Fluorescence Behavior of Europium (III) Chelate Compound in Silica Nanoparticles in the Presence and Absence of Au Nanoparticles.

The fluorescence behavior of {2,2',2″,2‴-{4'-{[(4,6-dichloro-1,3,5-triazin-2-yl)amino]biphenyl-4-yl}-2,2':6',2″-terpyridine-6,6″-diyl}bis(methylenenitrilo)}tetrakis(acetate)-Eu (DTBTA-Eu (III)) in silica nanoparticles (NPs) and capsules was investigated in relation to the following four locations of DTBTA-Eu (III): inside the SiO layers of the AuNP core covered with the shell of SiO (@SiO) [hereafter, AuNP@SiO-DTBTA-Eu (III)/SiO], which was not in contact with the surfaces of AuNPs; inside the SiO layers of @SiO formed by dissolving AuNPs [hereafter, @SiO-DTBTA-Eu(III)/SiO-NPs]; inside SiO-NPs [hereafter, DTBTA-Eu(III)/SiO]; and outside the surfaces of SiO-NPs [hereafter, SiO -NP-DTBTA-Eu (III)] in which DTATB-Eu (III) was bound to the outer surfaces of and inside SiO-NPs via 3-aminoorthosilicate (APS). [AuNP@SiO-DTBTA-Eu (III)/SiO, @SiO-DTBTA-Eu (III)/SiO-NPs, DTBTA-Eu (III)/SiO, and SiO-NP-DTBTA-Eu (III)] were prepared by a sol-gel method. Their fluorescence indicated three typical narrow high-intensity peaks of Eu at 585, 595, and 614 nm. Both the increase and decrease in fluorescence intensity were observed in the presence of Au NPs in the outer surfaces of (AuNP@SiO)-DTBTA-Eu (III) compared with free DTBTA-Eu (III) molecules. At high concentrations of AuNPs, the fluorescence intensity decreased because of a large absorbance from 300 to 600 nm. The lifetime of fluorescence increased in the presence of AuNPs and decreased in the absence of AuNPs. We also investigated the relationship between the addition of SiO-NPs and AuNPs to DTBTA-Eu (III) molecules in an aqueous solution and the behavior of lifetime.