Zero-Dimensional (Piperidinium)₂MnBr₄: Ring Puckering-Induced Isostructural Transition and Strong Electron–Phonon Coupling-Mediated Self-Trapped Exciton Emission

Abstract

We report on the synthesis, structure, and photophysical properties of a lead-free organic−inorganic hybrid halide, (Piperidinium) 2 MnBr 4 (PipMBr). It crystallizes in a monoclinic P2 1 / n structure, with isolated MnBr 4 tetrahedra representing a zerodimensional compound. It undergoes a reversible isostructural transition at 422/417 K in the heating/cooling cycle owing to the hydrogen-bonding rearrangement mediated by ring puckering of piperidinium cations. This compound exhibits green emission with a photoluminescence quantum yield of 51%. Interestingly, strong electron-longitudinal optical phonon coupling with γ LO of 237 meV is evidenced from the broadening of the temperature-dependent emission linewidth and the Raman spectrum. Such strong electron−phonon coupling and a relatively low Debye temperature (137 K) suggest the self-trapped exciton emission in this compound.

Temperature-Dependent Reversible Optical Properties of Mn-Based Organic–Inorganic Hybrid (C8H20N)2MnCl4 Metal Halides

“…The temperature region of this abnormal change is just consistent with the temperature of structural phase transition. The decrease of PL lifetimes can be attributed to the increase in the proportion of non-radiative processes with increasing temperature . In addition, the PL lifetime evolution with temperature during the cooling process is consistent with that during the heating process, which also confirms a reversible structural phase transition.…”

Electron–Phonon Coupling Mediated Self-Trapped-Exciton Emission and Internal Quantum Confinement in Highly Luminescent Zero-Dimensional (Guanidinium)6Mn3X12 (X = Cl and Br)

“…Electron–phonon coupling, a mechanism for STE formation, was assessed by analysis of the PL line width Γ( T ) over different temperatures and can be expressed as ,, normalΓ ( T ) = normalΓ 0 + normalΓ ac + normalΓ LO + normalΓ imp = normalΓ 0 + γ ac T + γ LO N LO ( T ) + γ imp .25em exp ( − E b k B T ) where Γ 0 accounts for temperature-independent inhomogeneous broadening, Γ ac and Γ LO are due to temperature-dependent homogeneous broadening by acoustic and longitudinal optical (Fröhlich) phonons, respectively, and Γ imp results from ionized impurities with the binding energy E b . N LO ( T ) = 1/[exp( E LO / k B T ) – 1] is a Bose–Einstein function, where E LO holds for the longitudinal optical phonon energy.…”

“…64,61 Among the different types of polarons, small polarons are conciliated by electron−phonon coupling and lead to STE formation. 22,61 Electron−phonon coupling, a mechanism for STE formation, was assessed by analysis of the PL line width Γ(T) over different temperatures and can be expressed as 21,25,66…”

“…Recently, some investigations demonstrated that the emission in Mn 2+ -tetrahedra-based OIH compounds results from the recombination of self-trapped excitons (STEs). − STEs are Frenkel-like bound excitons trapped in a deformable lattice and result from the synergistic effect of reduced lattice dimensionality, structural distortion, lattice softness, and halogen vacancies. − In such compounds, a longitudinal optical phonon scatters the charge carriers and restricts its delocalization via Fröhlich interaction, leading to the formation of STEs. , However, the Mn 2+ octahedral emission shows a larger Stokes shift and a broader emission band compared to the Mn 2+ tetrahedral emission, indicating the possibility of STE recombination in the octahedral emission. , In this paper, we report evidence for STE emission in an Mn 2+ -octahedra-based OIH halide, (Guanidinium) 6 Mn 3 Br 12 [GuMBr], which crystallizes in a trimeric zero-dimensional (0D) structure and exhibits intense red emission with a large Stokes shift, a broad emission band, and long-lived photoexcited electrons. Analysis of the temperature-dependent photoluminescence (PL) line width and Raman spectra confirms electron–phonon coupling.…”

Sc1−xErxAlO3perovskites: high-pressure synthesis, photoluminescence properties, andin vitrobioimaging

“…An activation energy of 0.249 eV is required to dissociate the exciton in the title compound. To determine PL thermal stability, we have calculated TQ 1/2 , which is the temperature at which the emission efficiency decreases to half of its initial value, using the formula: 50 The obtained TQ 1/2 of 462 K exhibits excellent thermal stability and its potential for optoelectronic application. Fig.…”