José P. Rainho

New phosphors based on Eu3+-doped microporous titanosilicates

Abstract Microporous titanosilicate ETS-10 doped with Eu3+ ions is used as a precursor for preparing novel dense materials, analogues of the mineral narsarsukite, which display a high and stable room-temperature luminescence. In the emission spectra of these phosphors a broad band (associated with the network of the titanosilicates) overlaps with the narrow intra- 4 f 6 5 D 0 → 7 F 0–4 lines. The presence of different Eu3+ local site symmetries, tentatively assigned to the C1,2, Cs or C2v point groups, is discussed based on the local field splitting of the 7 F 1,2 energy levels.

Photoluminescence of new Er3+-doped titanosilicate materials

Microporous titanosilicate ETS-10 doped with different concentrations of Er3+ ions is used as a precursor for preparing novel dense materials, analogues of the mineral narsarsukite, which display a high and stable room temperature emission in the visible and infrared spectral regions. The emission spectra of these phosphors display a visible broad band—associated with the narsarsukite matrix—and a series of narrow intra-4f114I13/2 → 4I15/2 lines. The number of Stark components detected in Er3+-doped narsarsukite indicates the presence of more than one optically active environment. No significant quenching of luminescence via ion–ion or ion–matrix interaction was detected in the range of Er3+ concentrations used. The presence of two multiphonon-assisted anti-Stokes excitation sidebands and an energy transfer mechanism between the host lattice and the optically-active Er3+ ions demonstrate that the ion–lattice interactions can play an important role in the interesting luminescence properties of these new titanosilicates.

Local Er(iii) environment in luminescent titanosilicates prepared from microporous precursorsElectronic supplementary information (ESI) available: Er LIII-edge k3-weighted EXAFS spectra and Fourier transforms. See http://www.rsc.org/suppdata/jm/b1/b107136j/

The local environment of Er3+ ions in microporous titanosilicate ETS-10 and in synthetic narsarsukite and glassy materials obtained by calcination of ETS-10 has been investigated by EXAFS, Raman and photoluminescence spectroscopies. Er LIII-edge EXAFS studies of Er3+-doped ETS-10 support the view that the exchanged Er3+ ions reside close to the (negatively charged) TiO6 octahedra. In ETS-10, Er3+ is partially bonded to framework oxygen atoms and hydration water molecules. The Er⋯Ti distance (3.3 A) is similar to the Na⋯Ti distances (3.15–3.20 A) reported previously for Na–ETS-10. Although the exact location of the ErO6 units within the host structure of Er3+-doped synthetic narsarsukite is still an open question, it is most likely that Er3+ substitutes Ti4+ rather than Na+ ions. EXAFS spectroscopy indicates that no significant clustering of erbium atoms occurs in the titanosilicate samples studied. Evidence for the insertion of Er3+ ions in the framework of narsarsukite has been obtained by Raman spectroscopy. This is indicated by the increasing full-width at half-maximum (FWHM) of the 775 cm−1 peak and the increasing intensity of the anatase peaks as the erbium content increases. In addition, as the narsarsukite Er3+ content increases a band at ca. 515 cm−1 firstly broadens and subsequently a new peak appears at ca. 507 cm−1. Er3+-doped narsarsukite exhibits a characteristic local vibrational frequency, ħωca. 330 cm−1, with an electron–phonon coupling, gca. 0.2, which constitutes additional evidence for framework Er3+ insertion. The number of lines in the infrared emission spectrum of synthetic narsarsukite indicates the presence of two optically-active erbium centres with very similar local environments and an average 4I13/2 lifetime of 7.8 ± 0.2 ms.

Novel Microporous and Layered Luminescent Lanthanide Silicates

Recent developments in the field of luminescent lanthanide silicates have been reviewed. Combining in a single material microporosity and optical properties may lead to new types of sensing devices. Optically active centers (lanthanide ions or molecules) may be introduced in the micropores or/and embedded in the materials framework. Layered lanthanide silicates also offer the potential for host-guest chemistry, affording efficient luminescent materials and allowing finetuning of properties. Preliminary work indicates that these new materials may be prepared, by hydrothermal methods, in the form of powders and films.

