Spectrally Resolved Photoluminescence Imaging of ZnO Nanocrystals at Single-Particle Levels

Positive Effects of a Perovskite Film on the Radioluminescence Properties of a ZnO:Ga Crystal Scintillator

To improve the radioluminescence (RL) performance of ZnO:Ga (GZO) crystal scintillators and overcome the challenge of their self-absorption, we proposed a two-layer composite scintillator consisting of a GZO wafer and a 70 nm lead halide perovskite film(CsPbBr₃, CH₃NH₃PbBr₃). The effects of the perovskite film on the RL properties were studied. The results showed that the perovskite quantum dot film substantially changed the RL spectrum of GZO and prevented self-absorption. The RL of the samples were enhanced by 66% to 151% through the photoluminescence (PL) of the perovskite film, while the energy-resolving power and spatial-resolving power were maintained at the same level as that of GZO image converters. The present experiments and discussions confirmed that the perovskite film improved the RL, and this study suggests a new wavelength regulation method among scintillators, converters, and back-end optical devices. The applications of perovskites in the field of radiation detection and imaging have been extended.

Multifunctional ZnO/SiO2 Core/Shell Nanoparticles for Bioimaging and Drug Delivery Application

Semiconducting nanoparticles with luminescent properties are used as detection probes and drug carriers in in-vitro and in-vivo analysis. ZnO nanoparticles, due to its biocompatibility and low cost, have shown potential application in bioimaging and drug delivery. Thus, ZnO/SiO₂ core/shell nanoparticle was synthesised by wet chemical method for fluorescent probing and drug delivery application. The synthesised core/shell nanomaterial was characterized using XRD, FTIR, UV-VIS spectroscopy, Raman spectroscopy, TEM and PL analysis. The silicon shell enhances the photoluminescence and aqueous stability of the pure ZnO nanoparticles. The porous surface of the shell acts as a carrier for sustained release of curcumin. The synthesized core/shell particle shows high cell viability, hemocompatibility and promising florescent property. Graphical Abstract.

Time-Resolved Photoluminescence Microscopy for the Analysis of Semiconductor-Based Paint Layers

In conservation, science semiconductors occur as the constituent matter of the so-called semiconductor pigments, produced following the Industrial Revolution and extensively used by modern painters. With recent research highlighting the occurrence of various degradation phenomena in semiconductor paints, it is clear that their detection by conventional optical fluorescence imaging and microscopy is limited by the complexity of historical painting materials. Here, we illustrate and prove the capabilities of time-resolved photoluminescence (TRPL) microscopy, equipped with both spectral and lifetime sensitivity at timescales ranging from nanoseconds to hundreds of microseconds, for the analysis of cross-sections of paint layers made of luminescent semiconductor pigments. The method is sensitive to heterogeneities within micro-samples and provides valuable information for the interpretation of the nature of the emissions in samples. A case study is presented on micro samples from a painting by Henri Matisse and serves to demonstrate how TRPL can be used to identify the semiconductor pigments zinc white and cadmium yellow, and to inform future investigations of the degradation of a cadmium yellow paint.

Zinc oxide nanorods functionalized paper for protein preconcentration in biodiagnostics

Distinguishing a specific biomarker from a biofluid sample containing a large variety of proteins often requires the selective preconcentration of that particular biomarker to a detectable level for analysis. Low-cost, paper-based device is an emerging opportunity in diagnostics. In the present study, we report a novel Zinc oxide nanorods functionalized paper platform for the preconcentration of Myoglobin, a cardiac biomarker. Zinc oxide nanorods were grown on a Whatman filter paper no. 1 via the standard hydrothermal route. The growth of Zinc oxide nanorods on paper was confirmed by a combination of techniques consisting of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS,) scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDX) analysis. The Zinc oxide nanorods modified Whatman filter paper (ZnO-NRs/WFP) was further tested for use as a protein preconcentrator. Paper-based ELISA was performed for determination of pre-concentration of cardiac marker protein Myoglobin using the new ZnO-NRs/WFP platform. The ZnO-NRs/WFP could efficiently capture the biomarker even from a very dilute solution (Myoglobin < 50 nM). Our ELISA results show a threefold enhancement in protein capture with ZnO-NRs/WFP compared to unmodified Whatman filter paper, allowing accurate protein analysis and showing the diagnostic concept.

