| 1. |
- Enrichi, Francesco, et al.
(författare)
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Ag nanoaggregates as efficient broadband sensitizers for Tb3+ ions in silica-zirconia ion-exchanged sol-gel glasses and glass-ceramics
- 2018
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Ingår i: Optical materials (Amsterdam). - : Elsevier. - 0925-3467 .- 1873-1252. ; 84, s. 668-674
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we report the study of down-shifting silica-zirconia glass and glass-ceramic films doped by Tb3+ ions and Ag nanoaggregates, which combine the typical spectral properties of the rare-earth-ions with the broadband sensitizing effect of the metal nanostructures. Na-Tb co-doped silica-zirconia samples were obtained by a modified sol-gel route. Dip-coating deposition followed by annealing for solvent evaporation and matrix densification were repeated several times, obtaining a homogeneous crack-free film. A final treatment at 700 °C or 1000 °C was performed to control the nanoscale structural properties of the samples, resulting respectively in a glass (G) or a glass-ceramic (GC), where tetragonal zirconia nanocrystals are surrounded by an amorphous silica matrix. Ag introduction was then achieved by ion-exchange in a molten salt bath, followed by annealing in air to control the migration and aggregation of the metal ions. The comparison of the structural, compositional and optical properties are presented for G and GC samples, providing evidence of highly efficient photoluminescence enhancement in both systems, slightly better in G than in GC samples, with a remarkable increase of the green Tb3+ PL emission at 330 nm excitation: 12 times for G and 8 times for GC samples. Furthermore, after Ag-exchange, the shape of Tb3+ excitation resembles the one of Ag ions/nanoaggregates, with a broad significant absorption in the whole UV-blue spectral region. This broadband enhanced downshifting could find potential applications in lighting devices and in PV solar cells.
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| 2. |
- Enrichi, Francesco, et al.
(författare)
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Ag-Sensitized NIR-Emitting Yb3+-Doped Glass-Ceramics
- 2020
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Ingår i: Applied Sciences. - : MDPI. - 2076-3417. ; 10:6
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Tidskriftsartikel (refereegranskat)abstract
- The optical photoluminescent (PL) emission of Yb3+ ions in the near infrared (NIR) spectral region at about 950–1100 nm has many potential applications, from photovoltaics to lasers and visual devices. However, due to their simple energy-level structure, Yb3+ ions cannot directly absorb UV or visible light, putting serious limits on their use as light emitters. In this paper we describe a broadband and efficient strategy for sensitizing Yb3+ ions by Ag codoping, resulting in a strong 980 nm PL emission under UV and violet-blue light excitation. Yb-doped silica–zirconia–soda glass–ceramic films were synthesized by sol-gel and dip-coating, followed by annealing at 1000 °C. Ag was then introduced by ion-exchange in a molten salt bath for 1 h at 350 °C. Different post-exchange annealing temperatures for 1 h in air at 380 °C and 430 °C were compared to investigate the possibility of migration/aggregation of the metal ions. Studies of composition showed about 1–2 wt% Ag in the exchanged samples, not modified by annealing. Structural analysis reported the stabilization of cubic zirconia by Yb-doping. Optical measurements showed that, in particular for the highest annealing temperature of 430 °C, the potential improvement of the material’s quality, which would increase the PL emission, is less relevant than Ag-aggregation, which decreases the sensitizers number, resulting in a net reduction of the PL intensity. However, all the Ag-exchanged samples showed a broadband Yb3+ sensitization by energy transfer from Ag aggregates, clearly attested by a broad photoluminescence excitation spectra after Ag-exchange, paving the way for applications in various fields, such as solar cells and NIR-emitting devices.
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| 3. |
- Enrichi, Francesco, et al.
(författare)
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Ag-Sensitized Yb3+ Emission in Glass-Ceramics
- 2018
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Ingår i: Micromachines. - : MDPI. - 2072-666X. ; 9:8
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Trave, Enrico, et al.
(författare)
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Control of silver clustering for broadband Er3+ luminescence sensitization in Er and Ag co-implanted silica
- 2018
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Ingår i: Journal of Luminescence. - : Elsevier. - 0022-2313 .- 1872-7883. ; 197, s. 104-111
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the optical properties of Er and Ag co-implanted silica slabs were investigated in order to shed light on the observed improvement of the rare-earth emission properties through a sensitization process activated by Ag implantation. A full ion implantation approach was adopted since it represents an effective way to create a thin doped layer, where luminescent Er ions can interact with Ag-related sensitizing species. The results evidenced that the sensitization process is effectively promoted in presence of Ag ultra-small structures, like few-atom aggregates or multimers, which can be already formed at the early stages of the metal clustering process. On the other hand, the precipitation of large, plasmonic clusters, occurring at high temperature post-Ag implantation annealing, produces a decrease of the fluorescence enhancement effect. Furthermore, it is suggested that the overall sensitization mechanism originates from an Ag-Er energy transfer that determines the possibility of a broadband photostimulation of the rare-earth ions, even by pumping in non-resonant excitation condition. Thanks to these features, the investigated Er and Ag co-implanted system can be considered for the realization of high-performing optical amplifiers in waveguide.
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| 5. |
- Zur, Lidia Z., et al.
(författare)
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Comparison between glass and glass-ceramic silica-hafnia matrices on the down-conversion efficiency of Tb3+/Yb3+ rare earth ions
- 2019
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Ingår i: Optical materials (Amsterdam). - : Elsevier. - 0925-3467 .- 1873-1252. ; 87, s. 102-106
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the investigation of energy transfer efficiency in Tb3+-Yb3+ co-doped SiO2-HfO2 glass and glass-ceramic waveguides is presented. Cooperative energy transfer between these two ions allows to cut one UV or 488 nm photon in two 980 nm photons and could have important applications in improving the performance of photovoltaic solar cells. Thin films with different molar concentrations of rare earths, up to a total concentration of 21%, were prepared by a sol-gel route, using dip-coating deposition technique on SiO2 substrates. The ratio between Yb3+ and Tb3+ ions in all the prepared thin films is constant and equal to 4. The energy transfer between Tb3+ and Yb3+ ions in glass and glass-ceramic waveguides shows the higher efficiency for glass-ceramic with a maximum quantum transfer efficiency of about 190% for the sample containing 19% of rare earths.
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