Juan F. Galisteo-López

Environmental effects on the photophysics of organic-inorganic halide perovskites

The photophysical properties of films of organic–inorganic lead halide perovskites under different ambient conditions are herein reported. We demonstrate that their luminescent properties are determined by the interplay between photoinduced activation and darkening processes, which strongly depend on the atmosphere surrounding the samples. We have isolated oxygen and moisture as the key elements in each process, activation and darkening, both of which involve the interaction with photogenerated carriers. These findings show that environmental factors play a key role in the performance of lead halide perovskites as efficient luminescent materials.

Experimental evidence of polarization dependence in the optical response of opal-based photonic crystals

We report angle resolved reflectivity measurements showing the polarization dependence of the pseudogap in artificial opals. This kind of photonic crystals consist of silica spheres ordered in a face-centered-cubic lattice. The analyzed gap originates from the (111) family of planes. It is shown that the width of the Bragg peak observed in the reflectance spectra follows the bands determining the pseudogap, which are selectively excited according to the polarization (s or p) of the light impinging on the opal. Moreover, it is found that the coupling of light with the photonic bands occurs according to their predicted symmetry, which was assigned by arguments based on group theory.

Studying light propagation in self-assembled hybrid photonic-plasmonic crystals by fourier microscopy.

Hybrid metallodielectric systems where dielectric components are combined with metals supporting surface plasmons are able to spatially redistribute the electromagnetic field intensity within its volume through hybrid photonic-plasmonic modes. While most of the work done recently in this kind of systems has been focused on the way such redistribution takes place and how light couples to or is emitted from such samples, the way light propagation takes place has not been studied in depth. Here we consider light propagation in hybrid systems fabricated by self-assembly methods measuring their equifrequency surfaces both in reflection and emission configurations. Comparing spectroscopic measurements with equifrequency surfaces provides a deeper insight into the way light propagates in these structures, showing the possibilities they may present for several applications.

Tunable magneto-photonic response of nickel nanostructures

In this letter, we present both experimental and numerical studies of the magneto-optical (MO) properties of nickel infiltrated opals. Ni can show interesting MO properties that can be controlled by nanostructuration through colloidal crystals templating. Nanostructuration allows the coupling of light to surface plasmon modes of Ni, and a clear dependence of the MO response as a function of the structural parameters of the template has been observed. This dependence can be used in future tunable devices such as switchers or MO modulators.

Tuning and optical study of the ΓX and ΓL photonic pseudogaps in opals

In this letter we demonstrate a method to tune and optically investigate the two highest-symmetry pseudogaps in artificial opals which occur at the L an X points of the Brillouin zone and correspond to propagation along the (111) and (100) crystallographic directions, respectively. In particular we show that in artificial opals the gap at the X point, which is closed for bare opals, can be opened by controlled infiltration with a high refractive index material such as ZnO. To prove this we take advantage of the fact that, in artificial opals grown by the vertical deposition method, regions with both (100) and (111) orientations of the face centerd cubic lattice occur naturally.

Fine Tuning the Emission Properties of Nanoemitters in Multilayered Structures by Deterministic Control of their Local Photonic Environment

Deterministic control on the dynamics of organic nanoemitters is achieved through precise control of its photonic environment. Resonators are fabricated by a combination of spin- and dip-coating techniques, which allows placement of the emitters at different positions within the sample, thus acting as a probe of the local density of states.

Intrinsic losses in self-assembled hybrid metallodielectric systems

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. V C 2011 American Institute of Physics. [doi:10.1063/1.3626856]

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.

Protective ligand shells for luminescent SiO2-coated alloyed semiconductor nanocrystals

SiO2 encapsulation of alloyed CdSeZnS nanocrystals (NCs) shows differences in terms of optical properties and luminescence quantum yield, depending on the surface composition, size, and ligand content. In this work, emphasis has been placed on the fine control required to obtain luminescent SiO2 encapsulated NCs by studying the role of oleic acid (OA), stearic acid (SA), and dodecanethiol (DDT) ligands on the alloyed NCs. While the use of anchored DDT molecules is essential to preserve the optical properties, intercalated OA and SA play a critical role for SiO2 nucleation, as stated by (1)H NMR (including DOSY and NOESY) spectroscopy. These results emphasize the importance of surface chemistry in NCs; it is crucial to control their reactivity, and therefore their impact, in different applications, from optics to biomedicine.

One-Step-Process Composite Colloidal Monolayers and Further Processing Aiming at Porous Membranes

Composite materials consisting of a monolayer of polystyrene spheres (diameters of 430 and 520 nm) and porous silica, filling in the interstices, have been fabricated and characterized. The proposed growth method introduces some novelties as far as the fabrication of this kind of monolayers is concerned, as it probes the compatibility of coassembly (in which a silica precursor, tetraethyl orthosilicate (TEOS), is added to the base colloid) with confined growth in a wedge-shaped cell, while profiting from the advantages of both techniques. Using this method, it is possible to fabricate the composite monolayer in a single growth step. A systematic study of the influence of TEOS concentration in the initial colloid was performed in order to improve the quality of the two-dimensional crystals produced. Thus, it was demonstrated that the two methods are compatible. Furthermore, the composites were then subjected to thermal treatment so that the polymer is removed to reveal the inverse structure. After the calcination the membranes still present very good quality and so the proposed approach is effective for the fabrication of porous membranes. A comparison of reflectance spectra, between composite monolayers fabricated using this method and composites achieved by infiltrating polystyrene bare opals with silica chemical vapor deposition, is also established. The procedure presented is expected to establish the route for an easier and quicker fabrication of inverse monolayers of high refractive index materials with applications in light control.