Electron paramagnetic resonance study of ErSc2NC80

We present an electron paramagnetic resonance (EPR) study of ErSc2N@C80 fullerene in which there are two Er3+ sites corresponding to two different configurations of the ErSc2N cluster inside the C80 cage. For each configuration, the EPR spectrum is characterized by a strong anisotropy of the g factors (gx,y = 2.9, gz = 13.0 and gx,y = 5.3, gz = 10.9). Illumination within the cage absorption range (<600 nm) induces a rearrangement of the ErSc2N cluster inside the cage. We follow the temporal dependence of this rearrangement phenomenologically under various conditions.Comment: 7 pages, 7 figure

Switchable ErSc2N rotor within a C80 fullerene cage: An EPR and photoluminescence excitation study

Systems exhibiting both spin and orbital degrees of freedom, of which Er3+ is one, can offer mechanisms for manipulating and measuring spin states via optical excitations. Motivated by the possibility of observing photoluminescence and electron paramagnetic resonance from the same species located within a fullerene molecule, we initiated an EPR study of Er3+ in ErSc2N@C80. Two orientations of the ErSc2N rotor within the C80 fullerene are observed in EPR, consistent with earlier studies using photoluminescence excitation (PLE) spectroscopy. For some crystal field orientations, electron spin relaxation is driven by an Orbach process via the first excited electronic state of the 4I_15/2 multiplet. We observe a change in the relative populations of the two ErSc2N configurations upon the application of 532 nm illuminations, and are thus able to switch the majority cage symmetry. This photoisomerisation, observable by both EPR and PLE, is metastable, lasting many hours at 20 K.Comment: 4 pages, 4 figure

Local order around rare earth ions during the devitrification of oxyfluoride glasses.

International audienceErbium L(3)-edge extended x-ray absorption fine structure (EXAFS) measurements were performed on rare earth doped fluorosilicate and fluoroborate glasses and glass ceramics. The well known nucleating effects of erbium ions for the crystallization of cubic lead fluoride (based on x-ray diffraction measurements) and the fact that the rare earth ions are present in the crystalline phase (as indicated by Er(3+) emission spectra) seem in contradiction with the present EXAFS analysis, which indicates a lack of medium range structural ordering around the Er(3+) ions and suggests that the lead fluoride crystallization does not occur in the nearest neighbor distance of the rare earth ion. Molecular dynamics simulations of the devitrification process of a lead fluoride glass doped with Er(3+) ions were performed, and results indicate that Er(3+) ions lower the devitrification temperature of PbF(2), in good agreement with the experimental results. The genuine role of Er(3+) ions in the devitrification process of PbF(2) has been investigated. Although Er(3+) ions could indeed act as seeds for crystallization, as experiments suggest, molecular dynamics simulation results corroborate the experimental EXAFS observation that the devitrification does not occur at its nearest neighbor distance

Garnet-Type Nanophosphors for White LED Lighting

International audience9 In this article we present a short review of the main wet chemical methods developed for the preparation 10 of Ce 3+-doped Y3Al5O12 (YAG:Ce) nanocrystals for their use as nanophosphors in LED lighting 11 technology : combustion, co-precipitation, sol-gel, modified-Péchini and solvothermal routes. We 12 highlight the key synthesis steps and discuss them in the view of the size, crystal quality and 13 agglomeration state of the obtained nanocrystals. The photoluminescence internal quantum yield of 14 these nanocrystals is also discussed in light of their morphology. In addition, we report on other garnet-15 type nanophosphors (Gd3Sc2Al3O12, (Gd,Y)3Al5O12, etc) doped with lanthanide ions (Ce 3+ , but also 16 Eu 3+ or Dy 3+) developed with the goal of obtaining a warmer white light. The spectroscopic properties 17 of these nanophosphors, in particular their emission range, is discussed in relation with the doping 18 nature, doping concentration and crystal field of the host matrices. 19 20 2

Luminescent Yb3+,Er3+-Doped α-La(IO3)3 Nanocrystals for Neuronal Network Bio-Imaging and Nanothermometry

International audienceDual-light emitting Yb 3+ ,Er 3+-codoped α-La(IO3)3 nanocrystals, known to exhibit both second harmonic signal and photoluminescence (PL), are evaluated as optical nanoprobes and thermal sensors using both conventional microscopes and a more sophisticated micro-PL setup. When loaded in cortical and hippocampal neurons for a few hours at a concentration of 0.01 mg/mL, a visible PL signal arising from the nanocrystals can be clearly detected using an epifluorescent conventional microscope, enabling to localize the nanocrystals along the stained neurons and to record PL variation with temperature of 0.5% K −1. No signal of cytotoxicity, associated with the presence of nanocrystals, is observed during the few hours of the experiment. Alternatively, a micro-PL setup can be used to discriminate the different PL lines. From ratiometric PL measurements, a relative thermal sensitivity of 1.2% K −1 was measured

