Flame-Made Silica-Coated Nanophosphors

Nanophosphors are a promising new class of inorganic labels for bio-imaging applications, possessing a narrow emission bandwith, good photostability and low toxicity. Additionally, silica coating of nanoparticles enhances the dispersibility, bio-compatibility and the surface functionalization properties demonstrably. Combining these excellent properties in silica coated core-shell nanophosphors could lead to the replacement of disadvantageous existing bio-imaging probes such as organic dyes (photobleaching) and quantum dots (blinking, toxicity).

In this study, pure and silica coated Y₂O₃:Tb³⁺ nanophosphors were synthesized by flame spray pyrolysis. The produced particles consisted of the monoclinic crystal phase and showed bright green phosphorescence [1]. By conducting an annealing study of the silica coated, as well as the uncoated samples, modifications in size and crystallinity could be observed. While the coated samples showed a general enhancement in crystallinity, the uncoated crystals expressed a phase transition from the monoclinic to the cubic crystal phase and an increase in crystal size. Analyzing the luminescent properties of these particles, a higher light output could be detected in case of the monoclinic Y₂O₃:Tb³⁺. Consequently, in terms of Tb³⁺ phosphorescence in an Y₂O₃ host matrix, the monoclinic crystal phase can be considered superior to the cubic phase.

[1] G.A. Sotiriou, M. Schneider, S.E. Pratsinis, Color-Tunable Nanophosphors by Codoping Flame-Made Y₂O₃ with Tb and Eu, J. Phys. Chem. C 115, 1084 (2010).