Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related Cs₄PbBr₆ Microdisks: Synthesis and Single-Particle Imaging Study

Abstract

Quantum-confined perovskites are a new class of promising materials in optoelectronic applications. In this context, a zero-dimensional perovskite-related substance, CsPbBr, having high exciton binding energy can be an important candidate, but its photoluminescence (PL) is a topic of recent debate. Herein, we report an ambient condition controlled synthesis of CsPbBr microdisks of different shapes and dimensions which exhibit fairly strong green PL (quantum yield up to 38%, band gap ∼2.43 eV) in the solid state. Using confocal fluorescence microscopy imaging of the single particles, we show that the fluorescence of CsPbBr microdisks is inherent to these particles. Fluorescence intensity and lifetime imaging of the microdisks reveals significant spatial heterogeneity with a bright central area and somewhat dimmer edges. This intensity and lifetime distribution is attributed to enhanced trap-mediated nonradiative deactivation at the edges compared to the central region of the microdisks. Our results, which unambiguously establish the PL of these CsPbBr and suggest its possible origin, brighten the potential of these materials in photon-emitting applications.

Zero-Dimensional Cesium Lead Halides: History, Properties, and Challenges

“…53 Ling et al found that the PL lifetime of their CsPbBr 3 |Cs 4 PbBr 6 composite increased as the Cs 4 PbBr 6 ratio increased. 40 In the case of Cs 4 PbBr 6 microdisks, an average PL lifetime of 11.95 ns was recorded at the center of the disks only, 20 whereas a shorter PL lifetime (9.26 ns) was recorded at the disks’ edges, indicating that there is a spatial inhomogeneity within the disks. Generally, PL lifetimes of the bulk (single crystals and powders) green-emitting Cs 4 PbBr 6 , in most reports discussed above and others, are in agreement with PL lifetimes of CsPbBr 3 NCs, suggesting that the high PLQY is due to Cs 4 PbBr 6 -passivated CsPbBr 3 NCs.…”

“…Recombination from midbandgap states due to crystal defects was also hypothesized as being the origin of the green PL in Cs 4 PbBr 6 microdisks. 20 …”

“…For instance, unlike CsPbBr 3 and its hybrid perovskite counterpart, which are usually found to be bromine-deficient, 80−83 Cs 4 PbBr 6 is often reported to have a Br:Pb ratio that is usually higher than 6, thus implying that Cs 4 PbBr 6 are rather halide rich. 14,18,20,80 One could therefore expect a rather low density of V Br .…”

In Situ Fabricated Perovskite Nanocrystals: A Revolution in Optical Materials

“…[74,75] Contradictory and controversial explanations were proposed, a clarified mechanism behind the PL performance of Cs 4 PbBr 6 is highly required. [76] We will clarify in the following sections that the fabrication procedure can be described as in situ growth of strong emissive CsPbBr 3 PNCs in the matrix of single Cs 4 PbBr 6 crystal due to the nonstoichiometry induced partial phase transformation process.…”

“…Even that perovskite single crystals show better stability and easy processability for application exploration, they are not suitable for light emission uses due to their weak PL response at room temperature. Recently, Cs 4 PbBr 6 single crystallites with micro or macro sizes gained increasing attention due to abnormal strong visi ble light emission properties at room temperature, [75,111,112] however, the nanosized NCs of this kind of material are nonluminescent. [113][114][115] The emissive Cs 4 PbBr 6 can be achieved through antisolvent vapor-assisted crystallization, [74] precursor injection at room [116] or elevated temperature, [115] spin-coating with nonstoichiometric precursors [116,117] or inhomogeneous interface reaction (IIR).…”