Efficient green-emitting Tb3+-doped di-ureasil coating phosphors for near-UV excited light-emitting diodes

Light-emitting diodes (LEDs) are replacing conventional lighting sources, like incandescent and fluorescent lamps, due to their higher efficiency, lower energy consumption and environmental friendliness characteristics. Additional applications envisaging “engineered light” able to control the human circadian rhythm are now in place with emphases on green-emitting LEDs. In this work, transparent and flexible coatings based on organic–inorganic di-ureasil hybrids doped in-situ with a terbium (Tb3+) complex involving salicylic acid as ligands were synthesized. The materials are transparent, essentially amorphous and thermal stable up to 180 °C. Under near-UV excitation, bright green emission with high quantum yield (0.565 ± 0.057) and enhanced photostability are observed. Green-emitting prototypes were fabricated using a commercial near-UV-emitting LED (NUV-LED) combined with the Tb3+-doped di-ureasil coating showing narrow-band green emission with yellowish-green color coordinates (Commission Internationale de l'Éclairage, CIE 1931) of (0.329, 0.606) and high luminous efficacy (21.5 lm/W). This efficacy is the largest one reported for analogous prototypes formed by an NUV-LED coated with a green-emitting phosphor prepared under mild synthetic conditions (<100 °C), demonstrating that in-situ formation of carboxylate lanthanide-based complexes is an energy saving process with potential for solid-state lighting and backlight for flexible displays.publishe

Surface crystallization of ionic liquid crystals

The evidence for surface crystallization in ionic liquids is scarce. The existing reports seem to be contradictory as for its driving forces, since in the two compounds investigated in the literature, the contribution of coloumbic and van der Waals forces is very different. In this work 1-dodecyl-3- methylimidazolium tetrafluoroborate was studied and its surface crystallization characterized by surface tension, ellipsometry and optical microscopy. The results obtained seem to reconcile previous observations, and it was further shown, using the same techniques, that this phenomenon is prevalent in other ionic liquids. MD simulation results illustrate the different possibilities of organization, providing reasonable models to rationalize the experimental observations.This work was developed with the scope of the project CICECO – Aveiro Institute of Materials, UID/CTM/50011/2019, Associate Laboratory LSRE-LCM, UID/EQU/50020/2019, and of Instituto de Telecomunicaço˜es/IT (UID/EEA/50008/2013) – funded by national funds through FCT/MCTES (PIDDAC). M. A. R. M. acknowledges financial support from NORTE-01-0145-FEDER- 000006 – funded by NORTE2020 through PT2020 and ERDF, and P. J. C. acknowledges the FCT for the contract IF/00758/2015. A. R. Bastos from UA is acknowledged for help in the ellipsometry measurements. M. C. C. aknowledges FAPESP (2012/05027-1) and CNPq (310272/2017) for financial support.info:eu-repo/semantics/publishedVersio

Walsh-coded orthogonal chaotic shift keying for key distribution in visible light communication systems

In contemporary society, secure communications employing chaotic communication schemes have opened new challenges. Chaotic communication schemes in which signals are spectrally spread, with low power spectral density, become useful to improve resilience against multipath fading, making them increasingly important for indoor applications in the framework of visible light communication (VLC). Here, we will explore the 16-QAM orthogonal shift key in combination with Walsh coded chaotic basis for application of a secure VLC link, used simultaneously for illumination and security-enhanced data transmission. The experimental results are carried out for a 12 Baud symbol rate, indicating a symbol error rate below the FEC hard threshold limit for an optical irradiance higher than 25 mW/cm 2, covering a 1.4 m2 operating area.publishe

Solar spectral management in space using lanthanide-based downshifting layers

Photovoltaic (PV) cells are still the most used energy generation devices for aerospace applications. Although multijunction solar cells represent the standard commercial technology for powering spacecraft, spacecraft companies are still using Si-based PV cells to decrease the cost of satellites at the expense of efficiency and energy generation losses. One of the limitations on solar energy conversion is the mismatch between the solar spectrum and the absorption of the PV technology in use. Thus, strategies to overcome this have been proposed, namely the use of luminescent downshifting layers (DSLs) which are very promising to shape the incident sunlight. In this sense, downshifting materials with absorption in the UV/blue spectral region have been privileged considering the solar spectrum in space environments (AM0 solar spectrum), in which the UV component is larger than that on Earth surface (AM1.5 solar spectrum). Here, we propose the use of Eu3+-doped di-ureasil organic-inorganic hybrid materials as DSLs to be used on large area Si-based PV cells (∼0.1 m2) for space applications. Electrical measurements on the PV cell, done before and after the deposition of the DSLs, confirm the positive effect of the coatings on the device performance, with a relative increase on the generated electrical power of ∼2.6 %. Here, we report, for the first time, a DSL specifically designed for space applications and with the largest active area reported so far

Recent advances in luminescent lanthanide based Single-Molecule Magnets

International audienc

Reprogrammable and Reconfigurable Photonic Molecular Logic Gates Based on Ln3+ Ions

