Doped metal oxide nanocrystals (MO NCs), such as Sn doped In2O3 (ITO) or doped zinc oxide (ZnO) and cadmium oxide (CdO) display localized surface plasmon resonances due to their carrier density around 10^21 cm^-3. Such optical properties are tunable across the near infrared spectral range upon doping control. The dynamic modulation becomes possible through the pseudo-capacitive charge injection by applying an electrochemical potential or through the interaction with light beyond their bandgap, i.e. photodoping. The latter allows accumulation of multiple electrons within one NC through the absorption of several photons, as the holes react with sacrificial hole scavengers. Capacitance values comparable to commercially available supercapacitor materials are extracted. In this presentation, I will discuss the fundamental physical and chemical processes underlying photodoping of MO NCs. I will further discuss the possibility of multi-charge transfer processes following photodopin and highlight open questions with regards to their implementation as novel light-driven multi-charge accumulation components in the next generation of solar energy devices.
Hybrid plasmonic photonic structures combine the plasmonic response with the photonic band gap, holding promise for utilization as optical switches and sensors. Here, we demonstrate the active modulation of the optical response in such structures with two different external stimuli, e.g. laser pulses and bacteria. First, we report the fabrication of a miniaturized (5 x 5 mm) indium tin oxide (ITO) grating employing femtosecond laser micromachining, and we show the possibility to modulate the photonic band gap in the visible via ultrafast photoexcitation in the infrared part of the spectrum. Note that the demonstrated time response in the picosecond range of the spectral modulation have an industrial relevance. Moreover, we manufacture one-dimensional photonic crystals consisting of a solution-processed dielectric Bragg stack exposing a top-layer of bio-active silver. We assign the bacterial responsivity of the system to polarization charges at the Ag/bacterium interface, giving rise to an overall blue shift of the photonic band gap.
Here we discuss the light transmission modulation by periodic and disordered one dimensional (1D) photonic structures. In particular, we will present some theoretical and experimental findings highlighting the peculiar optical properties of: (i) 1D periodic and disordered photonic structures made with two or more materials1,2; (ii) 1D photonic structures in which the homogeneity3 or the aggregation4 of the high refractive index layers is controlled. We will focus also on the fabrication aspects of these structures.
A tuning of the light transmission properties of 1D photonic structures employing an external stimulus is very attracting and opens the way to the fabrication of optical switches for colour manipulation in sensing, lighting, and display technology. We present the electric field-induced tuning of the light transmission in a photonic crystal device, made by alternating layers of silver nanoparticles and titanium dioxide nanoparticles. We show a shift of around 10 nm for an applied voltage of 10 V. We ascribe the shift to an accumulation of charges at the silver/TiO2 interface due to electric field, resulting in an increase of the number of charges contributing to the plasma frequency in silver, giving rise to a blue shift of the silver plasmon band, with concomitant blue shift of the photonic band gap. The employment of a relatively low applied voltage gives the possibility to build a compact and low-cost device 1 . We also propose the fabrication of 1D photonic crystal and microcavities employing a magneto-optical material as TGG (Tb3Ga5O12). With these structures we can observe a shift of 22 nm with a magnetic field of 5 T, at low temperature (8 K). The option to tune the colour of a photonic crystal with magnetic field is interesting because of the possibility to realize contactless optical switches 2 . We also discuss the possibility to achieve the tuning of the photonic band gap with UV light in photonic crystals made with indium tin oxide (ITO).
We describe different types of photonic structures that allow tunability of the photonic band gap upon the application of external stimuli, as the electric or magnetic field. We review and compare two porous one-dimensional (1-D) photonic crystals: in the first one, a liquid crystal has been infiltrated in the pores of the nanoparticle network, whereas in the second one, the optical response to the electric field of metallic nanoparticles has been exploited. Then, we present a 1-D photonic crystal made with indium tin oxide (ITO) nanoparticles, and we propose this system for electro-optic tuning. Finally, we describe a microcavity with a defect mode that is tuned in the near-infrared by the magnetic field, envisaging a contact-less magneto-optic switch. These optical switches can find applications in information and communications technologies and electrochromic windows.
