8 research outputs found
Enhanced spontaneous emission of CsPbI3 perovskite nanocrystals using a hyperbolic metamaterial modified by dielectric nanoantenna
In this work, we demonstrate, theoretically and experimentally, a hybrid dielectric-plasmonic multifunctional structure able to provide full control of the emission properties of CsPbI3 perovskite nanocrystals (PNCs). The device consists of a hyperbolic metamaterial (HMM) composed of alternating thin metal (Ag) and dielectric (LiF) layers, covered by TiO2 spherical MIE nanoresonators (i.e., the nanoantenna). An optimum HMM leads to a certain Purcell effect, i.e., an increase in the exciton radiative rate, but the emission intensity is reduced due to the presence of metal in the HMM. The incorporation of TiO2 nanoresonators deposited on the top of the HMM is able to counteract such an undesirable intensity reduction by the coupling between the exciton and the MIE modes of the dielectric nanoantenna. More importantly, MIE nanoresonators result in a preferential light emission towards the normal direction to the HMM plane, increasing the collected signal by more than one order of magnitude together with a further increase in the Purcell factor. These results will be useful in quantum information applications involving single emitters based on PNCs together with a high exciton emission rate and intensity
Superradiance Emission and Its Thermal Decoherence in Lead Halide Perovskites Superlattices
Self-assembled nanocrystals (NCs) into superlattices (SLs) are alternative materials to polycrystalline films and single crystals, which can behave very differently from their constituents, especially when they interact coherently with each other. This work concentrates on the Superradiance (SR) emission observed in SLs formed by CsPbBr3 and CsPbBrI2 NCs. Micro-Photoluminescence spectra and transients in the temperature range 4–100 K are measured in SLs to extract information about the SR states and uncoupled domains of NCs. For CsPbBr3 SLs with mostly homogeneous SR lines (linewidth 1–5 meV), this work measures lifetimes as short as 160 ps, 10 times lower than the value measured in a thin film made with the same NCs, which is due to domains of near identical NCs formed by 1000 to 40 000 NCs coupled by dipole–dipole interaction. The thermal decoherence of the SR exciton state is evident above 25 K due to its coupling with an effective phonon energy of ≈8 meV. These findings are an important step toward understanding the SR emission enhancement factor and the thermal dephasing process in perovskite SLs.Financial support from the Spanish Ministry of Science (MICINN) through project no. PID2020- 120484RB-I00 is gratefully acknowledged. G.M.M. also thanks the support from the Spanish MICINN & AEI (project RTI2018-099015-J-I00). I.M.S. thanks the funding of MCIN/AEI/10.13039/501100011033 with the project STABLE PID2019-107314RB-I00. S.G. acknowledges her “Grisolia” grant from Generalitat Valenciana, and G.M.M. thanks the Ramon y Cajal programme (contract RYC2020-030099-I). Thanks are also due to Dr. Raúl Iván Sánchez Alarcón for his help with X-ray diffraction characterization of NC films and SLs
Homogeneous and inhomogeneous broadening in single perovskite nanocrystals investigated by micro-photoluminescence
Metal halides with perovskite crystalline structure have given rise to efficient optoelectronic and photonic devices. In the present work, we have studied the light emission properties of single CsPbBr3 and CsPbI3 semiconductor perovskite nanocrystals (PNCs), as the basis for a statistical analysis of micro-photoluminescence (micro-PL) spectra measured on tens of them. At room temperature, the linewidth extracted from PL spectra acquired in dense films of these nanocrystals is not very different from that of micro-PL measured in single nanocrystals. This means that the homogeneous linewidth due to exciton-phonon interaction is comparable or larger than the inhomogeneous effect associated to the micro-PL peak energy dispersion due to the nanocrystal size distribution defined by the chemical synthesis of the PNCs. Contrarily, we observe very narrow micro-PL lines in CsPbBr3 and CsPbI3 PNCs at 4 K, in the range of 1–5 meV and 0.1–0.5 meV, respectively, because they are limited by spectral diffusion. Aging of PNCs under ambient conditions has been also studied by micro-PL and a clear reduction of their nanocube edge size in the order of the nm/day is deduced
Van Der Waals Heteroepitaxy of GaSe and InSe, Quantum Wells and Superlattices
Bandgap engineering and quantum confinement in semiconductor heterostructures
provide the means to fine-tune material response to electromagnetic fields and
light in a wide range of the spectrum. Nonetheless, forming semiconductor
heterostructures on lattice-mismatched substrates has been a challenge for
