Preparation of luminescent inorganic core/shell-structured nanoparticles
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Preparation of luminescent inorganic core/shell-structured nanoparticles Moritz Milde1, Sofia Dembski1, Sabine Rupp1, Carsten Gellermann1, Gerhard Sextl1,2, Miroslaw Batentschuk3, Andres Osvet3, Albrecht Winnacker3 1
Fraunhofer Institute for Silicate Research, Neunerplatz 2, 97082 Wuerzburg, Germany Department of Chemical Technology of Materials Synthesis, University of Wuerzburg, Roentgenring 11, 97070 Wuerzburg 3 Chair WW6 Materials for Electronics and Energy Technology (i-MEET), University of Erlangen-Nuremberg, Martensstr. 7, 91058 Erlangen, Germany 2
ABSTRACT SiO2 nanoparticles (NPs) were coated with Eu3+-doped calcium phosphate (CP) and Mn2+-doped ZnO to give Zn2SiO4 via a modified Pechini sol-gel process. Annealing at high temperatures resulted in NPs with an amorphous core and a crystalline luminescent shell. It was shown that this procedure can be applied to silica cores with diameters below 300 nm. By transmission electron microscopy, elemental analysis and from X-ray diffraction patterns it was determined that shell composition and structure are influenced by the annealing temperature and pH of the coating solution. Measurements of photoluminescence intensities displayed their dependency on the concentration of dopant in the resulting core/shell NPs. INTRODUCTION Luminescent inorganic NPs on the basis of non-semiconductor materials have gained increasing interest over the past few years from scientists mainly in fields of applied research. Areas of potential applications include optics and optoelectronics or biological and medical diagnostics [1,2]. Because of excellent optical characteristics such as long luminescence lifetimes, narrow emission bands and a high photostability, these NPs promise to be an alternative to toxic semiconductor NPs (quantum dots, QDs) for biological labeling applications [3]. The preparation of dispersible NPs with a defined structure, size and surface texture still remains a challenge. During the last decade, several wet-chemical methods have been developed to produce isolated luminescent inorganic NPs e.g. sol-gel-synthesis, solvothermal reaction, coprecipitation and microemulsion methods [4,5]. Each of these methods has its own applicability, advantages and disadvantages. Here, we present the preparation of core/shell-structured inorganic luminescent NPs utilizing a Pechini-type sol-gel process. This process was already applied to a variety of phosphors e.g. Zn2SiO4, LaPO4, YVO4 [6,7]. However, up to now sizes of the silica cores used were > 300 nm. It was shown that the formation of an inorganic shell is also possible for cores below that size. Moreover this approach was adapted to other systems such as calcium phosphate (CP). Using this strategy it is possible to obtain spherical NPs with a narrow size distribution predefined by the silica cores. Only a thin layer of phosphor material is needed to determine the optical properties of these NPs. Due to their chemical and physical properties the core/shell systems SiO2/Ca10(PO4)6(OH)2 and SiO2/Zn2SiO4 are promising candidat
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