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Abstract:

Inorganic CsPbX3 (X = Cl, Br, I) perovskite nanocrystals (PNCs) are promising materials for next-generation optoelectronic applications due to their tunable emission and high color purity. However, there is still room to improve their photoluminescence quantum yields (PLQYs) in order to promote their applications. Herein, the PLQY of blue light emitting CsPb(Cl/Br)3 PNCs was increased to 83% with ammonium hexafluorophosphate by choosing an appropriate treatment time. The salt peeled off the outermost surface of PNCs with halide vacancies and then passivated the surface. This method is effective at improving the PLQYs of different CsPbX3 (X = Cl, Br, I) PNCs covering the entire visible spectrum; the PLQYs were improved to 25% for CsPbCl3 at 398 nm, 83% for CsPb(Cl/Br)3 at 448 nm, 96% for CsPbBr3 at 504 nm, 86% for CsPb(Br/I)3 at 568 nm, and 98% for CsPbI3 at 687 nm.

Abstract:

We alloyed Zn²⁺ into CsPbI₃ perovskite nanocrystals by partial substitution of Pb²⁺ with Zn²⁺, which does not change their crystalline phase. The resulting alloyed CsPb_0.64Zn_0.36I₃ nanocrystals exhibited an improved, close-to-unity photoluminescence quantum yield of 98.5% due to the increased radiative decay rate and the decreased non-radiative decay rate. They also showed an enhanced stability, which correlated with improved effective Goldschmidt tolerance factors, by the incorporation of Zn²⁺ ions with a smaller radius than the Pb²⁺ ions. Simultaneously, the nanocrystals switched from n-type (for CsPbI₃) to nearly ambipolar for the alloyed nanoparticles. The hole injection barrier of electroluminescent LEDs was effectively eliminated by using alloyed CsPb_0.64Zn_0.36I₃ nanocrystals, and a high peak external quantum efficiency of 15.1% has been achieved.

Abstract:

For data security applications, the use of fluorescent inks has become the most promising approach because of their convenience and low cost. However, traditional fluorescent inks are usually visible either under ambient light or UV light, whereas the improved stimuli-responsive inks are restricted to a single color. For the first time, full-color stimuli-responsive inks for information coding, encryption, and decryption are reported, which rely on the facile preparation and conversion of perovskite quantum dots. The information printed by the halide salt solution is invisible under ambient and UV light but becomes readable under UV light after spraying a unique developer. Besides, the primitive information can be stored for many years, even decades. Even after the decryption process, it still can be stored for at least several weeks. Most importantly, using butyl amine and acetic acid as encryption and decryption reagents, respectively, can switch off/on the luminescence. In this way, the printed information can be encrypted and decrypted, which shows great potential for information security applications.

Abstract:

Cesium lead halide perovskites emitting blue light in the 460-470 nm range of wavelengths have so far been plagued with rather poor luminescent performance, placing inevitable limitations on the development of perovskite nanocrystal-based blue light-emitting devices. Herein, a selective surface defect elimination process with the help of hydrated nitrates was introduced into the perovskite/toluene solution to strip the undesired surface defects and vacancies and to boost the photoluminescence quantum yield of true-blue-light-emitting (at 466 nm) CsPb(Cl/Br)₃ perovskite nanocrystals to the impressive value of 85%. Unlike the conventional passivation strategy, the anionic nitrate ions are able to desorb the undesired surface metallic lead and combine with excess surface metal ions, leaving perovskite quantum dots with better crystallinity and fewer surface defects.

Abstract:

A method is proposed to improve the photo/electroluminescence efficiency and stability of CsPbI₃ perovskite nanocrystals (NCs) by using SrCl₂ as a co-precursor. The SrCl₂ is chosen as the dopant to synthesize the CsPbI₃ NCs. Because the ion radius of Sr²⁺ (1.18 Ã…) is slightly smaller than that of Pb²⁺ (1.19 Ã…) ions, divalent Sr²⁺ cations can partly replace the Pb²⁺ ions in the lattice structure of perovskite NCs and cause a slight lattice contraction. At the same time, Cl^- anions from SrCl₂ are able to efficiently passivate surface defect states of CsPbI₃ nanocrystals, thus converting nonradiative trap states to radiative states. The simultaneous Sr²⁺ ion doping and surface Cl^- ion passivation result in the enhanced photoluminescence quantum yield (up to 84%), elongated emission lifetime, and improved stability. Sr²⁺ -doped CsPbI₃ NCs are employed to produce light-emitting devices with a high external quantum yield of 13.5%.