| 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. |
- Bortoluzzi, Marco, et al.
(författare)
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Green-emitting manganese (II) complexes with phosphoramide and phenylphosphonic diamide ligands
- 2018
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Ingår i: Inorganic Chemistry Communications. - : Elsevier. - 1387-7003 .- 1879-0259. ; 92, s. 145-150
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Tidskriftsartikel (refereegranskat)abstract
- Tetrahedral manganese(II) complexes having formulae [MnX2{O = PR(NMe2)2}2] (X = Br, I; R = NMe2, Ph) were isolated and characterized, and in the case of [MnBr2{O = PPh(NMe2)2}2] the structure was ascertained by means of single crystal X-ray diffraction. All the complexes showed intense green emission assigned to the Mn(II) 4T1(4G) → 6A1(6S) transition upon excitation with UV light, with photoluminescence lifetimes in the range 100–1000 μs. Bromo-complexes maintain their luminescence features once dispersed in polycaprolactone matrix.
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| 3. |
- Bortoluzzi, Marco, et al.
(författare)
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Luminescent copper(I) coordination polymer with 1-methyl-1H-benzotriazole, iodide and acetonitrile as ligands
- 2019
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Ingår i: Inorganic Chemistry Communications. - : Elsevier. - 1387-7003 .- 1879-0259. ; 102, s. 141-146
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Tidskriftsartikel (refereegranskat)abstract
- The Cu(I) coordination polymer [Cu3(μ3-I)3(μ-btzMe)(NCCH3)]n (btzMe = 1-methyl-1H-benzotriazole) was prepared and characterized by X-Ray diffraction. The compound showed strong green emission upon excitation with wavelengths below 475 nm, with lifetime of 47 μs. The emission was attributed to 3(X,M)LCT transition on the basis of experimental data and DFT calculations.
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| 4. |
- Bortoluzzi, Marco, et al.
(författare)
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Luminescent lanthanide complexes with phosphoramide and arylphosphonic diamide ligands
- 2020
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Ingår i: Chemické zvesti. - : Springer. - 0366-6352 .- 1336-9075. ; 74:11, s. 3693-3704
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Tidskriftsartikel (refereegranskat)abstract
- The sensitization of Eu(III) luminescence by the phosphoramide and arylphosphonic diamide ligands OP(NMe2)2Ind, OP(NMe2)2Cbz, OP(NMe2)2Ph, OP(NMe2)2(1-Naph) and OP(NMe2)2(2-Naph) (Ind = indol-1-yl; Ph = phenyl; Cbz = carbazol-9-yl; 1-Naph = naphtalen-1-yl; 2-Naph = naphtalen-2-yl) was verified by coordination to the [Eu(NO3)3] metal fragment. The emission spectra of the corresponding complexes showed only the 5D0 → 7FJ transitions of the metal centre, with the exception of the carbazolyl derivative. Some of the ligands were also able to sensitize Tb(III) luminescence, in agreement with the triplet state energies estimated from the phosphorescence spectra of the analogous Gd(III) nitrates. On the basis of the photoluminescence results achieved using nitrate as ancillary ligand, heptacoordinate Eu(III) complexes having general formula [Eu(β-dike)3L] (β-dike = dibenzoylmethanate, tenoyltrifluoroacetonate; L = phosphoramide or arylphosphomic diamide ligand) were prepared and characterized. All the complexes exhibited bright red emission upon excitation with near-UV and violet-blue light, with intrinsic quantum yields ranging between 18 and 36%.
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| 5. |
- Bortoluzzi, Marco, et al.
(författare)
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The conjugate base of malonaldehyde as antenna-ligand towards trivalent europium and terbium ions
- 2018
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Ingår i: Chemické zvesti. - : Springer. - 0366-6352 .- 1336-9075. ; 72:4, s. 809-819
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Tidskriftsartikel (refereegranskat)abstract
- Coordination compounds having formulae [M(MA)3]n and M(MA)(Me2Tp)2 (M = Y, Eu, Tb; MA = conjugate base of malonaldehyde; Me2Tp = tris(3,5-dimethyl-pyrazol-1-yl)borate) were synthesized and characterized. The photoluminescence features of the europium and terbium derivatives were investigated. By comparing the herein reported photoluminescence data with those relative to analogous nitro- and bromomalonaldehyde derivatives, it appears that the conjugate base of malonaldehyde is a more efficient antenna-ligand for the sensitization of Tb(III) luminescence. The experimental data were rationalized on the basis of DFT calculations. Tb(MA)(Me2Tp)2 was used as dopant for the preparation of luminescent plastic materials based on poly(methyl methacrylate).
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| 6. |
- Botella, Pablo, et al.
