Luís D. Carlos

Lanthanide-Containing Light-Emitting Organic-Inorganic Hybrids: A Bet on the Future

Interest in lanthanide-containing organic-inorganic hybrids has grown considerably during the last decade, with the concomitant fabrication of materials with tunable attributes offering modulated properties. The potential of these materials relies on exploiting the synergy between the intrinsic characteristics of sol-gel derived hosts (highly controlled purity, versatile shaping and patterning, excellent optical quality, easy control of the refractive index, photosensitivity, encapsulation of large amounts of isolated emitting centers protected by the host) and the luminescence features of trivalent lanthanide ions (high luminescence quantum yield, narrow bandwidth, long-lived emission, large Stokes shifts, ligand-dependent luminescence sensitization). Promising applications may be envisaged, such as light-emitting devices, active waveguides in the visible and near-IR spectral regions, active coatings, and bio-medical actuators and sensors, opening up exciting directions in materials science and related technologies with significant implications in the integration, miniaturization, and multifunctionalization of devices. This review provides an overview of the latest advances in Ln(3+)-containing siloxane-based hybrids, with emphasis on the different possible synthetic strategies, photoluminescence features, empirical determination.

A Miniaturized Linear pH Sensor Based on a Highly Photoluminescent Self-Assembled Europium(III) Metal–Organic Framework†

The field of lanthanide-based metal–organic frameworks (LnMOFs) with twoor three-dimensional structures is rapidly growing because of the discovery of new crystalline structures that exhibit interesting properties and have potential applications in catalysis, sensors, contrast agents, non-linear optics, 22] displays, and electroluminescent devices. For photoluminescence applications, it is necessary to prepare lanthanide-containing materials with high quantum efficiencies, in order to achieve the required miniaturization and reduce energy losses from undesirable quenching processes. Moreover, it is highly desirable to combine the properties of ligands and antennae in one organic moiety. A well-known powerful sensitizing ligand for Eu ions in solution is 1,10-phenanthroline-2,9-dicarboxylic acid (H2PhenDCA), in which both carboxylic and phenanthroline moieties may coordinate to the metal center. 27] The proximity between the coordinative parts means that this chelating agent has the tendency to form zero-dimensional (molecular) complexes that are useful in some solution-based analytical applications, but cannot be applied as solid sensors or light-emitting materials. Thus, it is of interest to obtain the twoor three-dimensional insoluble counterparts of these zero-dimensional water-soluble complexes. To achieve this goal, we have used hydrothermal synthesis, which is a powerful technique for the preparation of metastable compounds that may not be accessible by using conventional methods. 29] Hydrothermal synthesis also allows the use of chelating agents that are sparingly soluble in water at temperatures below 373 K, thus enhancing the lanthanidecoordinating ability of the ligand. Herein, we report the synthesis, structure, and sensing properties of a new Eu metal–organic framework ITQMOF-3-Eu (ITQMOF = Instituto de Tecnologia Quimica Metal Organic Framework) that contains the ligand 1,10-phenanthroline-2,9-dicarboxylic acid. The excellent balance between absorption, energy transfer, and emission rate of the Eu ITQMOF-3 (ITQMOF-3-Eu) allowed the fabrication of a miniaturized pH sensor prototype that functions in the biologically interesting range (5–7.5). By combining this material and an optical fiber, a linear photoluminescence response, which also allows the self-calibration of the emitting signal within this pH range, was achieved. The ITQMOF-3Eu material was obtained by reacting the H2PhenDCA ligand and the Eu salt or oxide under hydrothermal conditions (see the Supporting Information). The crystal has a strong red luminescence under ultraviolet light (see Figure 1 a). Chemical and elemental analyses showed that the formula of the material is [Eu3(C14H6N2O4)4(OH)(H2O)4]·2 H2O.

A luminescent molecular thermometer for long-term absolute temperature measurements at the nanoscale

Temperature is a fundamental thermodynamic variable, the measurement of which is crucial in countless scientific investigations and technological developments, accounting at present for 75%–80% of the sensor market throughout the world.[1] Traditional liquid-filled and bimetallic thermometers, thermocouples, pyrometers, and thermistors are generally not suitable for temperature measurements at scales below 10 μm. This intrinsic limitation has encouraged the development of new non-contact accurate thermometers with micrometric and nanometric precision, a challenging research topic increasingly hankered for [1–2].

Ratiometric Nanothermometer Based on an Emissive Ln3+-Organic Framework

Luminescent thermometers working at the nanoscale with high spatial resolution, where the conventional methods are ineffective, have emerged over the last couple of years as a very active field of research. Lanthanide-based materials are among the most versatile thermal probes used in luminescent nanothermometers. Here, nanorods of metal organic framework Tb0.99Eu0.01(BDC)1.5(H2O)2 (BDC = 1-4-benzendicarboxylate) have been prepared by the reverse microemulsion technique and characterized and their photoluminescence properties studied from room temperature to 318 K. Aqueous suspensions of these nanoparticles display an excellent performance as ratiometric luminescent nanothermometers in the physiological temperature (300-320 K) range.

