Deep Impact? On 15 February 2013, the Russian district of Chelyabinsk, with a population of more than 1 million, suffered the impact and atmospheric explosion of a 20-meter-wide asteroid—the largest impact on Earth by an asteroid since 1908. Popova et al. (p. 1069 , published online 7 November; see the Perspective by Chapman ) provide a comprehensive description of this event and of the body that caused it, including detailed information on the asteroid orbit and atmospheric trajectory, damage assessment, and meteorite recovery and characterization.

Lead halide perovskites with nanoscale geometries have received recent attention due to the defect-tolerant high photoluminescence quantum yield at tunable emission wavelengths and the possibility of room-temperature synthesis that does not compromise the physical properties of the materials. These characteristics offer opportunities to advance displays that cover the widest perceivable color. However, lead toxicity obstructs the commercialization of this technology. Therefore, recent efforts have investigated lead-free halide perovskite nanocrystals. Here, we provide our perspectives on the most exciting achievements in the materials design and photophysical properties of lead-free perovskite nanocrystals, particularly for applications in light-emitting devices. This Perspective includes a short summary on the characteristic features of halide perovskite nanocrystals; discussion on the candidate elements to replace lead; methods to prepare colloidal lead-free perovskite nanocrystals; methods to control and enhance the optical properties; a recent demonstration of utilizing lead-free perovskite nanocrystals in light-emitting devices; and an outlook on the field.

No abstract

Electrochemiluminescence (ECL) is a self‐emission of light from electrochemically excited luminophores via a series of redox reactions. Over the past decade, light‐emitting devices based on gel‐phase ECL active materials, i.e., gel electrolyte composites (referred to as ECL gels) containing an ECL luminophore, electrolyte, and network matrix, have attracted considerable attention as a complementary device platform to conventional electroluminescent devices for low‐cost printable displays and solid‐state light sources. Although the ECL phenomenon is extensively exploited in analytical diagnostics and sensing, the development of printable and fast‐response gel‐type luminescent materials may further expand the potential application of ECL in solid‐state flexible, bendable, and stretchable light‐emitting devices. This review summarizes the operation mechanisms of ECL‐based light‐emitting devices, ECL emitters and electrolytes, engineering strategies for obtaining printable high‐strength/high‐conductivity ECL gels, and emerging applications of gel‐type ECL devices.

A stimulus-response system and conscious response enable humans to respond effectively to environmental changes and external stimuli. This paper presents an artificial stimulus-response system that is inspired by human conscious response and is capable of emulating it. The system is composed of an artificial visual receptor, artificial synapse, artificial neuron circuits, and actuator. By incorporating these artificial nervous components, a series of conscious response processes that markedly reduces response time as a result of learning from repeated stimuli are demonstrated. The proposed artificial stimulus-response system offers the promise of a new research field that would aid the development of artificial intelligence–based organs for patients with neurological disorders.