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  • Lighting the way for improved lanthanide fluorophores

Mar 2007
David Shenkenberg

Lanthanide-based nanoparticles could become useful for fluorescence imaging because they can be excited with near-IR light and they emit visible light. However, most of them do not fluoresce brightly, except for some that are excited via a mechanism similar to that of a photon avalanche. Although those nanoparticles are bright, it takes a lot of time and laser power to excite them.

Therefore, researchers have created lanthanide nanoparticles that fluoresce via a novel mechanism. As a result, they fluoresce brightly and are readily excitable with low laser power.

Researchers created lanthanide-based nanoparticles that fluoresce more brightly and are excitable with low laser power. Using the appropriate filters, one can observe both red and green emission. Reprinted with permission from the Journal of the American Chemical Society.

The researchers, who are from the University of Victoria in British Columbia, Canada, and the University of South Dakota in Vermillion, created a thin nanoparticle film of La0.45Yb0.50Er0.05F3 with a silica matrix. They excited the film with a Coherent 980-nm, CW diode laser. They analyzed the fluorescence with an Edinburgh Instruments fluorimeter equipped with a Hamamatsu photomultiplier tube. To determine the time at which the fluorescence intensity rose, they also used an optical chopper at 2.7 Hz.

As reported in the Jan. 24 issue of the Journal of the American Chemical Society, the film emits red and green light after excitation. Even at a low laser power density of 4.5 W/cm2, the researchers could see the emitted light with the naked eye. The intensity of the red and green light approached steady-state levels 5.7 and 3.0 ms, respectively, after the onset of 980-nm pumping. Because it takes longer for the fluorescence intensity to rise by a photoavalanche mechanism, the researchers ruled that out. They believe that such speed could be achieved only by a repetitive feedback loop.

Thus, the researchers successfully created a lanthanide-based nanoparticle film with enhanced fluorescence properties. They are currently examining whether the silica matrix influences those properties.

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