Doped zinc silicate nanoparticles (Zn2SiO4) embedded in the SiO2 host matrix, were prepared by the sol-gel method. First, doped zinc oxide (ZnO) nanoparticles were synthesized by the solvothermal route and then confined in a monolithic silica (SiO2) matrix by the sol-gel route. Finally, SiO2/Zn2SiO4:X (X = Mn, V, and Ca) nanocomposites were obtained by a simple solid-state reaction for 2 h at 1200 degrees C under a natural atmosphere. Structural, morphological, and optical properties of the different samples were investigated. The X-ray diffraction (XRD) pattern showed that rhombohedral alpha-Zn2SiO4 is the most dominant crystalline phase at high temperatures for all samples. Transmission electron microscopy (TEM) images revealed that the average grain size of the samples is about 70 nm. Photoluminescence (PL) spectra depict the presence of wide visible range emission; yellow, green, and red for Mn, V, and Ca respectively. The obtained results make doped-Zn2SiO4 nanophosphor a potential candidate for optoelectronic devices. For the different samples, the PL intensity increases linearly when the measurement temperature decreases. In light of this observation, it can be predicted that this material is promising for several technological applications, in particular for non-contact luminescence thermometry.

Nanocomposite based on alpha-Zn2SiO4:Ca nanoparticles embedded in silica matrix was synthetized by sol-gel method followed by thermal treatment at high temperature. The structural, morphological and optical properties were investigated. XRD analysis presents weak willemite peaks at 600 degrees C which has become clearer at 1200 degrees C with a grain size of about 60 nm. Optical analysis reveals a decrement in bandgap value from 5.44 eV to 5.24 eV after the incorporation of calcium ions (Ca2+). The PL spectrum presents two emission bands in red region. The most intense one appears at 735 nm and can be attributed to Non Bridging Oxygen Hole Center (NBOH) emission while the second, located at 685 nm, is attributed to silanol group Si-OH. The obtained results prove that, the incorporation of calcium in the nanocomposite enhance the creation of very active deep centers promising for many advanced technological applications.

In this contribution we present an experimental study of 3D opal photonic crystals. The samples are opals constituted by colloidal silica spheres, realized with self-assembly technique. The sphere diameter is selected in order to obtain coupling of the photonic band gap with the emission from CdSe/ZnS colloidal quantum dots. The quantum dots infiltrated in the opals is expected to be enhanced or suppressed depending on the detection angle from the photonic crystal. The structural and optical characterization of the SiO2 opal photonic crystals are performed by field-emission scanning electron microscopy and reflectivity spectroscopy. Measurements performed on samples permits to put into evidence the influence of the different preparation methods on the optical properties. Study of self-activated luminescence of the pure opals is also presented. It is shown that the luminescence of the sample with QDs have original QD emission and not due to the photonic crystal structure. The optical properties of colloidal core-shell semiconductor quantum dots of CdSe/ZnS which are prepared in our lab will be mention.

In this paper electrical and optical properties of GaInAsN layers with small (< 0.6%) nitrogen content have been studied by temperature dependent Hall effect and low-temperature photoluminescent measurements. Dilute nitride layers several microns thick have been grown by low-temperature liquid-phase epitaxy at different epitaxial temperatures. Polycrystalline GaN has been used as a source of nitrogen. The composition of the epitaxial GaInAsN layers has been determined by a combination of X-ray microanalysis and XRD measurements. Temperature dependences in the range 80-300 K of Hall free carrier concentrations and mobility have been analyzed. The effect of nitrogen on the electronic structure of the epitaxial layers have been studied from PL spectral features at 4.5 K.

