Structural Characterisation of Printable Noble Metal/Poly(Vinyl-­Alcohol) Nanocomposites for Optical Applications

This work was conducted under the aegis of the Engineering and Physical Sciences Research Council (EPSRC) of the United Kingdom (EP/I004173/1). Amin Abdolvand is an EPSRC Career Acceleration Fellow at the University of Dundee.In order to enable exploitation of noble metal/poly(vinyl-alcohol) nanocomposites for device fabrication, solutions of poly(vinyl-alcohol) suitable for piezo-driven inkjet printing techniques are identified and discussed in terms of their material properties. The printable poly(vinyl-alcohol) medium is then exploited as a host material through the formation of silver or gold nanoparticles in order to create nanocomposites that exhibit a surface plasmon resonance behaviour associated with the small metallic inclusions. To mitigate some of the material redistribution effects associated with the drying of printed droplets containing finely divided materials, the metallic nanoparticles are formed after the printing and drying process is completed, by way of an in-situ reduction of an appropriate metal salt by the poly(vinyl-alcohol)-host matrix itself, which takes place at modest temperatures compatible with most substrate materials. An obvious application for such nanocomposites is in optical elements whereby the surface plasmon resonance associated with the metal is the functional aspect of devices such as sensors or active optical elements. High Resolution Transmission Electron Microscopy was used to examine the dimensions, distribution, morphology and crystal structure of the silver and gold nanoparticles in detail allowing discussion of their suitability for these applications and what further optimisation may be necessary to adequately control their formation.Publisher PDFPeer reviewe

Self-Assembly of CsPbBr3Perovskites in Micropatterned Polymeric Surfaces: Toward Luminescent Materials with Self-Cleaning Properties

In this work, we present a series of porous, honeycomb-patterned polymer films containing CsPbBr3 perovskite nanocrystals as light emitters prepared by the breath figure approach. Microscopy analysis of the topography and composition of the material evidence that the CsPbBr3 nanocrystals are homogeneously distributed within the polymer matrix but preferably confined inside the pores due to the fabrication process. The optical properties of the CsPbBr3 nanocrystals remain unaltered after the film formation, proving that they are stable inside the polystyrene matrix, which protects them from degradation by environmental factors. Moreover, these surfaces present highly hydrophobic behavior due to their high porosity and defined micropatterning, which is in agreement with the Cassie-Baxter model. This is evidenced by performing a proof-of-concept coating on top of 3D-printed LED lenses, conferring the material with self-cleaning properties, while the CsPbBr3 nanocrystals embedded inside the polymeric matrix maintain their luminescent behavior.This work was funded by the Ministry of Science, Innovation and Universities (project TEC2017-86102-C2-2-R) and Junta de Andalucía (Research group INNANOMAT, ref. TEP-946) and co-financed by the 2014-2020 ERDF Operational Programme and by the Department of Economy, Knowledge, Business and University of the Regional Government of Andalusia (ref: FEDER-UCA18-106586). Co-funding from UE is also acknowledged. A.S.d.L. acknowledges the Ministry of Science, Innovation and Universities for his Juan de la Cierva Incorporación postdoctoral fellowship (IJC2019-041128-I). R.A. also acknowledges the support of the Spanish MINECO through projects: Retos-Colaboración 2016 Project Safetag (no. RTC-2016-5197-2) and Retos de la Sociedad Project Nirvana (no. PID2020-119628RB-C31) by MCIN/AEI/10.13039/ 501100011033 and the “Agencia Valenciana de la Innovació” for the Valorització 2018 Project Hidronio (no. INNVAL10/ 18/032) and Valorització 2021 Project CATIOX (no. INNVA1/2021/56). R.A. also thanks the Spanish MINECO for their Ramón y Cajal Fellowship (no. RYC-2015-18349). SEM and TEM measurements were carried out at the DME-SCICyT- ELECMI-UCA

Colloidal Quantum Dots-PMMA Waveguides as Integrable Microwave Photonic Phase Shifters

