Carbon-dot based light-emitting diodes (LEDs) with driving current controlled color change are reported. These devices consist of a carbon-dot emissive layer sandwiched between an organic hole transport layer and an organic or inorganic electron transport layer fabricated by a solution-based process. By tuning the device structure and the injecting current density (by changing the applied voltage), we can obtain multicolor emission of blue, cyan, magenta, and white from the same carbon dots. Such a switchable EL behavior with white emission has not been observed thus far in single emitting layer structured nanomaterial LEDs. This interesting current density-dependent emission is useful for the development of colorful LEDs. The pure blue and white emissions are obtained by tuning the electron transport layer materials and the thickness of electrode.

A study of hybrid inverted quantum-dot (QD) light-emitting diodes constructed with and without AlO interlayers is presented. The AlO interlayers are deposited at ZnO/QDs or/and QDs/4,4'-bis(carbazol-9-yl)biphenyl interfaces, resulting in large improvement of device performance, including luminance, current efficiency, and device lifetime. Especially, the devices with QD emitters sandwiched by two AlO layers exhibits outstanding performance, the longest operation lifetime, and mediate efficiency. The maximum current efficiency of 15.3 cd/A is obtained, an enhancement factor of 35% in comparison to that (11.3 cd/A) of conventional device without AlO layer. Moreover, device lifetime is also largely enhanced, over 110 000 h for the device containing two AlO interlayers, nearly 40% enhancement relative to that of conventional device that shows a lifetime of only 80 000 h. On the basis of electrical property and photoluminescence spectroscopy studies, we demonstrate that the AlO interlayers play crucial roles in suppressing the leakage current across the device and reducing exciton quenching induced by ZnO.

Although Mn 2+ doping in semiconductor nanocrystals (NCs) has been studied for nearly three decades, the near 100% photoluminescence (PL) quantum yield (QY) of Mn 2+ emission has never been realized so far. Herein, greatly improved PL QYs of Mn 2+ emissions are reported in Mn 2+doped CsPbCl 3 NCs with various Mn 2+ doping concentrations after CdCl 2 post-treatment at room temperature. Specifically, the near-unity QY and near single-exponential decay of red Mn 2+ emission peaking at 627 nm in doped CsPbCl 3 NCs are obtained for the first time. The temperature dependence of steady-state and time-resolved PL spectra reveals that the CdCl 2 posttreatment significantly reduces the nonradiative defect states and enhances the energy transfer from host to Mn 2+ ions. Moreover, the Mn 2+ :CsPbCl 3 NCs after CdCl 2 post-treatment exhibit robust stability and high PL QYs after multipurification. The results will provide an effective route to obtain doped perovskite NCs with high performance for white lighting emitting diodes.

A seeded growth method to produce colloidal carbon dots (CDs) through controlling the number of seeds and reaction time, which is demonstrated to be an effective way to tune their optical properties, is developed. Color‐tunable fluorescence of CDs with blue, green, yellow, and orange emissions under UV excitation is achieved by increasing the size of the seed CDs, with the color depending on the size of the π‐conjugated domains. Strong multicolor photoluminescence of powdered samples enables realization of efficient down‐conversion white‐light‐emitting devices with correlated color temperature ranging from 9579 to 2752 K and luminous efficacy from 19 to 51 lm W−1. Moreover, color‐tunable room‐temperature phosphorescence of CD powders is demonstrated in the broad spectral range of 500–600 nm. It is related to the presence of the nitrogen‐containing groups at the surface of CDs, which form interparticle hydrogen bonds to protect the CD triplet states from quenching, and to the existence of the polyvinylpyrrolidone polymer chains at the surface of CDs. The color‐tunable room‐temperature phosphorescence from CDs demonstrated in this work exhibits potential for data encryption.

The pressure-dependent optoelectronic properties of all-inorganic perovskite CsPbBr 3 nanocrystals (NCs) are investigated with steady-state and transient spectroscopy. The steady-state absorption and photoluminescence (PL) spectra under pressure show that CsPbBr 3 NCs pass through three electronic states (ES-I, ES-II, and ES-III) separated with two knee points located at 0.38 and 1.08 GPa, respectively, which are also confirmed by the PL dynamics. Analyzed with the two-carrier model of free carriers and trapped carriers, the PL dynamics show that the lifetime increases in ES-I, decreases in ES-II, and increases in ES-III for free carriers, while it is almost invariable for trapped carriers. The transformation from ES-I to ES-II is assigned to the contraction of the Pb−Br bond length while the transformation from ES-II to ES-III originated mostly from the distortion of the PbBr 6 octahedron. Apparently, the contraction of the Pb−Br bond and the distortion of octahedra benefit the tailoring of the generation and diffusion of carriers during the CsPbBr 3 NCs compression. These results in this work help us to design and optimize the perovskite-based optoelectronic devices of high performance.