Non-locality and collective emission in disordered lasing resonators

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs Works 3.0 Unported license.Random lasing is observed in optically active resonators in the presence of disorder. As the optical cavities involved are open, the modes are coupled, and energy may pour from one state to another provided that they are spatially overlapping. Although the electromagnetic modes are spatially localized, our system may be actively switched to a collective state, presenting a novel form of non-locality revealed by a high degree of spectral correlation between the light emissions collected at distant positions. In a nutshell, light may be stored in a disordered nonlinear structure in different fashions that strongly differ in their spatial properties. This effect is experimentally demonstrated and theoretically explained in titania clusters embedded in a dye, and it provides clear evidence of a transition to a multimodal collective emission involving the entire spatial extent of the disordered system. Our results can be used to develop a novel type of miniaturized, actively controlled all-optical chip. © 2013 CIOMP. All rights reserved.The research leading to these results has received funding from the ERC under the EC’s Seventh Framework Program (FP7/2007–2013) grant agreement n.201766, EU FP7 NoE Nanophotonics4Enery Grant No. 248855; the Spanish MICINN CSD2007-0046 (Nanolight.es); MAT2009-07841 (GLUSFA); and Comunidad de Madrid S2009/MAT2012-31659.Peer Reviewe

Active subnanometer spectral control of a random laser

We demonstrate an experimental technique that allows to achieve a robust control on the emission spectrum of a micro random laser and to select individual modes with sub-nanometer resolution. The presented approach relies on an optimization protocol of the spatial profile of the pump beam. Here we demonstrate not only the possibility to increase the emission at a wavelength, but also that we can isolate an individual peak suppressing unwanted contributions form other modes

Micropore Filling and Multilayer Formation in Stöber Spheres upon Water Adsorption

The presence of porosity critically affects the performance of solid systems. The pore accessibility to adsorbate molecules and the corresponding adsorption/desorption behavior are crucial aspects to understand the properties of porous materials but are difficult to address, principally when dealing with narrow micropores. A prominent example is colloidal silica (Stöber) spheres whose microporosity, inaccessible for some adsorbates, can be readily filled by water molecules to a large extent but exhibiting a complex adsorption behavior with unexpected hystereses. Here, we perform water adsorption isotherms on Stöber spheres at different temperatures using an original analysis of the Dubinin–Radushkevich representation to examine both the accessibility to the microporosity and the formation of water multilayers on the outer sphere surface. The micropore filling (and emptying) is found to be limited by the kinetic energy of the water molecules, causing low-pressure hysteresis. We further discover that the (temperature-dependent) completion of the micropore filling delays the onset of multilayer adsorption, leading to hysteresis at a high relative pressure. The number of adsorbed water layers is determined, and the adsorption-induced swelling of the spheres is discussed.This work was funded by Spanish MINECO projects MAT2014-58731-JIN and MAT2016-80285-p and Spanish MCIU project RTI2018-093921-B-C41

Colloidal crystals and water: Perspectives on liquid–solid nanoscale phenomena in wet particulate media

Solid colloidal ensembles inherently contain water adsorbed from the ambient moisture. This water, confined in the porous network formed by the building submicron spheres, greatly affects the ensemble properties. Inversely, one can benefit from such influence on collective features to explore the water behavior in such nanoconfinements. Recently, novel approaches have been developed to investigate in-depth where and how water is placed in the nanometric pores of self-assembled colloidal crystals. Here, we summarize these advances, along with new ones, that are linked to general interfacial water phenomena like adsorption, capillary forces, and flow. Water-dependent structural properties of the colloidal crystal give clues to the interplay between nanoconfined water and solid fine particles that determines the behavior of ensembles. We elaborate on how the knowledge gained on water in colloidal crystals provides new opportunities for multidisciplinary study of interfacial and nanoconfined liquids and their essential role in the physics of utmost important systems such as particulate media.Ministerio de Economía, Industria y Competitividad MAT2014-58731-JIN y MAT2015-68075-RComunidad de Madrid S2013/MIT-274

Colloidal crystals and water: Perspectives on liquid–solid nanoscale phenomena in wet particulate media

Solid colloidal ensembles inherently contain water adsorbed from the ambient moisture. This water, confined in the porous network formed by the building submicron spheres, greatly affects the ensemble properties. Inversely, one can benefit from such influence on collective features to explore the water behavior in such nanoconfinements. Recently, novel approaches have been developed to investigate in-depth where and how water is placed in the nanometric pores of self-assembled colloidal crystals. Here, we summarize these advances, along with new ones, that are linked to general interfacial water phenomena like adsorption, capillary forces, and flow. Water-dependent structural properties of the colloidal crystal give clues to the interplay between nanoconfined water and solid fine particles that determines the behavior of ensembles. We elaborate on how the knowledge gained on water in colloidal crystals provides new opportunities for multidisciplinary study of interfacial and nanoconfined liquids and their essential role in the physics of utmost important systems such as particulate media

Photophysical Analysis of the Formation of Organic–Inorganic Trihalide Perovskite Films: Identification and Characterization of Crystal Nucleation and Growth

In this work we demonstrate that the different processes occurring during hybrid organic–inorganic lead iodide perovskite film formation can be identified and analyzed by a combined in situ analysis of their photophysical and structural properties. Our observations indicate that this approach permits unambiguously identifying the crystal nucleation and growth regimes that lead to the final material having a cubic crystallographic phase, which stabilizes to the well-known tetragonal phase upon cooling to room temperature. Strong correlation between the dynamic and static photoemission results and the temperature-dependent X-ray diffraction data allows us to provide a description and to establish an approximate time scale for each one of the stages and their evolution. The combined characterization approach herein explored yields key information about the kinetics of the process, such as the link between the evolution of the defect density during film formation, revealed by a fluctuating photoluminescence quantum yield, and the gradual changes observed in the PbI2-related precursor structure.Unión Europea Seventh Framework Programme (FP7/2007-2013)/ERC Grant Agreement No. 307081 (POLIGHT)España, Ministerio de Economía y Competitividad Grants MAT2014- 54852-R and MAT2012-31659España, Comunidad de Madrid programme S2013/MIT-274

Optical gain in DNA-DCM for lasing in photonic materials

We present a detailed study of the gain length in an active medium obtained by doping of DNA strands with DCM dye molecules. The superior thermal stability of the composite and its low quenching, permits to obtain optical gain coefficient larger than 300 cm^-1. We also show that such an active material is excellent for integration into photonic nano-structures, to achieve, for example, efficient random lasing emission, and fluorescent photonic crystals

Assembly of Covalent Organic Frameworks into Colloidal Photonic Crystals

Self-assembly of colloidal particles into ordered superstructures is an important strategy to discover new materials, such as catalysts, plasmonic sensing materials, storage systems, and photonic crystals (PhCs). Here we show that porous covalent organic frameworks (COFs) can be used as colloidal building particles to fabricate porous PhCs with an underlying face-centered cubic (fcc) arrangement. We demonstrate that the Bragg reflection of these can be tuned by controlling the size of the COF particles and that species can be adsorbed within the pores of the COF particles, which in turn alters the Bragg reflection. Given the vast number of existing COFs, with their rich properties and broad modularity, we expect that our discovery will enable the development of colloidal PhCs with unprecedented functionality