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Papers by Stephan Guy

Chiral halide perovskite nanocrystals have many applications in next-generation optoelectronic de... more Chiral halide perovskite nanocrystals have many applications in next-generation optoelectronic devices due to their interaction with circularly polarized light. Through the careful selection of chiral organic surface ligands, control over the circular dichroism (CD) and circularly polarized luminescence (CPL) of these materials can be achieved. However, while recent developments of CD-active perovskites have seen significant advances, effective CPL remains a challenge. Here, we synthesize colloidal perovskite nanoplatelets exhibiting room temperature CPL with dissymmetry factors up to glum=4.3×10^(-3) and gabs=8.4×10^(-3). Methylammonium lead bromide nanoplatelets are synthesized with a mixture of chiral dimethyl benzyl ammonium ligands and achiral octylammonium ligands, the precise ratio of which is shown to be critical to achieving high g-factors. We investigate the competitive binding of these surface ligands using 1H NMR, and use an equilibrium model to demonstrate the ligand af...

CLEO/Europe Conference on Lasers and Electro-Optics

Radiation Effects and Defects in Solids, 1995

Abstract We report on the investigation of the photon avalanche effect in YAG: 5 at% Tm at room t... more Abstract We report on the investigation of the photon avalanche effect in YAG: 5 at% Tm at room temperature leading to intense blue emission after pumping at 616.4 nm. A theoretical model based on rate equations reproduces quite well the experimental results under low and intermediate excitation density. Above this, an extra blue intensity is observed and additional terms should be included in the model.

Journal of Alloys and Compounds, 2000

Here, we present an overview of the specific spectroscopic properties of fluoride planar waveguid... more Here, we present an overview of the specific spectroscopic properties of fluoride planar waveguides which emphasize the difference between rare earth-doped waveguide and bulk and demonstrate their potentiality to be used as lasers and amplifiers. We illustrate this with recent results obtained at strategic wavelengths for telecommunications. Furthermore, we are dealing with even more confined structures such as optical microcavities that are resonators in which at least one of the dimensions is of the order of the optical wavelength. These structures enable to control the spontaneous emission properties of rare-earth doped materials placed inside them.

SPIE Proceedings, 2015

Second Harmonic Generation (SHG) was used to investigate the two enantiomers of a chiral bridged ... more Second Harmonic Generation (SHG) was used to investigate the two enantiomers of a chiral bridged binaphthol derivative 1(+) and 1(-) at the air-water interface under lateral compression in a Langmuir trough. For each enantiomer, surface pressure and SH intensity were measured simultaneously during compression and decompression cycle of the molecular film. S polarized output SHG intensity as a function of the input polarization angle of the fundamental beam demonstrated the supramolecular origin for the chirality. The formation of 1(+) and 1(-) aggregates in the film was deduced from the non-vanishing SHG intensities collected for the 90° input and S output polarization angles.

We demonstrate the feasibility of artifact-free measurements of Circularly Polarised Luminescence... more We demonstrate the feasibility of artifact-free measurements of Circularly Polarised Luminescence (CPL) spectra on an imaging spectrometer. The polarization is spatially separated on two measurement channels using an achromatic quarter-wave plate associated with a polarizing beam splitter. The two channels are then imaged on a spectrometer to give the left and right circularly polarized spectra. The artifacts have been highlighted via the Mueller formalism and verified experimentally. As they add spectral contributions from either the shape of the luminescence or its derivative, they are almost impossible to eliminate by pre-calibration. We show that, at the cost of a second measurement that reverses the role of the two measuring arms, these artifacts are reduced in proportion to the stability of the lamp. The experimental results show the ability of our setup to measure CPL spectra on different kind of molecules in an accurate way with a dramatic (3 orders of magnitude) reduction i...

Advanced Optical Materials

Chirality, 2021

The interest for lanthanide circularly polarized luminescence (CPL) has been quickly growing for ... more The interest for lanthanide circularly polarized luminescence (CPL) has been quickly growing for 10 years. However, very few of these studies have involved correlation between the dissymmetry factor (glum ) and the chemical modifications in a series of chiral ligands. Four polymeric compounds of Eu(III) were prepared by using a series of binaphtyl derivatives for which the size of the π system as well as the number of stereogenic elements (i.e., the binaphtyl moiety) are modulated. The resulting {[Eu(hfac)3 ((S)/(R)-Lx )]}n (x = 1 and 3) and {[Eu(hfac)3 ((S,S,S)/(R,R,R)-Lx )]}n (x = 2 and 4) have been characterized by powder X-ray diffraction by comparison with the X-ray structures on single crystal of the Dy(III) analogs. In solution, the structure of the complexes is deeply modified and becomes monomeric. The nature of the ligand induces change in the shape of the CPL spectra in CH2 Cl2 solution. Furthermore, a large |glum | = 0.12 of the magnetic-dipole transition for the [Eu(hfac)3 ((S,S,S)/(R,R,R)-L2 )] complex involving the ligand with three stereogenic elements and an extended 𝜋 system has been measured. This report also shows CPL measurements in solid state for the series of {[Eu(hfac)3 ((S)/(R)-Lx )]}n (x = 1 and 3) and {[Eu(hfac)3 ((S,S,S)/(R,R,R)-Lx )]}n (x = 2 and 4) polymers.

