Tunable Visible Emission Research Articles

Fluorescence tuning of Zn(ii)-based metallo-supramolecular coordination polymers and their application for picric acid detection

A series of metallo-supramolecular coordination polymers displayed strong and tunable visible luminescent emission and possessed the capability for detection of picric acid (PA) with high sensitivity and selectivity.

Study on visible emission of Cu-ion-doped perovskite hafnate in view of excitation energy dependence

We studied on the visible emission of Cu-ion-doped perovskite hafnate SrHfO3 (SHO:Cu) with the photo-excitation energy dependence. The polycrystalline SHO:Cu samples were newly synthesized in the solid state reaction method. From the X-ray diffraction measurement it was found that the crystalline structure of SHO:Cu is nearly identical to that of undoped SrHfO3. Interestingly, the photoluminescence excitation (PLE) spectra change significantly with the emission energy, which is linked to the strong dependence of the visible emission on the photo-excitation energy. This unusual emission behavior is likely to be associated with the mixed valence states of the doped Cu ions, which were revealed by X-ray photoelectron spectroscopy. We compared our finding of tunable visible emission in the SHO:Cu compounds with the cases of similar materials, SrTiO3 and SrZrO3 with Cu-ion-doping.

Light Emitting Properties of Si-Rich-Si3N4 Films Grown By PECVD Method

Bandgap engineering of Si-based materials through the control of the distribution of Si nanoclusters’ (Si-ncs) offered future applications of Si-based nanostructured materials in optoelectronics as low-cost, miniaturized, and CMOS-compatible, light-emitting and photovoltaic devices. In the past, most efforts were concentrated on the development of luminescent Si-ncs embedded in SiO2 host. However, its insulating nature remains a barrier for the production of future electrically pumped LEDs and efficient photovoltaic cells. This detrimental aspect can be coped with a medium of higher conductivity and lower band gap, for instance, Si nitride. Tunable room temperature visible light emission from Si-ncs embedded in Si nitride matrices has been recently demonstrated. Present work deals with the Si-rich Silicon nitride films were grown by PECVD technique on silicon substrates. The film stoichiometry was controlled via variation of NH3/SiH4 ratio from R=0.45 up to 1.0. Thermal treatment was performed at 1100°C for 30min in nitrogen flow to form Si-ncs. To control structural and light emitting properties of the films Raman scattering, X-ray diffraction (XRD), Transmission electron microscopy (TEM) and photoluminescence (PL) methods were used. The evolution of PL spectra with the temperature of measurements from 20 to 300 K was studied also aiming at the determination of the types of optical transitions. The PL spectra were found to be complex and the shape and magnitude of PL spectra depends on silicon nitride stoichiometry. The increase of gas ratio from R=0.63 to R=1 results in the shift of PL peak position from 1.6 eV up to 2.7 eV. Analysis of the temperature dependence of PL spectra revealed the presence of several PL components with the maxima at 2.9-3.0 eV, 2.5-2.7 eV, 1.9-2.2 eV and 1.8-1.9 eV. The peak position of the former three PL components unchanged with the decrease of temperature of the measurements. This allows describing all these components to the defects of silicon nitride host. At the same time, PL band peaked at 1.8-1.9 eV showed high-energy shift with sample cooling and can be ascribed to the exciton recombination inside Si-ncs. The presence of these latter was confirmed by Raman scattering spectra and TEM images. The nature of light emitting defects in silicon nitride, the mechanism of photoluminescence and the way for the optimization of light emitting properties are discussed.

Graphene‐based nanomaterials as molecular imaging agents

Molecular imaging (MI) is a noninvasive, real-time visualization of biochemical events at the cellular and molecular level within tissues, living cells, and/or intact objects that can be advantageously applied in the areas of diagnostics, therapeutics, drug discovery, and development in understanding the nanoscale reactions including enzymatic conversions and protein-protein interactions. Consequently, over the years, great advancement has been made in the development of a variety of MI agents such as peptides, aptamers, antibodies, and various nanomaterials (NMs) including single-walled carbon nanotubes. Recently, graphene, a material popularized by Geim & Novoselov, has ignited considerable research efforts to rationally design and execute a wide range of graphene-based NMs making them an attractive platform for developing highly sensitive MI agents. Owing to their exceptional physicochemical and biological properties combined with desirable surface engineering, graphene-based NMs offer stable and tunable visible emission, small hydrodynamic size, low toxicity, and high biocompatibility and thus have been explored for in vitro and in vivo imaging applications as a promising alternative of traditional imaging agents. This review begins by describing the intrinsic properties of graphene and the key MI modalities. After which, we provide an overview on the recent advances in the design and development as well as physicochemical properties of the different classes of graphene-based NMs (graphene-dye conjugates, graphene-antibody conjugates, graphene-nanoparticle composites, and graphene quantum dots) being used as MI agents for potential applications including theranostics. Finally, the major challenges and future directions in the field will be discussed.

