Direct Light-Driven Modulation of Luminescence from Mn-Doped ZnSe Quantum Dots

Carbon Dots: Synthesis, Characterizations, and Recent Advancements in Biomedical, Optoelectronics, Sensing, and Catalysis Applications

Carbon nanodots (CNDs), a fascinating carbon-based nanomaterial (typical size 2-10 nm) owing to their superior optical properties, high biocompatibility, and cell penetrability, have tremendous applications in different interdisciplinary fields. Here, in this Review, we first explore the superiority of CNDs over other nanomaterials in the biomedical, optoelectronics, analytical sensing, and photocatalysis domains. Beginning with synthesis, characterization, and purification techniques, we even address fundamental questions surrounding CNDs such as emission origin and excitation-dependent behavior. Then we explore recent advancements in their applications, focusing on biological/biomedical uses like specific organelle bioimaging, drug/gene delivery, biosensing, and photothermal therapy. In optoelectronics, we cover CND-based solar cells, perovskite solar cells, and their role in LEDs and WLEDs. Analytical sensing applications include the detection of metals, hazardous chemicals, and proteins. In catalysis, we examine roles in photocatalysis, CO2 reduction, water splitting, stereospecific synthesis, and pollutant degradation. With this Review, we intend to further spark interest in CNDs and CND-based composites by highlighting their many benefits across a wide range of applications.

Multiple underlying images tuned by Mn-doped Zn-Cu-In-S quantum dots

In this study, ZnS capped Cu-In-S (ZCIS) quantum dots doped with Mn ions are synthesized by a thermal injection method, with luminescence covering almost the entire visible area. The large Stokes shift effectively inhibits the self-absorption effect under luminescence, and the quantum yield of ZCIS quantum dots increased from 38% to 50% after ZnS capping and further to 69% after doping with Mn. First, red-, yellow-, and blue-emitting quantum dots were synthesized and then, polychromatic ensembles were obtained by mixing the trichromatic quantum dots in a different ratio. Using the home-built inkjet printer, multilayered and multicolor mixed patterns were obtained for information pattern storage and multilayer pattern recognition and reading.

Facile Synthesis of Cadmium-Free Zn-In-S:Ag/ZnS Nanocrystals for Bio-Imaging

High quality cadmium-free Zn-In-S:Ag doped-nanocrystals (d-NCs) were synthesized via a simple one-step noninjection route using silver nitrate, indium acetate, zinc acetate, oleylamine, S powder and 1-dodecanethiol as starting materials in an organic phase. The size and optical properties can be effectively tailored by controlling the reaction time, reaction temperature, Ag(+) dopant concentration, and the molar ratio of In to Zn. The photoluminescence wavelength of as-prepared Zn-In-S:Ag NCs covered a broad visible range from 458 nm to 603 nm. After being passivated by protective ZnS shell, the photoluminescence quantum yield (PLQY) of Zn-In-S:Ag(+) /ZnS was greatly improved to 43.5%. More importantly, the initial high PLQY of the obtained core/shell d-NCs in organic media can be preserved when being transferred into the aqueous media via ligand exchange. Finally, high quality Zn-In-S:Ag(+) /ZnS d-NCs in aqueous phase were applied as bio-imaging agents for identifying living KB cells.

Long-lived population inversion in isovalently doped quantum dots

Optical gain from colloidal quantum dots has been desired for several decades since their discovery. While gain from multiexcitations is by now well-established, nonradiative Auger recombination limits the lifetime of such population inversion in quantum dots. CdSe cores isovalently doped by one to few Te atoms capped with rod-shaped CdS are examined as a candidate system for enhanced stimulated emission properties. Emission depletion spectroscopy shows a behavior characteristic of 3-level gain systems in these quantum dots. This implies complete removal of the 2-fold degeneracy of the lowest energy electronic excitation due to the large repulsive exciton-exciton interaction in the doubly excited state. Using emission depletion measurements of the trap-associated emission from poorly passivated CdS quantum dots, we show that 3-level characteristics are typical of emission resulting from a band edge to trap state transition, but reveal subtle differences between the two systems. These results allow for unprecedented observation of long-lived population inversion from singly excited quantum dots.

Hundred-thousand light holes push nanoscopy to go parallel

With the application of the elements of all major super-resolution techniques including stimulated emission depletion, structure illumination microscopy, and photo-activated localization microscopy, the incoherent crossed standing-wave microscopy achieves parallel super-resolution imaging.

Analytical description of high-aperture STED resolution with 0-2π vortex phase modulation

Stimulated emission depletion (STED) can achieve optical superresolution, with the optical diffraction limit broken by the suppression on the periphery of the fluorescent focal spot. Previously, it is generally experimentally accepted that there exists an inverse square root relationship with the STED power and the resolution, but with arbitrary coefficients in expression. In this paper, we have removed the arbitrary coefficients by exploring the relationship between the STED power and the achievable resolution from vector optical theory for the widely used 0-2π vortex phase modulation. Electromagnetic fields of the focal region of a high numerical aperture objective are calculated and approximated into polynomials of radius in the focal plane, and analytical expression of resolution as a function of the STED intensity has been derived. As a result, the resolution can be estimated directly from the measurement of the saturation power of the dye and the STED power applied in the region of high STED power.

STED microscopy and its applications: new insights into cellular processes on the nanoscale

For about a decade, superresolution fluorescence microscopy has been advancing steadily, maturing from the proof-of-principle stage to routine application. Of the various techniques, STED (stimulated emission depletion) microscopy was the first to break the diffraction barrier. Today, it is a prominent and versatile form of superresolution light microscopy. STED microscopy has shed a sharper light on numerous topics in cell biology, but also in material sciences. Both disciplines extend into the nanometer range, making detailed studies of structural and functional relationships difficult or even impossible to achieve using diffraction-limited microscopy. With recent advancements like spectral multiplexing or live-cell imaging, STED microscopy makes nanoscale materials and components of the cell accessible for fluorescence-based investigations. With multicolor superresolution imaging, even the interactions between biological and engineered nanostructures can be studied in detail. This review gives an introduction into the working principle of STED microscopy, provides a detailed overview of recent advancements and new techniques implemented for use with STED microscopy and shows how these have been applied in the life sciences and nanotechnologies.