SYNTHÈSE ET CARACTÉRISATION DE NANOCRISTAUX COLLOÏDAUX DE SEMI-CONDUCTEURS III-V DOPÉS PAR DES TERRES RARES

This thesis focuses on the synthesis of III-V colloidal semiconductor nanocrystals (NCs) doped with rare earth (RE) ions by various synthetic methods. Nearly monodisperse series of InP and In(Zn)P core NCs as well as of strongly luminescent InP/ZnS and In(Zn)P/ZnS core/shell NCs were successfully synthesized by reaction of the In precursor (indium myristate) with different phosphorous precursors such as yellow phosphorous, PH3 gas or P(TMS)3 in the non-coordinating solvent 1-octadecene. The prepared NCs were characterized by powder XRD, TEM, EDX, XRF, UV-vis absorption and steady-state (SSPL) as well as time-resolved photoluminescence (TRPL) spectroscopy. Alloy In(Zn)P and In(Zn)P/ZnS QDs were synthesized in a heating-up one-pot method by adding zinc stearate during the nucleation and growth process of InP NCs. The alloy In(Zn)P/ZnS QDs showed high PL quantum yield (QY) up to 70% and their emission could easily be tuned in the range from 480 to 590 nm (FWHM: 50 nm) by varying the Zn2+:In3+ molar ratio and the reaction temperature. The high PL QY is rationalized by band-edge fluctuation occurring in the In(Zn)P alloy structure, which contributes to the confinement of photoexcited carriers. Eu-doped In(Zn)P/ZnS NCs were successfully synthesized in a three-step one-pot method, namely (step 1) synthesis of the In(Zn)P host NCs; (step 2) Eu-dopant growth; (step 3) synthesis of the outer ZnS shell. Complementary optical measurements - absorption, PL, PLE, phosphorescence and TRPL spectroscopy - confirmed the successful doping of the In(Zn)P/ZnS NCs with Eu and revealed resonant energy transfer between the In(Zn)P host and the Eu3+ guest ions. Finally, we have studied the influence of the surrounding environment on the optical characteristics of alloy In(Zn)P/ZnS QDs by comparing close-packed NC films and colloidal solutions. The SSPL spectra from the close-packed In(Zn)P/ZnS NCs are peaking at shorter wavelengths in comparison with those taken from the colloidal ones. In addition, TRPL studies show that the close-packed In(Zn)P/ZnS NCs possess a shorter luminescence decay time and a strongly increased spectral shift with the delay time from the excitation moment in comparison with the colloidal ones. Förster resonance energy transfer and/or excited charge-carrier transfer between the In(Zn)P/ZnS NCs are the main reasons for the observed behavior. The evidence of charge-carrier transfer in close-packed layers of In(Zn)P/ZnS QDs is very important for their integration into optoelectronic devices, such as QD LEDs or LEFETs.Cette thèse s'est axée sur la synthèse de nanocristaux (NCs) colloïdaux semi-conducteurs III -V dopés par des ions de terre rare (TR) à l'aide de diverses méthodes de synthèses. Des séries quasi-monodisperses de nanocristaux InP et In(Zn)P ainsi que des NCs cœur/coquille fortement luminescent d'InP/ZnS et d'In(Zn)P/ZnS ont été synthétisés avec succès en faisant réagir le précurseur d'In (myristate d'indium) avec différents précurseurs phosphorés tel que le phosphore jaune, le PH3 gazeux ou le P(TMS)3 dans le 1-octadecene, solvant non-coordinant. Ces NCs ont été caractérisés par DRX sur poudre, MET, EDX, SFX, absorption UV-vis ainsi que par spectroscopies de photoluminescence en régime stationnaire (SSPL) et résolue en temps (TRPL). Les QDs constitués d'alliages tels que l'In(Zn)P et l'In(Zn)P/ZnS ont été synthétisés à l'aide d'une technique " one-pot " par réchauffement en additionnant le stéarate de zinc pendant la nucléation et la croissance des NCs d'InP. Les QDs composés d'un alliage In(Zn)P/ZnS présentent de fort rendement quantique (RQ) de photoluminescence (PL), supérieur à 70 %. Leur émission peut être facilement modulée dans la gamme spectrale allant de 480 à 590 nm (FWHM : 50 nm) en faisant varier le rapport molaire Zn2+ : In3+ et la température de réaction. Le fort RQPL est dû aux fluctuations existantes dans la bande passante de la structure de l'alliage In(Zn)P, qui contribue au bon confinement des photo-excitateurs. Les NCs In(Zn)P/ZnS dopés Eu ont été synthétisés avec succès en utilisant une méthode " one-pot " en trois étapes : (étape 1) synthèse des NCs " hôtes " en In(Zn)P ; (étape 2) croissance de la couche dopante contenant l'Eu ; (étape 3) synthèse de la coquille externe en ZnS. Des mesures optiques complémentaires - absorption, PL, PLE, spectroscopies de phosphorescence et TRPL - sont venues confirmer la réussite du dopage des NCs d'In(Zn)P/ZnS par l'Eu et ont mis en évidence l'existence d'un transfert énergétique par résonnance entre le In(Zn)P " hôte " et les ions Eu3+ " invités ". Enfin, nous avons étudié l'influence de l'environnement sur les caractéristiques optiques des QDs d'alliage In(Zn)P/ZnS en comparant des NCs inclus dans une couche mince et dispersés en solution colloïdale. Le spectre obtenu en SSPL pour des NCs In(Zn)P/ZnS inclus en couche mince présente un pic à des longueurs d'ondes plus courtes par rapport au spectre obtenu en solution. De plus, les études spectroscopiques TRPL ont montré qu'en couche mince, les NCs d'In(Zn)P/ZnS présentent des durée de vie de luminescence plus courtes ainsi qu'un du décalage spectral fortement accru avec le temps retard du moment d'excitation par rapport aux NCs en solution. Les transferts énergétique par résonnance de Förster et/ou les transferts de porteurs de charges excitées entre les NCs d'In(Zn)P/ZnS sont les principales raisons d'observer ce comportement. La présence des transferts de porteurs de charges au sein des couches minces contenant des QDs d'In(Zn)P/ZnS est très importante pour leur intégration dans des dispositifs optoélectroniques tels que les QD LEDs ou les transistors à effet de champs luminescents (LEFETs)