Preparation of core-shell NaGdF4 nanoparticles doped with luminescent lanthanide ions to be used as upconversion-based probes.

Sodium gadolinium fluoride (NaGdF4) is an ideal host material for the incorporation of luminescent lanthanide ions because of its high photochemical stability, low vibrational energy and its ability to mediate energy exchanges between the lanthanide dopants. This protocol describes the detailed experimental procedure for synthesizing core-shell NaGdF4 nanoparticles that incorporate lanthanide ions into different layers for efficiently converting a single-wavelength, near-IR excitation into a tunable visible emission. These nanoparticles can then be used as luminescent probes in biological samples, in 3D displays, in solar energy conversion and in photodynamic therapy. The NaGdF4 nanoparticles are grown through co-precipitation in a binary solvent mixture of oleic acid and 1-octadecene. Doping by lanthanides with controlled compositions and concentrations can be achieved concomitantly with particle growth. The lanthanide-doped NaGdF4 nanoparticles then serve as seed crystals for subsequent epitaxial growth of shell layers comprising different lanthanide dopants. The entire procedure for the preparation and isolation of the core-shell nanoparticles comprising two epitaxial shell layers requires ∼15 h for completion.

Tunable visible upconversion emission in Er3+/Yb3+-codoped KCaBO3 phosphors by introducing Ho3+ ions

Herein, the tunable upconversion (UC) emission from KCaBO3 phosphors, codoped with fixed Er3+,Yb3+ and various Ho3+-concentrations, has been demonstrated. Under 980nm laser excitation, strong tunability from green to red color emission was successfully achieved via controlling the Ho3+-codoping in KCaBO3:Er3+,Yb3+,xHo3+ phosphor due to efficient two-photon excitations and inter-ion energy transfer (from Yb3+ to Er3+/Ho3+) mechanisms. Substantial decrease in the green–red intensity ratio from 3.94 to 0.21 and systematic enhancement in energy transfer efficiency (η), with the increment of Ho3+-content, supported the above mechanisms.

Gold nanoclusters with enhanced tunable fluorescence as bioimaging probes

Development of unique bioimaging probes offering essential information's about bio environments are an important step forward in biomedical science. Nanotechnology offers variety of novel imaging nanoprobes having high-photo stability as compared to conventional molecular probes which often experience rapid photo bleaching problem. Although great advances have been made on the development of semiconductor nanocrystals-based fluorescent imaging probes, potential toxicity issue by heavy metal component limits their in vivo therapeutic and clinical application. Recent works show that fluorescent gold clusters (FGCs) can be a promising nontoxic alternative of semiconductor nanocrystals. FGCs derived imaging nanoprobes offer stable and tunable visible emission, small hydrodynamic size, high biocompatibility and have been exploited in variety in vitro and in vivo imaging applications. In this review, we will focus on the synthetic advances and bioimaging application potentials of FGCs. In particular, we will emphasize on functional FGCs that are bright and stable enough to be useful as bioimaging probes.

Carbon Nanoparticle-based Fluorescent Bioimaging Probes

Fluorescent nanoparticle-based imaging probes have advanced current labelling technology and are expected to generate new medical diagnostic tools based on their superior brightness and photostability compared with conventional molecular probes. Although significant progress has been made in fluorescent semiconductor nanocrystal-based biological labelling and imaging, the presence of heavy metals and the toxicity issues associated with heavy metals have severely limited the application potential of these nanocrystals. Here, we report a fluorescent carbon nanoparticle-based, alternative, nontoxic imaging probe that is suitable for biological staining and diagnostics. We have developed a chemical method to synthesise highly fluorescent carbon nanoparticles 1–10 nm in size; these particles exhibit size-dependent, tunable visible emission. These carbon nanoparticles have been transformed into various functionalised nanoprobes with hydrodynamic diameters of 5–15 nm and have been used as cell imaging probes.