In this work we study the ultrafast exciton dynamics in CdTe nanorods by using two-dimensional electronic spectroscopy (2DES). By simultaneously exciting the lowest three excitonic transitions (i.e. S1, S2 and S3) we extract the electron and hole relaxation pathways, owing to the combined temporal and spectral resolution of 2DES. In particular, we directly observe hot hole relaxation from the second to the first exciton state in about 30 fs by excitation of the S2 transition. Additionally, we extract a direct charge relaxation to S1 by disentangling the overlapping bleach and excited state induced energy level shifts after excitation of S3.
Semiconductor-metal hybrid nanostructures are interesting materials for photocatalysis. Their tunable properties offer a highly controllable platform to design light-induced charge separation, a key to their function in photocatalytic water splitting. Hydrogen evolution quantum yields are influenced by factors as size, shape, material and morphology of the system, additionally the surface coating or the metal domain size play a dominant role.
In this paper we present a study on a well-defined model system of Au-tipped CdS nanorods. We use transient absorption spectroscopy to get insights into the charge carrier dynamics after photoexcitation of the bandgap of CdS nanorods. The study of charge transfer processes combined with the hydrogen evolution efficiency unravels the effects of surface coating and the gold tip size on the photocatalytic efficiency. Differences in efficiency with various surface ligands are primarily ascribed to the effects of surface passivation. Surface trapping of charge carriers is competing with effective charge separation, a prerequisite for photocatalysis, leading to the observed lower hydrogen production quantum yields. Interestingly, non-monotonic hydrogen evolution efficiency with size of the gold tip is observed, resulting in an optimal metal domain size for the most efficient photocatalysis. These results are explained by the sizedependent interplay of the metal domain charging and the relative band-alignments. Taken together our findings are of major importance for the potential application of hybrid nanoparticles as photocatalysts.
We present the electric field-induced tuning of the light transmission in a photonic crystal device. The device, with alternating layers of Silver and Titanium dioxide nanoparticles, shows a shift of around 10 nm for an applied voltage of 10 V. An accumulation of charges at the Silver/TiO2 interface due to electric field leads to an increase of the number of charges contributing to the plasma frequency in Silver. This results in a blue shift of the Silver plasmon band, with concomitant blue shift of the photonic band gap as a result of the decrease in the Silver dielectric function.
We present the possibility to tailor the optical properties of 1D photonic structures by using more than two materials and by clustering the high refractive index (hRI) layer in the structures. In particular, we show that: i) with a photonic crystal made of i different materials, the photonic band gap splits in i-1 bands; ii) with a proper choice of the layer thickness, disordered photonic structures made with a high number of layers show periodic transmission peaks; iii) when the size of the hRI layer clusters, randomly distributed within the low refractive index layers, follows a power law distribution, the total light transmission follows a sigmoidal function. Furthermore, we discuss the fabrication aspects to realize the above mentioned photonic structures.
The investigation of the differences between ordered and disordered materials (in the hundreds of nanometer lengthscale) is a crucial topic for a better understanding of light transport in photonic media. Here we study the light transmission properties of 1D photonic structures in which disorder is introduced in two different ways. In the first study, we have grouped the high refractive index layers in layer clusters, randomly distributed among layers of low refractive index. We have controlled the maximum size of such clusters and the ratio of the high-low refractive index layers (here called dilution). We studied the total transmission of the disordered structure within the photonic band gap of the ordered structure as a function of the maximum cluster size, and we have observed a valley in trend of the total transmission for a specific maximum cluster size. This value increases with increasing dilution. Furthermore, within one dilution we observe oscillations of the total transmission with increasing cluster size. In the second study, we have realized photonic structures with a random variation of the layer thickness. The structures were fabricated by radio-frequency (RF) sputtering technique. The transmission spectrum of the disordered structure was simulated by taking into account the refractive index dispersion of the materials, resulting in a good agreement between the experimental data and the simulations. We found that the transmission of the photonic structure in the range 300– 1200 nm is lower with respect the corresponding periodic photonic crystal. The studied disordered 1D photonic structures are very interesting for the modelization and realization of broad band filters and light harvesting devices.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.