Defect Passivation of Mn²⁺-Doped CsPbCl₃ Perovskite Nanocrystals as Probed by Scanning Tunneling Spectroscopy: Toward Boosting Emission Efficiencies

Abstract

In recent years, Mn-doped CsPbCl 3 perovskite nanocrystals (NCs) have received widespread attention for solid-state lighting applications. However, a low PL quantum efficiency/yield coupled with a short lifetime of the PL emission forbade the material from further applied advancements. Defect states have been assumed to act as nonradiative recombination sites yielding a truncated PL quantum yield (PLQY). In this direction, simultaneous codoping with transition metals in the host lattice emerged as an effective strategy toward the improvement of PL intensity. However, despite intense research, a complete understanding of this approach remained elusive. Hence, further in-depth studies on the underlying mechanism are essential for their successful use as an optoelectronic material in different devices. In this work, we revisited energy levels of Cu 2+ −Mn 2+ codoped CsPbCl 3 perovskite NCs as a case study. Through scanning tunneling spectroscopy (STS), we observed direct evidence of defect states in the NCs and the microscopic origin of defect passivation upon codoping. The STS studies provided the density of states of the NCs and thereby band-and defect-state energies of the pristine semiconductor; the studies also infer defect passivation of the NCs through doping and codoping processes. The codoped perovskites yielded a high PLQY of 80%, which is one of the highest in the inorganic perovskite to date. This work on perovskite NCs shows the unique advantage of STS measurements over traditional PL studies or decay dynamics toward achieving a complete understanding of defect passivation in the light of their energy levels.

Magnetic Transitions and Energy Transfer Processes in Sb-Based Zero-Dimensional Metal Halide Nanocrystals Doped with Manganese

“…30%. Such a substantial enhancement of the PL efficiency of lightly doped samples with respect to the undoped particles is consistent with a surface passivation effect by the Mn 2+ dopants located near the particle surface …”

“…Empty squares and circles are the PL excitation (PLE) spectra for the STE- and Mn-PL, respectively acquired by time-gated experiments. (b) Normalized PLE spectra of XMnCl 3 samples (XC 4 N 2 H 7 , black line; Cs, dark gray; C 4 H 12 N, light gray) as reported in refs − . (c) Normalized STE-PL decay traces (colored curves) and respective fitting results using a single stretched exponential decay equation (black lines).…”

“…Such a substantial enhancement of the PL efficiency of lightly doped samples with respect to the undoped particles is consistent with a surface passivation effect by the Mn 2+ dopants located near the particle surface. 78 Next, we investigate the thermal processes affecting the photophysics of Mn-doped Rb 7 Sb 3 Cl 16 NCs by performing PL experiments as a function of temperature (from T = 300 to 10 K) on the lightest ([Mn 2+ ] = 2%) and heaviest ([Mn 2+ ] = 40%) doped NCs, as well as on their undoped counterparts. In agreement with recent results, 26 the PL of the undoped NCs intensifies by nearly 400-fold upon lowering T, accompanied by concomitant slowing down of the decay kinetics (Figures 3a and S8).…”

Exciton Recombination versus Energy Transfer: Mapping Competing Excited-State Dynamics in Various Mn-Doped CsPb(Cl1–yBry)3 Perovskite Nanocrystals for Achieving White Light Emission

“…With increasing concentration of Mn in the feedstock solution, the band-edge absorption apparently blue-shifted from 400 nm ( x = 0) to 370 nm ( x = 0.80) owing to alloying with Mn (Figure A). As the dopant concentration of Mn incorporated into CsPbCl 3 nanocrystals was well reported by previous literature precedence, there is a linear correlation of the blue shift in the excitonic peak as a function of the concentration of Mn determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). ,, More manganese ions are doped in the nanocrystals; the excitonic peaks of CsPbCl 3 nanocrystals with a band-edge absorption of 400 nm are shifted to a shorter wavelength due to the lattice contraction, resulting from the alloying of Pb with dopant Mn. , It is also worth noting that above x = 0.60, the significant blue shift of excitonic band-edge absorption is mainly due to the band gap change through alloying Pb/Mn. It has been reported that CsMnCl 3 has a direct band gap of 4.08 eV and through alloying Mn and Pb, the band gap can be tuned in the range of 4.08–2.19 eV .…”

ZnAl2O4:Eu3+ Nanoparticle Phosphors Co-doped with Li+ for Red Light-Emitting Diodes

“…The obtained activation energy was found to be 0.11 eV for ZnAl 2 O 4 :3% Eu 3+ and 0.14 eV for ZnAl 2 O 4 :3% Eu 3+ , 2% Li + nanophosphors. The higher activation energy leads to a lesser amount of nonradiative transition and consequently less thermal quenching. − Here, co-doping with Li + increases the activation energy, and therefore, the co-doped nanophosphors exhibit stable emission at high temperature that indicates the suitability of the ZnAl 2 O 4 :3% Eu 3+ , 2% Li + nanophosphors for practical LED applications.…”