G. Ledoux

• Dr. Ing. Habil.
• Researcher at Claude Bernard University Lyon 1

Control of the 1D/2D dimensionality and photoluminescence of copper and silver thiolate coordination polymers through weak interactions: bright emissive 1D vs. no emissive 2D.

Heat transfer at the interface between two materials is becoming increasingly important as the size of electronic devices shrinks. Most studies concentrate on the interfacial thermal conductance between either crystalline-crystalline or amorphous-amorphous materials. Here, we investigate the interfacial thermal conductance at crystalline-amorphous...

Heat transfer at the interface between two materials is becoming increasingly important as the size of electronic devices shrinks. Most studies concentrate on the interfacial thermal conductance between either crystalline-crystalline or amorphous-amorphous materials. Here, we investigate the interfacial thermal conductance at crystalline-amorphous...

In this study, a reversible pressure‐sensing material with high sensitivity is presented. Mixed β‐diketonate complexes of Tb³⁺ and Eu³⁺ [(Ln)(acac)3phen] are synthesized with phenanthroline as an ancillary ligand. The organic ligands provide the antenna effect to make the Ln³⁺ complex excitable at 405 nm. Eu³⁺ emission results from efficient energy...

Non-contact temperature measurement at the nanoscale by photoluminescence using a nano-sensor in a confined fluid has been performed in the present work. Upconversion lanthanide-doped nanoparticles applied to ratiometric thermometry could be considered as a self-referenced nanosensor. Gadolinium orthovanadate (GdVO4) nanoparticles doped with Yb3+ a...

We report luminescence decay characteristics of the InGaN/GaN scintillator heterostructures doped with Zn. Unusually large shifting of luminescence band caused by Zn acceptors incorporated in InGaN is observed both in time-resolved and excitation-dependent spectra. Origins of the shifts are discussed, and model based on donor-acceptor pair recombin...

Measurement of liquid temperature in single or multiphase systems is a topic of high interest for fluid mechanics in order to have a better understanding of heat exchange and phase changes in many physical problems as well as for improving industrial processes. Laser-induced fluorescence thermometry is a powerful tool to investigate liquid temperat...

Silver nanoparticles are known and widely used for their antimicrobial activities. Nevertheless, once they are released into the natural or biological environments, they can become toxic with time, because of the dissolution of some Ag(I) ions that can then react with thiol-based molecules, such as glutathione and/or compete with copper proteins. T...

The d10 coinage metal coordination polymers (CPs) are known to display photophysical properties which can be tuned depending on the functionality of the ligand. Three new CPs made of d10 coinage metals and methyl thiosalicylate, [M(o-SPhCO2Me)]n (M = Cu, Ag, Au), are reported. They are all constructed from one-dimensional metal-sulfur networks, in...

Cr -doped Al2O3-YAG and Al2O3-YAG-ZrO2 eutectic ceramics rods of 3mm in diameter were solidified from the melt by micro-pulling down (µ-PD) technique. The Cr dopant affect the microstructure and the...

A new tridimentional Metal Organic Chalcogenolate, made of 1,3-benzenedithiolate bridging ligand and Ag(I), [Ag 2 (1,3-BDT)] n , is reported. This coordination polymer has good thermal stability in air and while it is insulator,...

Hydrodynamic cavitation was evaluated for its reactive oxygen species production in several convergent-divergent microchannel at the transition from micro to milli scale. Channel widths and heights were systematically varied to study the influence of geometrical parameters at the transitory scale. A photomultiplier tube was used for time-resolved p...

Shiny coordination polymers: Three new one‐dimensional coordination polymers, made of Cu(I), Ag(I), Au(I) and thiosalicylate ligands, have been fully characterized by powder X‐ray diffraction and pair distribution function. They exhibit bright photoemission, in the solid‐state, in the red and near‐infrared domain at room temperature, offering a sus...

The discovery of a universal memory that exhibits fast access speed, high‐density storage, and non‐volatility has fuelled research into phase‐change materials over the past decades. In spite of the efficiency of the inorganic chalcogenides for phase‐change random access memory (PCRAM), they still have some inherent drawbacks, such as high temperatu...

The discovery of an universal memory that exhibits fast access speed, high‐density storage, and non‐volatility has fueled research into phase‐change materials over the past decades. In spite of the efficiency of the inorganic chalcogenides for Phase‐Change Random Access Memory (PCRAM), they still have some inherent drawbacks, such as high temperatu...

