ABSTRACT
Inverse photoemission (IPE) is a radiative electron capture process where an electron is transiently captured in the conduction band (CB) followed by intraband de-excitation and spontaneous photon emission. IPE in quantum dots (QDs) bypasses optical selection rules for populating the CB and provides insights into the capacity for electron capture in the CB, the propensity for spontaneous photon emission, intraband transition energies where both initial and final states are in the CB, and the generation of photons with frequencies lower than the bandgap. Here, we demonstrate using time-dependent perturbation theory that judicious application of electric fields can significantly enhance the IPE transition in QDs. For a series of CdSe, CdS, PbSe, and PbS QDs, we present evidence of field-induced enhancement of IPE intensities (188% for Cd54Se54), field-dependent control of emitted photon frequencies (Δω = 0.73 eV for Cd54Se54), and enhancement of light-matter interaction using directed Stark fields (103% for Cd54Se54).
ABSTRACT
All-inorganic metal halide perovskites (ABX3, X = Cl, Br, or I) show great potential for the fabrication of optoelectronic devices, but the toxicity and instability of lead-based perovskites limit their applications. Shell passivation with a more stable lead-free perovskite is a promising strategy to isolate unstable components from the environment as well as a feasible way to tune the optical properties. However, it is challenging to grow core/shell perovskite nanocrystals (NCs) due to the soft ionic nature of the perovskite lattice. In this work, we developed a facile method to grow a lead-free CsMnCl3 shell on the surface of CsPbCl3 NCs to form CsPbCl3/CsMnCl3 core/shell NCs with enhanced environmental stability and improved photoluminescence (PL) quantum yields (QYs). More importantly, the resulting core/shell perovskite NCs have color-tunable PL due to B-site ion diffusion at the interface of the core/shell NCs. Specifically, B-site Mn diffusion from the CsMnCl3 shell to the CsPbCl3 core leads to a Mn-doped CsPbCl3 core (i.e., Mn:CsPbCl3), which can turn on the Mn PL at around 600 nm. The ratio of Mn PL and host CsPbCl3 PL is highly tunable as a function of the thermal annealing time of the CsPbCl3/CsMnCl3 core/shell NCs. While the halide anion exchange for all-inorganic metal halide perovskites has been well-developed for band-gap-engineered materials, interfacial B-site diffusion in core/shell perovskite NCs is a promising approach for both tunable optical properties and enhanced environmental stability.
