Interest on the nonlinear optical (NLO) switches that turn on/off the second-harmonic generation (SHG) triggered by the external stimulus (such as heat) have continuously grown, especially on the solid-state NLO switches showing superior stability, reversibility, and reproducibility. Herein, we discover (NH 4 ) 2 PO 3 F, as an entirely new solid-state NLO switch showing outstanding switch contrast and reversibility as well as strong SHG intensity (1.1 × KH 2 PO 4 (KDP)) and high laser-induced damage threshold (2.0 × KDP), undergoes a unique first-order phase transition that originates from a reversible hydrogen-bond rearrangement and needs to overcome an energy barrier. Accordingly, we put forward a strategy to continuously modify such an energy barrier by reducing the number of hydrogen bonds per unit cell via an isoelectronic replacement of NH 4 + by K + with a similar size yet incapability of providing any hydrogen bond. Consequently, K x (NH 4 ) 2−x PO 3 F (x = 0−0.3) exhibiting excellent switching performance are obtained. Remarkably, K x (NH 4 ) 2−x PO 3 F not only realizes a continuously tunable T c spanning from 270 to 150 K, representing the widest NLO switching temperature range ever known but also indicates the first solid-state NLO switch example with continuous T c . Intrinsically, such a T c decline depends on the weakening degree of the hydrogen-bonding interactions in the unit cell. These new insights will shed useful light on the future material design and open new application possibilities.

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Organic−inorganic hybrid nonlinear optical (NLO) crystals have been attracting increasing attention because of their unique ability to combine the structural diversity of the organic moiety and the high stability of the inorganic moiety. However, organic NLO genes are rare. Herein, a new organic NLO material gene, the 2aminopyrimidinium cation (C 4 H 6 N 3 ) + ((2AP) + ), is reported, which constructs a novel organic−inorganic hybrid (C 4 H 6 N 3 ) + (H 2 PO 3 ) − (2APP) that exhibits excellent NLO properties and thermal stability, e.g., strong second-harmonic generation (SHG) intensity (2 × KDP), large birefringence (0.225 at 589.3 nm), high laser-induced-damage threshold (1.7 × KDP), and one of the highest thermal stabilities among the metal-free-(2AP) + -containing compounds. Our first-principles theoretical studies confirm the dominant contribution of (2AP) + to optical properties. The inorganic phosphite anions well separate the (2AP) + cations to successfully eliminate the unwanted centrosymmetric trap that is induced by the dipole−dipole interactions between (2AP) + cations. Furthermore, the unique layered structure decorated by the uniformly oriented individual (2AP) + chromophores, dramatically enhances the quantum yield of purple fluorescence (Φ = 30.6%), which is 3 orders of magnitude higher than that of pure 2AP and its derivatives.

Lithium-ion (Li-ion) batteries have been competitive in Electric Vehicles (EVs) due to their high energy density and long lifetime. However, there are still issues, which have to be solved, related to the fast-charging capability of EVs. The pulsed current charging technique is expected to improve the lifetime, charging speed, charging/discharging capacity, and the temperature rising of Li-ion batteries. However, the impact of the pulsed current parameters (i.e., frequency, duty cycle, and magnitude) on characteristics of Li-ion batteries has not been fully understood yet. This paper summarizes the existing pulsed current modes, which are positive Pulsed Current Mode (PPC) and its five extended modes, and Negative Pulsed Current (NPC) mode and its three extended modes. An overview of the impact of pulsed current techniques on the performance of Li-ion batteries is presented. Then the main impact factors of the PPC strategy and the NPC strategy are analyzed and discussed. The weight of these impact factors on lifetime, charging speed, charging/discharging capacity, and the temperature rising of batteries is presented, which provides guidance to design advanced charging/discharging strategies as well as to determine future research gaps.