In this chapter, we will introduce the fundamentals and the main types of
solid-state fluorophores in common use for fluorescence microscopy. The photophysics
underlying the absorption and emission processes are universal and shared with other
fluorophores already presented (e.g. organic molecules, see Chapters 2 and 3).
However, fluorescent/luminescent solid state matrices present their own peculiarities,
and it is convenient to introduce them in a generic way. As the reader will notice
progressesing through the chapter, there is no common chemical basis for the presented
solid-state fluorophores. The common theme is precisely solid state structures
composed of a relatively large number of atoms (106-1012 atoms/structure) as compared
to the low number of atoms (101-103 atoms/structure) of the fluorophores already
presented in other chapters. The solid state is broadly divided into three categories
according to the (increasing) electrical conductivity: insulators (dielectrics),
semiconductors and conductors (metals). There are luminescent representatives within
each of these categories. Therefore, we will begin the chapter by explaining the
physical basis of electrical conductivity, which is directly related to the optical
properties of the material, and then move forward to introduce the different subtypes of
luminescent solid-state markers. To understand the electrical/optical properties of
solids we will first present the band structure model.
Keywords: Band structure model, Carbon nanoparticle (C-dot), Conduction band,
Conductor, Dielectric, Electroluminescence, Electron, Energy gap (Eg), Hole,
Insulator, Lanthanide-doped nanoparticle, Light emitting diode (LED), Metal,
Nanodiamond, Nanoparticle, Photoluminescence, Quantum dot (Qdot),
Semiconductor, Silica nanoparticle (Si-dot), Solid-state physics, Valence band.
