Emission and Excitation Mechanisms of Phosphors

In this chapter, basic concepts involved in luminescencewill be discussed.Wewill take a closer look at a number of excitation mechanisms which are involved in generating luminescence and processes which lead to luminescence, taking illustrative examples from luminescentmaterials applied in fluorescent lamps and cathode ray tubes.With respect to fluorescent lamps, we will restrict ourselves to discharge lamps based on the low-pressure Hg discharge. Other applications will be treated more extensively in separate chapters. A separate chapter in this book is devoted to scintillators, used in medical detectors. Here the excitation mechanism strongly resembles the one in cathode ray phosphors. Phosphors for Light-Emitting Diodes (LEDs) and phosphors for Plasma Display Panels (PDPs) are treated separately as well, the processes leading to excitation and emission being comparable to those in fluorescent lamps. Possibleways to influence the emission colorwill be discussed, this being of strong relevance for applications. We will also give an overview of the most popular devices that rely on luminescent materials, and finally we will touch upon processes that result in nonradiative recombination. Recently, organic luminescent materials have attracted considerable interest in view of their application in organic light-emitting diodes. In this chapter, however, we discuss inorganic phosphors only.