Y3Al5O12 (YAG) nanocrystals codoped with Nd³⁺ and Cr³⁺ ions have been produced by a modified solvothermal method. The incorporation of both Nd³⁺ and Cr³⁺ 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 lumin...

With an objective to have easy access to high quality BaYF5 matrix, we report here new anhydrous precursors of barium and yttrium which show a good compatibility in terms of co-thermal decomposition. These complexes not only fill the void of precursors for Ba-based upconverting (UC) nanomaterials but also provide a way to minimize the –OH concentra...

We explore the effect of the shell thickness on the time response of CdS/CdSe/CdS spherical quantum wells (SQWs) nanoscintillators under X-ray excitation. We first compare the spectral and timing properties under low and intense optical excitation, which allows us to identify the complex temporal and spectral response of the highly excited species....

This work aims to investigate supercavitating flow around a 2D rectangular body. A millimetric rectangle object is etched in a silicon wafer that is anodically bonded between two Pyrex wafer, making the sample transparent and enabling back lighting high speed shadowgraph visualization. Corresponding preliminary 2D numerical simulations are performe...

We present recent experiments performed by our group, that were devoted to quantify the rate of hydroxyl radicals OH• produced by the collapse of bubbles downstream cavitating flows. The originality of our approach is funded on the use of hydrodynamic cavitating microflows. We have used luminol as the working fluid, because of its chemiluminescent...

Hydrodynamic cavitation experiments in microfluidic systems have been performed with an aqueous solution of luminol as the working fluid. In order to identify where and how much reactive radical species are formed by the violent bubble collapse, the resulting chemiluminescent oxidation reaction of luminol was scrutinized downstream of a constrictio...

Gold thiolate coordination polymers (CPs) are anisotropic materials with 1D or 2D networks exhibiting a large palette of photoluminescence properties. In this paper, we show that, from both lamellar acid and ester, [Au(p-SPhCO2X)]n CPs (X = H, Me), it is possible to perform post-synthesis esterification or saponification reactions. Three new 2D pha...

A major challenge in the field of up-converting (UC) nanomaterials is to enhance their efficiencies. The –OH defects on the surface of the nanoparticles are thought to be the main cause of luminescence quenching, but there are no comparative studies in the literature showing the impact of anhydrous vs. hydrous synthesis on up-conversion efficiency....

Obtaining transparent glasses made of functional coordination polymers (CPs) represents a tremendous opportunity for optical applications. In this context, the first transparent and red-emissive glasses of gold thiolate CPs have been obtained by simply applying mechanical pressure to amorphous powders of CPs. The three gold-based CP glasses are com...

Surface fluorination improves the photocatalytic activity of TiO2 and the influences of various features of fluorinated TiO2 (TiO2-F) have often been discussed in the literature. The present paper addresses the changes induced by surface fluorination on the morphological, structural, surface and electronic features of TiO2. In particular, X-ray dif...

Shaping of functional materials is of tremendous importance for applications. Among the coordination polymers compounds, one of the challenges is to get fibers that can be self-standing and flexible while keeping their crystallinity and properties. Here the synthesis and characterizations of free-standing fibers of a Au(I)-based coordination polyme...

In this paper, we describe the design and characterization of 400-nm-long (88 periods) AlxGa1-xN/AlN (0 ≤ x ≤ 0.1) quantum dot superlattices deposited on self-assembled GaN nanowires for application in electron-pumped ultraviolet sources. The optical performance of GaN/AlN superlattices on nanowires is compared with the emission of planar GaN/AlN s...

- Synthesis and structural characterization of LiYF4: 20%Yb3+,0.5% Tm3+ nanocrystals - UC of the nanocrystals compared to a single crystal - Upconversion quantum yield measurements and results - lifetime in the excited state 3H4!3H6 - excitation in the excited state of 1G4!3H6 - emission of the 1D2!3H6 under di�erent excitation conditions - lifetim...

Motivated by the technologically important spectral conversion of sunlight for efficient photocatalysis, we present a detailed analysis of the multi-color excitation of LiYF4:Yb3+,Tm3+ nanocrystals leading to UV emission through upconversion. We demonstrate in particular that the combination of blue and IR light for generating upconversion UV emiss...