“© © 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.”A novel scheme for the control of microwave signals carried at optical wavelengths by use of PbS colloidal quantum dots embedded in PMMA waveguides is presented. When these structures are pumped at wavelengths where PbS has efficient absorption (980 or 1310 nm), a phase shift in a signal carried at 1550 nm is induced. Optimal conditions have been analyzed by studying the influence of the microwave signal and the waveguide structure. In a proof-of-concept experiment, a continuous phase shift up to 35° at 25 GHz has been demonstrated, with good thermal stability (<2° at 25 GHz) when the samples are heated 20 °C above room temperature. The potential benefits of the use of this active-waveguide technology in microwave photonics are due to the continuous scan of the phase delay, its high tuning speed, and its small size, which leads to the possibility of integration.This work was supported in part by the Infraestructura FEDER under Grants UPVOV08-3E-008 and FEDER UPVOV10-3E-492, in part by the Research Excellency Award Program GVA PROMETEO 2013/012, Next generation Microwave Photonic Technologies, and in part by the Spanish MCINN under Projects TEC2011-29120-C05-01, TEC2011-29120-C05-02, and TEC2011-29120-C05-05.Ricchiuti, AL.; Suárez Álvarez, I.; Barrera Vilar, D.; Rodríguez Cantó, PJ.; Fernandez-Pousa, CR.; Abargues, R.; Sales Maicas, S.... (2014). Colloidal Quantum Dots-PMMA Waveguides as Integrable Microwave Photonic Phase Shifters. IEEE Photonics Technology Letters. 26(4):402-404. https://doi.org/10.1109/LPT.2013.2295253S40240426

Polymer/QDs Nanocomposites for Waveguiding Applications

In this paper we review our recent progress in a still young type of active waveguides based on hybrid organic (polymer)—inorganic (semiconductor quantum dots) materials. They can be useful for the implementation of new photonic devices, because combining the properties of the semiconductor nanostructures (quantum size carrier confinement and temperature independent emission) with the technological capabilities of polymers. These optical waveguides can be easily fabricated by spin-coating and UV photolithography on many substrates (SiO2/Si, in the present work). We demonstrate that it is possible to control the active wavelength in a broad range (400–1100 nm), just by changing the base quantum dot material (CdS, CdSe, CdTe and PbS, but other are possible), without the necessity of changing fabrication conditions. Particularly, we have determined the optimum conditions to produce multi-color photoluminescence waveguiding by embedding CdS, CdSe and CdTe quantum dots into Poly(methyl methacrylate). Finally, we show new results regarding the incorporation of CdSe nanocrystals into a SU-8 resist, in order to extrapolate the study to a photolithographic and technologically more important polymer. In this case ridge waveguides are able to confine in 2D the light emitted by the quantum dots

High spatial resolution mapping of individual and collective localized surface plasmon resonance modes of silver nanoparticle aggregates: correlation to optical measurements

Non-isolated nanoparticles show a plasmonic response that is governed by the localized surface plasmon resonance (LSPR) collective modes created by the nanoparticle aggregates. The individual and collective LSPR modes of silver nanoparticle aggregated by covalent binding by means of bifunctional molecular linkers are described in this study. Individual contributions to the collective modes are investigated at nanometer scale by means of energy-filtering transmission electron microscopy and compared to ultraviolet–visible spectroscopy. It is found that the aspect ratio and the shape of the clusters are the two main contributors to the low-energy collective modes

Efficient excitation of photoluminescence in a two-dimensional waveguide consisting of a quantum dot-polymer sandwich-type structure

International audienceIn this Letter, we study a new kind of organic polymer waveguide numerically and experimentally by combining an ultrathin (10–50 nm) layer of compactly packed CdSe/ZnS core/shell colloidal quantum dots (QDs) sandwiched between two cladding poly(methyl methacrylate) (PMMA) layers. When a pumping laser beam is coupled into the waveguide edge, light is mostly confined around the QD layer, improving the efficiency of excitation. Moreover, the absence of losses in the claddings allows the propagation of the pumping laser beam along the entire waveguide length; hence, a high-intensity photoluminescence (PL) is produced. Furthermore, a novel fabrication technology is developed to pattern the PMMA into ridge structures by UV lithography in order to provide additional light confinement. The sandwich-type waveguide is analyzed in comparison to a similar one formed by a PMMA film homogeneously doped by the same QDs. A 100-fold enhancement in the waveguided PL is found for the sandwich-type case due to the higher concentration of QDs inside the waveguide

Photoconductivity and optical properties of silicon coated by thin TiO2 film in situ doped by Au nanoparticles

Light trapping enhancement by plasmonic active metal nanoparticles NPs is believed to be a promising approach to increase silicon based solar cell efficiency. Therefore, we investigated TiO2 films in situ doped by Au NPs TiO2 AuNPs deposited by spin coating on a silicon substrate. Photoconductivity and optical properties of the TiO2 AuNPs Si structures were studied in comparison with those of TiO2 Si reference samples. We found that an introduction of the 4050nm diameter AuNPs into the antireflective TiO2 layer deteriorates the antireflection properties and decreases the external yield of photogeneration of charge carriers. This is due to an increase of the layer reflection in the red IR part of the spectrum, and due to the parasitic absorption of light by AuNPs in the blue green part. Charge carrier recombination effect at the TiO2 AuNPs Si interface is also found to decrease the external yield. We conclude that the TiO2 AuNPs layers could potentially be applied on the rear but not on the front side of Si solar cell