Silicon nanoparticle based fluorescent biological label via low temperature thermal degradation of chloroalkylsilane

A simple low temperature colloid-chemical synthetic method is reported for size controlled synthesis of hydrophobic silicon nanoparticles in the 1-10 nm range. These silicon nanoparticles show size dependent tunable visible emission from blue to red with fluorescence quantum yield in the range of 6-13%. These silicon nanoparticles can be subjected to extensive surface chemistry without significant loss of their fluorescence properties. The as-synthesized red emitting nanoparticles have been transformed into water soluble functional nanoprobes of 18 nm hydrodynamic diameter and 5% fluorescence quantum yield and used as fluorescent biological labels.

FORMATION OF II–VI SEMICONDUCTOR NANOCRYSTALS WITH TUNABLE VISIBLE EMISSION IN AQUEOUS SOLUTION PROMOTED BY HYDRAZINE

II–VI Semiconductor nanocrystals (NCs) with tunable visible emission, such as CdS , CdSe and CdTe , were synthesized in aqueous solution using thiols as capping molecules. Hydrazine was found to promote the growth of NCs through a special mechanism. In only a few hours, the synthesis process was completed at room temperature. Under moderate conditions, the capping molecules not only changed the growth rate of NCs simply by varying the concentration, but also altered the spectral properties of NCs. The capping molecules with amino groups were propitious to the growth of CdS NCs, whereas the kinetic growth of CdS NCs was more affected by the surface passivation efficiency of NCs than by steric hindrance in the system. The fastest growth of the CdS NCs was achieved when glutathione was used as a capping molecule, while the emission of CdS and CdSe NCs were shown to remain steady and tunable using the same capping molecule. The growth rate of 3-mercaptopropionic acid-capped CdS and CdSe NCs slowed down significantly, while CdTe NCs were obtained with excellent emission properties when capped with the same molecule. Furthermore, our approach will also be useful for the study of the kinetic growth of NCs in aqueous solution.

One-pot fast synthesis of spherical ZnS/Au nanocomposites and their optical properties

Spherical ZnS/Au nanocomposites have been synthesized through a fast one-step microwave-hydrothermal route. Surfactant polyvinylpyrrolidone (PVP) was used as shape modifier to control the size of products. The use of different sulfur sources also resulted in nanospheres with different sizes. The formation mechanism of the nanocomposites is discussed. The UV–vis and photoluminescence properties of the as-prepared nanocomposites with different Au doping concentrations showed tunable UV and visible emission intensity.

Fast One-Step Synthesis of Biocompatible ZnO/Au Nanocomposites with Hollow Doughnut-Like and Other Controlled Morphologies

Hollow doughnut-like ZnO/Au nanocomposites have been synthesized through a fast one-step microwave-assisted hydrothermal route. The formation mechanism of the product is closely connected with the coordination and selective adsorption effect of trisodium citrate (TSC). Other different structures, such as ZnO nanorods/Au nanoparticles, ZnO nanodisks/Au nanoparticles, and ZnO nanospheres/Au nanoparticles have also been obtained in control experiments. The UV–vis and photoluminescence properties of the as-prepared hollow structures with different Au concentrations showed tunable UV and visible emission intensity. The hollow ZnO/Au nanocomposites are photostable with a strong resonance Raman signal. The colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assays showed that ZnO/Au nanomaterials have low biological cytotoxicity on human colon cancer cells (LOVO cells) at the concentration of 50 μg/mL. The as-prepared ZnO/Au nanocomposites with good biocompatibility may have potential applications in biomedicine and biosensors.

Enhanced visible photoluminescence in ZnO quantum dots by promotion of oxygen vacancy formation

We report on the synthesis of ZnO quantum dots (QDs) rich in oxygen vacancies by inducing an oxygen deficient environment. The precise tunability of particle size is achieved by counter ion capping of the precursor used for synthesis. The prepared QDs show size tunable visible emission with high quantum yield.

