Luminescence nanoparticle encapsulation

If dendrimers contain both luminescent units and coordination sites, they can perform as luminescent ligands for metal ions [10]. Coupling luminescence with metal coordination can indeed be exploited for a variety of purposes that include investigation of dendrimer structures [11], encapsulated metal nanoparticles [12],... 

Peng, H.S., Wu, C.F., Jiang, Y.F. et al. 2007a. Highly luminescent Eu3+ chelate nanoparticles prepared by a reprecipitation-encapsulation method. Langmuir 23(4) 1591-1595. 

The quenching of the luminescence of lanthanide complexes by the presence of water [51] can be supressed by encapsulating lanthanide complexes such as, e.g., europium-P-diketonato complexes (europium-(2-naphthoyl trifluoroacetone)3, (Eu(NTFA)3, and europium-(2-naphthoyl trifluoroacetone)3(trioctylphosphine oxide)2, (Eu(NTFA)3(TOPO)2), in polystyrene (PS) nanoparticles. The luminescence observed in aqueous dispersions and the increase of luminescence lifetime indicate protection from the environmental water [52]. 

Another way for turning on the luminescence of lanthanides ions is the encapsulation of macrocyclic Eu(iii) chelates by discrete, monodisperse SiOj nanoparticle. The free complex, see Fig. 14, exhibits primarily weak ligand-derived emission at room temperature, typical for these compounds, and displays intense metal-centered luminescence from the Eu only in rigid matrix at 77 K. Upon encapsulation by the NPs, Eu-derived luminescence is switched on at room temperature, yielding strong emission bands characteristic of Eu(m) complexes with a corresponding enhancement factor of 6 x... 

Recently also, silica materials doped with sensitiser-modified NIR luminescent lanthanide complexes have been described [73] as well as NIR luminescent meso-porous materials [74] doped with such complexes. These reports do not describe the behaviour of these materials as nanoparticles in suspension, but the synthesis procedure might be adapted to obtain such materials suitable for use in biological media. The encapsulated lanthanide complexes appear to have luminescent characteristics very similar to the complexes in solution (e.g. luminescence decay times), although the silica-based ytterbium(III) and neodymium(lll) materials show a roughly twofold increase in NIR luminescence intensity when they are dried for 3 weeks at 50°C. No indications exist that the encapsulation in these materials drastically improves the photoluminescence quantum yield of NIR luminescent lanthanide complexes. 

A dielectric oxide layer such as silica is useful as shell material because of the stability it lends to the core and its optical transparency. The thickness and porosity of the shell are readily controlled. A dense shell also permits encapsulation of toxic luminescent semiconductor nanoparticles. The classic methods of Stober and Her for solution deposition of silica are adaptable for coating of nanocrystals with silica shells [864,865]. These methods rely on the pH and the concentration of the solution to control the rate of deposition. The natural affinity of silica to oxidic layers has been exploited to obtain silica coating on a family of iron oxide nanoparticles including hematite and magnetite [866-870]. The procedures are mostly adaptations of the Stober process. Oxide particles such as boehmite can also be coated with silica [871]. Such a deposition process is not readily extendable to grow shell layers on metals. The most successful method for silica encapsulation of metal nanoparticles is that due to Mulvaney and coworkers [872—875]. In this method, the smface of the nanoparticles is functionalized with aminopropyltrimethylsilane, a bifunctional molecule with a pendant silane group which is available for condensation of silica. The next step involves the slow deposition of silica in water followed by the fast deposition of silica in ethanol. Changes in the optical properties of metal nanoparticles with silica shells of different thicknesses were studied systematically [873 75]. This procedure was also extended to coat CdS and other luminescent semiconductor nanocrystals [542,876-879]. 

Hannah DC, Yang J, Podsiadlo P, Chan MKY, Demortiere A, Gosztola DJ, Prakapenka VB, Schatz GC, Kortshagen U, Schaller RD (2012) On the origin of photoluminescence in silicon nanocrystals pressure-dependent structural and optical studies. Nano Lett 12 4200 205 Harun NA, Horrocks BR, Fulton DA (2011) A miniemulsion polymerization technique for encapsulation of silicon quantum dots in polymer nanoparticles. Nanoscale 3 4733-4741 Heinrich JL, Curtis CL, Credo GM, Kavanagh KL, Sailor MJ (1992) Luminescent colloidal silicon suspensions from porous silicon. Science 255 66-68 Heitmaim J, Mueller F, Zacharias M, Goesele U (2005) Silicon nanocrystals size matters. Adv Mater 17 795-803... 

Li Q, Yan B (2014) Luminescent hybrid nanoparticles prepared by encapsulated lanthanide chelates to the silica microsphere. Colloid Polym Sci 292 1385-1393... 

Hollow siUca nanoparticles can be synthesized under moderate conditions using luminescent CdSe/ZnS nanoparticles, as described by Darbandi et al. [9]. The synthesis is conducted at room temperature within reverse micelles and by way of a modified water-in-oil microemulsion system, where silica is formed from the hydrolysis of TEOS. Here, the silica acts as a host for the CdSe/ZnS nanoparticles while the latter is simultaneously dissolved. The extent of this dissolution is determined by the amount of ammonia aqueous solution used and the reaction time. In a typical synthesis, cyclohexane is added to polyethylene glycol nonylphenyl ether (the surfactant), pre-prepared luminescent CdSe/ZnS nanopartides in chloroform, and TEOS, and the mixture then stirred vigorously to form the microemulsion. After 30 min, aqueous ammonia is added to initiate the encapsulation, and the reaction is then left overnight at room temperature before the nanopartides are precipitated. By increasing the amount of ammonia used, the core particles become increasingly dissolved to the point where hollow spheres can be obtained (250 (xl ammonia solution). Similarly, an increase in the duration of the reaction will yield nanopartides with increasingly dissolved cores. 

Magnetic and Fluorescent Hybrid Silica Nanoparticles Based on the Co-Encapsulation of y-Fe203 Nanocristals and [MoeBriJ " Luminescent Nanosized Clusters by Water-in-Oil Microemulsion... 

In conclusion, metal atom clusters such as Moe-based cluster units are promising light emitters for the preparation of luminescent silica nanoparticles, hi addition, a magnetic property can be added in a simple one-pot microemulsion process by the co-encapsulation of cluster units with y-Fe203 nanocrystals. Then, already luminescent and magnetic nanoparticles can also be rendered plasmonic by growing gold nanocrystals on their surface. Finally we showed that the silica matrix efficiently prevent plants or human cells from the toxicity of the clusters. 

Nerambourg, N. Aubert, T. Neaime, C. Cordier, S. Mortier, M. Patriarche, G. Grasset, F., Magnetic and luminescent hybrid silica nanoparticles based on the co-encapsulation of y-Fe203 nanoparticles and [MoeBr ] " phosphorescent nanosized clusters by water-in-oil microemulsion processes Toward magnetic, luminescent and plasmonic nanostructures, just submitted. 

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