Tunable Photoluminescence Emission Research Articles

Tunable photoluminescence emissions and large dielectric constant of the electroactive poly(vinylidene fluoride–hexafluoropropylene) thin films modified with SnO2nanoparticles

Fabrication of optically active, electroactive and percolative SnO2NPs/PVDF–HFP nanocomposite thin films with remarkable dielectric constants.

Tunable Direct Bandgap Optical Transitions in MoS2 Nanocrystals for Photonic Devices

Highly luminescent MoS2 nanocrystals (NCs) with controlled size distribution have been achieved using a simple yet inexpensive and impurity free sono-chemical exfoliation method followed by gradient centrifugation. The size of nanocrystals could be varied within the diameter range of ∼4 to 70 nm. Typical MoS2 nanocrystal has exhibited high crystalline quality with 0.25 nm lattice fringe spacing for (002) planes for 2-H phase of MoS2. Raman spectra has revealed that both out-of-plane and in-plane vibrational modes are stiffen due to the edge effect of MoS2 NCs. The size tunable optical properties of MoS2 NCs have been investigated by optical absorption and photoluminescence spectroscopy. The coexistence of direct band gap emission from 2D MoS2 nanosheets and quantum confined nanocrystals has been achieved. A strong and tunable photoluminescence (560–518 nm) emission due to the quantum size effect of tiny NCs below a critical dimension is reported for the first time. The photocurrent measurement of the Au/M...

Tunable photoluminescence and direct white-light emission in Mg-based coordination networks.

The bpy, dpe and dppe were introduced as auxiliary ligands, respectively, to construct three magnesium-1,4-NDC coordination polymers (Mg-CPs) that exhibited tunable photoluminescence (PL) and direct white-light emission upon varying the excitation light.

Photoluminescence and white-light emission in two series of heteronuclear Pb(ii)–Ln(iii) complexes

Tunable photoluminescence and single component white light emission is achieved in Pb(ii)–Eu(iii) heteronuclear complexes.

Bmim]2SbCl5: a main group metal-containing ionic liquid exhibiting tunable photoluminescence and white-light emission.

An antimony-based photoluminescent ionic liquid, namely [Bmim]2SbCl5, has been synthesized and characterized. It exhibits bright yellow and white light emission, with quantum yield as high as 86.3% under UV irradiation.

Ag2Te quantum dots with compact surface coatings of multivalent polymers: Ambient one-pot aqueous synthesis and the second near-infrared bioimaging

In this study, we described a facile ambient one-pot aqueous synthesis of fluorescent Ag2Te quantum dots (QDs) adopting multivalent polymers (poly(maleic anhydride) homopolymers) as stabilizers. In experiments, Ag2Te QDs were synthesized via a stepwise addition of the stabilizers, precursors (AgNO3/Na2TeO3) and promoters (NaBH4/N2H4·H2O) in ambient one-pot aqueous solution. By regulating the compositions of raw materials, water-dispersed Ag2Te QDs (3.8–4.7nm) were achieved and exhibited tunable photoluminescence (PL) emission (995–1068nm) in the second near-infrared (NIR-II) region, accompanying with the minimized surface coating thickness (1.5–1.9nm). Such compact coating of multivalent polymers promoted PL emission of Ag2Te QDs, so showing high PL quantum yields (PLQYs: 13.1–15.2%). In addition to compact sizes and high PLQYs, experimental results testified that the Ag2Te QDs demonstrated high photo-/colloidal stability and ultralow cytotoxicity, which implied their promising applications, especially serving as an effective nanoprobe for bioimaging in the NIR-II biological window.

