Rare-earth doped glasses and light managing in solar cells

Glasses doped with rare earth elements possess unique photoluminescence properties. They find application in several devices, such as lasers, optical amplifiers, and sensors. More recently, rare-earth doped glass thin films have been the subject of investigation for the development of frequency-converting layers able to increase the efficiency of silicon solar cells. Another approach to the improvement of the performance of a solar cell is based on the capture of a larger flux of light by the detector, which can be obtained by surface texture, plasmonics, or waveguide structures. Here, the recent advances in this area will be briefly reviewed

Rare-earth-activated glasses for solar energy conversion

The solar cells efficiency may be improved by better exploitation of the solar spectrum, making use of the down-conversion mechanism, where one high energy photon is cut into two low energy photons. The choice of the matrix is a crucial point to obtain an efficient down-conversion process with rare-earth ions. When energy transfer between rare earth ions is used to activate this process, high emission and absorption cross sections as well as low cut-off phonon energy are mandatory. In this paper we present some results concerning 70SiO2-30HfO2 glass ceramic planar waveguides co-activated by Tb3+/Yb3+ ions, fabricated by sol gel route using a top-down approach, and a bulk fluoride glass of molar composition 70ZrF4 23.5LaF3 0.5AlF3 6GaF3 co-activated by Pr3+/Yb3+ ion. Attention is focused on the assessment of the energy transfer efficiency between the two couples of rare earth ions in the different hosts

M-line spectroscopic, spectroscopic ellipsometric and microscopic measurements of optical waveguides fabricated by MeV-energy N+ ion irradiation for telecom applications

Irradiation with N+ ions of the 1.5 - 3.5 MeV energy range was applied to optical waveguide formation. Planar and channel waveguides have been fabricated in an Er-doped tungsten-tellurite glass, and in both types of bismuth germanate (BGO) crystals: Bi4Ge3O12 (eulytine) and Bi12GeO20 (sillenite). Multi-wavelength m-line spectroscopy and spectroscopic ellipsometry were used for the characterisation of the ion beam irradiated waveguides. Planar waveguides fabricated in the Er-doped tungsten-tellurite glass using irradiation with N+ ions at 3.5 MeV worked even at the 1550 nm telecommunication wavelength. 3.5 MeV N+ ion irradiated planar waveguides in eulytine-type BGO worked up to 1550 nm and those in sillenite-type BGO worked up to 1330 nm

Er3+ ion dispersion in tellurium oxychloride glasses

Erbium-doped tellurite glasses in the 60TeO2–20ZnO–20ZnCl2–xErCl3 systems, with erbium concentration between x = 1 and 10 mol%, were prepared and their refractive index and density were measured. Er3+ photoluminescence at 1.5 μm and the corresponding lifetime measurements were performed. A full width at half maximum value of about 53 nm for all the samples and lifetimes ranging between 4.2 and of 2.2 ms were obtained from the comparison of the radiative lifetimes calculated by Judd–Ofelt analysis and the measured lifetimes, quantum efficiency higher than 50% was assessed even in the most doped samples. A quenching concentration for the 1.5 μm emission of about 10% was estimated

Spectroscopic assessment of silica–titania and silica–hafnia planar waveguides

Silicate glasses remain the most investigated systems for optical planar waveguides, since they offer a reasonable solubility for rare-earth ions, they are transparent in the near-infrared–visible region and they are compatible with integrated optics (IO) technology. In the last decade, various technologies have been employed for the fabrication of silica (SiO2)-based IO components and a broad variety of silicate glass systems have been investigated. Besides the SiO2–titania (TiO2) system, which has been widely studied, it has recently been shown that SiO2–hafnia (HfO2) could be a further viable system for 1.5 µm applications. This paper compares spectroscopic results, in particular infrared and Raman spectra, in order to assess the structural and optical properties of erbium-activated SiO2–TiO2 and SiO2–HfO2 planar waveguides, prepared by two different techniques: rf sputtering and the sol–gel method. Particular attention is devoted to the homogeneity of the material structures obtained in each case

Wigner distribution moments measured as fractional Fourier transform intensity moments

It is shown how all global Wigner distribution moments of arbitrary order can be measured as intensity moments in the output plane of an appropriate number of fractional Fourier transform systems (generally anamorphic ones). The minimum number of (anamorphic) fractional power spectra that are needed for the determination of these moments is derived