Solution Based Synthesis of Cs4PbBr6 Perovskite Particles with High Luminescence and Stability

Direct chemical-vapor-deposition growth of alloyed perovskite microcrystals for tunable emissions

Tunable composition of perovskite micro/nanostructures are perfect candidate for the designing of multifunctional optoelectronic circuits. Especially, integrated polychromatic luminescence based on the perovskite materials along a single substrate or chip is essential to the integrated photonic devices and multicolor displays. Here, we reported a synthesis of composition tunable CsPbI3(1-x)Br3x(X = 0.65-0.9) perovskite microstructures on a single substrate via a magnetic-pulling CVD method. The PL emissions can be changed gradually from green (558 nm, 2.23 eV) to red (610 nm, 2.03 eV) under a focused 375 nm laser illumination. Furthermore, these composition-graded alloyed perovskite microcrystals show stable emissions after six months in air, which may find applications in multicolor display and broad band light sources in the future.

Synthesis of double perovskite and quadruple perovskite nanocrystals through post-synthetic transformation reactions

Lead-free halide perovskite nanocrystals (NCs) represent a group of emerging materials which hold promise for various optical and optoelectronic applications. Exploring facile synthetic methods for such materials has been of great interest to not only fundamental research but also technological implementations. Herein, we report a fundamentally new method to access lead-free Bi-based double perovskite (DP) and quadruple perovskite (or layered double perovskite, LDP) NCs based on a post-synthetic transformation reaction of Cs3BiX6 (X = Cl, Br) zero-dimensional (0D) perovskite NCs under mild conditions. The produced NCs show good particle uniformity, high crystallinity, and comparable optical properties to the directly synthesized NCs. The relatively slow kinetics and stop-on-demand feature of the transformation reaction allow real-time composition-structure-property investigations of the reaction, thus elucidating a cation-alloyed intermediate-assisted transformation mechanism. Our study presented here demonstrates for the first time that post-synthetic transformation of 0D perovskite NCs can serve as a new route towards the synthesis of high-quality lead-free perovskite NCs, and provides valuable insights into the crystal structures, excitonic properties and their relationships of perovskite NCs.

Synthesis of lead-free Cs4(Cd1-xMnx)Bi2Cl12 (0 ≤ x ≤ 1) layered double perovskite nanocrystals with controlled Mn-Mn coupling interaction

Lead-free perovskites and their analogues have been extensively studied as a class of next-generation luminescent and optoelectronic materials. Herein, we report the synthesis of new colloidal Cs4M(ii)Bi2Cl12 (M(ii) = Cd, Mn) nanocrystals (NCs) with unique luminescence properties. The obtained Cs4M(ii)Bi2Cl12 NCs show a layered double perovskite (LDP) crystal structure with good particle stability. Density functional theory calculations show that both samples exhibit a wide, direct bandgap feature. Remarkably, the strong Mn-Mn coupling effect of the Cs4M(ii)Bi2Cl12 NCs results in an ultra-short Mn photoluminescence (PL) decay lifetime of around 10 μs, around two orders of magnitude faster than commonly observed Mn2+ dopant emission in NCs. Diluting the Mn2+ ion concentration through forming Cs4(Cd1-xMnx)Bi2Cl12 (0 < x < 1) alloyed LDP NCs leads to prolonged PL lifetimes and enhanced PL quantum yields. Our study provides the first synthetic example of Bi-based LDP colloidal NCs with potential for serving as a new category of stable lead-free perovskite-type materials for various applications.

Negative photoconductivity in Cs4PbBr6 single crystal

Negative photoconductivity is firstly observed in large size Cs₄PbBr₆ single crystal that grown from Cs-rich solution. The Br vacancy and free excitons are responsible for this novel phenomena.