Lidia Zur

Glass and glass-ceramic photonic systems

The development of optically confined structure is a major topic in both basic and applied physics not solely ICT oriented but also concerning lighting, laser, sensing, energy, environment, biological and medical sciences, and quantum optics. Glasses and glass-ceramics activated by rare earth ions are the bricks of such structures. Glass-ceramics are nanocomposite systems that exhibit specific morphologic, structural and spectroscopic properties allowing developing new physical concepts, for instance the mechanism related to the transparency, as well as novel photonic devices based on the enhancement of the luminescence. The dependence of the final product on the specific parent glass and on the fabrication protocol still remain an important task of the research in material science. Looking to application, the enhanced spectroscopic properties typical of glass ceramic in respect to those of the amorphous structures constitute an important point for the development of integrated optics devices, including optical amplifiers, monolithic waveguide laser, novel sensors, coating of spherical microresonators, and up and down converters. This paper presents some results obtained by our consortium regarding glass-based photonics systems. We will comment the energy transfer mechanism in transparent glass ceramics taking as examples the up and down conversion systems and the role of SnO2 nanocrystals as sensitizers. Coating of spherical resonators by glass ceramics, 1D-Photonic Crystals for luminescence enhancement, laser action and disordered 1-D photonic structures will be also discussed. Finally, RF-Sputtered rare earth doped P2O5- SiO2-Al2O3-Na2O-Er2O3 planar waveguides, will be presented.

One-dimensional disordered photonic structures with two or more materials

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.

Ag-Sensitized Yb3+ Emission in Glass-Ceramics

Rare earth doped materials play a very important role in the development of many photonic devices, such as optical amplifiers and lasers, frequency converters, solar concentrators, up to quantum information storage devices. Among the rare earth ions, ytterbium is certainly one of the most frequently investigated and employed. The absorption and emission properties of Yb3+ ions are related to transitions between the two energy levels 2F7/2 (ground state) and 2F5/2 (excited state), involving photon energies around 1.26 eV (980 nm). Therefore, Yb3+ cannot directly absorb UV or visible light, and it is often used in combination with other rare earth ions like Pr3+, Tm3+, and Tb3+, which act as energy transfer centres. Nevertheless, even in those co-doped materials, the absorption bandwidth can be limited, and the cross section is small. In this paper, we report a broadband and efficient energy transfer process between Ag dimers/multimers and Yb3+ ions, which results in a strong PL emission around 980 nm under UV light excitation. Silica-zirconia (70% SiO2-30% ZrO2) glass-ceramic films doped by 4 mol.% Yb3+ ions and an additional 5 mol.% of Na2O were prepared by sol-gel synthesis followed by a thermal annealing at 1000 °C. Ag introduction was then obtained by ion-exchange in a molten salt bath and the samples were subsequently annealed in air at 430 °C to induce the migration and aggregation of the metal. The structural, compositional, and optical properties were investigated, providing evidence for efficient broadband sensitization of the rare earth ions by energy transfer from Ag dimers/multimers, which could have important applications in different fields, such as PV solar cells and light-emitting near-infrared (NIR) devices.

Energy transfer and multicolor emission in germanate glasses containing Ce3+ and Pr3+ for white light-emitting diodes

White light emitting devices have attracted great attention for their use in liquid crystal monitor screens and white light emitting diodes (W-LEDs). Glasses singly or doubly doped with lanthanide ions may be good white light emitters. In particular, various glass systems containing Pr3+ were studied from this point of view. In this work, germanate glasses doubly doped with Ce3+ and Pr3+ ions were prepared by traditional melt quenchingtechnique. The excitation and emission spectra of lanthanide ions were measured. The emission bands corresponding to characteristics transitions of Pr3+ and transition of Ce3+ ions from 5d level to 4f levels (2F7/2 and 2F5/2) are quite well observed. It indicates that the energy transfer process between Ce3+ and Pr3+ ions in germanate glasses occurs. From the emission spectra, the Commission Internationale de I’Eclairage (CIE) chromaticity coordinates (x, y) were calculated in relation to potential application for white LEDs. Luminescence decay analysis is also presented and discussed in details. The obtained results suggest the possibility of using these Ce3+/Pr3+ co-doped glass systems for future application to white light generation.