(författare)
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Investigation on the Luminescence Properties of InMO4 (M = V5+, Nb5+, Ta5+) Crystals Doped with Tb3+ or Yb3+ Rare Earth Ions
- 2020
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 5:5, s. 2148-2158
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Tidskriftsartikel (refereegranskat)abstract
- We explore the potential of Tb- and Yb-doped InVO4, InTaO4, and InNbO4 for applications as phosphors for light-emitting sources. Doping below 0.2% barely change the crystal structure and Raman spectrum but provide optical excitation and emission properties in the visible and near-infrared (NIR) spectral regions. From optical measurements, the energy of the first/second direct band gaps was determined to be 3.7/4.1 eV in InVO4, 4.7/5.3 in InNbO4, and 5.6/6.1 eV in InTaO4. In the last two cases, these band gaps are larger than the fundamental band gap (being indirect gap materials), while for InVO4, a direct band gap semiconductor, the fundamental band gap is at 3.7 eV. As a consequence, this material shows a strong self-activated photoluminescence centered at 2.2 eV. The other two materials have a weak self-activated signal at 2.2 and 2.9 eV. We provide an explanation for the origin of these signals taking into account the analysis of the polyhedral coordination around the pentavalent cations (V, Nb, and Ta). Finally, the characteristic green (5D4 → 7FJ) and NIR (2F5/2 → 2F7/2) emissions of Tb3+ and Yb3+ have been analyzed and explained.
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| 7. |
- Cailotto, Simone, et al.
(författare)
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Design of Carbon Dots for Metal-free Photoredox Catalysis
- 2018
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 10:47, s. 40560-40567
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Tidskriftsartikel (refereegranskat)abstract
- The photoreduction potential of a set of four different carbon dots (CDs) was investigated. The CDs were synthesized by using two different preparation methods—hydrothermal and pyrolytic—and two sets of reagents—neat citric acid and citric acid doped with diethylenetriamine. The hydrothermal syntheses yielded amorphous CDs, which were either nondoped (a-CDs) or nitrogen-doped (a-N-CDs), whereas the pyrolytic treatment afforded graphitic CDs, either non-doped (g-CDs) or nitrogen-doped (g-N-CDs). The morphology, structure, and optical properties of four different types of CDs revealed significant differences depending on the synthetic pathway. The photocatalytic activities of the CDs were investigated as such, that is, in the absence of any other redox mediators, on the model photoreduction reaction of methyl viologen. The observed photocatalytic reaction rates: a-N-CDs ≥ g-CDs > a-CDs ≥ g-N-CDs were correlated with the presence/absence of fluorophores, to the graphitic core, and to quenching interactions between the two. The results indicate that nitrogen doping reverses the photoredox reactivity between amorphous and graphitic CDs and that amorphous N-doped CDs are the most photoredox active, a yet unknown fact that demonstrates the tunable potential of CDs for ad hoc applications.
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| 8. |
- 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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| 9. |
- Enrichi, Francesco, et al.
(författare)
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Ag-sensitized Tb3+/Yb3+ codoped silica-zirconia glasses and glass-ceramics : systematic and detailed investigation of the broadband energy-transfer and downconversion processes
- 2021
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Ingår i: Ceramics International. - : Elsevier. - 0272-8842 .- 1873-3956. ; 47:13, s. 17939-17949
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Tidskriftsartikel (refereegranskat)abstract
- Various studies report that Tb3+/Yb3+ co-doped materials can split one UV or 488 nm (visible) photon in two near infrared (NIR) photons at 980 nm by an energy-transfer process involving one Tb3+ and two Yb3+ ions. Additionally, it was demonstrated that Ag multimers can provide an efficient optical sensitizing effect for rare earth ions (RE3+ ions), resulting in a broadband enhanced excitation, which could have a significant technological impact, overcoming their limited spectral absorptions and small excitation cross sections. However, a systematic and detailed investigation of the down-conversion process enhanced by Ag nanoaggregates is still lacking, which is the focus of this paper. Specifically, a step by step analysis of the energy-transfer quantum-cutting chain in Ag-exchanged Tb3+/Yb3+ co-doped glasses and glass-ceramics is presented. Moreover, the direct Ag-Yb3+ energy-transfer is also considered. Results of structural, compositional, and optical characterizations are given, providing quantitative data for the efficient broadband Ag-sensitization of Tb3+/Yb3+ quantum cutting. A deeper understanding of the physical processes beneath the optical properties of the developed materials will allow a wiser realization of more efficient energy-related devices, such as spectral converters for silicon solar cells and light-emitting devices (LEDs) in the visible and NIR spectral regions.
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| 10. |
- 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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