Basic Principles of Photoluminescence

Photoluminescence can be defined as the radiation emitted from a molecule or a solid which, after it has absorbed energy from an external source and been transferred into an electronic excited state, returns to its ground electronic state. Although it can be said that photoluniinescence consists of both fluorescence and phosphorescence, the distinction between the two is generally phenomenological, but, as shown later, a more theoretical distinction can be proposed. This review is presented in the context of photoluminescence as an analytical tool, the basic principles of which can 

Absorption Spectrum, Franck-Condon Principle, and Vibrational Structljre 

The principles of photoluminescence applied to solid oxide surfaces can be most easily understood by assuming some simplifications. For example, we can start by considering the Morse potential energy curves (Fig. 1) related to an ion pair such as M-+0-, taken as a harmonic oscillator to represent an oxide, typically an alkaline earth oxide. The absorption of light close to the fundamental absorption edge of this oxide leads to the excitation of an electron in the oxide ion followed by a charge-transfer process to create an exciton (an electron-hole pair), which is essentially 

In absorbing light, the system acquires the associated excitation energy and moves to an upper electronic excited state. There are many ways by 

The sequence of steps involved in fluorescence is described in Fig. 2. The initial absorption takes the molecule or ion pair from the ground electronic singlet state (So) to the electronically excited singlet state (5i), and the resulting absorption (excitation) spectrum should resemble that showm in Fig. 3a. 

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