Extrinsic photoluminescence properties of individual micro-particle of Cs₄PbBr₆ perovskite with “defect” structure

Abstract

Optical performance of the lead halide perovskites with zero-dimension (0D) structure has been in a hot debate for optoelectronic applications. Here, Cs 4 PbBr 6 hexagonal micro-particles with a remarkable green emission are first fabricated via a low-temperature solution-process employed ethanol as solvent. Our results underline that the existence of bromine vacancies and the introduction of hydroxyl induce a narrowed band gap with the formation of a defect level, which contributes to the extrinsic photoluminescence (PL) properties synergistically. Thanks to the high exciton binding energy and the unique morphology with a regular geometric structure of the as-obtained micro-particles, two-photon pumped amplified spontaneous emission (ASE) and single mode lasing from an individual Cs 4 PbBr 6 particle are realized. Our results not only provide an insight into the origin of optical emission from Cs 4 PbBr 6 , but also demonstrate that the versatile Cs 4 PbBr 6 offers a new opportunity for novel nonlinear photonics applications as an up-conversion laser.

Low‐Dimensional‐Networked Cesium Lead Halide Perovskites: Properties, Fabrication, and Applications

“…[38] The second theory involving a vacancy-assisted PL emission was offered, which regarded the strong PL emission as due to the intrinsic nature of Cs 4 PbBr 6 , in which Br vacancies (in most cases), tribromide and interstitial hydroxyl served as radiative recombination centers. [32,[39][40][41][42][43][44][45] From DFT calculation results, it was found that i) Br vacancies had a small formation energy under Br-deficit conditions; ii) their transition level matched well with the emissive energy; iii) their electronic charge density was highly localized (Figure 3a,b). [29] Therefore, one could obtain Cs 4 PbBr 6 with stronger PL emission if more defects could be induced under extremely Br-poor conditions.…”

“…However, to the best of our knowledge, we did not find any formula to follow. For Cs 4 PbBr 6 , the synthesis could be performed with a CsBr/PbBr 2 ratio ranging from 1:4, [42] 1:2, [89] 1:1, [38,44,49,57,86,94] 2:1, [85,88] 3:1 [87] to 4:1. [95] In the production of CsPb 2 X 5 , the CsX/PbX 2 ratio could be one of 1:10, [96] 1:5, [88] 1:3, [59] 1:2.5, [67] 1:2, [97] 1:1.…”

On the Role of Cs4PbBr6 Phase in the Luminescence Performance of Bright CsPbBr3 Nanocrystals

“…The other strong opinion proposes that the green luminescence is due to point defects in Cs 4 PbBr 6 structure. Some possible defects that may cause green luminescence were identified, for example the Br vacancy [ 40 , 41 , 42 ]. For more details, please refer to review papers published on this subject, for example the most recent, [ 28 ], which supports the opinion based on the presence of nanoinclusions, and provides persuasive arguments rebutting the Br vacancy concept.…”

Revisiting the origin of green emission in Cs4PbBr6

“…Studies reported by Yang et al also support the defect mechanism, but offer yet another reason for green emission. 71 In this case, Cs 4 PbBr 6 micro-particles were synthesized involving ethanol as a polar solvent. Assisted by DFT calculations, they infer that the impact of the OH- group (presumably from ethanol) was to reduce the band gap of the Cs 4 PbBr 6 host from 3.75 eV to 3.5 eV, also downshifting the Br-vacancy level from 2.75 eV to 2.44 eV, which approximately matches with the ∼520 nm green emission.…”