Exciton-carrier coupling in a metal halide perovskite nanocrystal assembly probed by two-dimensional coherent spectroscopy

The surface chemistry and inter-connectivity within perovskite nanocrystals play a critical role in determining the electronic interactions. They manifest in the Coulomb screening of electron-hole correlations and the carrier relaxation dynamics, among other many-body processes. Here, we characterize the coupling between the exciton and free carrier states close to the band-edge in a ligand-free formamidinium lead bromide nanocrystal assembly via two-dimensional coherent spectroscopy. The optical signatures observed in this work show: (i) a nonlinear spectral lineshape reminiscent of Fano-like interference that evidences the coupling between discrete electronic states and a continuum, (ii) symmetric excited state absorption cross-peaks that suggest the existence of a coupled exciton-carrier excited state, and (iii) ultrafast carrier thermalization and exciton formation. Our results highlight the presence of coherent coupling between exciton and free carriers, particularly in the sub-100 femtosecond timescales

Tunable emission in dye-doped truxene-based organogels through RET

Organic systems comprising a truxene-based organogel doped with an organic dye have been fabricated and their photophysical properties examined in the search for an organic matrix with tunable luminescent properties. The addition of the organic dopant has been observed to introduce changes in the morphology of the gel which alters the ratio between monomer and excimer species. Further, the luminescent properties of the doped organogel have been studied and their evolution with dopant concentration explained in terms of resonant energy transfer between the excimer species (acting as a donor) and the organic dopant (acceptor). The interplay between blue, green and red emission bands associated with monomers, excimers and organic dopants allows tuning the luminescence of the system within the visible region reaching white light emission under certain conditions. The origin of the energy transfer is found to be the aggregation of the molecules upon solvent evaporation, the more stable xerogel phase being the extreme case which constitutes a technologically relevant approach where solvent evaporation is not an issue.Peer reviewe

Light confinement by two-dimensional arrays of dielectric spheres

We present a study on the ability of two-dimensional close-packed arrays of submicron dielectric spheres to confine electromagnetic radiation. Substrates having different nature, either dielectric or metallic, are considered, and the evolution of the strong spatial redistribution of the total field intensity is monitored by means of numerical simulations. The physical origin of the different modes of the system is further studied by measuring the optical response of the hybrid structures and reproducing it with an analytic effective medium model. The study evidences that the use of metallic substrates provides the best scenario for enhancing light-matter interaction in this kind of system, pointing out that the hybrid modes arising from the combination of periodic dielectric lattices and metallic substrates cannot be treated as purely photonic or plasmonic. © 2012 American Physical Society.M. Lopez-García was supported by the FPI Ph.D. program from the MICINN. This work was supported by the Spanish MICINN CSD2007-0046 (Nanolight.es) and MAT2009- 07841 projects; Comunidad de Madrid S2009/MAT-1756 (PHAMA) program and EU Nanophotonics4Energy (Contract No. 248855). A. García-Martín also acknowledges financial support from the Spanish MICINN (“MAGPLAS” 312 MAT2008-06765-C02-01/NAN, Funcoat Consolider Ingenio 2010 CSD2008-00023 and “MAPS” MAT2011-29194- c02-01) and European Comission (NMP3-SL-2008-214107- Nanomagma) projects.Peer Reviewe

Intrinsic losses in self-assembled hybrid metallodielectric systems

3 figuras, 3 páginas.The light confinement properties of hybrid metallodielectric systems have been studied employing numerical simulations to obtain the optical response as well as the total field intensity associated with the different modes of the structure. The effect of intrinsic losses, absorption, and out-of-plane leakage on the quality factors (Q) of different modes is discussed, and the results obtained are interpreted in terms of the optical constants of the metallic substrate. Large Q values (up to 600) can be attained in this kind of samples, much larger than in their purely dielectric counterpart, pointing to the ability of these systems to efficiently confine electromagnetic radiation.J. F. Galisteo-López was supported by the JAE Postdoctoral Program from CSIC. M. López-García was supported by the FPI PhD program from the MICINN. This work was supported by the Spanish MICINN CSD2007-0046 (Nanolight.es)and MAT2009-07841 (GLUSFA) projects and Comunidad de Madrid S2009/MAT-1756 (PHAMA) programme. A. García-Martín also acknowledges financial support from the Spanish MICINN (“MAGPLAS” MAT2008-06765-C02-01/NAN,Funcoat Consolider Ingenio 2010 CSD2008-00023) and European Comission (NMP3-SL-2008-214107-Nanomagma).Peer reviewe

FRET-tuned resonant random lasing

We report the fabrication and characterization of a novel type of optical gain material. A biopolymeric matrix (DNA-lipid complex) doped with two families of organic dyes is combined with a strongly scattering medium. While the optical gain of the biopolymer complex is controlled via the FRET efficiency between the incorporated dyes, multiple scattering provides the necessary feedback to achieve lasing. This introduces two mechanisms to control the lasing wavelength: optical gain (via resonant energy transfer) and resonant scattering. In this way, an organic laser with a spectral tunability range over 40 nm is demonstrated. © 2014 American Chemical Society.This work was supported by the Spanish MINECO CSD2007-0046 (Nanolight.es) and MAT2012-31659 (SAMAP) projects, Comunidad de Madrid S2009/MAT-1756 (PHAMA) programme, and EU Nanophotonics4Energy contract 248855.Peer Reviewe

