Nanoscale Characterization with Fluorescent Nanoparticles
Luminescence or °uorescence equally refers to the emission of light by a material a¥er absorption of energy. ™is e£ect, which has been known for a very long time, has now become a powerful and useful tool of characterization in physics, chemistry, and biology. With the massive and rapid development of nanotechnologies, °uorescent materials are now synthesized under di£erent forms, from micropowders to nanoparticles, crystalline or amorphous, to perfectly spherical or with a complicated shape. ™is miniaturization, associated with the development of very sensitive detection techniques, can enable us to develop new instruments and, in particular, to use a single luminescent particle as a tool to determine some specišc physical properties of its local environment. In this chapter, we describe some particular applications of luminescent materials that concern the development of nanoscale sensors. It is organized in two sections. In Section 32.2, we describe the optical properties and the synthesis of some luminescent materials. We will limit ourselves to inorganic rare-earth-doped °uoride particles that exhibit intense light emission. In Section 32.3, we describe some applications of these particles for the characterization of structures. We šrst show that a single submicron luminescent particle can be manipulated and šxed at the end of an atomic force microscope tip. We then show that this particle can act as a nanodetector of light, being able to image evanescent šelds localized near metallic or dielectric nanostructures. A¥erward, since luminescence is a strongly temperature-dependent e£ect, we show that this particle can act as a nanoscale thermometer, being able to measure the temperature of an electronic device with a submicron lateral resolution.