A few approaches have been employed to tune the band gap of colloidal organic-inorganic trihalide perovskites (OTPs) nanocrystals by changing the halide anion. However, to date, there is no report of electronic structure tuning of perovskite NCs upon changing the organic cation. We report here, for the first time, the room temperature colloidal synthesis of (EA)x(MA)1-xPbBr3 nanocrystals (NCs) (where, x varies between 0 and 1) to tune the band gap of hybrid organic-inorganic lead perovskite NCs from 2.38 to 2.94 eV by varying the ratio of ethylammonium (EA) and methylammonium (MA) cations. The tuning of band gap is confirmed by electronic structure calculations within density functional theory, which explains the increase in the band gap upon going toward larger "A" site cations in APbBr3 NCs. The photoluminescence quantum yield (PLQY) of these NCs lies between 5% to 85% and the average lifetime falls in the range 1.4 to 215 ns. A mixture of MA cations and its higher analog EA cations provide a versatile tool to tune the structural as well as optoelectronic properties of perovskite NCs.

For the first time, we have synthesized APbBr (A = Cs/MA/FA, where MA = CHNH and FA = CH(NH)) bulk as well as nanoparticles (NPs) by solid-state reactions at room temperature. This facile strategy yields different shape structures e.g. square and rectangular (CsPbBr), spherical (MAPbBr) and parallelogram (FAPbBr) NPs.

Core/intermediate/shell (C/I/S) structures with Type-I emission are well-known and are gaining immense importance due to their superior luminescence properties. Here, we report a unique C/I/S structure composed of CdSe/CdS/ZnSe that exhibits both Type-I and Type-II phenomena. The structures have been well characterized using a combination of optical and structural techniques. The photoluminescence (PL) and photoluminescence excitation (PLE) data indicate the formation of a combined Type-I and Type-II structure in one material, results supported by simple theoretical calculations. Single particle fluorescence reveals colocalization of both the emissions. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results confirm the structure of these particles. The time-resolved fluorescence studies show the possibility of tuning the lifetime of these materials by changing the Type-I/Type-II thickness ratios. It is possible to form these two separate excitons in the same system separated by a CdS intermediate layer that acts both as a barrier and an active member of the Type-II system allowing the generation and recombination of two excitons, in violation of Kasha's rule.

Mixed-dimensional van der Waals nanohybrids (MvNHs) of two-dimensional transition-metal dichalcogenides (TMDs) and zero-dimensional perovskites are highly promising candidates for high-performance photonic device applications. However, the growth of perovskites over the surface of TMDs has been a challenging task due to the distinguishable surface chemistry of these two different classes of materials. Here, we demonstrate a synthetic route for the design of MoSe2–CsPbBr3 MvNHs using a bifunctional ligand, i.e., 4-aminothiophenol. Close contact between these two materials is established via a bridge that leads to the formation of a donor–bridge–acceptor system. The presence of the small conjugated ligand facilitates faster charge diffusion across MoSe2–CsPbBr3 interfaces. Density functional theory calculations confirm the type-II band alignment of the constituents within the MvNHs. The MoSe2–CsPbBr3 nanohybrids show much higher photocurrent (∼2 × 104-fold photo-to-dark current ratio) as compared to both pure CsPbBr3 nanocrystals and pristine MoSe2 nanosheets owing to the synergistic effect of pronounced light–matter interactions followed by efficient charge separation and transportation. This study suggests the use of a bifunctional ligand to construct a nanohybrid system to tune the optoelectronic properties for potential applications in photovoltaic devices.

Objectives:The aim of this study was: (i) to formulate pit and fissure sealants (PFS) containing nano-hydroxyapatite (nHAP) filler; nHAP filler and silica co-filler; nHAP and nano-Amorphous Calcium Phosphate (nACP) co-filler, (ii) to evaluate physical properties; degree of conversion (DOC), curing depth (CD) and mechanical properties; microshear bond strength (MBS) of fortified PFS, and (iii) to assess remineralization potential and release of Ca2= and PO4 ions from newly synthesized sealants.Materials and Methods:Four PFS were prepared using monomers with mixture of 35.5 wt % BisGMA, 35.5 wt % triethylene glycol dimethacrylate and 28 wt % hydroxyethyl methacrylate. Bioactive nanofillers (nHAP and n-ACP) were added in various concentrations (0%–30%). Three commercial sealants were used as follows: unfilled (Clinpro; 3M ESPE), Fluoride releasing (Delton FS plus, Dentsply), ACP filled (Aegis, Bosworth). The samples (n = 35.5/gp) were tested for MBS, DOC, and CD. Remineralization potential was assessed by scanning electron microscopy (SEM). The concentrations of Ca2= and PO4 released from the sealant specimens were analyzed with Ultraviolet-visible Spectrophotometer. Data obtained was statistically analyzed (one-way analysis of variance, Tukey's test, P < 0.05).Results:10% hydroxyapatite (HAP) =20% ACP sealant showed significantly higher DOC. A remineralized region on the surface between fissure sealant and tooth enamel was observed by SEM in all three HAP filled bioactive sealants. Decreasing the solution pH significantly increased ion release from sealant filled with 10% nHAP = 20% nACP (P ≤ 0.001).Conclusion:Results suggested that admixture of nHAP and nACP to PFS showed remineralizing capability, without declining their mechanical and physical properties.