Synthesis and Luminescence of Eu3+-Doped Narsarsukite Prepared by the Sol-Gel Process

The sol-gel synthesis and structural characterisation of narsarsukite powders are reported. Samples doped with different Eu3+ amounts (Ti/Eu = 20 and 200), calcined at 800°C, have been characterised by powder XRD, 23Na, 29Si MAS NMR, Raman and luminescence spectroscopies. Eu3+-doped narsarsukite displays a high and stable room-temperature luminescence. The presence in narsarsukite of two different Eu3+ local environments is inferred based both on the distinct 5D0 → 7F0 lines observed and on the local field splitting of the 7F1,2 levels. For low lanthanide contents, the Eu3+ ions are essentially localised in a centrosymmetric environment characterized by a low-energy 5D0 → 7F0 line and a relatively long 5D0 lifetime (3.56–3.96 ms). In contrast, at high lanthanide contents the Eu3+ ions are also present in a second local site with a less covalent first coordination shell. This corresponds to a high-energy 5D0 → 7F0 line and a short 5D0 lifetime (0.84–0.99 ms). Therefore, it is likely that Eu3+ ions substitute for both Ti4+ and Na+, although the former ions are preferentially replaced at low Eu3+ content.

Inorganic nanoparticles in organic-inorganic hybrid hosts for planar waveguides

Planar waveguides have been prepared on the ZrO2-(3-glycidiloxypropyl)trimethoxysilane (GPTS) system. Stable sols containing ZrO2 nanoparticles have been prepared and characterized by Photon Correlation Spectroscopy. The nanosized sol was embedded in (3-glycidoxipropil)trimethoxisilane (GPTS) used as a hybrid host for posterior deposition. The optical parameters of the waveguides such as refractive index, thickness and propagating modes and attenuation coefficient were measured at 632.8, 543.5 and 1550 nm by the prism coupling technique as a function of the ZrO2 content. The planar waveguides present thickness of a few micra and support well confined propagating modes. Er3+ doped samples display weak and broad (Δλ≈96nm) emission at 1.5μm.

Preparation of Photoluminescent Materials from a Lanthanide-Doped Microporous Titanosilicate Precursor

The thermal transformation of Eu3+-doped and undoped microporous titanosilicate AM-3 has been reported. AM-3 is stable up to 600 °C and transforms into the analogue of the mineral narsarsukite at 800 °C. The narsarsukite obtained from AM-3 is purer than that prepared from the titanosilicates ETS-10, ETS-4 and AM-1, and is suitable for hosting optically-active Ln3+ ions. The materials have been studied by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR), Raman and photoluminescence pectroscopies.

Optical Characterization of C 60 Organic Semiconductor and Bilayers

Preparation and characterization either by optical absorption, photoluminescence and micro-Raman spectroscopy of individual components as well as bilayers consisting of organic dye semiconductor Zinc Phthalocyanine (ZnPc) and fullerene, C 60 , thin films are reported. The layers and structures were deposited in vacuum and some fullerene films were also prepared by casting the C 60 solution in benzene. The optical absorption and photoluminescence dependencies on film thickness in bilayers C 60 /ZnPc were observed and may be discussed in a context of interface induced simmetry reduction of C 60 molecules.

Fullerite C60 high-pressure phases. Raman study

Abstract Fullerite C 60 high-pressure phases were studied using micro-Raman spectroscopy. High-pressure phases of C 60 fullerite have been obtained under hydrostatic conditions of 7.8 GPa at 1000–1600 °C. The new phase consists of strongly interacting agglomerates. Compared with pristine C 60 , the spectra of the transformed material reveal irreversible changes depending on the treatment conditions. The Raman spectra of high-pressure phases exhibit some sp 3 - as well as strong sp 2 -hybridized carbon contributions. We discuss these results in terms of a slight shortening of distance between the C 60 molecules.