Tuning the emission properties of Ru(phen)3(2+) doped silica nanoparticles by changing the addition time of the dye during the Stöber process.

A series of tris(1,10-phenanthroline)ruthenium ion (Ru(phen)(3)(2+)) doped silica nanoparticles were prepared by introducing the dye at different stages of the Stöber process. The emission properties of the doped silica particles were found to be dependent on the time (0-8 h) of the dye introduced into the reaction system. A turnover of the emission properties was identified for the doped silica particles by introducing the dye before and after 3 h of the reaction. Compared to the particles prepared by adding the dye at the beginning of the reaction (0 h doping), the particles prepared by introducing the dye before 3 h of the reaction (3 h doping) showed enhanced emission intensity and blue-shifted emission with the delayed addition time. The particles prepared by introducing the dye during the period of 3-8 h of the reaction showed decreased emission intensity and red-shifted emission with the delayed addition time compared to those prepared by introducing the dye at 3 h of the reaction. The emission intensity of the 3 h doping silica particles was about 3.3 times that of the 0 h doping particles, and the emission maximum shifted from 592 to 575 nm correspondingly. The 8 h doping particles showed emission maximum at 581 nm, and their emission intensity was only 15% of that of the 3 h doping particles. However, both the emission intensity and maximum of the 8 h doping particles would be similar to those of the 3 h doping particles after further deposition of silica protection layer. The switching of the emission properties of the doped silica particles prepared by introducing the dye before and after 3 h is attributed to the suppressed aggregation of the dye molecules and decreased thickness of the silica protection layer, respectively.