitance-voltage measurements confirmed that a proper thickness of the HfO2 EBL can effectively balance the injection of electrons and holes, resulting in an increase of radiative recombination in the ZnO active layer and thus enhancing the EL performance of the devices. Five independent emissions corresponding to five different transition processes were proposed to clarify the EL origination of the n-ZnO/HfO2/p-Si heterojunction LEDs by Gaussian deconvolutions. It is hoped that results in this work should be helpful for the development of ZnO-based LEDs that can integrate ZnO with the Si planar technology.

Infiltrated Zinc Oxide in Poly(methyl methacrylate): An Atomic Cycle Growth Study

We have investigated the growth of zinc oxide in a polymer matrix by sequential infiltration synthesis (SiS). The atomic cycle-by-cycle self-terminating reaction growth investigation was done using photoluminescence (PL), Raman, and X-ray photoemission spectroscopy (XPS). Results show clear differences between Zn atom configurations at the initial stages of growth. Mono Zn atoms (O–Zn and O–Zn–O) exhibit pure UV emission with little evidence of deep level oxygen vacancy states (VO). Dimer Zn atoms (O–Zn–O–Zn and O–Zn–O–Zn–O) show strong UV and visible PL emission from VO states 20 times greater than that from the mono Zn atom configuration. After three precursor cycles, the PL emission intensity drops significantly exhibiting first evidence of crystal formation as observed with Raman spectroscopy via the presence of longitudinal optical phonons. We also report a first confirmation of energy transfer between polymer and ZnO where the polymer absorbs light at 241 nm and emits at 360 nm, which coincides with...

Luminescent coverglass for improved absorption efficiency in III–V photovoltaic modules

An initial demonstration is reported in terms of maximising performance of photovoltaic modules. Experimental results of a triple junction solar cell covered with a 3 mm red-emitting luminous glass which can be efficiently excited by ultraviolet light indicate that this combination exhibits significantly enhanced efficiency of 36.5% under one-sun of AM1.5G. Integrating a luminescent (LSC) glass onto modules without converting any fabrication process at the device level is considered to be one of the predominant advantages of this device. Additionally, in order to achieve strong visible emission, it is mandatory to determine a thickness of LSC coverglass due to the edge reflection.