Observation of Defect Luminescence in 2D Dion–Jacobson Perovskites

Abstract

The luminescent property of 2D perovskite materials promotes their applications in light emitting diodes, phosphor powders, and scintillators. Recently, an interesting extrinsic low‐energy broadband luminescence is hotly investigated. However, the understanding of such emissions is still at the early stage. In this study, based on a modified solvent evaporation method, centimeter‐size (BDA)PbI4 (BDA = NH3C4H8NH32+) single crystals are grown which, besides the band–band emission, show a large Stokes‐shifted broadband luminescence. We find such emission can be effectively excited by sub‐gap photons and conclude defects‐induced shallow traps are the corresponding luminescence centers. Density functional theory (DFT) calculations indicate that in‐plane iodine vacancies can introduce shallow electron traps in the band gap and give rise to the broadband emission.

Highly Stable Lead‐Free Perovskite Single Crystals with NIR Emission Beyond 1100 nm

“…[9a] Given the low exciton binding strength at defect states, these trapped charge carriers can be thermally released back to band edges, followed by a redistribution among the STE and defect states. [17] The reuse of released charge carriers not only enhances STE emission intensity but also reduces defect-induced nonradiative recombination, as corroborated by the increased emission intensity and prolonged lifetime in the high-temperature region (Figure S11, Supporting Information). Notably, the intensity ratio between the STE emission peaks remains unchanged as temperature increases, suggesting negligible interaction between these STE states.…”

“…Considering that the position and shape of the emission bands are independent of excitation wavelength and temperature (Figure 2d), such emission is associated with STE states rather than emission induced by intrinsic lattice defects such as vacancies and interstitials. [17] The experimental evidence suggests that upon excitation, two STEs (STE-1 and STE-2) with higher energy can readily form in the low-temperature range and subsequently emit light (Figure 2e). In contrast, the low-energy STE state (STE-3) only www.advopticalmat.de forms at elevated temperatures as thermal softening of the crystal lattice facilitates structural distortion.…”

Highly efficient blue emitting one dimensional lead-free nanocrystals

“…For STE, the PL intensity will continue increasing with power, while defect luminescence will saturate at certain excitation power. 28,29 As shown in Fig. 4c, the PL intensity increases linearly with excitation power, suggesting the broadband emission does not arise from permanent defects.…”

Structural Reconstruction in Lead-Free Two-Dimensional Tin Iodide Perovskites Leading to High Quantum Yield Emission

“…Further, the organic spacers can be functionalized to tune the electronic, optical, and charge-transport properties of 2D halide perovskites. , While strongly bound excitons in low-dimensional halide perovskites result in fast and narrow emission originating from their band-edge radiative relaxation, largely Stokes shifted broad and delayed emission is also observed in them which is attributed to defects and STEs. ,− Broadband emission from low-dimensional perovskites and metal halide layered structures are important for producing white LEDs. − STEs are formed when exciton creates a potential well by deforming the lattice locally and getting trapped in it. While emissive defect states in perovskites are extrinsic and accessible with below-bandgap excitation, ,, STEs are intrinsically formed and are not accessible with below-bandgap excitation. , Emission from STEs is temperature-dependent where a sufficiently low temperature is favorable for excitons to access the self-trapping states. ,, At room temperature or higher, a thermal detrapping of STEs and quenching of broadband emission may take place. Therefore, producing broadband white light emission from halide perovskites at room temperature is challenging.…”

“…34−36 creates a potential well by deforming the lattice locally and getting trapped in it. While emissive defect states in perovskites are extrinsic and accessible with below-bandgap excitation, 31,33,37 STEs are intrinsically formed and are not accessible with below-bandgap excitation. 11,24 Emission from STEs is temperature-dependent where a sufficiently low temperature is favorable for excitons to access the self-trapping states.…”