Chemically—driven isothermal close space vapour transport was used to prepare pure MoO ₂ thin films which were eventually converted to MoO ₃ by annealing in air. According to temperature-dependent Raman measurements, the MoO ₂ /MoO ₃ phase transformation was found to occur in the 225 °C–350 °C range while no other phases were detected during the transition. A clear change in composition as well as noticeable modifications of the band gap and the absorption coefficient confirmed the conversion from MoO ₂ to MoO ₃ . An extensive characterization of these two pure phases was carried out. In particular, a procedure was developed to determine the dispersion relation of the refractive index of MoO ₂ from the shift of the interference fringes of the used SiO ₂ /Si substrate. The obtained data of the refractive index was corrected taking into account the porosity of the samples calculated from elastic backscattering spectrometry. The Debye temperature and the residual resistivity were extracted from the electrical resistivity temperature dependence using the Bloch–Grüneisen equation. MoO ₃ converted samples presented a very high resistivity and a typical semiconducting behavior. They also showed intense and broad luminescence spectra composed by several contributions whose temperature behavior was examined. Furthermore, surface photovoltage spectra were taken and their relation with the photoluminescence is discussed.

For over 20 years nanostructured porous silicon (nanoPS) has found a vast number of applications in the broad fields of photonics and optoelectronics, triggered by the discovery of its photoluminescent behavior in 1990. Besides, its biocompatibility, biodegradability, and bioresorbability make porous silicon (PSi) an appealing biomaterial. These properties are largely a consequence of its particular susceptibility to oxidation, leading to the formation of silicon oxide which is readily dissolved by body fluids. This paper reviews the evolution of the applications of PSi and nanoPS from photonics through biophotonics, to their use as cell scaffolds, whether as an implantable substitute biomaterial, mainly for bony and ophthalmological tissues, or as an in-vitro cell conditioning support, especially for pluripotent cells. For any of these applications, PSi/nanoPS can be used directly after synthesis from Si wafers, upon appropriate surface modification processes, or as a composite biomaterial. Unedited studies of fluorescently active PSi structures for cell culture are brought to evidence the margin for new developments.

Porous silicon (PS) can be optically described as a homogeneous mixture of air, silicon, and, eventually, silicon dioxide, which explains the great tunability of its refractive index. This behavior makes porous silicon a very interesting material for the development of interference filters for use in optoelectronic applications. For the accurate design of such filters, the precise determination of the optical constants of PS is mandatory. However, since PS is a dispersive and absorbing material, determination of its complex refractive index is not trivial. In the present work, a genetic algorithm has been used to precisely determine the complex refractive index and thickness of thin films from their reflectance spectra in the visible wavelength range. This algorithm was applied to porous silicon. The precise spectral values of the refractive index obtained for PS layers of different characteristics have been used to design and fabricate interference filters with a predetermined optical behavior. In addition, the performance of the algorithm in two different working modes is discussed.