Internal stress induced natural self-chemisorption of ZnO nanostructured films

The energetic particles bombardment can produce large internal stress in the zinc oxide (ZnO) thin film, and it can be used to intentionally modify the surface characteristics of ZnO films. In this article, we observed that the internal stress increased from −1.62 GPa to −0.33 GPa, and the naturally wettability of the textured ZnO nanostructured films changed from hydrophobicity to hydrophilicity. According to analysis of surface chemical states, the naturally controllable wetting behavior can be attributed to hydrocarbon adsorbates on the nanostructured film surface, which is caused by tunable internal stress. On the other hand, the interfacial water molecules near the surface of ZnO nanostructured films have been identified as hydrophobic hydrogen structure by Fourier transform infrared/attenuated total reflection. Moreover, a remarkable near-band-edge emission peak shifting also can be observed in PL spectra due to the transition of internal stress state. Furthermore, our present ZnO nanostructured films also exhibited excellent transparency over 80% with a wise surface wetting switched from hydrophobic to hydrophilic states after exposing in ultraviolet (UV) surroundings. Our work demonstrated that the internal stress of the thin film not only induced natural wettability transition of ZnO nanostructured films, but also in turn affected the surface properties such as surface chemisorption.

Synthesis of rare-earth doped ZnO nanorods and their defect–dopant correlated enhanced visible-orange luminescence

Rare-earth doped sub-10 nm diameter ZnO nanorods show defect–dopant assisted enhanced visible-orange luminescence and also display multicolour rare-earth emission.

Pseudohalide (SCN(-))-Doped MAPbI3 Perovskites: A Few Surprises

Pseudohalide thiocyanate anion (SCN(-)) has been used as a dopant in a methylammonium lead tri-iodide (MAPbI3) framework, aiming for its use as an absorber layer for photovoltaic applications. The substitution of SCN(-) pseudohalide anion, as verified using Fourier transform infrared (FT-IR) spectroscopy, results in a comprehensive effect on the optical properties of the original material. Photoluminescence measurements at room temperature reveal a significant enhancement in the emission quantum yield of MAPbI3-x(SCN)x as compared to MAPbI3, suggestive of suppression of nonradiative channels. This increased intensity is attributed to a highly edge specific emission from MAPbI3-x(SCN)x microcrystals as revealed by photoluminescence microscopy. Fluoresence lifetime imaging measurements further established contrasting carrier recombination dynamics for grain boundaries and the bulk of the doped material. Spatially resolved emission spectroscopy on individual microcrystals of MAPbI3-x(SCN)x reveals that the optical bandgap and density of states at various (local) nanodomains are also nonuniform. Surprisingly, several (local) emissive regions within MAPbI3-x(SCN)x microcrystals are found to be optically unstable under photoirradiation, and display unambiguous temporal intermittency in emission (blinking), which is extremely unusual and intriguing. We find diverse blinking behaviors for the undoped MAPbI3 crystals as well, which leads us to speculate that blinking may be a common phenomenon for most hybrid perovskite materials.

Bioactive polymersomes self-assembled from amphiphilic PPO-glycopolypeptides: synthesis, characterization, and dual-dye encapsulation

Glycopolypeptide-based polymersomes have promising applications as vehicles for targeted drug delivery because they are capable of encapsulating different pharmaceuticals of diverse polarity as well as interacting with specific cell surfaces due to their hollow structural morphology and bioactive surfaces. We have synthesized glycopolypeptide-b-poly(propylene oxide) by ROP of glyco-N-carboxyanhydride (NCA) using the hydrophobic amine-terminated poly(propylene oxide) (PPO) as the initiator. This block copolymer is composed of an FDA-approved PPO hydrophobic block in conjugation with hydrophilic glycopolypeptides which are expected to be biocompatible. We demonstrate the formation of glycopolypeptide-based polymersomes from the self-assembly of glycopolypeptide-b-poly(propylene oxide) in which the presence of an ordered helical glycopolypeptide segment is required for their self-assembly into spherical nanoscale (∼50 nm) polymersomes. The polymersomes were characterized in detail using a variety of techniques such as TEM, AFM, cryo-SEM, and light-scattering measurements. As a model for drugs, both hydrophobic (RBOE) and hydrophilic (calcein) dyes have been incorporated within the polymersomes from solution. To substantiate the simultaneous entrapment of the two dyes, spectrally resolved fluorescence microscopy was performed on the glycopeptide polymersomes cast on a glass substrate. We show that it is possible to visualize individual nanoscale polymersomes and effectively probe the dyes' colocalization and energy-transfer behaviors therein as well as investigate the variation in dual-dye encapsulation over a large number of single polymersomes. Finally, we show that the galactose moieties present on the surface can specifically recognize lectin RCA120, which reveals that the polymersomes' surface is indeed biologically active.

