Power-Dependent Photoluminescence Efficiency in Manganese-Doped 2D Hybrid Perovskite Nanoplatelets

Abstract

Substitutional metal doping is a powerful strategy for manipulating the emission spectra and excited state dynamics of semiconductor nanomaterials. Here, we demonstrate the synthesis of colloidal manganese (Mn2+)-doped organic–inorganic hybrid perovskite nanoplatelets (chemical formula: L2[APb1–x Mn x Br3] n−1Pb1–x Mn x Br4; L, butylammonium; A, methylammonium or formamidinium; n (= 1 or 2), number of Pb1–x Mn x Br6 4– octahedral layers in thickness) via a ligand-assisted reprecipitation method. Substitutional doping of manganese for lead introduces bright (approaching 100% efficiency) and long-lived (>500 μs) midgap Mn2+ atomic states, and the doped nanoplatelets exhibit dual emission from both the band edge and the dopant state. Photoluminescence quantum yields and band-edge-to-Mn intensity ratios exhibit strong excitation power dependence, even at a very low incident intensity (<100 μW/cm2). Surprisingly, we find that the saturation of long-lived Mn2+ dopant sites cannot explain our observation. Instead, we propose an alternative mechanism involving the cross-relaxation of long-lived Mn-site excitations by freely diffusing band-edge excitons. We formulate a kinetic model based on this cross-relaxation mechanism that quantitatively reproduces all of the experimental observations and validate the model using time-resolved absorption and emission spectroscopy. Finally, we extract a concentration-normalized microscopic rate constant for band edge-to-dopant excitation transfer that is ∼10× faster in methylammonium-containing nanoplatelets than in formamidinium-containing nanoplatelets. This work provides fundamental insight into the interaction of mobile band edge excitons with localized dopant sites in 2D semiconductors and expands the toolbox for manipulating light emission in perovskite nanomaterials.

Luminescence Enhancement Due to Symmetry Breaking in Doped Halide Perovskite Nanocrystals

“…For Mn, these d states do not hybridize with the perovskite host band edges and instead act as the commonly observed energy loss channel for excitations, resulting in a spin- and symmetry–forbidden transition. This is commonly observed upon a threshold Mn doping concentration as a long-lived orange (∼600 nm) emission. , It limits the application of manganese doping to achieve color-pure and bright blue emission in LEDs: a maximal doping concentration of about 0.2% (Mn/Pb atomic ratio) exploits the doping-induced radiative rate benefits without yet forming those additional loss channels in significant amounts which overall reduce the PLQE of the blue perovskite emission beyond this concentration.…”

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

“…Cesium lead halide perovskite nanocrystals (CsPbX 3 ; X = Cl, Br, I) represent one of the most promising classes of semiconducting materials that have revolutionized the fields of optoelectronic and photovoltaic devices. − In particular, colloidal synthesis of such nanomaterials with the aid of surface-capping ligands can further help achieve the desirable optoelectronic and light harvesting properties including tunable band gap, emission wavelength, charge carrier lifetime, carrier diffusion length, quantum yield, etc. through modulating the size of the nanocrystals owing to quantum confinement effects. − Additionally, incorporating transition metals (doping) into such host lattices of the nanocrystals provides an additional degree of freedom, allowing for tuning the electronic, magnetic, and optical properties of nanocrystals. − These dopants include transition metals such as Cd 2+ , Zn 2+ , and Mn 2+ as well as lanthanide ions such as Yb 3+ , Tb 3+ , etc. ,,− Specifically, Mn-doped CsPbCl 3 and CsPbBr 3 nanocrystals, wherein divalent Pb 2+ sites are substitutionally replaced with dopant ions, have been intensively investigated since the doping allows for efficient broadband emission centered at ∼600 nm as a result of the exciton-to-dopant energy transfer. − …”

High-Efficiency Fast-Radiative Blue-Emitting Perovskite Nanoplatelets and Their Formation Mechanisms

“…Ion doping is a powerful tool for optimizing the optoelectronic performance and stability of nanoscale perovskite emitters by means of improving short-range order in lattices, enhancing exciton oscillator strength, and regulating exciton bandgap and binding energy. − In this work, we discover that the doping of Eu 3+ , Sb 3+ , and Ba 2+ ions yields blue-emitting NPLs with a thickness of five monolayers, among which the PLQY value of CsPbBr 3 :Sb 3+ NPLs is as high as 95%, and its radiation lifetime is extremely short at 1.48 ns. The greatly reduced ligand dosage addresses the above-mentioned challenges in NPLs.…”