several decades, leading to restrictions for device integration and the lack of
efficient devices in important wavelength bands. Here, we show that the van der
Waals epitaxy of two-dimensional (2D) GaSe and InSe heterostructures occur on
substrates with substantially different lattice parameters, namely silicon and
sapphire. The GaSe/InSe heterostructures were applied in the growth of quantum
wells and superlattices presenting photoluminescence and absorption related to
interband transitions. Moreover, we demonstrate a self-powered photodetector
based on this heterostructure on Si that works in the visible-NIR wavelength
range. Fabricated at wafer-scale, these results pave the way for an easy
integration of optoelectronics based on these layered 2D materials in current
Si technology.Comment: 16 Pages, 5 figures. Supplementary Information included in the end
(+10 pages, +10 Figures, + 2 Tables). Partially presented at 21st ICMBE -
September 202
Revealing giant exciton fine-structure splitting in 2D perovskites using van der Waals passivation
The study of two-dimensional (2D) van der Waals materials has been an active
field of research in the development of new optoelectronics and photonic
applications over the last decade. Organic-inorganic layered perovskites are
currently some of the most promising 2D van der Waals materials, due to their
exceptional optical brightness and enhanced excitonic effects. However, low
crystal quality and spectral diffusion usually broaden the exciton linewidth,
obscuring the fine structure of the exciton in conventional photoluminescence
experiments. Here, we propose a mechanical approach for reducing the effect of
spectral diffusion by means of hBN-capping on layered perovskites with
different thicknesses, revealing the exciton fine structure. We used a
stochastic model to link the reduction of the spectral linewidth with the
population of active charge fluctuation centres present in the organic spacer
taking part in the dynamical Stark shift. Active fluctuation centres are
reduced by a factor of 3.7 to 7.1 when we include hBN-capping according to our
direct spectral measurements. This rate is in good agreement with the analysis
of the overlap between the squared perovskite lattice and the hexagonal hBN
lattice. Van der Waals forces between both lattices cause the partial clamping
of the perovskite organic spacer molecules, and hence, the amplitude of the
dynamical Stark shift characteristic of the spectral diffusion effect is
reduced. Our work provides an easy and low-cost solution to the problem of
accessing important fine-structure excitonic state information, along with an
explanation of the important carrier dynamics present in the organic spacer
that affect the quality of the optical emission
Purcell Enhancement and Wavelength Shift of Emitted Light by CsPbI3 Perovskite Nanocrystals Coupled to Hyperbolic Metamaterials
Manipulation of the exciton emission rate in nanocrystals of lead halide perovskites (LHPs) was demonstrated by means of coupling of excitons with a hyperbolic metamaterial (HMM) consisting of alternating thin metal (Ag) and dielectric (LiF) layers. Such a coupling is found to induce an increase of the exciton radiative recombination rate by more than a factor of three due to the Purcell effect when the distance between the quantum emitter and HMM is nominally as small as 10 nm, which coincides well with the results of our theoretical analysis. Besides, an effect of the coupling-induced long wavelength shift of the exciton emission spectrum is detected and modeled. These results can be of interest for quantum information applications of single emitters on the basis of perovskite nanocrystals with high photon emission rates
Revealing giant exciton fine-structure splitting in two-dimensional perovskites using van der Waals passivation
Organic–inorganic layered perovskites are currently some of the most promising 2D van der Waals materials. Low crystal quality usually broadens the exciton line width, obscuring the fine structure of the exciton in conventional photoluminescence experiments. Here, we propose a mechanical approach to reducing the effect of spectral diffusion by means of hBN capping on layered perovskites, revealing the exciton fine structure. We used a stochastic model to link the reduction of the spectral line width with the population of charge fluctuation centers present in the organic spacer. van der Waals forces between both lattices cause the partial clamping of the perovskite organic spacer molecules, and hence the amplitude of the overall spectral diffusion effect is reduced. Our work provides a low-cost solution to the problem of accessing important fine-structure excitonic state information, along with an explanation of the important carrier dynamics present in the organic spacer that affect the quality of the optical emission