Photoluminescence (PL) of rare earth (RE) ions has been observed in RE ion-doped perovskite nanocrystals (PeNCs); however, the electroluminescence (EL) originating from the RE ions is still not achieved in perovskite light-emitting diodes (PeLEDs). Herein, we demonstrate the first observation of EL from the PeLEDs based on Sm3+-doped CsPbCl3 PeNCs, which is realized by benefiting from the as-prepared Sm3+-doped CsPbCl3 PeNCs with photoluminescence quantum yield (PLQY) as high as 85% synthesized through a modified hot-injection method. The color of the EL can be modulated from the blue to the orange spectral region by varying the Sm3+ ion doping concentration. Therefore, the single-component white light-emitting PeLEDs with chromaticity coordinate (CIE) of (0.32, 0.31), a maximum luminance of 938 cd/m2, EQE of 1.2%, and color rendering index (CRI) of 93 are realized, which are desirable results for practical application. This work demonstrates the unique application of RE-doped PeNCs and provides a strategy for devices using white light PeLEDs.

Colloidal perovskite nanocrystals (NCs), especially the fully inorganic cesium lead halide (CsPbX, X = Cl, Br, I) NCs, have been considered as promising candidates for lighting and display applications due to their narrow band emission, tunable band gap and high photoluminescence quantum yields (QYs). However, owing to the anion exchange in the CsPbX NCs, stable multi-color and white light emissions are difficult to achieve, thus limiting their practical optoelectronic applications. In this work, dual ion Bi/Mn codoped CsPbCl perovskite NCs were prepared through the hot injection method for the first time to the best of our knowledge. Through simply adjusting the doping ion concentrations, the codoped NCs exhibited tunable emissions spanning the wide range of correlated color temperature (CCT) from 19 000 K to 4250 K under UV excitation. This interesting spectroscopic behaviour benefits from efficient energy transfer from the perovskite NC host to the intrinsic energy levels of Bi or Mn doping ions. Finally, taking advantage of the cooperation between the excitonic transition of the CsPbCl perovskite NC host and the intrinsic emissions from Bi and Mn ions, white light emission with the Commission Internationale de l'Eclairage (CIE) color coordinates of (0.33, 0.29) was developed in the codoped CsPbCl NCs.

In recent years, significant advances have been achieved in the red and green perovskite quantum dot (PQD)-based light-emitting diodes (LEDs). However, the performances of the blue perovskite LEDs are still seriously lagging behind that of the green and red counterparts. Herein, we successfully developed Ni2+ ion-doped CsPbCl x Br3–x PQDs through the room-temperature supersaturated recrystallization synthetic approach. We simultaneously realized the doping of various concentrations of Ni2+ cations and modulated the Cl/Br element ratios by introducing different amounts of NiCl2 solution in the reaction medium. Using the synthetic method, not only the emission wavelength from 508 to 432 nm of Ni2+ ion-doped CsPbCl x Br3–x QDs was facially adjusted, but also the photoluminescence quantum yield (PLQY) of PQDs was greatly improved due to efficient removal of the defects of the PQDs. Thus, the blue emission at 470 nm with PLQY of 89% was achieved in 2.5% Ni2+ ion-doped CsPbCl0.99Br2.01 QDs, which increased nearly three times over that of undoped CsPbClBr2 QDs and was the highest for the CsPbX3 PQDs with blue emission, fulfilling the National Television System Committee standards. Benefiting from the highly luminous Ni2+ ion-doped PQDs, the blue-emitting LED at 470 nm was obtained, exhibiting an external quantum efficiency of 2.4% and a maximum luminance of 612 cd/m2, which surpassed the best performance reported previously for the corresponding blue-emitting PQD-based LED.

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 photoluminescence quantum yield (PLQY) of blue-violet emission of CsPbCl quantum dots (QDs) is still low, which has limited their application in multi-colour displays. It is important to search for efficient perovskite phosphors within this wavelength range. In this work, we first considerably enhanced the photoluminescence quantum yield (PLQY) of the CsPbCl QDs from 3.2 to 10.3% by the introduction of potassium ions (K). Then, various lanthanide elements (La, Y, Eu, Lu) were further doped into KCsPbCl QDs. The lanthanide doped KCsPbCl QDs still demonstrated emissions around 408 nm and the PLQY was further improved to 31%. Finally, we carried out anion exchange by gradually substituting chlorine with bromine. Efficient and tunable emissions ranging from 408-495 nm were obtained, with a maximum PLQY of 90%. This work provides a new approach to improve the efficiency of the blue-violet light of perovskite QDs.

Carbon dots (CDs), one of the most significant classes of carbon-based nanophosphors, have attracted extensive attention in recent years. However, few attempts have been reported for realizing CDs with tunable emissions, especially for obtaining the red-light emissions with high photoluminescence quantum yields. Herein, we synthesized CDs with different chromatic blue, green and red emissions by facilely changing the reaction solvent during hydrothermal conditions. The photoluminescence quantum yields of 34%, 19% and 47% for the blue, green and red emissions, respectively, were achieved. Furthermore, the solid-state CD/PVA composite films were constructed through mixing the CDs with PVA polymer, in which the self-quenching of photoluminescence of CDs had been successfully avoided benefiting from the formation of hydrogen bonds between the CDs and PVA molecules. Finally, the warm white light emitting diode (WLED) was fabricated by integrating CD/PVA film on a UV-LED chip. The WLED exhibited the Commission International de l'Eclairage coordinates (CIE) of (0.38, 0.34), correlated color temperature of 3913 K and color rendering index of 91, respectively, which were comparable with the commercial WLEDs.

White light-emitting diodes (WLEDs) based on all-inorganic perovskite CsPbX 3 (X = Cl, Br, I) nanocrystals (NCs) have attracted extensive interests. However, the native ion exchange among halides makes them extremely difficult to realize the white emission. Herein, we demonstrate a novel strategy to obtain WLED phosphors based on the codoping of different metal ion pairs, such as Ce 3+ /Mn 2+ , Ce 3+ /Eu 3+ , Ce 3+ /Sm 3+ , Bi 3+ /Eu 3+ , and Bi 3+ /Sm 3+ into stable CsPbCl 3 and CsPbCl x Br 3−x NCs. Notably, by the typical anion exchange reaction, the highly efficient white emission of Ce 3+ /Mn 2+ -codoped all-inorganic CsPbCl 1.8 Br 1.2 perovskite NCs was achieved, with an optimal photoluminescence quantum yield of 75%, which is much higher than the present record of 49% for single perovskite phosphors. Moreover, the WLED with a luminous efficiency of 51 lm/W based on the 365 nm ultraviolet chip and CsPbCl 1.8 Br 1.2 :Ce 3+ /Mn 2+ nanophosphor was achieved. This work represents a novel device for perovskite-based phosphor-converted WLEDs.

Co-doping of cation (La3+) and anion (F−) ions is a feasible method to improve the optical properties of CsPbCl3 QDs, and high photoluminescence quantum yield of 36.5% is achieved in CsPb(Cl0.7F0.3)3:La3+ QDs.