Luminescence properties of In(Zn)P alloy core/ZnS shell quantum dots

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Europium doped In(Zn)P/ZnS colloidal quantum dots

Chemically synthesised In(Zn)P alloy nanocrystals are doped with Eu(3+) ions using europium oleate as a molecular precursor and are subsequently covered with a ZnS shell. The presence of zinc in the synthesis of the InP core nanocrystals leads to the formation of an In(Zn)P alloy structure, making it possible to obtain stable fluorescence emission at 485 nm. We demonstrate by means of steady state and time resolved photoluminescence measurements that resonant energy transfer takes place from the In(Zn)P/ZnS host to the Eu(3+) dopant ions. It results in the characteristic phosphorescence lines of Eu(3+) originating from the transitions between the lowest-lying excited state (5)D0 to the (7)FJ (J = 1, 2, 3, 4) ground states. The maximum phosphorescence efficiency is obtained for an initially applied Eu(3+) : In(3+) molar ratio of 0.3 : 1, resulting in a final doping level of approximately 4

Time-resolved photoluminescence measurements of InP/ZnS quantum dots

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Chitosan-derived carbon aerogel nanocomposite as an active electrode material for high-performance supercapacitors

The valorization of shrimp wastes to develop advanced materials brings economic and environmental advantages. This paper presents a facile and eco-friendly synthesis of shrimp chitosan-derived carbon (CCS) and CCS/NiO@Ni(OH)2 (CSSN) aerogel nanocomposite for supercapacitor application, in which NiO and Ni(OH)2 nanoparticles were tightly attached to the porous surface of CCS aerogel. As a result, CCSN-300 aerogel carbonized at 300 °C has high porosity and electrical conductivity and demonstrates its potential as an active electrode material for supercapacitors. The CCSN-300 aerogel material electrode exhibits a high capacitance of 316 mAh g−1 at 1.0 A g−1. Furthermore, the CCS//CCSN-300 device had a capacitance of 209 F g−1 at 1.0 A g−1 and over 84% remaining after the 10,000 cycles. Moreover, it has a high energy density of 65 Wh kg−1 at a power density of 1500 W kg−1. The results demonstrate that chitosan-derived carbon composites hold great promise in high application efficiency for energy storage

