Recently, Kovalenko and co‐workers and Li and co‐workers developed CsPbX3 (X = Cl, Br, I) inorganic perovskite quantum dots (IPQDs), which exhibited ultrahigh photoluminescence (PL) quantum yields (QYs), low‐threshold lasing, and multicolor electroluminescence. However, the usual synthesis needs high temperature, inert gas protection, and localized injection operation, which are severely against applications. Moreover, the so unexpectedly high QYs are very confusing. Here, for the first time, the IPQDs' room‐temperature (RT) synthesis, superior PL, underlying origins and potentials in lighting and displays are reported. The synthesis is designed according to supersaturated recrystallization (SR), which is operated at RT, within few seconds, free from inert gas and injection operation. Although formed at RT, IPQDs' PLs have QYs of 80%, 95%, 70%, and FWHMs of 35, 20, and 18 nm for red, green, and blue emissions. As to the origins, the observed 40 meV exciton binding energy, halogen self‐passivation effect, and CsPbX3@X quantum‐well band alignment are proposed to guarantee the excitons generation and high‐rate radiative recombination at RT. Moreover, such superior optical merits endow them with promising potentials in lighting and displays, which are primarily demonstrated by the white light‐emitting diodes with tunable color temperature and wide color gamut.

Molybdenum disulfide (MoS2) and tungsten disulfide (WS2), two representative transition metal dichalcogenide materials, have captured tremendous interest for their unique electronic, optical, and chemical properties. Compared with MoS2 and WS2, molybdenum ditelluride (MoTe2) and tungsten ditelluride (WTe2) possess similar lattice structures while having smaller bandgaps (less than 1 eV), which is particularly interesting for applications in the near‐infrared wavelength regime. Here, few‐layer MoTe2/WTe2 nanosheets are fabricated by a liquid exfoliation method using sodium deoxycholate bile salt as surfactant, and the nonlinear optical properties of the nanosheets are investigated. The results demonstrate that MoTe2/WTe2 nanosheets exhibit nonlinear saturable absorption property at 1.55 μm. Soliton mode‐locking operations are realized separately in erbium‐doped fiber lasers utilizing two types of MoTe2/WTe2‐based saturable absorbers, one of which is prepared by depositing the nanosheets on side polished fibers, while the other is fabricated by mixing the nanosheets with polyvinyl alcohol and then evaporating them on substrates. Numerous applications may benefit from the nonlinear saturable absorption features of MoTe2/WTe2 nanosheets, such as visible/near‐infrared pulsed laser, materials processing, optical sensors, and modulators.

Sn4+–O2−• centers are intentionally created in SnO2 nanoflowers by a thermodynamically instable synthetic process. The resulting SnO2 nanoflower‐based sensor is confirmed to be the most sensitive ppb‐level chemiresistor NO2 sensor to date. The Sn4+–O2−• centers with strong gas‐adsorbing and high eletron‐donating capability towards NO2 molecules decisively determine the sensor sensitivity.

Optoelectronic applications require materials both responsive to objective photons and able to transfer carriers, so new two‐dimensional (2D) semiconductors with appropriate band gaps and high mobilities are highly desired. A broad range of band gaps and high mobilities of a 2D semiconductor family, composed of monolayer of Group 15 elements (phosphorene, arsenene, antimonene, bismuthene) is presented. The calculated binding energies and phonon band dispersions of 2D Group 15 allotropes exhibit thermodynamic stability. The energy band gaps of 2D semiconducting Group 15 monolayers cover a wide range from 0.36 to 2.62 eV, which are crucial for broadband photoresponse. Significantly, phosphorene, arsenene, and bismuthene possess carrier mobilities as high as several thousand cm2 V−1 s−1. Combining such broad band gaps and superior carrier mobilities, 2D Group 15 monolayers are promising candidates for nanoelectronics and optoelectronics.

Halide perovskite materials have attracted intense research interest due to the striking performance in photoharvesting photovoltaics as well as photoemitting applications. Very recently, the emerging CsPbX3 (X = Cl, Br, I) perovskite nanocrystals have been demonstrated to be efficient emitters with photoluminescence quantum yield as high as ∼90%, room temperature single photon sources, and favorable lasing materials. Herein, the nonlinear optical properties, in particular, the multiphoton absorption and resultant photoluminescence of the CsPbBr3 nanocrystals, were investigated. Notably, a large two-photon absorption cross-section of up to ∼1.2 × 105 GM is determined for 9 nm sized CsPbBr3 nanocrystals. Moreover, low-threshold frequency-upconverted stimulated emission by two-photon absorption was observed from the thin film of close-packed CsPbBr3 nanocrystals. The stimulated emission is found to be photostable and wavelength-tunable. We further realize the three-photon pumped stimulated emission in green spectra range from colloidal nanocrystals for the first time. Our results reveal the strong nonlinear absorption in the emerging CsPbX3 perovskite nanocrystals and suggest these nanocrystals as attractive multiphoton pumped optical gain media, which would offer new opportunities in nonlinear photonics and revive the nonlinear optical devices.