Black α-CsPbI 3 perovskites are unable to maintain their phase stability under room conditions; hence, the α-CsPbI 3 phase transforms into a thermodynamically stable yellow δ-CsPbI 3 phase within a few days, which has a nonperovskite structure and high band gap for optoelectronic applications. This phase transformation should be prevented or at least retarded to make use of superior properties of α-CsPbI 3 in optoelectronic applications. In this study, Gd 3+ doping was employed with the aim of increasing the stability of α-CsPbI 3 . All doped α-CsPbI 3 nanocrystals with various levels of Gd 3+ , between 5 and 15 mol %, have shown greater phase stability than that of the pure α-CsPbI 3 phase from 5 days up to 11 days under ambient conditions. This prolonged phase stability can be attributed to three potential reasons: increased tolerance factor of the perovskite structure, distorted cubic symmetry, and decreased defect density in nanocrystals. Urbach energy values suggest the reduction of defect density in the doped nanocrystals. Also, use of 10 mol % Gd 3+ as a dopant material increases the photoluminescence quantum yield from 70 to 80% and fluorescence lifetime of α-CsPbI 3 from 47.4 to 64.4 ns. Further, density functional theory calculations are in a good agreement with the experimental results.

Nobel-metal nanostructures strongly localize and manipulate light at nanoscale dimension by supporting surface plasmon polaritons. In fact, the optical properties of the nobel-metal nanostructures strongly depend on their morphology and composition. Until now, various metal nanostructures such as nanocubes, nanoprisms, nanorods, and recently hollow nanostructures have been demonstrated. In addition, the plasmonic field can be further enhanced at nanoparticle dimers and aggregates because of highly localized and intense optical fields, which is known as "plasmonic hot spots". However, colloidally synthesized and circular-shaped nanoring nanostructures with plasmonic hot spots are still lacking. We, herein, show for the first time that colloidal bimetallic nanorings with plasmonic nanocavities and tunable plasmon resonance wavelengths can be synthesized via colloidal synthesis and galvanic replacement reactions. In addition, in the strong coupling regime, plasmons in nanorings and excitons in J-aggregates interact strongly and nanoring-shaped colloidal plexcitonic nanoparticles are demonstrated. The results reveal that the optical properties of the nanoring and the onset of strong coupling can be tamed by the galvanic replacement reaction. Further, the plasmonic nanocavity in the nanorings has immense potential for applications in sensing and spectroscopy because of the space, enclosed by the plasmonic nanocavity, is empty and accessible to a variety of molecules, ions, and quantum dots.

Colloidal synthesis of two‐dimensional lead halide perovskite nanoplatelets (2D LHP NPLs) with a general formula of L2[APbX3]n−1PbX4 has been widely performed by using hot‐injection or ligand assisted reprecipitation methods. Herein, for the first time, we report on seed‐mediated synthesis of two and three monolayers (n=2, 3) lead halide perovskite nanoplatelets without using A‐site cation halide salt (AX; A=Cesium, methylammonium, formamidinium and, X=Cl, Br, I) and long chain alkylammonium halide salts (LX; L=oleylammonium, octylammonium, butylammonium and, X=Cl, Br, I). The nanocrystal seeds have been prepared by reacting lead (II) halide salt and coordinating ligands in a nonpolar solvent and then they have been reacted with cesium oleate, formamidinium oleate or methylamine. Our facile synthesis route enabling further understanding of the growth dynamics of LHP NPLs provides highly stable, monodisperse NPLs with very narrow absorption and emission linewidths (min. 68 meV), and high PLQY (max. 37.6%).

All inorganic colloidal halide perovskite nanoplatelets and nanowires are highly anisotropic shaped semiconductor nanocrystals with highly tunable optical properties in the visible spectrum. These nanocrystals have large exciton binding energies...

Aging creates significant changes in the properties of the ferroelectric materials such as dielectric and piezoelectric properties. However, the influence of aging on the electrocaloric effect (ECE) has not yet been investigated. In this work, we investigate the effect of the aging on the ECE in acceptor (Li þ ) doped BaTiO 3 ceramics. We observe that aging induced defect polarization (P D ) reduces the saturation polarization of the doped samples until T c ¼ 115 C. Above that temperature P D loses its effectiveness and material behaves like a fresh sample. Suppression of polarization below T C due to aging effect results in a sharper slope change in the temperature dependence of electrical polarization in aged samples which causes an increase in the electrocaloric temperature change of Li þ doped BaTiO 3 ceramics up to 23% at T C . Above a critical Li doping amount, both negative and positive electrocaloric effect are observed in the same sample.

The advances in colloid chemistry and nanofabrication allowed us to synthesize Noble monometallic and bimetallic nanocrystals with tunable optical properties in the visible and near infrared region of the electromagnetic...

Carbon quantum dots (CDs) have recently received a tremendous amount of interest owing to their attractive optical properties. However, CDs have broad absorption and emission spectra limiting their application ranges. We herein, for the first time, show synthesis of water-soluble red emissive CDs with a very narrow line width (∼75 meV) spectral absorbance and hence demonstrate strong coupling of CDs and plasmon polaritons in liquid crystalline mesophases. The excited state dynamics of CDs has been studied by ultrafast transient absorption spectroscopy, and CDs display very stable and strong photoluminescence emission with a quantum yield of 35.4% and a lifetime of ∼2 ns. More importantly, we compare J -aggregate dyes with CDs in terms of their absorption line width, photostability, and ability to do strong coupling, and we conclude that highly fluorescent CDs have a bright future in the mixed light–matter states for emerging applications in future quantum technologies.

The main challenges to overcome for colloidal 2D Ruddlesden−Popper (RP) organo-lead iodide perovskite nanocrystals (NCs) are phase instability and low photoluminescence quantum yield (PLQY). Herein, we demonstrate colloidal synthesis of guanidinium (GA)-L 2 [GAPbI 3 ]PbI 4 , formamidinium (FA)-L 2 [FAPbI 3 ]PbI 4 , and GA and FA alloyed L 2 [GA 0.5 FA 0.5 PbI 3 ]PbI 4 NCs without using polar or high boiling point nonpolar solvents. Importantly, we show that optical properties and phase stability of L 2 [APbI 3 ]PbI 4 NCs can be affectively tuned by alloying with guanidinium and formamidinium cations. Additionally, the band gap of NCs can be rapidly engineered by bromide ion exchange in L 2 [GA x FA 1−x PbI 3 ]PbI 4 (0 ≤ x ≤ 1) NCs. Our approach produces a stable dispersion of L 2 [FAPbI 3 ]PbI 4 NCs with 12.6% PLQY that is at least three times higher than the previously reported PLQY in the nanocrystals. Furthermore, L 2 [GAPbI 3 ]PbI 4 and L 2 [GA 0.5 FA 0.5 PbI 3 ]-PbI 4 NC films exhibit improved ambient stability over 10 days, which is significantly higher than L 2 [FAPbI 3 ]PbI 4 NC films, which transform to an undesired 1D phase within 6 days. The colloidally synthesized guanidinium-and formamidinium-based 2D RP organo-lead iodide perovskite NCs with improved stability and high PLQY demonstrated in this study may find applications in solar cells and light-emitting diodes. Therefore, large A-site cation-alloyed 2D RP perovskite NCs may provide a new way to rationalize high-performance and stable perovskite solar cells and light-emitting diodes.