Photoluminescence Lifetimes and Thermal Degradation of Mn²⁺-Doped CsPbCl₃ Perovskite Nanocrystals

Abstract

The Mn2+-doped CsPbCl3 nanocrystals (NCs) with a low Mn2+ doping concentration were synthesized using different reaction temperatures to control the NC size from 5.3 to 17.4 nm and then were studied by means of steady-state and time-resolved photoluminescence (PL) spectroscopy at various temperatures. The Mn2+ emissions with different quantum yields in the doped NCs in hexane exhibited nearly size-independent and single-exponential decay lifetimes of 1.8 ms at room temperature. The PL lifetimes in all Mn2+ in CsPbCl3-doped NCs had similar temperature dependence from 80 to 300 K, whereas they were size-dependent at elevated temperatures, reflecting thermal degradation of doped NCs. The degradation mechanisms of Mn2+ PL were attributed to the amount of surface defects as nonradiative recombination centers generated in size-unchanged and grown Mn2+:CsPbCl3 NCs. The study provides the detailed understanding of the thermal degradation mechanisms in doped perovskite NCs for optoelectronic applications.

Halogen‐content‐dependent photoluminescence of Mn2+‐doped CsPbCl3 nanocrystals

“…As shown in Figure 5F, the temperature‐dependent Mn 2+ PL intensity initially increases and then decreases with increasing temperature for the samples with relatively higher OAm‐Cl contents, while it monotonously decreases with increasing temperature for the sample with lower OAm‐Cl content of 0.4 ml. The same dimming trend above 320 K can be attributed to the newly formed defect/trap states caused by the thermal degradation of the NCs and the enhanced electron‐phonon coupling process at a higher temperature 15,36,39 . While the opposite change trend between 80 to ∼320 K occurs, indicating the presence of the different defect states in the samples with sufficient and insufficient OAm‐Cl.…”

“…The same dimming trend above 320 K can be attributed to the newly formed defect/trap states caused by the thermal degradation of the NCs and the enhanced electron-phonon coupling process at a higher temperature. 15,36,39 While the opposite change trend between 80 to ∼320 K occurs, indicating the presence of the different defect states in the samples with sufficient and insufficient OAm-Cl. The increase of Mn 2+ PL intensity with increasing temperature below 300 K was usually observed in Mn 2+ -doped perovskite NCs, 12,25,37,38 which was considered to result from the thermally activated exciton fission by Zhao et al 15 While Brovelli et al 11 stated that shallow defect states play an important role in the host-todopant energy transfer process in Mn 2+ -doped perovskite NCs, and revealed a two-step process involving the initial localization of excitons in a shallow trap that mediates the sensitization of the dopants and repopulates the band-edge by thermally activated back-transfer.…”

“…stated that shallow defect states play an important role in the host‐to‐dopant energy transfer process in Mn 2+ ‐doped perovskite NCs, and revealed a two‐step process involving the initial localization of excitons in a shallow trap that mediates the sensitization of the dopants and repopulates the band‐edge by thermally activated back‐transfer. This trap‐mediated process also results in the monotonous increase of the Mn 2+ PL with the increasing temperature from 70 to 300 K. Keeping above in mind, the fast monotonous decrease of the Mn 2+ PL in the sample with 0.4 mL OAm‐Cl means more deep defect states in the host NCs, since the effect of the electron‐phonon coupling and thermal degradation are more evident for the sample with more defect states 36,39 . Comparing the difference between the samples with insufficient and sufficient OAm‐Cl contents, the effective compensation of the chloride vacancies by extra OAm‐Cl most likely endows the passivation of the deep defect states to the shallow ones.…”

“…This trap-mediated process also results in the monotonous increase of the Mn 2+ PL with the increasing temperature from 70 to 300 K. Keeping above in mind, the fast monotonous decrease of the Mn 2+ PL in the sample with 0.4 mL OAm-Cl means more deep defect states in the host NCs, since the effect of the electron-phonon coupling and thermal degradation are more evident for the sample with more defect states. 36,39 Comparing the difference between the samples with insufficient and sufficient OAm-Cl contents, the effective compensation of the chloride vacancies by extra OAm-Cl most likely endows the passivation of the deep defect states to the shallow ones.…”

Lead‐Free Semiconductors: Soft Chemistry, Dimensionality Control, and Manganese‐Doping of Germanium Halide Perovskites

“…Doping with up to 46% Mn 2+ is currently possible, leading to modified magnetic and optical properties . Mn 2+ ‐doping enhances stability, increases quantum yield to 60%, and results in long exciton lifetimes ,. These enhanced properties are useful for LEDs, and solar cell downconverters …”