In this paper, we describe the design and characterization of 400-nm-long (88 periods) AlxGa1-xN/AlN (0 < x < 0.1) quantum dot superlattices deposited on self-assembled GaN nanowires for application in electron-pumped ultraviolet sources. The optical performance of GaN/AlN superlattices on nanowires is compared with the emission of planar GaN/AlN s...

The photoluminescence of gold thiolate clusters brings about many potential applications, but its origin is still elusive because of its complexity. A strategy in understanding the structure–properties relationship is to study closely related neutral gold thiolate coordination polymers (CPs). Here, a new CP is reported, [Au(m-SPhCO2H)]n. Its struct...

A set of multicomponent sulfide-based phosphors of general formula ARES2: 0.05% Eu, where A represents any combination of Rb, K, Na and RE is any combination of La, Gd, Lu and Y, was synthesized in the form of transparent hexagonal crystalline platelets by inorganic reaction under the flow of H2S gas. X-ray diffraction and X-ray fluorescence were e...

While doping of semiconductors or oxides is crucial for numerous technological applications, its control remains difficult especially when the material is reduced down to the nanometric scale. Pulsed laser ablation in liquids (PLAL) of a solid target could offer a new way to synthesise doped-nanoparticles. This technique is already known as a clean...

The structures of two lamellar silver thiolate coordination polymers [Ag(p-SPhCO2H)]n (1) and [Ag(p-SPhCO2Me)]n (2) are described for the first time. Their inorganic part is composed of distorted Ag3S3 honeycomb networks separated by noninterpenetrated thiolate ligands. The main difference between the two compounds arises from dimeric hydrogen bond...

The aim of this work is to elucidate how different growth mode and composition of barriers can influence the QW properties and their PL and to find optimal QW capping process, to suppress the In desorption from QWs and to maintain the QW PL efficiency. It concentrates on the technology procedure for growth of upper quantum well (QW) interfaces in I...

InGaN/GaN multiple quantum well structures are studied as a potential candidate for superfast scintillation detectors showing the leading decay time around 1 ns and an intense luminescence. Photoluminescence properties of these structures with quantum well (QW) number ranging from 10 to 60 are described and discussed. It is shown that with increase...

In this work, the influence of Si doping position on the photoluminescence (PL) properties of InGaN/GaN quantum wells (QWs) is studied. A set of samples with different positions of Si doping with respect to the multi quantum well (MQW) active region was prepared and studied by PL, SIMS and AFM and structure band alignments were simulated. Based on...

We have performed hydrodynamic cavitation experiments with an aqueous luminol solution as the working fluid. Light emission, together with the high frequency noise which characterizes cavitation, was emitted by the two-phase flow, whereas no light emission from luminol was recorded in the single phase liquid flow. Light emission occurs downstream t...

Two copper(II)-carboxylate disulfide coordination polymers [Cu2((O2CPhS)2)2(H2O)2]n(1, 2) and one copper(I)-thiolate coordination polymer [Cu(p-SPhCO2H)]n(3) have been synthesized using either the 4-mercaptobenzoic acid (HSPhCO2H) or the 4,4'-dithiodibenzoic acid ((SPhCO2H)2) as ligand. These three compounds were characterized by X-ray diffraction,...

In this work we compare luminescence results obtained on InGaN/GaN multiple quantum well (QW) structures with 10 and 30 QWs. The aim is to increase the intensity of faster blue QW emission and decrease the luminescence of the QW defect band, showing a slower luminescence decay time, which is undesired for fast scintillator applications. We demonstr...

One of the key issues in upconversion materials is the design of an appropriate complex nano-architecture in order to control energy migration. We propose here a numerical tool based on a Monte-Carlo approach capable of modeling the energy migration in particles with diameters of up to a few tens of nanometers. In order to validate the approach, th...

The presented work describes a functional demonstration device representing the source of white light with tunable color correlated temperature. Tunability is achieved by using two different kinds of excitation diodes (nearUV and blue) in combination with a proper KxNa1-xLuS2:Eu²⁺ phosphor. Its luminescence due to the Eu²⁺ 5d-4f allowed transition...

A copper thiolate coordination polymer, [Cu(p-SPhCO2Me)]n, is described and exhibits, under UV, luminescence thermochromism, associated to a unique well-separated triple emission. This compound is the most promising candidate as a...

