Habib Elhouichet

Silver nanoparticles enhanced luminescence properties of Er3+ doped tellurite glasses: Effect of heat treatment

Tellurite glasses doped Er3+ ions and containing Silver nanoparticles (Ag NPs) are prepared using melt quenching technique. The nucleation and growth of Ag NPs were controlled by a thermal annealing process. The X-ray diffraction pattern shows no sharp peak indicating an amorphous nature of the glasses. The presence of Ag NPs is confirmed from transmission electron microscopy micrograph. Absorption spectra show typical surface plasmon resonance (SPR) band of Ag NPs within the 510–550 nm range in addition to the distinctive absorption peaks of Er3+ ions. The Judd-Ofelt (J-O) intensity parameters, oscillator strengths, spontaneous transition probabilities, branching ratios, and radiative lifetimes were successfully calculated based on the experimental absorption spectrum and the J-O theory. It was found that the presence of silver NPs nucleated and grown during the heat annealing process improves both of the photoluminescence (PL) intensity and the PL lifetime relative to the 4I13/2 → 4I15/2 transition. Opt...

Energy transfer in porous-silicon/laser-dye composite evidenced by polarization memory of photoluminescence

The optical properties of nanocomposites are studied for rhodamine B RhB dye molecules embedded in nanoscale porous silicon PS and porous silica P-silica. The samples are prepared by simple immersion of porous matrix substrates in RhB solutions. Fourier transform infrared spectroscopy suggests that RhB molecules fully penetrate into the porous matrix. Efficient photoluminescence has been observed in all experimental nanocomposites. The measurement of the polarization memory PM effect provides a clear evidence for the presence of an excitation energy transfer from PS to RhB molecules, in contrast to the PM behavior in RhB /P-silica composite.

Hydrothermal synthesis, phase structure, optical and photocatalytic properties of Zn2SnO4 nanoparticles.

Zinc stannate (Zn2SnO4 or ZTO) nanoparticles were synthesized via hydrothermal method using NaOH as a mineralizer. X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) of the synthesized ZTO nanoparticles revealed the formation of highly pure ZTO phase with the spinel-like structure. The nanoparticles have spherical shape with an average size of about 25 nm. The Raman spectrum of the sample was dominated by the A(1g) vibration mode of pure ZTO phase. From UV-Vis measurement, a band gap E(g) of 3.465 eV was determined. The photocatalytic activity of the ZTO nanoparticles was evaluated for the photodegradation of rhodamine B (RhB) under visible light irradiation. The influence of catalyst concentration and irradiation time on the photocatalytic process was investigated. The ZTO catalyst showed the best photocatalytic performance at a concentration of 0.2 g/L, and the photodecomposition of RhB followed first-order kinetics with a rate constant k=0.0249 min(-1). The ZTO-assisted photocatalytic degradation of RhB occurred via two competitive processes: a photocatalytic process and a photosensitized process. The detection of hydroxyl radicals by fluorescence measurements suggests that these species play an important role in the photocatalytic process.

Photoluminescence properties of europium-doped porous silicon nanocomposites

Abstract We present new results concerning the photoluminescence properties of europium (Eu3+) incorporated in porous silicon (PS) matrix. Eu3+ ions were embedded in the matrix by simple impregnation of PS layers in chloride solution of europium. Complete and uniform penetration of Eu3+ into the pores is proved from RBS study. The PL spectrum shows the existence of several peaks superposed to the PL band of PS. These peaks are related to level transitions in Eu3+. The effect of the ray excitation on the PL shows that energy transfer is not the principal route for radiative recombination. A systematic study of the PL versus annealing temperature was performed. It was found that the optimised PL spectrum is found after annealing at 1000°C. Low-temperature study of the PL shows an important increase of the intensity and a broadness of the peaks due to the appearance of a second crystallographic site.

Nano-silver enhanced luminescence of Er3+ ions embedded in tellurite glass, vitro-ceramic and ceramic: impact of heat treatment

Tellurite glasses co-activated with erbium ions and silver nanoparticles (Ag NPs) are prepared using melt quenching technique. The effect of heat treatment on structural, luminescence and spectroscopic properties has been investigated. Both X-ray diffraction and Raman spectroscopy indicate the precipitation of crystalline phases after heat treatment. Based on the absorption measurements, the intensity parameters Ωt (t = 2, 4 and 6), the radiative transition probability (AT), fluorescence branching ratio (βJJ′) and radiative lifetimes (τr) of Er3+ ions were calculated using Judd–Ofelt theory. The results suggest that Er3+ ions have been incorporated into Ag NPs, which intensified the electromagnetic field around Er3+ ions. The luminescence properties of Er3+, doped prepared, were investigated. It was found that the presence of silver NPs, nucleated and grown during the heat annealing process, improves the photoluminescence (PL) intensity and the PL lifetime relative to the 4I13/2 → 4I15/2 transition. Such enhancements are attributed to the strong local electric field induced by the SPR of silver NPs as the major factor and the energy transfer from the surface of silver NPs to Er3+ ions. Using the Mc-Cumber method, emission cross-section (σe), absorption cross-section (σa), and gain cross-section (G(λ)) for the 4I13/2 → 4I15/2 transition were calculated. Compared with other glass hosts, the results indicate that the vitro-ceramic sample has good prospects as a gain medium applied for a 1.53 μm broad band and high-gain erbium-doped fiber amplifiers (EDFA).