Light Manipulating Organic Materials and Devices, 2014

Journal of Fluorine Chemistry, 2012

This paper present some recent developments on fluoride and oxyfluoride glasses, including glass ... more This paper present some recent developments on fluoride and oxyfluoride glasses, including glass composition, basic characterizations, technology and prospects, especially the development of rare earth doped fluoride glass channel waveguides for applications requiring integrated optical components. New Heavy Metal Fluoride Glasses compositions have been investigated namely manganese-rich fluorozirconates and strontium fluorohafnates. Numerous fluorophosphate glasses have also been obtained by the incorporation of NaPO 3 and Na 2 PO 3 F in the unstable MnF 2-BaF 2 and NbO 2 F-BaF 2 binary glasses. NMR and electrical conductivity measurements were conducted on these glasses. Rare earthdoped channeled planar waveguides were made from the rare earth doped ZBLA (57%ZrF 4-34%BaF 2-(5 À x)%LaF 3-4%AlF 3-x%REF 3) glass by ionic exchange using optical lithography. The spectroscopic properties of Pr 3+ doped ZBLA planar waveguides were investigated by comparison to bulk samples. For Er 3+ /Ce 3+ doped ZBLA channeled waveguide low background losses (0.3 dB/cm) and net gain in excess of 1 dB/cm at 1.5 mm were obtained for incident pump powers higher than 200 mW.

Journal of Alloys and Compounds, 2001

Angewandte Chemie International Edition, 2020

Tuning the dihedral angle (DA) of axially chiral compounds can impact biological activity, cataly... more Tuning the dihedral angle (DA) of axially chiral compounds can impact biological activity, catalyst efficiency, molecular motor performance, or chiroptical properties. Herein, we report gradual, controlled and reversible changes in molecular conformation of a covalently linked binaphthyl moiety, within a 3D polymeric network by the application of a macroscopic stretching force. We managed a direct observation of the DA changes by measuring the circular dichroism signal of an optically pure BINOLcrosslinked elastomer network. In accordance with computed spectra, stretching the elastomer resulted in a widening of the DA between naphthyl rings when the BINOL was doubly-grafted to the elastomer network, while no effect was observed when a single naphthyl ring of the BINOL was grafted to the elastomer network. Combining both experimental and theoretical results, we have determined that ~170% extension of the elastomers led to the transfer of a mechanical force to the BINOL moiety of 2.5 kcal*mol-1 *Å-1 (~175 pN) in magnitude and results in the opening of the DA of BINOL up to ~130°. This work was financially supported by the Agence Nationale de la Recherche (project "MECHANOCAT" ANR-15-CE29-0015-02), the Fondation pour la Recherche en Chimie (FRC, project number PSC-005), the Labex Chimie des Systèmes Complexes. S.Z. acknowledges the ANR for her postdoc fellowship. The ICS microscopy platform and the ICS characterization platform are acknowledged. A.C. acknowledges the HPC-Unistra for GPU time. Karim Benmlih is acknowledged for his technical help in the design and the buildup of the stretching device. We would like to thank S. Hoshang for providing us with the Scheme 1.

Philosophical Magazine, 2004

The fluorescence of rare-earth ions RE 3þ ¼ Pr 3þ , Er 3þ and Tm 3þ has been compared in the tran... more The fluorescence of rare-earth ions RE 3þ ¼ Pr 3þ , Er 3þ and Tm 3þ has been compared in the transition-metal fluoride glass (36 mol% PbF 2-24 mol% ZnF 2-35 mol% GaF 3-5 mol% YF 3-2Al mol% F 3) doped with either REF 3 or RECl 3. For the phonon-sensitive radiative transition, the lifetime is prolonged at low RECl 3 concentrations because the phonon energy and/or electron coupling are reduced. For Pr 3þ , the doping with PrCl 3 increases the lifetime by 50% with respect to PrF 3 doping. These results suggest that the Cl À ions remain in the coordination sphere of the RE 3þ ions in the ReCl 3-doped glass after melting. } 1. Introduction When doped with rare-earth (RE) ions, fluoride glasses are well-known materials for fibre lasers and fibre optical amplifiers and they are recognized as an important alternative to silica-based systems (Jacquier 1995, Adam 2002). Optical amplification at 1.3 mm has been demonstrated in praseodymium-doped fluoride fibres, which is not possible in silica-based fibres (Adam 2002). Among different fluoride glass families, the transition-metal fluoride glasses discovered by Miranday et al. (1981) are characterized by their high content of 3d transition-metal fluoride such as MF 2 (M ¼ Zn 2þ , Mn 2þ or Cu 2þ) and M 0 F 3 (M 0 ¼ Fe 3þ , Cr 3þ , Ga 3þ or V 3þ). They show an original network; for example in the PbF 2-ZnF 2-GaF 3 (PZG) system, ZnF 4À 6 and GaF 3À 6 octahedra share corners forming chains with the large Pb 2þ cations randomly distributed (Dupas et al. 1981, Le Bail et al. 1985, Boulard et al. 1989). The crystal chemistry is totally different from that of ZrF 4-based glasses (ZrF 4-BaF 2-LaF 4-AlF 3) (ZBLA) and ZrF 4-BaF 2-LaF 4-AlF 3-NaF (ZBLAN) characterized by a high (7 or 8) coordination number (Adam et al. 1987) and from that of vitreous BeF 2 built up from tetrahedra just like in silica glass. Table 1 lists the standard compositions and properties of fluorozirconate glasses (ZBLA and ZBLAN) and fluorogallate fluoride glass (PZG).

Optical Materials, 2003

We report frequency modulation spectroscopy measurements performed on erbium doped fluoride glass... more We report frequency modulation spectroscopy measurements performed on erbium doped fluoride glasses: PZG (39% PbF2, 19% ZnF2, 42% GaF3) and ZBAC (57% ZrF4, 34% BaF2, 5% CeF3, 4% AlF3). For the ZBAC glass, no changes of lifetime in channel waveguides versus bulk were observed as well as no pump power dependence from 1 to 100 mW. On the contrary, for