Tunable Visible Emission of Novel Zinc Oxide Nanocrystals

This letter reports ZnO nano nanocrystals with tunable visible fluorescent emission which utilizes optically stimulated luminescence (OSL). ZnO nano nanocrystals deposited on glass substrates, and the blue-shifted two narrow photoluminescence peaks at the violet band and green band have been observed for the first time. Such promising multiwavelength tunable nanocrystals can be easily fabricated and are very attractive for a variety of applications such as synchronous fluorescent sensing, DNA sequencing, bioprocess monitoring, etc. <?Pub _bookmark="" Command="[Quick Mark]"?>

Broad-band tunable visible emission of sol–gel derived SiBOC ceramic thin films

Strong broad band tunable visible emission of SiBOC ceramic films is reported and the results are compared with one of boron free SiOC ceramic films. The insertion of boron into the SiOC network is verified by Fourier-Transform Infrared Spectroscopy. Optical properties are studied by photoluminescence and ultraviolet-visible spectroscopy measurements. Boron addition causes a decrease in the emission intensity attributed to defect states and shifts the emission to the visible range at lower temperatures (800–900°C) leading to a very broad tunable emission with high external quantum efficiency.

Synthesis of zinc oxide nanoparticles with strong, tunable and stable visible light emission by solid-state transformation of Zn(ii)–organic coordination polymers

Ligand-free ZnO nanoparticles with a mean diameter of 100 nm were simply synthesized by solid-state transformation of Zn(II)–organic infinite coordination polymer particles (ICPs) at 550 °C. The well-crystallized ZnO nanoparticles exhibit strong visible emission centred at 600 nm and the emission light clearly appeared under UV light, representing the first example of strong, tunable and stable visible photoluminescence from relatively large ZnO nanoparticles both in solution and in the solid state. ZnO nanoparticles were synthesized by this approach without any surfactant or capping molecules and their visible emission is generally stable and remains almost unchanged while keeping samples in air for at least 3 months. The possible mechanism of strong visible emission was also proposed; oxygen vacancies and surface defects play an important role in the visible emission based on the results of electron paramagnetic resonance (EPR) spectra and decay lifetime curve. ZnO nanoparticles with strong visible emission centred at 500 nm could also be obtained by changing the compositions of coordination polymers. This solid-state transformation method provides a new approach to synthesize stable ZnO nanoparticles with strong and tunable visible emission by using coordination polymers.

Tunable Visible and Near-IR Emission from Sub-10 nm Etched Single-Crystal Si Nanopillars

Visible and near-IR photoluminescence (PL) is reported from sub-10 nm silicon nanopillars. Pillars were plasma etched from single crystal Si wafers and thinned by utilizing strain-induced, self-terminating oxidation of cylindrical structures. PL, lifetime, and transmission electron microscopy were performed to measure the dimensions and emission characteristics of the pillars. The peak PL energy was found to blue shift with narrowing pillar diameter in accordance with a quantum confinement effect. The blue shift was quantified using a tight binding method simulation that incorporated the strain induced by the thermal oxidation process. These pillars show promise as possible complementary metal oxide semiconductor compatible silicon devices in the form of light-emitting diode or laser structures.

Tunable visible emission and warm white photoluminescence of lithium-doped zinc oxide thin films

Visible emission of Li-doped ZnO (LZO) thin films prepared by a sol–gel method has been tuned in a wide range from blue-green to yellow. Blue-green, yellow, and warm white emissions are observed as 5.0 at.% LZO thin films are annealed in N2, air, and He, respectively. A strong dependence of the defect emission of LZO on annealing atmosphere suggests that the visible emissions of LZO are related to intrinsic defects rather than lithium impurities.

Controlled Synthesis and Biocompatibility of Water-Soluble ZnO Nanorods/Au Nanocomposites with Tunable UV and Visible Emission Intensity

ZnO nanorods/Au nanocomposites with Au nanocrystals growing at tips of ZnO nanorods or located along the surface of the nanorods can be synthesized via a facile low-cost solution method. The number of Au nanoparticles grown on ZnO nanorods can be controlled by tuning the molar ratio of ZnO to HAuCl4; thus, the ZnO/Au heterostructures displayed tunable UV and visible emission intensity. The cytotoxic studies on two different cell lines (CHO cells and Hela cells) indicated that ZnO/Au hybrid nanocrystals are biologically nontoxic. The MTT assays of these two cells are consistent, showing that ZnO/Au hybrid nanomaterials were low cytotoxic at concentrations of 10 μg/mL. It is found that cytotoxicity of ZnO/Au hybrid nanocomposites mainly comes from ZnO nanorods. Cellular uptake experiments revealed the ZnO/Au hybrid nanocrystals can enter into the endosomes and the cytosol. The as-prepared ZnO/Au hybrid nanocomposites with good biocompatibility may have potential applications in biomedicine.