Highly transparent and colour-tunable composite films with increased quantum dot loading

Transparent films incorporated with quantum dots are promising light conversion materials for many cutting-edge technologies including light-emitting diodes and luminescent solar concentrators. In this work, we demonstrated that a combination of water soluble quantum dots and ultrathin cellulose nanofibers is an advantageous strategy to fabricate highly emissive thin films of tens of micrometers. By varying the composition of quantum dots, these thin films exhibit tunable photoluminescence emissions, ranging from blue to red as well as white light. Because of the inherent nanoscale phase separation of cellulose nanofibers, the loading content of quantum dots can be increased up to 50 wt%, which results in a significant increase of the refractive index. The combination of high refractive index (∼1.56), colour-tunable emissions (450–650 nm) and high transparency (∼80%, at a wavelength longer than the absorption band of quantum dots) makes them promising candidates for photonic and optoelectronic devices.

Enhanced stability and emission intensity of aqueous CdTe/CdS core–shell quantum dots with widely tunable wavelength

The stability and photoluminescence (PL) emission intensity of quantum dots (QDs) are particularly interesting for various bioapplications. In this paper, monodisperse CdTe/CdS core–shell QDs were synthesized in aqueous phase. The size of CdTe core and the thickness of CdS shell played important roles in the properties of CdTe/CdS QDs. Transmission electron microscopy (TEM) images show that the average diameters of CdTe/CdS core–shell QDs increased to ∼5 nm compared with that of CdTe core QDs (∼3.6 nm). X-ray diffraction patterns show that the CdTe/CdS core–shell QDs possess cubic zinc blende structure. After the overgrowth of CdS shell on CdTe core, a widely tunable PL emission wavelength (485–720 nm) of the core–shell QDs can be obtained, which covers nearly the full visible spectrum. The PL intensity of the CdTe/CdS core–shell QDs shows two-fold increase compared with that of the CdTe core QDs. PL results show that the photostability of the samples is enhanced through the growth of CdS on the CdTe QDs.

Size-controlled synthesis of ZnO quantum dots in microreactors

In this paper, we report on a continuous-flow microreactor process to prepare ZnO quantum dots (QDs) with widely tunable particle size and photoluminescence emission wavelengths. X-ray diffraction, electron diffraction, UV–vis, photoluminescence and transmission electron microscopy measurements were used to characterize the synthesized ZnO QDs. By varying operating conditions (temperature, flow rate) or the capping ligand, ZnO QDs with diameters ranging from 3.6 to 5.2 nm and fluorescence maxima from 500 to 560 nm were prepared. Results obtained show that low reaction temperatures (20 or 35 °C), high flow rates and the use of propionic acid as a stabilizing agent are favorable for the production of ZnO QDs with high photoluminescence quantum yields (up to 30%).

The Use of a Microreactor for Rapid Screening of the Reaction Conditions and Investigation of the Photoluminescence Mechanism of Carbon Dots

A microreactor is applied and reported, for the first time, in the field of research of carbon dots (CDs), including rapid screening of the reaction conditions and investigation of the photoluminescence (PL) mechanism. Various carbonaceous precursors and solvents were selected and hundreds of reaction conditions were screened (ca. 15 min on average per condition). Through analyzing the screened conditions, tunable PL emission maxima, from about 330 to 550 nm with respectable PL quantum yields, were achieved. Moreover, the relationship between different developmental stages of the CDs and the PL properties was explored by using the microreactor. The PL emission was observed to be independent of the composition, carbonization extent, and morphology/size of the CDs. This study unambiguously presents that a microreactor could serve as a promising tool for the research of CDs.

Water-soluble multidentate polymers compactly coating Ag2S quantum dots with minimized hydrodynamic size and bright emission tunable from red to second near-infrared region.