Surface modified Mg-doped ZnO QDs for biological imaging

Nanocrystals of ZnO are currently attracting great interest as potential labels for biological applications, such as theranostic devices, due to their luminescent properties and low toxicity in vivo. It has been reported that doping with Mg

Photocontrol of luminescent inorganic nanocrystals via an organic molecular switch

The photoluminescence of ZnO nanocrystals is reversibly modulated via a diarylethene photoswitch, and the photophysics mechanism was unraveled.

The role of ligands in determining the exciton relaxation dynamics in semiconductor quantum dots

This article reviews the mechanisms through which molecules adsorbed to the surfaces of semiconductor nanocrystals, quantum dots (QDs), influence the pathways for and dynamics of intra- and interband exciton relaxation in these nanostructures. In many cases, the surface chemistry of the QDs determines the competition between Auger relaxation and electronic-to-vibrational energy transfer in the intraband cooling of hot carriers, and between electron or hole-trapping processes and radiative recombination in relaxation of band-edge excitons. The latter competition determines the photoluminescence quantum yield of the nanocrystals, which is predictable through a set of mostly phenomenological models that link the surface coverage of ligands with specific chemical properties to the rate constants for nonradiative exciton decay.

High-performance UV photodetection of unique ZnO nanowires from zinc carbonate hydroxide nanobelts

Zinc carbonate hydroxide nanobelts are prepared by the hydrolysis of zinc acetate aqueous solution in the presence of urea at 90 °C. The zinc carbonate hydroxide nanobelts can be facilely self-assembled in a circular flexible freestanding film with a diameter of 8.4 cm and thickness of ~48 μm. The calcination of the zinc carbonate hydroxide nanobelts at 300 °C under normal atmospheric condition results in the formation of ZnO nanowires. The zinc carbonate hydroxide nanobelts and resultant ZnO nanowires are characterized by XRD, SEM, TEM, TG-DSC, PL, and impedance measurement. The characterization results indicate that the ZnO nanowires exhibit unique nanostructure characterized by long chains of closely attached ZnO nanocrystals with ZnO/ZnO nanocrystal junctions. The unique ZnO nanowire-based UV photodetector exhibit much higher photoresponse currents (at the milliampere level) and on/off current ratio (~1000) than ZnO nanocrystal-based UV photodetector. Under the UV irradiance of 120 mW cm(-2) and low applied voltage of 0.5 V, the peak photoresponse current and on/off current ratio of the ZnO nanowire photodetector are 56 and 36 times higher than those of the ZnO nanocrystal UV photodetector, respectively. The reason for the superior photodetection performance of the ZnO nanowires over the ZnO nanocrystals is discussed.

Plasticization of poly(vinylpyrrolidone) thin films under ambient humidity: insight from single-molecule tracer diffusion dynamics

Studies on diffusion dynamics of single molecules (SMs) have been useful in revealing inhomogeneity of polymer thin films near and above the glass-transition temperature (T(g)). However, despite several applications of polymer thin films where exposure to solvent (or vapor) is common, the effect of absorbed solvent molecules on local morphology and rigidity of polymer matrices is yet to be explored in detail. High-T(g) hydrophilic polymers such as poly(vinylpyrrolidone) (PVP) are used as pharmaceutical coatings for drug release in aqueous medium, as they readily absorb moisture, which results in effective lowering of the T(g) and thereby leads to plasticization. The effect of moisture absorption on swelling and softening of PVP thin films was investigated by visualizing the diffusion dynamics of rhodamine 6G (Rh6G) tracer molecules at various ambient relative humidities (RH). Wide-field epifluorescence microscopy, in conjunction with high-resolution SM tracking, was used to monitor the spatiotemporal evolution of individual tracers under varied moisture contents of the matrix. In the absence of atmospheric moisture, Rh6G molecules in dry PVP films are translationally inactive, suggestive of rigid local environments. Under low moisture contents (RH 30-50%), translational mobility remains arrested but rotational motion is augmented, indicating slight swelling of the polymer network which marks the onset of plasticization. The translational mobility of Rh6G was found to be triggered only at a threshold ambient RH, beyond which a large proportion of tracers exhibit extensive diffusion dynamics. Interestingly, SM tracking data at higher moisture contents of the film (RH ≥ 60%) reveal that the distributions of dynamic parameters (such as diffusivity) are remarkably broad, spanning several orders of magnitude. Furthermore, Rh6G molecules display a wide variety of translational motion even at a fixed ambient RH, clearly pointing out the extremely inhomogeneous environment of plasticized PVP network. Intriguingly, it is observed that a majority of tracers undergo anomalous subdiffusion even under high moisture contents of the matrix. Analyses of SM trajectories using velocity autocorrelation function reveal that subdiffusive behaviors of Rh6G are likely to originate from fractional Brownian motion, a signature of tracer dynamics in viscoelastic medium.

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.