KEYWORDS: Perovskite, Nanocrystals, Excitons, Optical properties, Nanophotonics, Polymethylmethacrylate, Metals, Bromine, Temperature metrology, Near field optics
Metal halide perovskites in the form of nanocrystals are highly efficient light emitters at visible-NIR wavelengths. In this work, the optical properties of single nanocrystals and ensembles will be discussed, as also several applications in nanophotonics. At low temperatures, single nanocrystals can be also single photon emitters if blinking and spectral diffusion is conveniently reduced. In the case of nanocrystal assemblies, stimulated emission can be observed with thresholds lower than 10 μJ/cm2 under nanosecond laser excitation at low temperatures, whose physical origin is attributed to single exciton recombination. Finally, the coupling of perovskite nanocrystals to the optical modes of hyperbolic metaldielectric metamaterials has been studied and demonstrated an important Purcell enhancement of the exciton radiative emission by more than a factor three for CsPbI3 and around factor two for FAPbI3 when the distance between the emitters and HMM is 10 nm.
Nanometer-size colloidal semiconductor nanocrystals, or Quantum Dots (NQD), are very prospective active centers
because their light emission is highly efficient and temperature-independent. Nanocomposites based on the incorporation
of QDs inside a polymer matrix are very promising materials for application in future photonic devices because they
combine the properties of QDs with the technological feasibility of polymers. In the present work some basic
applications of these new materials have been studied. Firstly, the fabrication of planar and linear waveguides based on
the incorporation of CdS, CdSe and CdTe in PMMA and SU-8 are demonstrated. As a result, photoluminescence (PL) of
the QDs are coupled to a waveguide mode, being it able to obtain multicolor waveguiding. Secondly, nanocomposite
films have been evaluated as photon energy down-shifting converters to improve the efficiency of solar cells.
The modeling, fabrication and characterization of PSi fabricated from both (110) and (100) surface oriented silicon for
optical sensing is thoroughly reported. First, based on the generalized Bruggeman method, the birefringence and
sensitivity of the fabricated membranes were calculated as a function of the fabrication parameters such as porosity and
pore sizes; and external effects, such as the pores surface oxidation. Thereafter we report on the fabrication of PSi
membranes from (110) and (100) surface oriented silicon with pore sizes in the range of 50 - 80 nm, and the
characterization of their birefringence using a polarimetric setup. Their sensitivities were determined by filling the pores
with several liquids having different refractive index. As a result, sensitivities as high as 1407 nm/RIU were obtained for
the (110) samples at a 1500 nm wavelength and 382 nm/RIU for the (100) samples at the same wavelength.
The thermal oxidation of an Al-rich AlGaAs buried layer is a common established technique used to improve
the performances of some optoelectronic devices, like VCSEL or optical waveguides, in terms of electro-optical
confinement. This oxidation technique is usually proceeding laterally, which allows achieving good results but leads to
some difficulties on the control of the shape and size of the oxidized areas. In this work, a new technology to oxidize
GaAs/AlAs epitaxial structures which avoids these limitations is presented. This method consists of an oxidation through
the top of the sample, allowing in consequence a total control of the shape of oxidation by means of photolithography.
For this purpose the method has two steps: first, the intentional creation of defects in the top GaAs layer, in order to
make it possible the oxidant species diffusion through this material, and second the planar oxidation of the AlAs layer. In
this paper this technique is thoroughly studied: different methods to create defects in the GaAs layer have been analysed,
and the optimization of the procedure has been achieved leading to a uniform oxidation and a reduced lateral oxidation
spreading. Finally a comparison between the experiments and simulations has been realized in order to provide an
explanation for this type of vertical oxidation. This innovating technique allows addressing separately the electrical and
optical operating aspects of optoelectronic devices, thus opens to novel structures with controlled transverse optical
behaviour.
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