Tellurite glasses doped with Er3+, Er3+/Ce3+ and Er3+/Ce3+/Yb3+, have been elaborated from the conventional melt-quenching method. It was found that both the photoluminescence (PL) intensity and the PL lifetime relative to the 4[(13/2)-> 4[(15/2) transition of Er3+ were found to increase with Ce3+ co-doping and Yb3+ tri-doping. We show that an efficient energy transfer can occur from Ce3+ and Yb3+ to Er3+. Efficient green (533 nm, 546 nm) emission spectra, associated to the H-2(11/2)-> (4)[(15/2), and (4)[(3/2)-> (4)[(15/2) transitions of Er3+ respectively, were observed. By adding Ce3+ ions, the intensities of green up-conversion emissions were found to decrease hardly do to energy transfer rate of Er3+: (4)[(11/2)-> Ce3+:F-2(5/2). Band diagram energy is proposed to explain the up-converted PL, under 980 nm excitation, in mono-doped, codoped and tri-doped glasses. The results suggest that Er3+/Yb3+/Ce3+ tri-doped tellurite glass may be a potential material for developing optical amplifiers and up-conversion optical devices. (C) 2013 Elsevier B.V. All rights reserved.

The sol gel method is used for the preparation of undoped and manganese-doped Zn2SiO4 particles embedded in SiO2 host matrix with supercritical drying of ethyl alcohol in two steps. Zn2SiO4 and Zn2SiO4: Mn were prepared by simple solid-phase reaction in a natural atmosphere at 1200 °C after the incorporation of the nanoparticles of ZnO and ZnO: Mn, respectively, in the silica monolith. The photoluminescence (PL) measurements show a band centered at about 760 nm in the case of non-doped Zn2SiO4 which is attributed to energy transfer from Zn2SiO4 particles to NBOHs interface defects. In the case of Manganese doped Zn2SiO4, the PL reveals a band centered at about 525 nm attributed to Mn2+ in Zn2SiO4. Photoluminescence excitation (PLE) measurements show different origins of the emission. It was suggested that electronic transition 4T1(4G)→6A1(6S) associated with Mn2+ ions in willemite and the presence of Mn2+ in intensive crystal field were responsible for these luminescence band centered at 525 nm.

Green light emitting Mn2+ doped Zn2SiO4 particles embedded in SiO2 host matrix were synthesized by a sol–gel method. After the incorporation of ZnO:Mn nanoparticles in a silica monolith using sol–gel method with supercritical drying of ethyl alcohol in two steps, it was heat treated in air at 1200°C for 2h in order to obtain the SiO2/α-Zn2SiO4:Mn nanocomposites. The microstructure of phosphor crystals was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). XRD results indicate that the pure phase α-Zn2SiO4 with rhombohedral structure was obtained after thermal treatment at 1200°C. The SiO2/α-Zn2SiO4:Mn nanocomposites with a Mn doping concentration of 1.5at% exhibit two broadband emissions in the visible range: a strong green emission at around 525nm and a second one in the range between 560 and 608nm. This nanocomposite with a Mn doping concentration of 0.05 shows the highest relative emission intensity. Upon 255nm excitation, the luminescence decay time of the green emission of Zn2SiO4:Mn around 525nm is 11ms. The luminescence spectra at 525nm (4T1–6A1) and lifetime of the excited state of Mn2+ ions-doped Zn2SiO4 nanocrystals are investigated.

A two-step sol gel process was used for the preparation of Mn doped) beta-Zn2SiO4 nanoparticles embedded in silica host matrix after the incorporation of ZnO:Mn nanoparticles in silica monolith. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the phase purity, particle size and morphology. XRD results indicate that pure phase of beta-Zn2SiO4 with triclinic structure was obtained after thermal treatment at 1500 degrees C. However, photoluminescence (PL) technique was investigated for optical study. It was illustrated that the Mn doping content influenced the degree of aggregation and luminescence of the nanocomposite. This manganese doped zinc silica phase in silica host matrix, exhibit yellow emission centred at about 575 nm driven by T-4(1) to (6)A(1) relaxation in Mn2+. The crystallinity and luminescent property of nanocomposite were investigated. (C) 2013 Elsevier Ltd. All rights reserved.