Conversion of bipolar resistive switching and threshold switching by controlling conductivity behavior and porous volumes of UiO-66 thin films

In the age of big data, a memory with cross-bar array architecture is urgently required to facilitate high-density data storage. To eliminate the sneak path current of integrated circuits, threshold switching-based selectors have been utilized simultaneously with resistive switching memories. In this study, the successful absorption of uric acid (UA) into a UiO-66 matrix was realized at room temperature without any disruption of the host crystalline structure. Fourier transform infrared and Raman spectra revealed the presence of UA based on the interaction of its carbonyl group with the UiO-66 matrix, whereas the diffraction peaks in the X-ray diffraction spectra of the (111) and (200) index planes were slightly shifted to the lower 2θ values, demonstrating the interaction of the UA on the system is occupy porous cages and free volume structures. The occupation of UA in the porous volume of the framework has been estimated by the significant vanishing of surface area from 1299 to 950 cm3 g−1 as well as the almost dismission of UiO-66 porous cages of 12.5 Å by BET analysis. The electronic transitions from linkers to metals and intramolecular between nearest linkers of UA absorbed UiO-66 were heavily reduced via the evidence from photoluminescence spectroscopy. These changes in structural and electronic density lead to the change in the electrical conduction mechanism, operating voltage, and resistive switching characteristics from memory switching to threshold switching corresponding to Ag/UiO-66–PVA/Ag and Ag/UA@UiO-66–PVA/Ag device, respectively. The reduction and vanish of porous cages and free volume restrict the formation management of silver conducting filaments through the UA@UiO-66–PVA matrix. This study provides a new approach to controlling the conversion switching behavior between memory and threshold in metal–organic framework materials for high-density cross-bar architecture

Assembly of Mid-Nanometer-Sized Gold Particles Capped with Mixed Alkanethiolate SAMs into High-Coverage Colloidal Films

We investigated the influence of the mixed <i>n</i>-alkanethiolate self-assembled monolayer (SAM) formed on gold nanoparticles (AuNPs: 50.0 ± 3.2 nm in diameter) on their assembly into colloidal films. Dodecanethiol and octadecanethiol were selected as the short- and long-chain alkanethiols, respectively. The mixed SAMs were formed by immersing AuNPs in a mixed alkanethiol solution at different molar ratios. Au colloidal films were fabricated on indium tin oxide substrates by our previously reported hybrid method. The composition of the two alkanethiolates in the SAM was deduced from the intensity ratio of two Raman bands at 1080 and 1105 cm^–1. The surface coverage of the colloidal films increased by forming equimolar or dodecanethiolate-dominant mixed SAMs on AuNPs instead of a pure dodecanethiolate or octadecanethiolate SAM. The highest coverage exceeded 80%. This improvement is attributed to the high dispersion stability of AuNPs covered with equimolar or dodecanethiolate-dominant mixed SAMs

Insights into Molten Salts Induced Structural Defects in Graphitic Carbon Nitrides for Piezo-Photocatalysis with Multiple H2O2 Production Channels

Recently, the production of hydrogen peroxide (H2O2) from water (H2O) and oxygen (O2) in the presence of graphitic carbon nitrides (g-C3N4) via a piezo-photocatalytic process has considerably ignited global interest in achieving sustainability. To fabricate porous g-C3N4, soft templates are frequently employed, leading to structural modifications originating from heteroatoms. However, many recent reports have ignored the roles of trace quantity of heteroatoms. Hence, to understand the impacts of the mentioned factors, we fabricated g-C3N4 containing oxygen and halogen atoms in the structures for piezo-photosynthesis of H2O2. Based on our analyzed results, oxygen atoms might be inserted into g-C3N4 in-plane structures, while halogen atoms tend to become intercalated between g-C3N4 layers. Furthermore, the presence of ammonium molten salts during the synthesis alters the concentration of mono and cluster vacancies of carbon and nitrogen in the materials. These defective contributions would meaningfully accelerate catalytic performance by providing trapping states. From the mechanistic view, different reduction and oxidation channels would play a pivotal role in generating H2O2. Thus, this study highlights the importance of modulating in-plane and out-of-plane structures of g-C3N4, benefiting catalytic properties under simultaneous irradiation