Modulating the Photoluminescence of Bridged Silsesquioxanes Incorporating Eu³⁺-Complexed <i>n</i>,<i>n</i>′-Diureido-2,2′-bipyridine Isomers: Application for Luminescent Solar Concentrators

Two new urea-bipyridine derived bridged organosilanes (<b>P5</b> and <b>P6</b>) have been synthesized and their hydrolysis–condensation under nucleophilic catalysis in the presence of Eu³⁺ salts led to luminescent bridged silsesquioxanes (<b>M5-Eu</b> and <b>M6-Eu</b>). An important loading of Eu³⁺ (up to 11%_w) can be obtained for the material based on the 6,6′-isomer. Indeed the photoluminescence properties of these materials, that have been investigated in depth (photoluminescence (PL), quantum yield, lifetimes), show a significantly different complexation mode of the Eu³⁺ ions for <b>M6-Eu</b>, compared with <b>M4-Eu</b> (obtained from the already-reported 4,4′-isomer) and <b>M5-Eu</b>. Moreover, <b>M6-Eu</b> exhibits the highest absolute emission quantum yield value (0.18 ± 0.02) among these three materials. The modification of the sol composition upon the addition of a malonamide derivative led to similar luminescent features but with an increased quantum yield (0.26 ± 0.03). In addition, <b>M6-Eu</b> can be processed as thin films by spin-coating on glass substrates, leading to plates coated by a thin layer (∼54 nm) of Eu³⁺-containing hybrid silica exhibiting one of the highest emission quantum yields reported so far for films of Eu³⁺-containing hybrids (0.34 ± 0.03) and an interesting potential as new luminescent solar concentrators (LSCs) with an optical conversion efficiency of ∼4%. The ratio between the light guided to the film edges and the one emitted by the surface of the film was quantified through the mapping of the intensity of the red pixels (in the RGB color model) from a film image. This quantification enabled a more accurate estimation of the transport losses due to the scattering of the emitted light in the film (0.40), thereby correcting the initial optical conversion efficiency to a value of 1.7%

High-Performance Near-Infrared Luminescent Solar Concentrators

Luminescent solar concentrators (LSCs) appear as candidates to enhance the performance of photovoltaic (PV) cells and contribute to reduce the size of PV systems, decreasing, therefore, the amount of material needed and thus the cost associated with energy conversion. One way to maximize the device performance is to explore near-infrared (NIR)-emitting centers, resonant with the maximum optical response of the most common Si-based PV cells. Nevertheless, very few examples in the literature demonstrate the feasibility of fabricating LSCs emitting in the NIR region. In this work, NIR-emitting LSCs are reported using silicon 2,3-naphthalocyanine bis­(trihexylsilyloxide) (SiNc or NIR775) immobilized in an organic–inorganic tri-ureasil matrix (t-U(5000)). The photophysical properties of the SiNc dye incorporated into the tri-ureasil host closely resembled those of SiNc in tetrahydrofuran solution (an absolute emission quantum yield of ∼0.17 and a fluorescence lifetime of ∼3.6 ns). The LSC coupled to a Si-based PV device revealed an optical conversion efficiency of ∼1.5%, which is among the largest values known in the literature for NIR-emitting LSCs. The LSCs were posteriorly coupled to a Si-based commercial PV cell, and the synergy between the t-U(5000) and SiNc molecules enabled an effective increase in the external quantum efficiency of PV cells, exceeding 20% in the SiNc absorption region

Changes in Farm Production and Efficiency, 1977

The sol–gel preparation of a bridged silsesquioxane containing europium­(III) salts and 2-thenoyltrifluoroacetone has been achieved from a new ethane tetracarboxamide-based organosilane. Free-standing films with thicknesses up to 440 μm and maximum absolute quantum yield (<i>q</i>) of 0.34 ± 0.03 (excitation at 320 nm) were prepared by the drop cast method, while thin films (∼200–400 nm) spin-coated on glass substrates led to highly luminescent coatings with <i>q</i> = 0.60 ± 0.02 (excitation at 345 nm). The thin films were tested as planar luminescent solar concentrators and the optimized device displays an optical conversion efficiency of 12.3% in the absorbing spectral region of the active layer (300–380 nm)