The structure of a new lamellar gold thiolate coordination polymer is described. [Au(+I)( p -SPhCO 2 H)] n exhibits unique bent S-Au-S angles due to the presence of both aurophilic and hydrogen interactions. More interestingly,...

A predictive model for nanoparticle nucleation has not yet been successfully achieved. Classical nucleation theory fails because the atomistic nature of the seed has to be considered since geometrical structure as well as stoichiometry do not always match the bulk values. We present a fully microscopic approach based on a first-principle study of a...

Monitoring hydrodynamic cavitation of liquids through “labs on a chip” (i.e. microchannels with a shrinkage, such as microdiaphragms or microventuris) is an improvement in experimental approaches devoted to study the mechanisms involved in these multiphase flows. The small sizes of the reactors do not require big substructures. Flow rates of around...

In this work, we compare the luminescence results obtained on InGaN/GaN multiple quantum well (QW) structures with different numbers of QWs. Structures are designed for scintillating applications, where large QW number covering particle penetration depth is necessary, and fast luminescence response is required. Special attention is devoted to incre...

The 2016 edition of the International Conference on Defects in Insulating Materials (ICDIM 2016) was held in Lyon, France on July 10-15, 2016. A scientific community always originates from a common historical background and our common background is the science of color centers, which has been nicely reviewed by Prof. Heiz Pick in 1980 [1]. Because...

Upconversion phenomena refer to mechanisms which produce population in an excited state whose energy exceeds that of the excitation photon. Emission at a lower wavelength than the excitation source is therefore possible and in the last century upconversion has been extensively studied in rare earth–doped fluoride-based materials. Then the developme...

The first structure elucidation of a lamellar gold thiolate coordination polymer is described. [Au(p-SPhCO2Me)]n is obtained from the simultaneous esterification of mercaptobenzoic acid and reduction of the Au(iii) precursor. Despite the presence of aurophilic interactions, the intense phosphorescence (QY ∼ 70%) originates from intra-ligand and met...

This work examines the initial growth and collapse stages of bubbles induced by laser ablation in liquids. First, the bubble shape and size are tracked using an ultrafast camera in a shadowgraph imaging setup. The use of an ultrafast camera ensures a high control of the reproducibility, because a thorough measurement of each bubble lifetime is perf...

The present work is devoted to experimental investigations on the viscous heating associated with fluid flows in microchannels with non-adiabatic walls. A very simple model is proposed that demonstrate the relative influence of the thermal entrance length \(L^*\) on the temperature rise of a fluid flowing through a rectangular or trapezoidal microc...

Bottom-up synthesis of a series of GdF3 nanocrystals (NCs) co-doped with 20 mol% Yb3+, 2 mol% Tm3+ and varying amount of Na+ ions is reported using novel molecular precursors [Ln2(TFA)6(diglyme)2] [Ln = Gd (1), Tm (2), Yb (3)] and [Na4(TFA)4(diglyme)]∞ (4) [TFA = CF3COO−; diglyme = MeO(CH2CH2O)2Me]. The single crystal X-ray structures of the new co...

A predictive model for nanoparticle nucleation has not yet been successfully achieved. Classical nucleation theory fails because the atomistic nature of the seed has to be considered since geometrical structure as well as stoichiometry do not always match the bulk values. We present a fully microscopic approach based on a first-principle study of a...

An alternative approach for high-speed temperature measurement with micrometer-scale spatial resolution based on the luminescence of Ni-doped diamond micro-particles is described. Under picosecond pulsed laser excitation, these particles exhibit intense green luminescence; the lifetime of this luminescence decreases by several orders of magnitude u...

A gold(i)-thiophenolate coordination polymer, [Au(SPh)]n, has been synthesized by employing hydrothermal conditions at 120 [degree]C. This new synthesis led to isolate highly crystalline compound and to solve its structure from powder X-ray diffraction patterns. The compound forms double interpenetrated helical chains stabilized through C-H[small p...

Scintillating nanoparticles (NPs) in combination with X- or [gamma]-radiation have a great potential for deep-tissue cancer therapy because they can be used to generate singlet oxygen in tumours by means of the photodynamic effect. To understand the complex spatial distribution of energy deposition in a macroscopic volume of water loaded with nanos...