SiO2-SnO2:Er3+ transparent glass-ceramics: fabrication and photonic assessment

This work focuses on the fabrication processes and photonic assessment of SiO2-SnO2:Er3+ monoliths. To obtain the crack-free and densified system, the sol-gel derived synthesis protocols and heat-treatment processes were optimized. The absorption measurements were employed to assess the effect of the heat-treatment on the samples and specially to estimate the –OH content. The XRD patterns were used to investigate the crystallization as well as the structure of the monoliths. The emission spectra, performed at different excitation wavelengths, evidence the presence of Er3+ in the SnO2 nanocrystals and the energy transfer from SnO2 to the rare earth ions. In addition, the efficient role of SnO2 nanocrystals as Er3+ sensitizers are also experimentally confirmed in this system.

Role of Ag multimers as broadband sensitizers in Tb3+/Yb3+ co-doped glass-ceramics

Rare earth ions (RE3+) have typical photoluminescence emissions due to internal 4f orbital transitions. These emissions are narrow, with long excited state lifetimes and have the capability of spectral manipulation like wavelength shifting, down-conversion or up-conversion processes. Therefore, RE-doped materials are widely used for optical applications. However, the narrow absorption bandwidths and the small excitation cross sections for their optical transitions are major limiting factors for the full exploitation of their potentials. In this work, we show that the addition of metal nanoaggregates as broadband and efficient sensitizers can be a viable strategy to overcome these limits. Silica-zirconia (70% SiO2 – 30% ZrO2) glass-ceramic films doped by Tb3+/Yb3+ ions and an additional 5 mol.% of Na2O were prepared by sol-gel synthesis followed by a thermal annealing at 1000°C. Ag introduction was then obtained by ion-exchange in a molten salt bath and the samples were subsequently annealed in air at 380°C or 430°C to induce the migration and aggregation of the metal. The structural, compositional and optical properties of the materials were investigated, providing evidence for efficient broadband sensitization of the rare earth ions by energy transfer from Ag-dimers or multimers, which could have applications for increasing the efficiency of silicon solar cells.

Near-infrared emission in barium gallo-germanate glasses doped with Pr3+ and co-doped with Ce3+ and Pr3+ for broadband optical amplifiers

Near-infrared emission in barium gallo-germanate glasses containing rare earth ions for broadband optical amplifiers were studied. Among the rare earths, the trivalent praseodymium and cerium ions were selected as an optically active dopants. In order to examine the spectroscopic properties of these glasses doped with Pr3+ and co-doped with Ce3+ and Pr3+ ions the luminescence spectra were registered. The energy transfer processes between cerium and praseodymium ions in barium gallo-germanate glasses have been also investigated. The intense near-infrared luminescence bands corresponding to characteristic transitions of Pr3+ ions in singly and doubly doped glass systems were observed. It has been proved that our glasses exhibit intense 1.5 μm emission originating from 1D2 → 1G4 transition of Pr3+ under direct excitation (445 nm). Moreover, the experimental results indicated that energy transfer between Ce3+ and Pr3+ is not effective for barium gallo-germanate glasses.

Synthesis, structure and spectroscopic assessment of luminescent GdVO4:Dy3+ and DyVO4 nanoparticles

In this paper, we focused on the size effects of GdVO4:2mol% Dy3+ and DyVO4 particles on their structural and optical properties. Highly crystalline particles of different sizes and morphologies with tetragonal zircon-type phase were successfully synthesized by using different techniques of synthesis, such as reverse micelles, co-precipitation and hightemperature solid-state methods. The prepared samples exhibited a number of similarity and diversity in structural and optical properties with a decreasing in particle diameter.

Fabrication by rf-sputtering and assessment of dielectric Er3+ doped monolithic 1-D microcavity for coherent emission at 1.5 um

All Er3+ doped dielectric 1-D microcavity are fabricated by RF sputtering technique. The microcavity is composed of half wave Er3+ doped SiO2 active layer inserted, between two Bragg reflectors consisting of seven pairs of SiO2/TiO2 layers also doped with Er3+ ions. The morphology of the structure is inspected with scanning electron microscopy. Transmission measurements show the third and first order cavity resonance at 530 nm and 1535 nm, respectively. The photoluminescence measurements were obtained by optically exciting at the third order cavity resonance using 514.5 nm Ar+ laser with an excitation angle of 30°. The Full Width at Half Maximum of the emission peak at 1535 nm decrease with the pump power until the spectral resolution of the detection system of 2.3 nm. Moreover, the emission intensity presents a non-linear behavior with the pump power and a threshold at about 4 μW.

Glass based structures fabricated by rf-sputtering

In this paper we present some results obtained by our consortium regarding rf-sputtered glass-based structures.