Hydrodynamic size-minimized quantum dots (QDs) have outstanding physicochemical properties for applications in multicolor molecular and cellular imaging at the level of single molecules and nanoparticles. In this study, we have reported the aqueous synthesis of Ag2S QDs by using thiol-based multidentate polymers as capping reagents. By regulating the composition of the precursors (AgNO3 and sulfur-N2H4·H2O complex) and multidentate polymers (poly(acrylic acid)-graft-cysteamine-graft-ethylenediamine), as well as the reaction time, Ag2S QDs (2.6-3.7 nm) are prepared, displaying tunable photoluminescence (PL) emission from red to the second near-infrared region (687-1096 nm). The small hydrodynamic thickness (1.6-1.9 nm) of the multidentate polymers yields a highly compact coating for the QDs, which results in the bright fluorescent QDs with high PL quantum yields (QYs: 14.2-16.4%). Experimental results confirm that the QDs have high PL stability and ultralow cytotoxicity, as well as high PLQYs and small hydrodynamic sizes (4.5-5.6 nm) similar to fluorescent proteins (27-30 kDa), indicating the feasibility of highly effective PL imaging in cells and living animals.

DOX-CONJUGATED HIGH-QUALITY AgZnInS QDs FOR REVERSAL OF MULTIDRUG RESISTANCE

The synthesis of water-soluble quantum dots (QDs) has recently received extensive attention due to noninvasive detection of biological information in living subjects. In this paper, high-quality water-soluble (cadmium-free) quaternary AgZnInS QDs have been successfully synthesized using a green synthetic route. The as-prepared QDs exhibit tunable photoluminescence (PL) emission between 521 and 658 nm. Secondly, multidrug resistance (MDR) is a major impediment to the effective cancer chemotherapy. DOX, a widely used antitumor drug was modified on the surface of the QDs in this study. It, therefore, significantly enhanced the cytotoxicity of DOX to MDR cancer cells as the QDs could bring the DOX to nucleus.

Tunable photoluminescence and spectrum split from fluorinated to hydroxylated graphene

Tunable control over the functionalization of graphene is significantly important to manipulate its structure and optoelectronic properties. Yet the chemical inertness of this noble carbon material poses a particular challenge for its decoration without forcing reaction conditions. Here, a mild, operationally simple and controllable protocol is developed to synthesize hydroxylated graphene (HOG) from fluorinated graphene (FG). We successfully demonstrate that under designed alkali environment, fluorine atoms on graphene framework are programmably replaced by hydroxyl groups via a straightforward substitution reaction pathway. Element constituent analyses confirm that homogeneous C-O bonds are successfully grafted on graphene. Rather different from graphene oxide, the photoluminescence (PL) emission spectrum of the obtained HOG becomes split when excited with UV radiation. More interestingly, such transformation from FG facilitates highly tunable PL emission ranging from greenish white (0.343, 0.392) to deep blue (0.156, 0.094). Additionally, both experimental data and density function theory calculation indicate that the chemical functionalization induced structural rearrangement is more important than the chemical decoration itself in tuning the PL emission band tail and splitting energy gaps. This work not only presents a new way to effectively fabricate graphene derivatives with tunable PL performance, but also provides an enlightening insight into the PL origin of graphene related materials.

Homochiral Zinc(II) Coordination Compounds Based on In-Situ-Generated Chiral Amino Acid–Tetrazole Ligands: Circular Dichroism, Excitation Light-Induced Tunable Photoluminescence, and Energetic Performance

We employed two pairs of new in-situ-generated chiral amino acid-tetrazole ligands in constructing homochiral Zn(II) coordination compounds: [Zn(tzet)]n (1a for (S)-tzet and 1b for (R)-tzet, H2tzet = N-[2-(1H-tetrazol-5-yl)ethyl]tryptophan) and [Zn(tzep)(H2O)2]·H2O (2a for (S)-tzep and 2b for (R)-tzep, H2tzep = N-[2-(1H-tetrazol-5-yl)ethyl]proline), which were hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. Structural analysis reveals that 1 features a 2D homochiral framework generated by both tetrazolate and carboxylate bridges in tzet(2-) ligands. The isolated structure of 2 is stabilized by extensive hydrogen bonds, which leads to formation of a supramolecular 2D architecture. The absolute configuration induced at the nitrogen atoms of 1 and 2 is strictly related to the neighboring chiral carbon atoms by hydrogen-bond interactions. To further investigate their chirality, the combined experimental and theoretical analyses of circular dichroism spectra reveal the absolute configurations and nature of the Cotton effects. Solid-state excitation and emission spectra for 1 and 2 at room temperature were investigated with relevant density of states calculation, and tunable photoluminescence emission of 1 under different excitation wavelengths was discussed. As nitrogen-rich tetrazolate compounds, 1 and 2 possess higher enthalpies of combustion and may serve as a new family of promising energetic materials.

