Luminescent Oxide Nanoparticles Research Articles

Short Time and Low Temperature Reaction between Metal Oxides through Microwave-Assisted Hydrothermal Method

This work demonstrates the possibility of synthesis of cadmium tungstate at low temperatures using oxide precursors. Cadmium tungstate (CdWO4) scintillator was produced via microwave-assisted hydrothermal reaction using the precursors CdO and WO3. The methodology was based on microwave radiation for heating, which is remarkably faster than the solid-state route or conventional hydrothermal procedure. CdWO4 monoclinic (wolframite) structure was successfully obtained at 120°C for synthesis times as short as 20 min. This route does not require the use of templates or surfactants and yields self-assembled nanorods with size of around 24 ± 9 nm width and 260 ± 47 nm length. The growth mechanism for the formation of CdWO4 involves microwave-induced dissociation of the reagents and solvation of Cd2+ and WO42- ions, which are free to move and start the nucleation process. The luminescence properties of the produced nanoparticles were investigated, presenting a broad emission band at around 500 nm, which is comparable to that observed for samples produced using other chemical routes. This result highlights the great potential of the proposed method as a low-cost and time saving process to fabricate luminescent oxide nanoparticles.

Luminescent oxide nanoparticles with enhanced optical properties

Yttrium vanadate particles doped with europium are studied for their applications as biomolecule labels. Two parts of our recent work are presented. The first concerns the thermal treatment of particles incorporated in a solid matrix. After annealing at 1000 °C and redispersion in water by dissolution of the matrix, the structural and optical properties are greatly improved without any modification of size; the obtained nanoparticles appear as perfect single crystals of 39 nm and have the same emission properties as the bulk material. Their quantum yield is worth 39% for 5% europium doping and the emission lifetime is 1 ms. The second aspect concerns the functionalization of the nanoparticles by the sol–gel condensation of aminopropyltriethoxysilane at the surface of particles. The chemical accessibility of amino groups grafted on the particles is measured by reaction with an organic fluorescent tag fluorescein isothiocyanate (FITC). These amine-coated nanoparticles were coupled to a peptidic toxin via a cross linker and allowed observation of the toxin motion bound to its membrane receptor.

Organic Functionalization of Luminescent Oxide Nanoparticles toward Their Application As Biological Probes

Luminescent inorganic nanoparticles are now widely studied for their applications as biological probes for in vitro or in vivo experiments. The functionalization of the particles is a key step toward these applications, since it determines the control of the coupling between the particles and the biological species of interest. This paper is devoted to the case of rare earth doped oxide nanoparticles and their functionalization through their surface encapsulation with a functional polysiloxane shell. The first step of the process is the adsorption of silicate ions that will act as a primary layer for the further surface polymerization of the silane, either aminopropyltriethoxysilane (APTES) or glycidoxypropyltrimethoxysilane (GPTMS). The amino- or epoxy- functions born by the silane allow the versatile coupling of the particles with bio-organic species following the chemistry that is commonly used in biochips. Special attention is paid to the careful characterization of each step of the functionalization process, especially concerning the average number of organic functions that are available for the final coupling of the particles with proteins. The surface density of amino or epoxy functions was found to be 0.4 and 1.9 functions per square nanometer for GPTMS and APTES silanized particles, respectively. An example of application of the amino-functionalized particles is given for the coupling with alpha-bungarotoxins. The average number (up to 8) and the distribution of the number of proteins per particle are given, showing the potentialities of the functionalization process for the labeling of biological species.

Functionalized Luminescent Oxide Nanoparticles as Biological Probes

ABSTRACTSynthesis and functionalization of nanoparticles of yttrium vanadate doped with europium is described. Synthesis of yttrium vanadate leads to ovoid nanoparticles, with an average size of 24 nm. These nanoparticles are unstable in water, and surface charge can be brought by silicate, as proven by PCS, Zetametry and IR analyses. The nanoparticle surface is then functionalized with glycidoxypropyltrimethoxysilane. The rafting is characterized by 29Si MAS NMR, and ThermoGravimetric Analyses. This alkoxysilane presents an epoxy function which can then react with a nucleophilic molecule. The functionalization is studied by 29Si MAS NMR and TGA, whereas opening of the epoxy ring is studied by 13C MAS NMR. As an example of further reactivity, we chose to graft on the nanoparticles the active part of saxitoxin, a guanidinium group. This last functionalization is proven by optical experiments performed on a cell in biological conditions.

Emission properties and applications of nanostructured luminescent oxide nanoparticles

Abstract Rare earth doped oxide materials are well known for their numerous applications in light emitting devices. An interesting issue is to study the emission properties of nanoparticles, with the aim to understand the influence of small size and surface effects on the emission processes. These particles could furthermore be used in new applications such as the elaboration of transparent emitting devices or new biological labels. The work presented here concerns highly luminescent rare earth doped yttrium vanadates (YVO 4 :Eu) and lanthanum phosphate LaPO 4 :Ce,Tb· x H 2 O nanoparticles. Simple aqueous colloidal syntheses are used for the elaboration of concentrated colloids based on the progressive decomposition of polymeric precursors at moderate temperature (60–90 °C). Both types of particles exhibit strong emission (quantum yields of 25% and 45% for vanadates and phosphates, respectively), but significantly lower than that for the equivalent bulk materials. The alteration of the emission processes is discussed in terms of surface quenching effects. Improvements are obtained through the elaboration of core/shell nanostructures. Surface derivatization has been achieved through the controlled growth of an organically modified silica shell using a functionalized silane precursor. Two examples are given concerning the applications of those particles. The first one is the elaboration of transparent and highly luminescent thin films, obtained by the dispersion of the functionalized particles in a sol–gel silica matrix. The other one is the use of guanidine functionalized particles as biological labels for the single particle detection of sodium channels in cardiac cells.

Synthesis and properties of europium-based phosphors on the nanometer scale: Eu 2O 3, Gd 2O 3:Eu, and Y 2O 3:Eu

Nanocrystals of oxides containing europium as the main constituent or as a doping element in RE 2O 3 (RE=Y, Gd) have been prepared by direct oxide precipitation in high-boiling polyalcohol solutions and characterized by high-resolution TEM, absorption spectroscopy, and luminescence spectroscopy. The samples obtained consisted of concentrated and colloidally stable suspensions of luminescent oxide nanoparticles with an average grain diameter in the range 2–5 nm. The nanoparticles were found to be highly crystalline despite their ultrasmall size and the low temperature of 180 °C applied during the synthesis. Upon UV excitation, the red luminescence relative to the 5D 0→ 7F n transition within the cubic form of RE 2O 3 exhibits some important differences from that usually found in bulk materials.