Pressure-Induced Remarkable Enhancement of Self-Trapped Exciton Emission in One-Dimensional CsCu₂I₃ with Tetrahedral Units

Abstract

Self-trapped exciton (STE) emissions derived from inorganic octahedral units make metal halide perovskites promising photoluminescence materials for light-emitting applications. However, there is still little understanding of the intrinsic STE emissions in metal halide perovskites or derivatives with nonoctahedral units. In this work, via high pressure compression, remarkable STE emission enhancement is, for the first time, realized in one-dimensional CsCu 2 I 3 crystals with {CuCl 4 } tetrahedral units. The intertetrahedral distortion is believed to induce the slight emission enhancement of the ambient phase under initial compression. Notably, the obvious structural distortions of both inter-and intratetrahedra are responsible for the significant emission enhancement of the high pressure phase. This work not only sheds light on the structure−optical property relationships of tetrahedron-based halide complexes, but also may provide guidance for the design and fabrication of highly luminescent metal halides.

A Highly Efficient and Stable Blue‐Emitting Cs5Cu3Cl6I2 with a 1D Chain Structure

“…Li and colleagues recently observed a remarkable enhancement of STE emission in the largely distorted high‐pressure CsCu 2 I 3 phase. [ 31 ] The self‐trapped holes in alkali halides typically involve V K centers with the formation of X 2 − , which follows the local deformation of lattice. Thus, we may consider that the ICl − V K center forms in the mixed‐halide phase of Cs 5 Cu 3 Cl 6 I 2 on the basis of a general rule that the binding energy of a diatomic molecule is larger for hetero‐combination than homo‐combination.…”

Pressure‐Engineered Photoluminescence Tuning in Zero‐Dimensional Lead Bromide Trimer Clusters

“…Besides, above 9.6 GPa, the PL signal of (bmpy) 9 [ZnBr 4 ] 2 [Pb 3 Br 11 ] is gradually quenched (Figure 2 d), which could be attributed to the combined effect of structural collapse and deviatoric stress [8] . The structural amorphization could also bring about the abnormal redshift of the peak III above 13.1 GPa, as well as the decreased emission intensity after releasing pressure (Figure S7) [5g] …”

“…To quantitatively describe the structural responses of {PbBr 6 } octahedra, bond length elongation ( λ ) and bond angle deviation ( δ oct 2 ) are calculated [12] . As shown in Figure 3 d and 3e, the continuous increase of both λ and δ oct 2 suggests the gradually enhanced distortion of {PbBr 6 } octahedra below 1.5 GPa [5g] . Then, these two parameters are abruptly increased around 1.5 GPa, implying the considerable distortion of {PbBr 6 } octahedra.…”

“…Above ≈2 GPa, the geometry of [Pb 3 Br 11 ] 5− cluster is sufficiently distorted, considerably promoting the electron‐phonon coupling within the structures (Figure 4 d). Hence, more and deeper STE states are generated, giving rise to the new broadband emission from T1b′ (peak III) [5g, 14] . Under mild compression between ≈2 GPa and ≈10 GPa, the continuous blueshift of the peak III with enhanced intensity is observed, producing bright white‐light emission.…”

“…Firstly, the slightly suppressed distortion of [Pb 3 Br 11 ] 5− clusters in this range could reduce the energy barrier, thereby building a possible “energy bridge” to realize the effective transitions of STEs from T1a to T1b′ (Figure 4 c). [4b, 16] Secondly, the sufficient structural distortion with strong electron‐phonon coupling is able to increase the detrapping barrier and the activation energy of T1b′, facilitating the trapping and emission of STEs in T1b′ [5g, 17] . It has been reported that the chemical pressure via chlorine substitution in (bmpy) 9 [ZnBr 4 ] 2 [Pb 3 Br 11 ] could induce the blueshift of the emission peak [4a] .…”