Luminescent Nd3+, Cr3+ codoped YAG nanocrystals for thermal sensing: Influence of the excitation wavelength

International audienceAl 5 O 12 (YAG) nanocrystals codoped with Nd 3+ and Cr 3+ ions have been produced by a modified solvothermal method. The incorporation of both Nd 3+ and Cr 3+ inside the YAG network has been attested by X-ray diffraction and photoluminescence measurements. Modification of the excitation wavelength leads to ratiometric intensity changes between the luminescence attributed to Nd 3+ and that of Cr 3+. Temperature-dependent luminescence spectra have been analyzed according to the different excitation wavelengths. The highest relative thermal intensity (S r = 2.5%.K − 1) is obtained under a 532 nm excitation, which favors the direct and independent excitation of Cr 3+ and Nd 3+

Nanoparticulate coatings with efficient up-conversion properties

Nanoparticulate films with high up-conversion emission (UC) properties were prepared by spray-deposition of nanometer-sized YVO4:Yb,Er particles. The optical properties of YVO4:Yb,Er were optimized upon annealing before the film deposition in order to get the highest possible UC signal in the considered type of system. Thanks to a simple model and some time-resolved spectroscopic investigations, the contribution of the scattering to the UC signal could be separated from the intrinsic properties (crystallinity, surface defects) of the material. The films obtained by this technique present the advantages of having both high UC and good transparency.Work was partially supported by the Spanish Ministry of Economy and Competitiveness under project MAT2011-29255-C02-01. R.C.V. acknowledges her fellowship BES 2009-021748

YAG:Ce nanoparticle based converter layer for white LEDs

Our work is devoted to the development of YAG:Ce3+ nanoparticle based films for white LEDs. Very stable suspensions of YAG:Ce nanoparticles are synthesized by a glycothermal method at relatively low temperature (300 degrees C). Protected annealing in a silica matrix allows the further treatment of these nanoparticles at high temperature without any aggregation or growth while still allowing a significant improvement of their quantum yield and photostability. The obtained colloidal nanoparticles are finally incorporated into different matrices to be used as converter layer for white LEDs. First, the incorporation in silicone caps confirms that the annealed particles are much more efficient than the as-made ones and leads to white light generation. YAG:Ce nanoparticles are also dispersed into a sol-gel matrix of TiO2. Thanks to the relative matching of refractive indexes between TiO2 and YAG, and to the sub-wavelength particles size, YAG/TiO2 films do not scatter, as opposed to the same film containing the commonly used micron size phosphor. Nevertheless, they are not absorbent enough. Thus, YAG:Ce suspensions are then spray-coated to obtain thicker and non diluted films. These films scatter photons but this can be solved by filling their porosity with a high refractive index matrix. A yellow component is detected when deposited onto a blue LED, meaning that they absorb much more than the YAG:Ce/TiO2 system. When used as light converters for white LEDs, these spray-coated films could offer the opportunity to diminish the backscattered light absorption losses

Nanoparticulate Coatings with Efficient Up-Conversion Properties

Nanoparticulate films with high up-conversion emission (UC) properties were prepared by spray-deposition of nanometer-sized YVO₄:Yb,Er particles. The optical properties of YVO₄:Yb,Er were optimized upon annealing before the film deposition in order to get the highest possible UC signal in the considered type of system. Thanks to a simple model and some time-resolved spectroscopic investigations, the contribution of the scattering to the UC signal could be separated from the intrinsic properties (crystallinity, surface defects) of the material. The films obtained by this technique present the advantages of having both high UC and good transparency

Hybrid KTP-plasmonic nanostructures for enhanced nonlinear optics at the nanoscale

International audienceThe search for miniaturized components for nonlinear optical processes needs a way to overcome the eciency loss due to the eective size reduction of the active medium. We investigate here a combination of a nanosized nonlinear dielectric crystal and metallic nanoantennas that benets from both the intrinsic nonlinear conversion eciency of the nonlinear medium and the local-eld enhancement of plasmonic resonances in metallic nanostructures. Careful comparison between experiments and numerical simulations reveals that the observed 10 to 1000 fold enhancement in Second Harmonic Generation intensity between isolated elements and their hybrid structure can be attributed unequivocally to the eld enhancement eect of plasmonic resonances on the nonlinear crystal for gold-crystal structures, while the enhancement observed in aluminum-based hybrid structures is attributed to linear dielectric eect on the plasmonic antennas