FRET-mediated amplified spontaneous emission in DNA-CTMA complexes

The way FRET takes place in dye-doped biopolymer complexes is studied by time-resolved measurements. The efficiency of the energy transfer is controlled by the relative concentration of the donor/acceptor species and described with a distribution of processes. Amplified spontaneous emission in the system and its evolution with the FRET efficiency is monitored. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.This work was supported by the Spanish MINECO CSD2007-0046 (Nanolight.es) and MAT2012-31659 (SAMAP) projects; Comunidad de Madrid S2009/MAT-1756 (PHAMA) programme and EU Nanophotonics4Energy contract 248855. M. Ibisate acknowledges the MICINN Ramón y Cajal programme.Peer Reviewe

Ultrabroadband generation of multiple concurrent nonlinear coherent interactions in random quadratic media

Triply coincident nonlinear second harmonic interactions continuously tunable in an extremely large spectral range (800-1400 nm) are demonstrated in strontium barium niobate random quadratic crystal. The spectral dependence of the triple process is in agreement with a first order quasi-phase-matching collinear interaction. The analysis of the polarization states of the generated beams reveals mutually coherent interactions between different processes simultaneously contributing to the total intensity. The results constitute a necessary step in the implementation of ultra-broadband entangled photon pairs from randomly poled structures and are relevant to a wide range of applications, for which broadband polarization controlled light is required. © 2013 AIP Publishing LLC.This work was supported by FP7 NoE Nanophotonics4Energy EU Grant No. 248855; the Spanish MICINN CSD2007-0046 (Nanolight.es), MAT2010-17443, MAT2012-31659 (SAMAP); and the Comunidad de Madrid S2009/MAT-1756 (PHAMA) projects.Peer Reviewe

Nanostructured perovskite

The invention provides an optoelectronic device comprising a porous material and a materialwith perovskite crystal structure in contact with the porous material. The porous material is further characterised in that the pores present a well defined averagesize,in the range of 1-100nm, and characterised in thatit is anordered network which shows a periodicity in one, two or three spatial directions. The perovskite material is infiltrated within the porous material, resulting in a mesostructured and ordered perovskite material. This spatially confined perovskiteshows a luminescent emission whose range of wavelengths can be modified changing the pore size of the mesostructure. This invention solves the problem of tuning the emission of perovskite materialswithout varying theircomposition.The invention can be used as both light emitting and photovoltaic devices.Peer reviewedConsejo Superior de Investigaciones Científicas (España)A1 Solicitud de patente con informe sobre el estado de la técnic

Facile Synthesis of Hybrid Organic-Inorganic Perovskite Microcubes of Optical Quality Using Polar Antisolvents

Herein, we demonstrate a synthetic approach producing highly crystalline methylammonium lead bromide perovskite (MAPbBr) microcubes at room temperature by injecting a perovskite precursor solution into an environmentally friendly antisolvent (isopropyl alcohol). Confirmed by X-ray and electron diffraction, as well as electron microscopy, these MAPbBr microcubes are single crystals and have perfect cubic structure, with sizes varying between 1 and 15 μm depending on the synthesis conditions. The stoichiometry of the MAPbBr crystal is proven by energy-dispersive X-ray analysis. Finally, optical analysis carried out by means of laser scanning confocal microscopy evidences how the crystalline quality of the microcubes translates into a homogeneous photoluminescence throughout the cube volume.Peer Reviewe

Simultaneous generation of second to fifth harmonic conical beams in a two dimensional nonlinear photonic crystal

Broadly tunable multiple high-harmonic conical beams have been generated by means of a multistep χ(2) cascade processes in a two dimensional nonlinear photonic crystal. The nonlinear structure consists of a square lattice of inverted hexagonal domains with diameters and distances between domains as low as 1 μm. The large number of reciprocal lattice vectors provided by both the square nonlinear structure and the hexagonal shaped domains, along with imperfections on the size and shape of the individual domains make possible the simultaneous generation of second up to fifth harmonic conical beams in a single nonlinear structure by using different types of phase matching geometries. The frequency response can be tuned in an extremely large spectral range, and continuous generation of nonlinear conical beams covering the whole visible spectral region can be achieved. Further, the same photon energy can be generated at different orders, so that concentrically emitted conical beams with angular dispersion as large as Δθ = 50° can be observed. The results highlight the significance of highly controlled engineered 2D nonlinear structures to generate advanced multi-photon devices with large spatial and spectral tunable response.This work was supported by EU FP7 NoE Nanophotonics4Energy Grant No. 248855, the Spanish MICINN CSD2007-0046 (Nanolight.es), MAT2009-07841 (GLUSFA), MAT2010-17443 and Comunidad de Madrid (Grant S2009/MAT-1756 PHAMA).Peer Reviewe