All-In-One Optical Heater-Thermometer Nanoplatform Operative From 300 to 2000 K Based on Er3+ Emission and Blackbody Radiation

A single nanoplatform integrating laser-induced heat generation by gold nanoparticles and temperature sensing up to 2000 K via (Gd,Yb,Er)2 O3 nanorods is demonstrated, which presents considerable potential for nanoscale photonics and biomedicine. Blackbody emission is ascertained from the temperature increment with AuNP concentration, emission color coordinates as a function of the laser pump power, and Plancks law of blackbody radiation.

Lanthanide-based luminescent molecular thermometers

Non-invasive accurate thermometers with high spatial resolution and operating at sub-micron scales, where the conventional methods are ineffective, are currently a very active field of research strongly stimulated in the last couple of years by the challenging demands of nanotechnology and biomedicine. This perspective offers a general overview of recent examples of accurate luminescent thermometers working at micrometric and nanometric scales, particularly those involving advanced Ln3+-based functional organic–inorganic hybrid materials.

Full‐Color Phosphors from Amine‐Functionalized Crosslinked Hybrids Lacking Metal Activator Ions

Sol–gel derived hybrids that contain OCH2CH2 (polyethylene glycol, PEG) repeat units grafted onto a siliceous backbone by urea, –NHC(=O)NH–, or urethane, –NHC(=O)O–, bridges have been prepared. It is demonstrated that the white light PL of these materials results from an unusual convolution of a longer lived emission that originates in the NH groups of the urea/urethane bridges with shorter lived electron–hole recombinations occurring in the nanometer-sized siliceous domains. The PL efficiencies reported here (maximum quantum yields at room temperature of ≈ 0.20 ± 0.02 at a 400 nm excitation wavelength) are in the same range as those for tetramethoxysilane–formic acid, and APTES–acetic acid, sol–gel derived phosphors. The high quantum yields combined with the possibility of tuning the emission to colors across the chromaticity diagram present a wide range of potential applications for these hybrid materials.

Fine Tuning of the Relaxometry of γ-Fe2O3@SiO2 Nanoparticles by Tweaking the Silica Coating Thickness

We report the fine-tuning of the relaxometry of gamma-Fe2O3@SiO2 core-shell nanoparticles by adjusting the thickness of the coated silica layer. It is clear that the coating thickness of Fe2O3@SiO2 nanoparticles has a significant impact on the r(1) (at low B0 fields), r(2), and r(2)* relaxivities of their aqueous suspensions. These studies clearly indicate that the silica layer is heterogeneous and has regions that are porous to water and others-that are not. It is also shown, that the viability and the mitochondrial dehydrogenase expression of the microglial cells do not appear to be sensitive to the vesicular load with these core-shell nanoparticles. The adequate silica-shell thickness can therefore be tuned to allow for both a sufficiently high response as contrast agent, and-adequate grafting of targeted biomolecules.

Luminescent and Magnetic Cyano-Bridged Coordination Polymers Containing 4d-4f Ions: Toward Multifunctional Materials

A new family of cyano-bridged coordination polymers Ln(H(2)O)(5)[M(CN)(8)] (Ln = Eu, Tb, Sm, Gd; M = Mo, W) were obtained and characterized by X-ray diffraction, photoluminescence spectroscopy, and magnetic analyses. These compounds are isomorphous and crystallize in the tetragonal system P4/nmm, forming two-dimensional gridlike networks. The Eu- and Tb-containing coordination polymers are room-temperature optically active emitters displaying the characteristic (5)D(0) --> (7)F(0-4) (Eu(3+)) and (5)D(4) --> (7)F(6-2) (Tb(3+)) transitions. All of the coordination polymers except Eu(H(2)O)(5)[M(CN)(8)] present long-range magnetic ordering at low temperatures. The coexistence of luminescence with ferromagnetic ordering for Tb(H(2)O)(5)[M(CN)(8)] (M = Mo, W) suggests that these compounds may be considered as bifunctional magneto-luminescent coordination polymers exhibiting diverse physical responses when subjected to various external stimuli.

A Luminescent and magnetic cyano-bridged Tb3+-Mo5+ coordination polymer: toward multifunctional materials.

A new cyano-bridged coordination polymer network Tb(H2O)5-[Mo(CN)8] was obtained and characterized. This compound has a two-dimensional layered structure and presents luminescence along with a magnetic transition at low temperature.