<p>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)–Eu³⁺ (DTBTA–Eu (III)) in silica nanoparticles (NPs) and capsules was investigated in relation to the following four locations of DTBTA–Eu (III): inside the SiO₂ layers of the AuNP core covered with the shell of SiO₂ (@SiO₂) [hereafter, AuNP@SiO₂–DTBTA–Eu (III)/SiO₂], which was not in contact with the surfaces of AuNPs; inside the SiO₂ layers of @SiO₂ formed by dissolving AuNPs [hereafter, @SiO₂–DTBTA–Eu(III)/SiO₂-NPs]; inside SiO₂-NPs [hereafter, DTBTA–Eu(III)/SiO₂]; and outside the surfaces of SiO₂-NPs [hereafter, SiO₂ -NP–DTBTA–Eu (III)] in which DTATB–Eu (III) was bound to the outer surfaces of and inside SiO₂-NPs via 3-aminoorthosilicate (APS). [AuNP@SiO₂–DTBTA–Eu (III)/SiO₂, @SiO₂–DTBTA–Eu (III)/SiO₂-NPs, DTBTA–Eu (III)/SiO₂, and SiO₂-NP–DTBTA–Eu (III)] were prepared by a sol–gel method. Their fluorescence indicated three typical narrow high-intensity peaks of Eu³⁺ at 585, 595, and 614&#xa0;nm. Both the increase and decrease in fluorescence intensity were observed in the presence of Au NPs in the outer surfaces of (AuNP@SiO₂)–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&#xa0;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 SiO₂-NPs and AuNPs to DTBTA–Eu (III) molecules in an aqueous solution and the behavior of lifetime.</p>