Light-emitting Mn-doped semiconductor nanocrystals have been extensively studied for the last three decades for their intense and stable Mn d-d emission. In principle, this emission should be fixed ...at 585 nm (yellow), but recent studies have shown that the emission can be widely tuned even to 650 nm (red). This is a spectacular achievement as this would make Mn-doped nanocrystals efficient and tunable light emitters. Keeping these developments in view, the chemistry of the synthesis of these materials, their photophysical processes and the expected origins of their red emission are summarized in this Minireview. All the related important studies from 1992 onwards are chronologically discussed, and one particular case is elaborated on in detail. As these materials are potentially important for biology, and photovoltaic, sensing and light-emitting devices, this Minireview is expected to help researchers investigating the chemistry, physics and applications of these materials.
Bringing together two nanostructures of different materials in a single building block can create a new platform where both can share their electronic and optical characteristics. While these have ...been extensively studied for metal nanoparticles and chalcogenide semiconductor nanocrystals, the literature is limited for perovskite nanocrystals. Because perovskite nanocrystals typically follow a fast formation process and also require a specific environment, their growth on other materials or vice versa indeed remains difficult. However, some success has been achieved in lead halide perovskites with several metal halides, oxides, and chalcogenides and also with noble metals. These findings indeed opened up new directions for designing perovskite nanocrystal heterostructures, investigating their heterojunctions, analyzing new properties, and exploring their possible utilizations. Summarizing all these developments, this Focus Review demonstrates challenges associated with their formation, changes in their optical properties, stability, and several applications. In addition, this work addresses a few possible future research directions regarding these perovskite heterostructures.
Quantum dots with fabulous size-dependent and color-tunable emissions remained as one of the most exciting inventories in nanomaterials for the last 3 decades. Even though a large number of such dot ...nanocrystals were developed, CdSe still remained as unbeatable and highly trusted lighting nanocrystals. Beyond these, the ternary I–III–VI family of nanocrystals emerged as the most widely accepted greener materials with efficient emissions tunable in visible as well as NIR spectral windows. These bring the high possibility of their implementation as lighting materials acceptable to the community and also to the environment. Keeping these in mind, in this Perspective, the latest developments of ternary I–III–VI nanocrystals from their large-scale synthesis to device applications are presented. Incorporating ZnS, tuning the composition, mixing with other nanocrystals, and doping with Mn ions, light-emitting devices of single color as well as for generating white light emissions are also discussed. In addition, the future prospects of these materials in lighting applications are also proposed.
In a generic synthesis approach, all three CsPbX3 (X=Cl, Br and I) perovskite nanocrystals having near unity quantum yields is reported. This has been achieved by injecting the desired amount of ...preformed alkylammonium halide salts which acted as a dual source providing halide ions and the capping agent to an equimolar amount of non‐halide Pb and Cs precursors in a reaction flask at an optimized reaction temperature. The composition sensitivity of Pb to Cs ratio, high temperature reaction, and injection of ammonium halide remained the key parameters for obtaining the high quantum yields. Details of the reaction process, use of different reagents and setting up the reaction parameters are reported.
Three colors: A rational synthesis of CsPbX3 (X=Cl, Br, and I) nanocrystals gives all three perovskites with near unity photoluminescence quantum yield. Careful analysis of the reaction chemistry and the parameters allows a generic reaction to be developed.
Formation of Mn-doped ZnSe quantum dots (Mn:ZnSe d-dots) using nucleation-doping strategy was studied systematically and optimized through greener approaches. The resulting d-dots were with high ...(∼50%) photoluminescence (PL) quantum yield (QY), which was achieved by the controlled formation of small-sized MnSe nanoclusters as the core and a diffused interface between the nanocluster core and the ZnSe overcoating layers. Synthesis of the d-dots under high temperatures (240−300 °C) was achieved by varying the structure of the metal carboxylate precursors, concentration of the inhibitors, free fatty acid, and concentration of the activation reagents, fatty amines. Highly emissive d-dots synthesized under desired conditions were found to be extremely stable upon thermal treatment up to the boiling point of the solvent (about 300 °C), which was quantitatively studied using in situ measurements. The PL peak of the d-dots was controllably tuned in a surprisingly large optical window, from 565 to 610 nm. These highly emissive and stable d-dots possess characteristics of practical emissive materials, especially for applications requiring high power, high concentration of emitters, and under tough conditions.
Nanocrystal heterostructures are one of the frontline energy materials widely known for enhancing the rate of photocatalysis and tuning optical properties and are also used in photovoltaics. These ...nanostructures where two crystalline nanomaterials are placed together in a single building block and share lattices are extensively studied for chalcogenide semiconductors and metal oxides but limited for recently emerged perovskite nanocrystals. Due to differences in the crystal bonding nature, interface chemistry, and also the formation mechanism, some constraints are present in designing common reaction pathways for the simultaneous formation of perovskites and chalcogenides or similar nanocrystals sharing common lattice planes. Hence, more fundamental understanding of both nucleation and growth of both materials is required for inducing heteronucleations of one on the surface of another. Literature reports also revealed that epitaxial growth of lead halide perovskites with nonhalide or chalcogenide colloidal 0D nanocrystals could not be established yet. Hence, the field remains challenging, and more investigations on both experimental as well as theoretical studies are timely required. Keeping these in mind, in this perspective the state-of-the-art issues related to the formation of all inorganic halides and nonhalide heterostructures formed with epitaxial relations are discussed. At the beginning, the chemistry of these nanocrystals with similarities and dissimilarities in their nature and examples of different heterostructures are summarized, and then, different synthetic possibilities for overtaking the hurdles and designing such heterostructures are proposed.
Introducing a few atoms of impurities or dopants in semiconductor nanocrystals can drastically alter the existing properties or even introduce new properties. For example, mid‐gap states created by ...doping tremendously affect photocatalytic activities and surface controlled redox reactions, generate new emission centers, show thermometric optical switching, make FRET donors by enhancing the excited state lifetime, and also create localized surface plasmon resonance induced low energy absorption. In addition, researchers have more recently started focusing their attention on doped nanocrystals as an important and alternative material for solar energy conversion to meet the current demand for renewable energy. Moreover, the electrical and magnetic properties of the host are also strongly altered on doping. These beneficial dopant‐induced changes suggest that doped nanocrystals with proper selections of dopant–host pairs may be helpful for generating designer materials for a wide range of current technological needs. How properties relate to the doping of a variety of semiconductor nanocrystals are summarized in this Review.
Doping control: Doping semiconductor nanocrystals combines properties of both the dopant ion and the quantum confinement effect of the nanocrystal. This Review presents recent advances in synthesis, luminescence, photocatalysis, photovoltaic, plasmonic, magnetic, and magneto‐optic properties of doped semiconductor nanocrystals.
Au–Bi2S3 heteronanostructure photocatalysts were designed in which the coupling of a metal plasmon and a semiconductor exciton aids the absorption of solar light, enhances charge separation, and ...results in improved catalytic activity. Furthermore, these nanostructures show a unique pattern of structural combination, with Au nanoparticles positioned at the center of Bi2S3 nanorods. The chemistry of formation of these nanostructures, their epitaxy at the junction, and their photoconductance were studied, as well as their photoresponse properties.
Promising returns of gold on the side: In a designed Au–Bi2S3 heteronanostructure photocatalyst, Au nanoparticles were located at the center of the semiconductor nanorods (see picture), rather than at the tip, as usually reported. These nanostructures were found to be efficient visible‐light photocatalysts and to have excellent photocurrent and photoresponse properties.
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