Hydrothermal synthesis of ZTO/graphene nanocomposite with excellent photocatalytic activity under visible light irradiation.

A facile and efficient one-step hydrothermal approach for the synthesis of Zn2SnO4 nanoparticles/reduced graphene oxide (ZTO/rGO) nanocomposites using zinc acetate, tin chloride and graphene oxide (GO) as precursors, and sodium hydroxide as reducing agent has been developed. This approach allows simultaneous reduction of GO and growth of spinel ZTO nanoparticles (NPs) on the rGO sheets. The morphology and microstructure characterizations of ZTO/rGO nanocomposites revealed that this method leads to close interfacial contact of ZTO NPs and rGO and efficient dispersion of ZTO NPs on the surface of rGO sheets. The photocatalytic activity of the ZTO/rGO nanocomposite was investigated for the reduction of rhodamine B under visible light irradiation. Compared to pure ZTO NPs, ZTO/rGO nanocomposite exhibited superior photocatalytic activity with a full degradation of rhodamine B within 15min. The enhanced photocatalytic performance of ZTO/rGO was mainly attributed to excellent electron trapping and effective adsorption properties of rGO.

Study of ZnO nanoparticles based hybrid nanocomposites for optoelectronic applications

We report on the effect of nanoparticle concentration on the performance of hybrid polymer/zinc oxide (ZnO) thin films. We used scanning electron microscopy, atomic force microscopy, Raman spectroscopy, UV-Vis absorption, and photoluminescence spectroscopies to study the morphology, structure, and optical behavior of the different nanocomposites. Topographical analysis has shown that ZnO nanoparticles (n-ZnO) affect the morphology of thin film and indicated that the roughness of the samples was found to increase with the concentration of n-ZnO until 50 wt. %, then decreased for higher concentration. A clear contribution of nanoparticles in the nanocomposites absorption has been demonstrated in UV-Vis spectra with maintaining the absorption features of the polymer. Further investigations have revealed a decrease in band gap energy (Eg) with increasing nanoparticles amount in the polymer showing size variation depending on n-ZnO. The structures have shown overlapping emission bands from both ZnO and the pol...

Structural and Luminescence Properties of Highly Crystalline ZnO Nanoparticles Prepared by Sol--Gel Method

ZnO nanoparticles were synthesized using sol–gel method. The structural and optical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution TEM (HRTEM), Raman spectroscopy, and photoluminescence (PL). XRD analysis demonstrates that the nanoparticles have the hexagonal wurtzite structure and the particle size is increased with annealing temperature. The average size of the nanoparticles was determined by SEM as well as XRD data and found to be ~50 nm after annealing at 800 °C. A sharp, strong and dominant UV emission with a suppressed green emission has been observed at 300 and 10 K, indicating the good optical properties of ZnO nanoparticles. The 10 K UV band is dominated by a neutral-donor bound exciton, and the surface-related SX emission at 3.31 eV is evidenced.

Energy transfer from phosphorescent blue-emitting oxidized porous silicon to rhodamine 110

Nanocomposites consisting of oxidized porous Si (OPSi) impregnated with rhodamine 110 (Rh110) molecules are characterized in terms of luminescence properties. The photoluminescence and its polarization memory strongly indicates a trace of energy transfer from the fast blue luminescence band of OPSi to the green one of Rh110. Time-resolved experiments showed that energy transfer to Rh110 also takes place from the long-lived blue phosphorescence of OPSi. The transfer channel from nonradiative states of OPSi to Rh110 was also found. The ability of OPSi to harvest and transfer absorbed photon energy to a guest is promising for applications in optoelectronics and biology.

High photocatalytic activity of plasmonic Ag@AgCl/Zn2SnO4 nanocomposites synthesized using hydrothermal method

Ag@AgCl/Zn2SnO4 (ZTO) nanocomposites were successfully prepared by a hydrothermal method. The morphology, structure, composition, and optical properties of the developed composites were examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, UV-visible (UV-vis) spectrophotometry, X-ray photoelectron spectroscopy (XPS), and photoluminescence techniques. All analysis confirmed the anchoring of Ag@AgCl on ZTO. The photocatalytic activity of the Ag@AgCl/ZTO nanocomposites was evaluated for the photodegradation of rhodamine B (RhB) dye, phenol and bisphenol A (BPA) in aqueous solution, under visible light irradiation. An important improvement of the catalytic activity was observed using the nanocomposites as compared to ZTO solely. The photocatalytic enhancement can be attributed to a plasmonic effect at the interface between Ag@AgCl and ZTO. Thus, the good catalytic performance of the nanocomposites combined with their simple synthesis could provide a facile way to achieve highly efficient photocatalysts.