Undoped and vanadium-doped Zn2SiO4 particles embedded in silica host matrix were prepared by a simple solid-phase reaction after the incorporation of ZnO and ZnO:V nanoparticles, respectively, in silica monolith using the sol–gel method with supercritical drying of ethyl alcohol in two steps. After supercritical drying and annealing in the temperature range between 1423 and 1473K in an air atmosphere, the photoluminescence (PL) measurements show a band centered at about 760nm in the case of non-doped Zn2SiO4 which is attributed to energy transfer from Zn2SiO4 particles to NBOHs interface defects. In the case of vanadium doped Zn2SiO4, the PL reveals a band centered at about 540nm attributed to the vanadium in the interfaces between Zn2SiO4 particles and SiO2 host matrix. Photoluminescence excitation (PLE) measurements show different origins of the emission bands. The PLE band (∼240–350nm) may be understood as an energy transfer process from O2− to V5+ which occurs intrinsically in the vanadyl group.

We report the synthesis of vanadium-doped ZnO nanoparticles prepared by a sol–gel processing technique. In our approach, the water for hydrolysis was slowly released by esterification reaction followed by a supercritical drying in ethyl alcohol. Vanadium doping concentration of 10at% has been investigated. After treatment in air at different temperatures, the obtained nanopowder was characterized by various techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and photoluminescence (PL). Analysis by scanning electron microscopy at high resolution shows that the grain size increases with increasing temperature. Thus, in the case of thermal treatment at 500°C in air, the powder with an average particle size of 25nm shows a strong luminescence band in the visible range. The intensity and energy position of the obtained PL band depends on the temperature measurement increase. The mechanism of this emission band is discussed.

We report the elaboration of vanadium-doped ZnO nanoparticles prepared by a sol-gel processing technique. In our approach, the water for hydrolysis was slowly released by esterification reaction followed by a supercritical drying in ethyl alcohol. Vanadium doping concentration of 10 at.% has been investigated. After treatment in air at different temperatures, the obtained nanopowder was characterised by various techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and photoluminescence (PL). Analysis by scanning electron microscopy at high resolution shows that the grain size increases with increasing temperature. Thus, in the case of thermal treatment at 500 degrees C in air, the powder with an average particle size of 25 nm shows a strong luminescence band in the visible range. The intensity and energy position of the obtained PL band depends on the temperature measurement increase. The mechanism of this emission band is discussed. (c) 2012 Elsevier Ltd. All rights reserved.

Monodisperse red phosphor particles 100 nm in diameter with the Lu1.90Eu0.10O3 composition have been prepared using the developed technique for synthesizing spherical colloidal lutetium oxide particles with a size dispersion in the range 10–15%. The structure of spherical nanoparticles has been investigated, their excitation and photoluminescence spectra have been analyzed, and the lifetime of the 5 D 0 excited state of Eu3+ ions has been considered. It has been found that the luminescence decay time for spherical particles increases by a factor of 1.39 compared to that for a powdered phosphor Lu2O3: Eu (5 at %) prepared and treated under the same temperature conditions as the Lu2O3: Eu (5 at %) spherical particles. This effect has been associated with the change in the photonic local density of states in spherical optical cavities consisting of particles of the phosphor.

We described the engineering and characterization of photonic colloidal crystals based on silica spheres with incorporated YVO4:Eu luminescent nanoparticles. These structures exhibit strong angle-dependent luminescent properties. The controlled incorporation of a planar defect in the periodic structures gives rise to the creation of a pass band in the pseudo-gap. In the energy range of this pass band, we observed a strong increase in combination with a sharp width of the emission spectrum, which opens new possibilities for the design of low-threshold and/or single mode photonic crystal lasers.

The results on the optical properties of the normal and 'giant' multi-shell nanocrystal quantum dots (QDs) as CdSe/ZnS, CdSe/ZnSe/ZnS and CdSe/CdS/ZnS are presented for further improvement of the QDs quality as quantum yields (QY), photobleaching and blinking. The photoluminescence (PL) of CdSe core, monoshell and multishell QDs was studied to understand the radiative and non-radiative relaxation processes at 300 K and 4 K. In this temperature range, a 5-time decrease of PL intensity with increasing temperature was clearly observed in the CdSe core and less in normal CdSe/ZnS 2.5 monolayers (ML). The shift of the PL emission with increasing shell thickness in 'giant' QDs is interpreted as a decrease in the confinement of electrons in the QDs by an outer multishell. The results show that the PL quantum efficiency can be improved and optimised by adjusting the outer shell thickness.

