Flexible and Transparent Luminescent Cellulose-Transition Metal Cluster Composites

Red-NIR luminescent polymers are principally obtained from petroleum-based derivatives in which emitters, usually a critical raw material such as rare-earth or platinum group metal ions, are embedded. Considering the strong ecological impact of their synthesis and the major risk of fossil fuel energy shortage, there is an urgent need to find alternatives. We describe a luminescent nanocomposite based on red-NIR phosphorescent molybdenum nanoclusters, namely Cs₂Mo₆I₈(OCOC₂F₅)₆, embedded in an eco-friendly cellulose biopolymer matrix that is obtained by a simple solvent casting technique. While homogeneity is kept up to 20 wt% of cluster complex doping, annealing hybrids leads to a large increase of their emission efficiency, as demonstrated by quantum yield measurements.

Unique and outstanding quantum dots (QD)/tunicate cellulose nanofibrils (TCNF) nanohybrid platform material for use as 1D ink and 2D film

Quantum dots (QD)/polymer materials have wide applications in biological imaging, clinical diagnostics, anti-counterfeiting materials, light-emitting devices and solar cells. The development of QD/cellulose nanofibrils (CNF) hybrids with a more perfect structure and excellent properties is important for improving known applications. A unique tunicate CNF (TCNF) was homogeneously blended with outstanding CdSe/CdS core/shell QD to prepare a novel QD/TCNF hybrid. The QD were monodispersed on a single TCNF fibril surface as an evenly distributed monolayer with an extremely high packing density and no visible aggregation. The prepared hybrid is an excellent platform nanomaterial which was demonstrated by its good writing fidelity when applied as a 1D ink and by its good processability in the preparation of 2D films with acceptable transparency and flexibility. This one-step direct blending approach provides a facile shortcut to effectively fabricate cellulose-based high-performance functional QD nanomaterials at the single-fibril level.

Hybrid fluorescent liquid crystalline composites: directed assembly of quantum dots in liquid crystalline block copolymer matrices

Hybrid fluorescent liquid crystalline (LC) composites containing inorganic quantum dots (QDs) are promising materials for many applications in optics, nanophotonics and display technology, combining the superior emission capability of QDs with the externally controllable optical properties of LCs. In this work, we propose the hybrid LC composites that were obtained by embedding CdSe/ZnS QDs into a series of host LC block copolymers of different architectures by means of a two-stage ligand exchange procedure. The ABA/BAB triblock copolymers and AB diblock copolymers with different polymerization degrees are composed of nematogenic phenyl benzoate acrylic monomer units and poly(4-vinylpyridine) blocks, which are capable of binding to the QD surface. Our results clearly show that the spatial distribution of QDs within composite films as well as the formation of QD aggregates can be programed by varying the structure of the host block copolymer. The obtained composites form a nematic LC phase, with isotropization temperatures being close to those of the initial host block copolymers. In addition, the influence of the molecular architecture of the host block copolymers on fluorescence properties of the obtained composites is considered. The described strategy for the QD assembly should provide a robust and conventional route for the design of highly ordered hierarchical hybrid materials for many practical applications.

ZCIS/ZnS QDs fluorescent aerogels with tunable emission prepared from porous 3D nanofibrillar bacterial cellulose

Bacterial cellulose (BC) features a nanofibrillar network structure that can provide a good template for quantum dots (QDs), to overcome the fluorescence quenching-effect of QDs in polymer composites. Here, we fabricated novel fluorescent aerogels with tunable emission by covalently binding environmentally-friendly ZnS(CuInS₂)/ZnS core-shell quantum dots along the nanofibrillar BC. A new ligand of 3-(mercaptopropyl)trimethoxysilane allows QDs to transfer from toluene to alcohol solvent and stably bind to the BC. After supercritical CO₂ drying, the resulting BC-QDs aerogels maintain the porous nanofibrillar morphology of BC with ultra-light-weight, the QDs are well-distributed along the BC fiber surfaces without aggregation. The emission wavelength can be tuned in a wide range from 470 to 750 nm by simply adjusting the QDs core component or shell layers. This work provides a new approach for fabricating QDs-polymer hydrogels and aerogels with well distributed QDs via chemical binding that potential as smart sensor, catalysis, and 3D display applications.

Preparation and dielectric properties of cyanoethyl cellulose/BaTiO3 flexible nanocomposite films

Cyanoethyl cellulose-based high dielectric permittivity nanocomposite films were successfully prepared for the first time by introducing BaTiO₃ into cyanoethyl cellulose.

Fluorescent cellulose aerogels containing covalently immobilized (ZnS)x(CuInS2)1-x/ZnS (core/shell) quantum dots

Photoluminiscent (PL) cellulose aerogels of variable shape containing homogeneously dispersed and surface-immobilized alloyed (ZnS)x(CuInS2)1-x/ZnS (core/shell) quantum dots (QD) have been obtained by (1) dissolution of hardwood prehydrolysis kraft pulp in the ionic liquid 1-hexyl-3-methyl-1H-imidazolium chloride, (2) addition of a homogenous dispersion of quantum dots in the same solvent, (3) molding, (4) coagulation of cellulose using ethanol as antisolvent, and (5) scCO2 drying of the resulting composite aerogels. Both compatibilization with the cellulose solvent and covalent attachment of the quantum dots onto the cellulose surface was achieved through replacement of 1-mercaptododecyl ligands typically used in synthesis of (ZnS)x(CuInS2)1-x/ZnS (core-shell) QDs by 1-mercapto-3-(trimethoxysilyl)-propyl ligands. The obtained cellulose-quantum dot hybrid aerogels have apparent densities of 37.9-57.2 mg cm-3. Their BET surface areas range from 296 to 686 m2 g-1 comparable with non-luminiscent cellulose aerogels obtained via the NMMO, TBAF/DMSO or Ca(SCN)2 route. Depending mainly on the ratio of QD core constituents and to a minor extent on the cellulose/QD ratio, the emission wavelength of the novel aerogels can be controlled within a wide range of the visible light spectrum. Whereas higher QD contents lead to bathochromic PL shifts, hypsochromism is observed when increasing the amount of cellulose at constant QD content. Reinforcement of the cellulose aerogels and hence significantly reduced shrinkage during scCO2 drying is a beneficial side effect when using α-mercapto-ω-(trialkoxysilyl) alkyl ligands for QD capping and covalent QD immobilization onto the cellulose surface.

Tuning the Luminescence Properties of Colloidal I-III-VI Semiconductor Nanocrystals for Optoelectronics and Biotechnology Applications

In the past 5 years, colloidal I-III-VI nanocrystals such as CuInS2, CuInSe2, and AgInS2 have been intensively investigated for the potential to replace commonly available colloidal nanocrystals containing toxic elements in light-emitting and solar-harvesting applications. Many researchers from different disciplines are working on developing new synthetic protocols, performing spectroscopic studies to understand the luminescence mechanisms, and exploring various applications. To achieve enhanced performance, it is very desirable to obtain high-quality materials with tunable luminescence properties. In this Perspective, we highlight the current progress on tuning the luminescence properties of I-III-VI nanocrystals, especially focusing on the advances in the synthesis, spectroscopic properties, as well as the primary applications in light-emitting devices and bioimaging techniques. Finally, we outline the challenges concerning luminescent I-III-VI NCs and list a few important research tasks in this field.