Fluorescence from Coated Oxide Nanoparticles

Abstract

In many cases, coated nanoparticles behave like isolated ones. Using the microwave plasma process, it is possible to produce oxide nanoparticles with ceramic or polymer coating. Coating the particles has the additional advantage that by proper selection of the coating it is possible to suspend the particles in distilled water without using any colloid stabilizer. From quantum dots made of sulfides or selenides, it is well known from literature that fluorescence depends strongly on the coating of the kernels. In the case of CdSe, the kernels are coated with CdS. Within this study, similar phenomena are found with coated oxide nanoparticles having sizes of ca. 6 nm exhibiting a very narrow particle size distribution. The coating consists of a second ceramic phase or a polymer one, each one influencing fluorescence differently. Obviously, the type of coating is a tool to modify fluorescence. This behavior is demonstrated on kernels made of A1 2 0 3 , ZrO 2 , HfO 2 , ZnO etc. PMMA, PTFE, or A1 2 0 3 were used as coating material. In most cases, the fluorescence spectra showed broad bands. In some cases, such as ZnO, additionally, a sharp emission line in the UV appears. It is interesting to note that coatings made of fluorine containing polymer materials did not lead to fluorescence intensities comparable with PMMA coatings. The observed spectra are equivalent whether the powder is in aqueous suspensions or dry on a quartz glass carrier. The experimental results in this study indicate that the combination of non-fluorescent oxide core with a non-fluorescent polymer coating may lead to a nanocomposite with strong fluorescence. This is a phenomenon not described in literature until now.

Synthesis and Properties of Nanocomposites

“…Coating of the surface of the particles with a polymer protects the oxide surface against ambient air, even against water. [48,49] It was discovered that wide gap insulating oxides exhibit luminescence when coated with m-PMMA. [49] This is shown in Figure 12 depicting the luminescence of different oxide nanoparticle powder specimen coated with m-PMMA.…”

“…[48,49] It was discovered that wide gap insulating oxides exhibit luminescence when coated with m-PMMA. [49] This is shown in Figure 12 depicting the luminescence of different oxide nanoparticle powder specimen coated with m-PMMA. It is obvious, nanoparticles of HfO 2 , a wide band insulator, exhibit the highest and nanoparticles of WO x , a semi-conductor, the lowest luminescence intensity.…”

Hybrid Zinc Oxide Nanoparticles for Biophotonics

“…ZnO nanoparticles are fluorescent semiconductors with low toxicity and high photo stability. [1][2][3] ZnO nanowires also exhibit significant two-photon emission efficiencies. Hence, ZnO can be elected as a potential replacement for conventional dyes and cyto-toxic nanoparticles such as CdTe, CdSe quantum dots for bio-medical applications.…”

Microwave Plasma Synthesis of Materials—From Physics and Chemistry to Nanoparticles: A Materials Scientist’s Viewpoint

“…Finally, in the last decade the properties and the application potential of the resulting materials have increased very much in interest [20,[51][52][53][54][55][56][57][58][59][60].…”

“…Usually, it is a property of organic molecules, of isolated ceramic nanoparticles [230,231], or quantum dot nanoparticles [207,[232][233][234]. It is also found in microwave plasma synthesized ceramic nanoparticles coated with a polymer shell [51,197,198], or coated with an organic dye [97,198,199,202]. It is one interesting property of nanoparticles with applications found primarily in medical, biological, or pharmaceutical areas [235][236][237][238][239].…”