Vanadium-doped zinc oxide nanoparticles have been synthesized by sol-gel method. In our approach the water for hydrolysis used in the synthesis of nanopowder was slowly released followed by a thermal drying in ethyl alcohol at 250°C. The obtained nanopowder was characterized by various techniques such as particle size analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and photoluminescence (PL). In the as-prepared state, the powder with an average particle size of 25nm presents a strong luminescence band in the visible range. From photoluminescence excitation (PLE) the energy position of the obtained PL band depends on the excitation wavelength and this PL band can be also observed under visible excitations. This result is very promising for visible photo catalysis applications, which was confirmed by methylene blue photo-degradation using visible lamp as a light source.

The spectra of spontaneous and stimulated luminescence of Lu 2 O 3 : Eu (7 at %) nanopowders at different optical pumping intensities have been investigated. The obtained results—changes in the shape of the red luminescence spectra and in the lifetime of the 5 D 0 excited state of Eu 3+ ions—indicate the onset of superluminescence with an increase in the excitation power. It has been found that an increase in the optical pumping intensity leads to a decrease in the luminescence decay time of the Lu 2 O 3 : Eu (7 at %) phosphor in the stimulated luminescence regime and to an increase in the quantum efficiency of red luminescence with a maximum at 611 nm.

In this work, Judd–Ofelt analysis is applied to an extensive series of Er3+-doped and Er3+, Yb3+-codoped in phosphate–borate glass in order to evaluate their potential as both glass laser systems and amplifier materials. A spectroscopic investigation is presented.The phenomenological Judd–Ofelt parameters Ω2, Ω4 and Ω6 are determined for both rare-earth ions together with their quality factors and compared to the equivalent parameters for other host glasses. The absorption cross section for the 4I13/2→4I15/2 transition is determined. Photoluminescence (PL) and its decay behaviour studies were carried out for the transition 4I13/2→4I15/2.

Monodisperse SiO2/Lu1.86Eu0.14O3 core-shell heteroparticles have been obtained using a method developed previously for the synthesis of spherical colloidal particles of silicon dioxide with a size spread of 2–2.5%, followed by the coprecipitation of europium-doped lutetium oxide nanocoating on these spheres. The structure of heteroparticles was studied and their photo- and cathodoluminescence spectra were analyzed. The luminescence decay time in heteroparticles is almost twice that in Lu1.86Eu0.14O3 phosphor powder prepared and treated under the same thermal conditions.

Manganese-doped Zn2SiO4 particles imbedded in silica host matrix were successfully prepared by a simple solid-phase reaction under natural atmosphere at 1200 °C for 2 h after the incorporation of ZnO:Mn nanoparticles in silica aerogel monolith using sol–gel method with supercritical drying of ethyl alcohol in two steps. The obtained sample, exhibits a strong photoluminescence (PL) bands in the visible range at 525 and 610 nm. Photoluminescence excitation (PLE) measurements show different origins of the emission. It was suggested that electronic transition associated with Mn2+ ions in willemite and the presence of Mn2+ in intensive crystal field were responsible for theses luminescence bands. In the other hand, this emission of the final composite is time stable: no change in the spectra was observed even after being aged for over 1 year.

The present work demonstrates the possibility to use liquid phase epitaxy to incorporate nitrogen in epitaxial GaAsN/GaAs and GaInAsN/GaAs heterostructures, including nanoscaled ones. The structures are grown from Ga - and GaIn - melts containing polycrystalline GaN as a nitrogen source. The red shift of the absorption spectra corresponds to nitrogen content in the epitaxial layers near or less than 0.2 at %. Photoluminescence spectra of dilute nitride GaAsN and GaInAsN show emission from localized nitrogen states - N-nanoclusters of more than two N atoms. These studies show that the melt grown dilute GaAsN and GaInAsN nanostructures can be used for solar cells with extended long wavelength edge.