Structural non-centrosymmetry in semiconducting organic–inorganic hybrid halide perovskites can introduce functionalities like anomalous photovoltaics and nonlinear optical properties. Here we introduce a design principle to prepare Pb- and Bi-based two- and one-dimensional hybrid perovskites with polar non-centrosymmetric space groups. The design principle relies on creating dissimilar hydrogen and halogen bonding non-covalent interactions at the organic–inorganic interface. For example, in organic cations like I–(CH2)3–NH2(CH3)+ (MIPA), −CH3 is substituted by −CH2I at one end, and −NH3 + is substituted by −NH2(CH3)+ at the other end. These substitutions of two −H atoms by −I and −CH3 reduce the rotational symmetry of MIPA at both ends, compared to an unsubstituted cation, for example, H3C–(CH2)3–NH3 +. Consequently, the dissimilar hydrogen–iodine and iodine–iodine interactions at the organic–inorganic interface of (MIPA)2PbI4 2D perovskites break the local inversion symmetries of Pb–I octahedra. Owing to this non-centrosymmetry, (MIPA)2PbI4 displays visible to infrared tunable nonlinear optical properties with second and third harmonic generation susceptibility values of 5.73 pm V–1 and 3.45 × 10–18 m2 V–2, respectively. Also, the single crystal shows photocurrent on shining visible light at no external bias, exhibiting anomalous photovoltaic effect arising from the structural asymmetry. The design strategy was extended to synthesize four new non-centrosymmetric hybrid perovskite compounds. Among them, one-dimensional (H3N–(CH2)3–NH(CH3)2)BiI5 shows a second harmonic generation susceptibility of 7.3 pm V–1 and a high anomalous photovoltaic open-circuit voltage of 22.6 V.

We present a combination of thermodynamic and dynamic experimental signatures of a disorder driven dynamic cooperative paramagnet in a 50% site diluted triangular lattice spin-1 2 system: Y 2 CuTiO 6. Magnetic ordering and spin freezing are absent down to 50 mK, far below the Curie-Weiss scale ð−θ CW Þ of ∼134 K. We observe scaling collapses of the magnetic field and temperature dependent magnetic heat capacity and magnetization data, respectively, in conformity with expectations from the random singlet physics. Our experiments establish the suppression of any freezing scale, if at all present, by more than 3 orders of magnitude, opening a plethora of interesting possibilities such as disorder stabilized long range quantum entangled ground states.

We establish that the formally 0D (R-/S-MBA)2CuBr4, containing R-/S-α-methyl benzylamine (R-/S-MBA) connected to highly distorted CuBr4 tetrahedral units in alternating layers, possesses extraordinary chiro-optical properties. The concentration and path length-independent chiral anisotropy factor, g CD, for this compound is the highest in the orange-red part of the visible spectrum reported so far from any hybrid material, arising from a chirality transfer from the organic component to the inorganic layer through the extensive asymmetric hydrogen bonding network and electronic coupling, driving the CuBr4 tetrahedral units to follow the 21-screw axis. This sensitivity in the orange-red part of the visible spectrum is achieved by incorporating bromine in the copper coordination sphere, which significantly red-shifts the band edge absorption to ∼710 nm compared to ∼490 nm reported for the chloride analogue. DFT/TDDFT calculations allow us to understand the underlying electronic structure responsible for its remarkable optical properties. We find that this compound gets a partial 2D character, crucial for its broadband chiro-optical properties, arising from Cu–Br···Br–Cu interactions connecting the otherwise isolated CuBr4 units.

Lead halide perovskite (LHP) nanocrystals (NCs) are considered propitious materials due to their extraordinary optoelectronic properties. Their poor ambient stability hinders their practical applications. Among the several approaches taken to enhance the ambient stability, plasma treatment is considered one of the best approaches because it does not hinder charge transport or reduce relative NC content while allowing easy and scalable processing. The plasma treatment increases the overall ambient stability of LHPs but at the cost of photoluminescence quantum yield (PLQY). We found that a short duration of the plasma treatment enhances the PL intensity by 30%, along with enhanced moisture stability. However, longer duration of plasma treatment decreases the photoluminescence (PL), and the NCs become hydrophilic. In this work, we report the underlying chemistry of stability enhancement during plasma treatment and how it affects the PL intensity. We performed Ar−O 2 plasma treatment on the CsPbBr 3 NCs thin films, which induces the cross-linking of the passivating ligand oleylamine that creates a stronger network of ligands, providing better encapsulation and higher PL intensity. A longer duration of plasma treatment results in oxidation of the passivating ligands in the presence of oxygen that eventually degrades the NCs. We created double-layer fluorescent security tags using the PL-stabilized NCs and as-synthesized NCs, having the same emission profile. The security pattern was created using the stabilized perovskite and masked with the assynthesized perovskite, which is relatively unstable and can be washed off under certain treatments.

Extending our earlier investigation of magnetic properties of Nd2NiMnO6, we show that it exhibits a magnetic transition below ∼6 K to a ferrimagnetic state. This behavior is interpreted as arising from a long-range ordering of Nd moments antiferromagnetically coupled to the ferromagnetic Ni–Mn ordered moments. Due to the richness of its multiple magnetic transitions and the easily influenced magnetic state by the application of an external magnetic field, established in our earlier study, it has a remarkable inverse magneto-caloric effect (IMCE) at low temperatures (T < 50 K) together with a significant conventional magneto-caloric effect (CMCE) at the ferromagnetic ordering temperature (Tc ∼ 200 K). IMCE and CMCE correspond to the antiferromagnetic arrangement of Nd and Ni–Mn sublattices and ferromagnetic ordering of Ni–Mn sublattices, respectively. Nd2NiMnO6 with its second order phase transition follows the universal behavior of ∆SM(T); it also shows a power law dependency on the magnetic field as Δ S M ∝ H η .