a Ph.D. student under Prof. Anunay Samanta. His research interest is the synthesis and understanding of ultrafast photoinduced processes of highly luminescent perovskite nanocrystals.Sumanta Paul, after completing his Master's degree from the School of Chemistry, University of Hyderabad, in 2017, is working on his Ph.D. under the supervision of Prof. Anunay Samanta. His research focuses on the synthesis and study of photophysical properties of perovskite nanocrystals at the bulk and single-particle levels.

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Solvent-dependent switching of graphene oxide (GO) as fluorescence quencher or enhancer was observed. In some solvents, GO increases the fluorescence yield of a hydrophilic molecule 7-(diethylamino)-coumarin-3-carboxylic acid (7-DCA), and in some solvents GO act as a quencher of fluorescence.The intangibility between the carbon-based nanomaterials and biomolecules is an interesting area of research in biomedical imaging, biotechnology, material science, and so on. [1][2][3] To investigate the potential applications, utilization and biocompatibility of these carbon-based nanomaterials in biological systems, a proper understanding of the interaction between these carbon-based nanomaterials and biological systems are necessary. [4,5] One of the carbon-based nanomaterial is graphene oxide (GO); it took immense attention of the scientist in modern days research. Though GO took lots of attention to the scientist in different fields of researches, but the interaction of GO with the biologically active molecules like coumarin dyes has not studied extensively. So there is a scope to study the GO-dye molecule interaction to invent the role of GO on the photophysics of the dye molecules. Since GO has a large extent of hydrogen bonding ability so one should expect that GO can easily interact with organic dyes/drug molecules and modulate their spectral properties. Vovushaet al. studied the interaction of nucleobases and aromatic amino acids with GO and graphene flakes by using density functional theory, and they found that GO complexes are stabilized by hydrogen bonding interaction whereas, graphene complexes are stabilized by π-π stacking interaction. [6] The active functional groups which are present in the edges of GO bind the drug covalently, and the localized π electrons in the nanosheet are stabilized the drug through π-π interaction, and it is used for targeted drug delivery. [7,8] GO not only used for drug delivery but Kim et al. also reported that GO useful for gene delivery. [9] Lu et al. reported that single-stranded DNA adsorbed easily with the GO as compared to the double-stranded DNA because double-stranded DNA does not give the scope to bind DNA bases into the GO surface. [10] Kuchlyanet al. reported that fluorescence of tryptophan moiety of BSA gradually quenched upon the addition of GO, the reason behind it is π-π interaction between GO sheet and the indole structure of the tryptophan. [11] Nowadays, GO has been utilized with great interest in the field of near-infrared photothermal treatment of cancer, Alzheimer diseases etc.. [12][13][14] In recent years several researchers have investigated the adsorption phenomenon of biomolecules on GO surface. [6,[15][16] It is deeply-rooted that fluorescence of the organic fluorophore, [17,18] and biomolecules [19,20] were quenched in the presence of graphene oxide. Electron transfer, fluorescence resonance energy transfer (FRET), non-radiative dipole-dipole interaction are commonly responsible for this quenching phenomena. [21,22] Leblanc and co-workers stated that GO...

Cesium lead halide perovskite nanocrystals (NCs) are the most promising materials for photovoltaic and optoelectronic applications in recent years. However, lack of long-term stability and consequent deterioration of optical properties with time have been major challenges for commercialization of the perovskite-based devices. In this context, we report that even room-temperature treatment of blue-emitting CsPbCl1.5Br1.5 and CsPbClBr2 NCs, green-emitting CsPbBr3 NCs, and yellow-emitting CsPbBr1.5I1.5 NCs with sodium thiosulfate (Na2S2O3·5H2O) can not only lead to huge enhancement of the photoluminescence quantum yield (PLQY, to ∼100% for the blue/green-emitting NCs and ∼90% for the yellow-emitting NCs) but also add superior stability to these NCs under different environmental stresses. While the time-resolved PL and ultrafast transient absorption studies show suppression of the nonradiative recombination channels, other measurements reveal that the improved optical characteristics and stability of these substances are by the formation of Pb–S bonds between undercoordinated surface Pb and thiosulfate. The outstanding PLQY and much improved long-term stability of the treated NCs make them attractive components for perovskite-based optoelectronic applications.

While multiple protocols are currently available for obtaining green-and red-emitting lead halide perovskite nanocrystals (NCs) with near-unity photoluminescence quantum yield (PLQY), achieving this target for the blue-emitting NCs is still quite challenging. This is an impediment to the development of perovskite-based highly efficient white LEDs of which blue is an essential component. Herein, we show that room-temperature treatment of the blue-emitting CsPbCl 1.5 Br 1.5 , cyan-emitting CsPbClBr 2 and green-emitting CsPbBr 3 NCs with thioacetamide not only enhances the PLQY to near-unity (~97-99%) without affecting the PL maximum and bandwidth, but also improves the stability of the systems significantly. The investigation reveals that effective passivation of under-coordinated surface Pb 2 + through formation of PbÀ S and PbÀ NH 2 bonds and removal of excess lead atoms suppress the nonradiative recombination channels and enhances the PLQY and stability of the NCs. Outstanding PL efficiency and superior long-term stability make these systems potential ingredients for various lighting and display applications.