Trap-Mediated Two-Step Sensitization of Manganese Dopants in Perovskite Nanocrystals

Abstract

Halide perovskite nanocrystals hold promise for printable optoelectronic and photonic applications. Doping enhances their functionalities and is being investigated for substituting lead with environmentally friendlier elements. The most investigated dopant is Mn 2+ that acts as a color center sensitized by the host excitons. The sensitization mechanism is far from understood and no comprehensive picture of the energy-transfer process has been proposed. Similarly, the role of shallow states, particularly abundant in defect tolerant materials, is still unknown. Here, we address this problem via spectroscopic studies at controlled excitation density and temperature on Mn:CsPbCl 3 nanocrystals. Our results indicate a two-step process involving exciton localization in a shallow metastable state that mediates the thermally assisted sensitization of the Mn 2+ emission, which is completely quenched for T < 200 K. At T ≤ 60 K, however, such emission surprisingly reappears, suggesting direct energy transfer from band-edge states. Electron spin resonance supports this picture, revealing the signatures of conformational rearrangements below 70 K, possibly removing the potential barrier for sensitization. Our results demystify anomalous behaviors of the exciton-to-Mn 2+ energy-transfer mechanism and highlight the role of shallow defects in the photophysics of doped perovskite nanostructures.

Switching on Near-Infrared Light in Lanthanide-doped CsPbCl3 Perovskite Nanocrystals.pdf

“…On the other hand, Mn 2+ emission displays a peculiar trend, at first decreasing and then increasing (Figure 4a), similarly to what has already been observed and discussed in detail by Brovelli's group. [55] Notably, the NIR Er 3+ emission exhibits the same trend as the Mn 2+ emission (Figure 4b). Upon increasing the temperature from 13 to 113 K, the low population of Mn 2+ 4 T1 state results in weakened Er 3+ emission.…”

Mn2+‐Doped Metal Halide Perovskites: Structure, Photoluminescence, and Application

“…Thermally assisted sensitization of Mn 2+ emission through the shallow metastable state is completely quenched at T < 200 K, as a result, the band‐edge emission intensity increases and the dopant emission intensity decreases. The recovery of the Mn 2+ emission demonstrates that the Mn 2+ emission comes from direct energy transfer from band‐edge states to Mn 2+ d‐states when temperature is below 70 K. [ 144 ] Differently, Xu et al. found that the Mn 2+ PL intensity sharply declines from 300 to 150 K. When temperature is below 75 K, the Mn 2+ PL intensity enhances again, which is still lower than that at 300 K (Figure 6c).…”

“…a) PL spectra of the band‐edge and Mn 2+ emissions of Mn 2+ ‐doped CsPbCl 3 PNCs at different temperatures. [ 144 ] b) PL spectra of integrated intensity of band‐edge and Mn 2+ emissions at different temperatures. [ 144 ] c) Integrated I Mn / I Exc of CsPbCl 3 :Mn 2+ at different temperatures.…”

“…[ 144 ] b) PL spectra of integrated intensity of band‐edge and Mn 2+ emissions at different temperatures. [ 144 ] c) Integrated I Mn / I Exc of CsPbCl 3 :Mn 2+ at different temperatures. [ 145 ] d) Decay curves of CsPbCl 3 :Mn 2+ NCs at different temperatures.…”

Recent Progress and Development in Inorganic Halide Perovskite Quantum Dots for Photoelectrochemical Applications

“…Therefore, the IHPQDs band structure can be regulated through the following two ways. One is to change the ratio of halogen element (X) to adjust the position of valence band, and the other is to adjust the conduction band position by replacing Pb elements with other metal elements (such as Sn element) or doping with other elements (such as Mn, Zn) . For example, Ravi et al prepared CsPbX 3 (X = Cl, Br, I) QDs containing different halogen ion ratios, and the valence band maximum (VBM) of CsPbX 3 was found to shift significantly to higher energies by 0.80 eV (Figure b), from X = Cl (−6.24 eV) to I (−5.44 eV).…”