Tunable photoluminescence emission from Cadmium Tellurium nanorods with ethylenediamine template-assistance at a low temperature

Cadmium Tellurium (CdTe) nanorods were successfully synthesized by a novel soft-chemical solvothermal method with ethylenediamine template. The ethylenediamine plays a critical role in the formation of CdTe nanocrystals. Single-crystalline CdTe with rod-like and flower-like morphologies has been successfully synthesized at 120°C for 4h. The prepared nanorods have cubic characteristics with a diameter of about 60nm and a length of up to several micrometers. The nanorod exhibits a concentration tunable photoluminescence and a narrow full width at half-maximum (FWHM) value of PL spectra can be obtained, which may be useful for developing solar cell devices or LED, chemical sensors or in optical device. Based on a series of comparative experiments under different reaction conditions, the probable formation mechanism and photoluminescence emission of CdTe nanocrystals are proposed.

Fixed‐Component Lanthanide‐Hybrid‐Fabricated Full‐Color Photoluminescent Films as Vapoluminescent Sensors

Full-color lanthanide (Ln) photoluminescent materials have attracted considerable interest owing to their potential applications in display systems and lighting technologies. Herein, full-color photoluminescent films have been designed and fabricated facilely with a fixed-component Ln-based (Ln=Tb and Eu) polymer hybrid doped with a proton-sensitive amide-type β-diketonated photosensitizer, N-(2-pyridinyl)benzoylacetamide (HPBA). The tunable photoluminescence emissions of the films are achieved by changing the amounts of OH(-) in the hybrid rather than varying the relative concentrations of the lanthanide ions and photosensitizers, thus representing a new paradigm for full-color displays. The emission color can also be finely tuned through the variation of the excitation wavelength, and white-light emission can be achieved when the given film is excited at the visible region (405 nm). The photophysical properties and the mechanisms of the intra- and intermolecular energy transfer before and after deprotonation have been investigated in detail. Meanwhile, the films might find application as vapoluminescent sensors due to their good stability, sensitivity, reversibility, and quick response when triggered by a base-acid vapor.

Annealing temperature dependence of photoluminescent characteristics of silicon nanocrystals embedded in silicon-rich silicon nitride films grown by PECVD

Recently, light emission from silicon nanostructures has gained great interest due to its promising potential of realizing silicon-based optoelectronic applications. In this study, luminescent silicon nanocrystals (Si–NCs) were in situ synthesized in silicon-rich silicon nitride (SRSN) films grown by plasma-enhanced chemical vapor deposition (PECVD). SRSN films with various excess silicon contents were deposited by adjusting SiH4 flow rate to 100 and 200sccm and keeping NH3 one at 40sccm, and followed by furnace annealing (FA) treatments at 600, 850 and 1100°C for 1h. The effects of excess silicon content and post-annealing temperature on optical properties of Si–NCs were investigated by photoluminescence (PL) and Fourier transform infrared spectroscopy (FTIR). The origins of two groups of PL peaks found in this study can be attributed to defect-related interface states and quantum confinement effects (QCE). Defect-related interface states lead to the photon energy levels almost kept constant at about 3.4eV, while QCE results in visible and tunable PL emission in the spectral range of yellow and blue light which depends on excess silicon content and post-annealing temperature. In addition, PL intensity was also demonstrated to be highly correlative to the excess silicon content and post-annealing temperature due to its corresponding effects on size, density, crystallinity, and surface passivation of Si–NCs. Considering the trade-off between surface passivation and structural properties of Si–NCs, an optimal post-annealing temperature of 600°C was suggested to maximize the PL intensity of the SRSN films.

