A facile synthesis of green-emitting all-inorganic (CsPbBr 3 ) and organometallic [methylammonium (MA)PbBr 3 and formamidinium (FA)PbBr 3 ] perovskite nanocrystals (NCs) with near-unity photoluminescence quantum yields, narrow emission bandwidths (fwhm < 22 nm), and much improved colloidal stability has been reported here. A low-cost and highly reactive bromide precursor 1,3-dibromo-5,5-dimethylhydantoin was employed in our synthesis that not only rendered excellent stability to all three NCs (Cs/MA/FAPbBr 3 ) but also eased the synthesis of high-quality MAPbBr 3 NCs even at moderate temperatures. At high temperatures, MAPbBr 3 NCs decompose by releasing gaseous methylamine, making their synthesis a difficult task in conventional high-temperature hot injection method. Our synthesized NCs are coveted materials exemplified by their narrow particle size distributions, excellent colloidal stability in ambient conditions, and high tolerance toward UV light and polar solvents. All these astonishing properties signify their better suitability in real applications like displays, low-threshold lasers, and light-emitting diodes.

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.

Zero-dimensional (0D) carbonaceous materials, such as graphene quantum dots (GQDs) and fluorescent carbon dots (FCDs), are in the limelight for their intriguing optical and material properties. Excellent results of initial photophysical studies with these emergent nanodots garnered intense interest among the researchers that suggested an immediate opportunity of replacing cytotoxic fluorescent dyes with carbonaceous dots (CDs) in bioimaging and related applications. Several exciting properties of CDs, including the excitation-dependent multicolor emission, slow carrier cooling, subpicosecond (subps) interfacial charge transfer, and quantum emission, are of paramount importance for various real applications. Despite the initial success, their large-scale implementations in daily life remained challenging, mainly because of several serious issues, including elusive structures (especially for FCDs), the controversial origin of their emissions, and a lack of proper knowledge while correlating an unusual photophysical property to an intrinsic phenomenon. Such limitations not only present hurdles to their practical utilizations but also call into question their real potential. Recent reports have suggested that many of these exciting properties stemmed from external factors like the presence of a molecular impurity, sample heterogeneity (i.e., a mixture of CD subsets with different spectral identities), and the adopted synthesis methodology (i.e., top-down vs bottom-up). Hence, only a rigorous sample purification cannot help in realizing the actual merit of these emergent materials unless a sample-specific synthesis procedure is followed. A combination of both renders the maximum integrity to the CD samples. This review highlights several exciting properties of these coveted materials and how they are disturbed by the parameters discussed above. We further emphasize the actual promises of these materials, as shown by the recent fluorescence-based temporal and spectral studies. The results of these studies are even more fascinating compared to that of inadequately purified samples. Finally, we propose a standard sample purification methodology applicable to all types of carbonaceous materials.