Extraction of hot carriers is of prime importance because of its potential to overcome the energy loss that limits the efficiency of an optoelectronic device. Employing a femtosecond upconversion setup, herein we report a few picoseconds carrier cooling time of colloidal graphene quantum dots (GQDs) is at least an order of magnitude slower compared to that in its bulk form. A slower carrier cooling time of GQDs compared to that of the other semiconductor quantum dots and their bulk materials is indeed a coveted property of GQDs that would allow one easy harvesting of high energy species employing a suitable molecular system as shown in this study. A subpicosecond hot hole transfer time scale has been achieved in a GQD−molecular system composite with high transfer efficiency. Our finding suggests a dramatic enhancement of the efficiency of GQD based optoelectronic devices can possibly be a reality.

We report here the hot carrier (HC) cooling time scales within polyhedral CsPbBr 3 nanocrystals (NCs) characterized by different numbers of facets (6 to 26) utilizing a femtosecond upconversion setup. Interestingly, the observed cooling time scale slows many-fold (>10 times) upon opening the new facets on the NC surface. Furthermore, a temperature-dependent study reveals that cooling in multifaceted NCs is polaron mediated, where newly opened polar facets and the soft lattice of CsPbBr 3 NCs play pivotal roles. Our hallmark result of slow cooling in polyhedral NCs renders an excellent opportunity for harvesting high-energy carriers by a carefully chosen molecular system. To this end, employing the hole scavenger molecule aniline, we successfully extracted hot holes from optically pumped NCs. We believe that several intriguing properties of the polyhedral NCs, including rapid polaron formation, defect-tolerant nature, and the capability of soft lattice to support slow diffusion of charge carriers, resulted in decelerated cooling.

Photoinduced electron transfer (PET) from an excited-state CsPbBr 3 nanocrystal (NC) to rhodamine 6G (r6G) is studied in toluene using different fluorescence-based techniques. Because of weak solubility of r6G in toluene, excess r6G molecules adsorb at NC surface which result in a much slower rotational diffusion time scale of r6G in the presence of NCs. Study of intrinsic PET benefits from the soft molecular interactions leading to donor (NC)acceptor (r6G) complex formation, where solvent diffusion parameters would not play any role in the PET kinetics. Femtosecond transients of NCs are nicely fit to a Poisson expression originally proposed by Tachiya. Conclusive fittings to the temperature dependence quenching data reveal two interesting observations: (1) Even though the average number of surface trap state in a NC does not change with temperature (5−60 °C), the trap-state-induced quenching time scale is accelerated with increase in temperature, pointing toward a more efficient trapping at higher temperature. (ii) In the presence of r6G, a fast (∼150 ps per r6G molecule) interfacial PET time scale is observed, which remains unaffected by temperature (5−60 °C). Our findings demonstrate that even a simple "perovskite NC−electron acceptor" composite like that in the present study can ensure a rapid interfacial charge separation. Such information will help us to realize the actual potential of perovskites NCs in their real applications.

Graphene oxide-based nanocomposites (NCMs) exhibit diverse photonic and biophotonic applications. Innovative nanoengineering using a task-specific ionic liquid (IL), namely, 1-butyl-3-methyl tetrafluoroborate [C 4 mim][BF 4 ], allows one to access a unique class of luminescent nanocomposites formed between lanthanide-doped binary fluorides and graphene oxide (GO). Here the IL is used as a solvent, templating agent, and as a reaction partner for the nanocomposite synthesis, that is, “all three in one”. Our study shows that GO controls the size of the NCMs; however, it can tune the luminescence properties too. For example, the excitation spectrum of Ce 3+ is higher-energy shifted when GO is attached. In addition, magnetic properties of GdF 3 :Tb 3+ nanoparticles (NPs) and GdF 3 :Tb 3+ -GO NCMs are also studied at room temperature (300 K) and very low temperature (2 K). High magnetization results for the NPs (e.g., 6.676 emu g –1 at 300 K and 184.449 emu g –1 at 2 K in the applied magnetic field from +50 to −50 kOe) and NCMs promises their uses in many photonic and biphotonic applications including magnetic resonance imaging, etc.

Highly crystalline, phase pure Cu 3 P nanocrystals (NCs) have been successfully synthesized using ionic liquid-assisted solvothermal method at relatively low temperature (200°C). Herein, ionic liquids (ILs) are used as a structure directing/templating agent. Effect of ILs and precursor concentration on crystal phase, crystallite size, lattice strain, morphology and grain size of Cu 3 P NCs is studied. In the presence of IL, crystallite size and lattice strain significantly change with changing the concentration of red phosphorus. For example, smaller crystallite size (38.5 nm) and compressive lattice strain are obtained when 10 times of red phosphorous is used. However, bigger size (41.9 nm) and tensile lattice strains are obtained for the lower concentration of phosphorous (5 times). At higher phosphorus concentration, hexagonal shaped microcrystals with prominent grain are observed. HRTEM images reveal that spherical-shaped particles on further agglomeration through Ostwald ripening process form hexagonal-shaped bigger microstructures. However, on doping the rare-earth ions (RE 3? = Ce 3? /Tb 3?) in the Cu 3 P NCs show the green luminescence (at 542 nm) which is attributed to the emission of Tb 3? ions. To the best of our knowledge, this is the first report on rareearth doped Cu 3 P nanoparticles and shows promise on the luminescence aspect of Cu 3 P nanomaterials along with its already existing plasmonic and semiconducting properties.

This Letter reports the facile harvesting of hot carriers (HCs) in a composite of 12-faceted dodecahedron CsPbBr 3 nanocrystal (NC) and a scavenger molecule. We recorded ∼3.3 × 10 11 s −1 HC cooling rate in NC when excited with ∼1.4 times the band gap energy (E g ), increasing to >3 × 10 12 s −1 in the presence of scavengers at high concentration due to the HC extractions. Since the observed intrinsic charge transfer rate (∼1.7 × 10 12 s −1 ) in our NC− scavenger complex is about an order of magnitude higher than the HC cooling rate (∼3.3 × 10 11 s −1 ), carriers are harvested before their cooling. Further, a fluorescence correlation spectroscopy study reveals NC tends to form a quasi-stable complex with a scavenger molecule, ensuring charge transfer completed (τ ct ≈ 0.6 ps) much before the complex breaks apart (>600 μs). The overall results of our study highlight the promise shown by 12-faceted NCs and their implications in modern applications, including hot carrier solar cells.