Photonic and nanobiophotonic properties of luminescent lanthanide-doped hybrid organic–inorganic materials

Abstract

Research into lanthanide-doped organic-inorganic hybrid materials emerged in the 1990s with the development of interesting materials for optics: high efficiency and stable solid-state lasers, new fiber amplifiers and sensors, devices with upconversion, fast photochromic and non-linear responses, etc. Their interest relies on the possibility of combining properties of sol-gel host materials (shaping, tunable refractive index and mechanical properties, corrosion protection, specific adhesion, etc.) and the well-known luminescence of lanthanide ions (Ln). The fast development of photonic hybrids allowed the commercial exploitation of products with new or enhanced characteristics (megajoule pulsed Nd-YAG laser, protective coatings of glasses, screens or glasswares). However, recently, Ln-hybrid nanocomposites have found new applications in bio-sensors, bio-analytics and even clinical imaging diagnostics. These applications make use of the fluorescence properties of lanthanides that make luminescent hybrids ideal candidates for time-resolved fluoroimmunoassays, DNA hybridation assays, fluorescence imaging microscopy, or in vivo imaging. As a consequence, the goal of this review is twofold: (i) as a reminder of some general considerations that must be taken into account to design new optically active Ln-doped nanocomposites whatever the application field, and (ii) to show the most important advances achieved in the past years in different areas, paying special attention to bio-medical applications.

Progress on lanthanide-based organic–inorganic hybrid phosphors

“…The significant number of published examples that can be found were extensively reviewed elsewhere. [2][3][4] Here we will emphasise some illustrative examples in which the hybrid host belongs to one of the following classes: amineand amide-functionalized matrices; 5,6 organosilicas; 7,8 mesostructured materials; 9,10 ionogels; 11,12 and liganddecorated nanoparticles (NPs). [13][14][15] Besides the intra-4f lines, the emission spectra of Ln 3+ -based amine-and amide-functionalized organic-inorganic hybrids display a broad emission in the blue-green spectral region (380-550 nm) ascribed to the hybrid host.…”

“…2,4 When the energy gap is small (e.g. 7500 cm À1 for Sm 3+ and Dy 3+ ), it could be efficiently bridged by nonradiative processes involving the host lattice vibrational states, and the excited levels will present, in principle, low quantum efficiencies.…”

“…Core-shell or core-corona architectures combining diverse functionalities and surface modifications into a single hybrid material have been designed as biosensing platforms for in vivo imaging, diagnostics, targeting and therapy. 2 Time-resolved capability of Ln 3+ luminescent bioprobes and the availability of adequate bioconjugation protocols allow the development of highly sensitive immunoassays. Time-resolved microscopy has also benefited from the intrinsic advantages of Ln 3+ bioprobes and cell-penetrating optical probes, allowing not only the visualisation of live cells, but also carrying out targeted analyses of key biochemical metabolites.…”

“…1 The tailoring of these hybrid structures (and hence of their corresponding properties) passes for the capability of exploiting the synergy between the intrinsic characteristics of sol-gel derived organic-inorganic hybrid hosts-such as highly controlled purity, versatile shaping and patterning, easy control of the refractive index, photosensitivity, encapsulation of large amounts of isolated emitting centres, mechanical, optical and/or electronic properties, thermal and chemical stability, biocompatibility, hydrophobic-hydrophilic balance-and the luminescence features of Ln 3+ ions-such as high luminescence quantum yield, narrow bandwidth, long-lived emission, large Stokes shifts, and ligand-dependent luminescence sensitization. [2][3][4] All of these features offer excellent prospects for designing new luminescent materials with enhanced desired characteristics and high added value for specific targeted applications, thus opening exciting new directions in materials science and related technologies, with noteworthy results in the ecofriendly integration, miniaturization and multifunctionalization of devices.…”

“…It can be considered as being a follow up of three reviews on the same theme published in 2008 and 2009. [2][3][4] In view of the current trends of the subject, and balancing the literature published over the last year, the topics discussed below focus on the application of Ln 3+ -containing organic-inorganic hybrids as phosphors, in lighting, in integrated optics and optical telecommunications, in solar cells, and in biomedicine. Selected latest developments in these areas will be discussed, future prospects will be highlighted and main research targets will be presented.…”