Tunable fluorescence emission of ternary nonstoichiometric Ag–In–S alloyed nanocrystals

Low toxic, nonstoichiometric colloidal Ag-In-S ternary quantum dots with different Ag content were synthesized by a one-pot hot-injection method based on the reaction of metal acetylacetonates with sulfur dissolved in octadecene. X-ray diffraction (XRD), transmission electron microscopy, and high-resolution transmission electron microscopy (HRTEM) were used to characterize the size, structure, and morphology of these samples. ICP-MS was employed to analyze the compositions of Ag-In-S nanocrystals. The optical properties were characterized by UV-Vis absorption, photoluminescence (PL) spectroscopy, and time-resolved photoluminescence. Varying the fraction of cationic and capping agents, the compositions of Ag-In-S nanocrystals were precisely controlled. XRD and HRTEM results indicate the compositional homogeneity of Ag-In-S. The emission spectra across the different compositions exhibiting a single bandgap feature further confirm the formation of Ag-In-S alloy NCs, rather than phase separated Ag2S and In2S3. Composition-dependent tunable PL emissions have been observed. The relative PL quantum yield is up to 16 %, which exhibited substantially enhanced comparing with the stoichiometric AgInS2 semiconductor core QDs reported in previous literature. The PL decay curve of Ag-In-S has a biexponential characteristic, which indicates that the recombination of an electron and a hole is dominated by the surface defect and the recombination process associated with internal traps is reduced significantly. The large Stokes shift between the absorption peaks and their emissions should inhibit the reabsorption and Forster energy transfer between Ag-In-S nanocrystals, which provides the alternative in the further applications where high-concentrations of nanocrystals are needed.

Multifunctional 3-Fold Interpenetrated Porous Metal–Organic Frameworks Composed of Unprecedented Self-Catenated Networks

A 3-fold interpenetrating porous metal–organic framework, namely, Zn(bdc)(L)·solvents (1, L = N4,N4′-di(pyridin-4-yl)biphenyl-4,4′-dicarboxamide, H2bdc = terephthalic acid), composed of self-catenated nets with unprecedented hxg-d-4-Fddd topology is reported. Upon removal of guest molecules, the crystal lattice is unaffected, and the resulting permanent porosity can be applied for gas chromatography separation of various organic molecules. Furthermore, remarkable tunable photoluminescence and direct white emission dependent on excitation wavelength, as well as visible light photocatalytic activity, are also observed, creating a new multifunctional material antetype.

Facile Synthesis and Luminescence Characteristics of High-Quality CdS: Eu/ZnS Core/Shell Nanocrystals with Biocompatibility

In this paper, we report a facile method to synthesize high quality CdS: Eu nanocrystals (NCs) and CdS: Eu/ZnS NCs with strong photoluminescence (PL). The influence of various experimental variables including the concentration of Eu3+ ions, the reaction time and the reaction temperature were investigated systematically. In addition, the PL properties of CdS: Eu NCs exhibited pH sensitive. Under the acid condition, pH value of the CdS: Eu NCs solution played an important role in determining PL emission intensity. However, under the alkaline condition, the obtained CdS: Eu NCs exhibited a tunable PL emission wavelength (from 490 nm to 610 nm) when pH value was adjusted from pH 7 to 10. After coating with ZnS shell, the CdS: Eu/ZnS NCs showed enhanced PL intensity compare with one of the CdS: Eu NCs. The CdS: Eu NCs and CdS: Eu/ZnS NCs were characterized by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). In addition, the biocompatibility of these NCs was measured by hemolytic test, which indicated that CdS: Eu/ZnS NCs were more biocompatible than CdS: Eu NCs at the same conditions. It can be expected that CdS: Eu/ZnS NCs are promising biolabeling materials.