The miniaturization of the silicon chips is reaching its physical limits, and the transistors are so small that current leakage will become an insurmountable problem. Additionally, the actual chip shortage makes clear the excessive world dependence on silicon, stressing the need for silicon-free computing strategies. Quantum computing process information by manipulating photons, and computation performed by individual molecules are being proposed as alternatives, with potential benefits in terms of miniaturization, performance enhancement, and energy efficiency. Molecular logics can play a decisive role in the future of the computer industry, and the unique photonic characteristics of trivalent lanthanide ions make them suitable candidates to integrate future molecular logic applications. In this work, a Eu3+/Tb3+ co-doped organic–inorganic hybrid is presented as an illustrative all-photonic logic platform constructed through the decay dynamics of both lanthanide and hybrid host emissions. Besides combinatory AND, NAND, and INH logic gates, this system presents on-choice Eu3+, Tb3+, or host emission enabling the development of reprogrammable and reconfigurable photonic molecular logic gates. All-photonic temperature-reprogrammable changes from AND to INH logic gates and a reconfiguration among INH and AND1 or AND2 gates, based on the excitation wavelength are demonstrated, showing a clear step forward toward mirroring electronic logic counterpartspublishe

pH-Sensitive fluorescent sensor for Fe(III) and Cu(II) ions based on rhodamine B acylhydrazone: Sensing mechanism and bioimaging in living cells

Spirocyclic rhodamine derivatives have great potential to be used as fluorescent sensors. Rho- damine B hydrazide (RBH) and its derivatives have been employed to detect various analytes. The interactions of a sensor with an analyte might result in the protonation or hydrolysis of the sensor. Understanding these processes is useful for developing new sensors with improved characteristics. In this work, the performance of rhodamine B acylhydrazone (RBA) as a sensor for Fe3+ and Cu2+ ions is evaluated. In the presence of these ions, RBA undergoes protonation and the spirolactam ring opening. The ring opening renders the dye colored and fluorescent. RBA is then hydrolyzed to RBH leading to the decay of the absorbance in the visible range. The protonation and hydrolysis of RBA are acid-catalyzed, and metal ions contribute to these processes by lowering pH. Metal ions, unlike hydrogen ions, catalyze the transformation of RBH into rhodamine B and a phenanthrenone derivative. These products exhibit emission bands in the visible and near-infrared ranges, respectively. The obtained results can be applied to a variety of sensors based on rhodamines and Schiff bases. RBA can be employed for bioimaging. RBA quickly penetrates into cells, localizes in the organelles with acidic pH, probably in lysosomes, persists there for a long time, and gives bright fluorescence in the visible range. Cell incubation with Cu2+ ions produces fluorescence in the near-infrared range. RBA can be used as a multifunctional fluorescent biosensor to visualize cell compartments with acidic pH and detect Cu2+ ions in living cells.publishe

H bond spring behaviour in hybrid silica under pressure

National audienceBridged silsesquioxane nanomaterials exhibit original mechanical properties thanks to the association of non-covalent and covalent interactions. Thanks to in situ high pressure spectroscopic studies, achieved in diamond anvil cells, the mechanical behavior of these materials was followed as a function of pressure. Figure 1: Schematic representation of bottom-up structuring in organic-inorganic hybrid silica through self-assembling process Vibrational studies on organic models coupled to ab-initio simulations show that H bond response to pressure is strengthening. In hybrid materials the H bond shows its ability to absorb the mechanical constrains by the modulation of H bond interactions. We thus show that the rigidity yielded by the inorganic polymerization is counterbalanced by the presence of the intermolecular H bond network. The hybrid materials have therefore a reversible behavior, thanks to h bonds behaving as molecular springs. For higher pressure ranges inorganic network start to be strongly impacted in a dominant way so that an irreversible loss of long range order within the organic network is observed.In a second time, the influence of the nature of the organic substructure (thiourea versus urea link, aryl versus aliphatic core) on this spring behavior is discussed

H bond spring behaviour in hybrid silica under pressure

National audienceBridged silsesquioxane nanomaterials exhibit original mechanical properties thanks to the association of non-covalent and covalent interactions. Thanks to in situ high pressure spectroscopic studies, achieved in diamond anvil cells, the mechanical behavior of these materials was followed as a function of pressure. Figure 1: Schematic representation of bottom-up structuring in organic-inorganic hybrid silica through self-assembling process Vibrational studies on organic models coupled to ab-initio simulations show that H bond response to pressure is strengthening. In hybrid materials the H bond shows its ability to absorb the mechanical constrains by the modulation of H bond interactions. We thus show that the rigidity yielded by the inorganic polymerization is counterbalanced by the presence of the intermolecular H bond network. The hybrid materials have therefore a reversible behavior, thanks to h bonds behaving as molecular springs. For higher pressure ranges inorganic network start to be strongly impacted in a dominant way so that an irreversible loss of long range order within the organic network is observed.In a second time, the influence of the nature of the organic substructure (thiourea versus urea link, aryl versus aliphatic core) on this spring behavior is discussed