Fundamentals of Light Emission

Only a few fundamental problems remained, including an explanation of certain details of light emission and a phenomenon known as the photoelectric effect. But the solution to these problems, rather than marking an end in the study of physics, spelled the beginning of a new golden age of physics. These problems were solved through a bold new proposal— the... 

The possibility of controlling ihc morphological and structural order in the solid is therefore a fundamental requirement for the control and reproducibility of the emission properties of a luminescent material within an organic light emitting diode (OLED) device. 

Fundamentally, the properties of laser light are concomitants of its coherence, which is in turn a consequence of the nature of stimulated emission. Most of these properties, especially brightness, monochromaticity, directionality, polarization, and coherence itself, are useful (for many applications, indis-pensible) in a spectroscopic light source. The spectroscopic potential of lasers was recognized even before they were invented. Actual applications remained very specialized until tunable lasers were devised. 

Let us now briefly outline the structure of this review. The next section contains information concerning the fundamentals of the electrochemistry of semiconductors. Part III considers the theory of processes based on the effect of photoexcitation of the electron ensemble in a semiconductor, and Parts IV and V deal with the phenomena of photocorrosion and light-sensitive etching caused by those processes. Photoexcitation of reactants in a solution and the related photosensitization of semiconductors are the subjects of Part VI. Finally, Part VII considers in brief some important photoelectrochemical phenomena, such as photoelectron emission, electrogenerated luminescence, and electroreflection. Thus, our main objective is to reveal various photo-electrochemical effects occurring in semiconductors and to establish relationships among them. 

The general theory for the absorption of light and its extension to photodissociation is outlined in Chapter 2. Chapters 3-5 summarize the basic theoretical tools, namely the time-independent and the time-dependent quantum mechanical theories as well as the classical trajectory picture of photodissociation. The two fundamental types of photofragmentation — direct and indirect photodissociation — will be elucidated in Chapters 6 and 7, and in Chapter 8 I will focus attention on some intermediate cases, which are neither truly direct nor indirect. Chapters 9-11 consider in detail the internal quantum state distributions of the fragment molecules which contain a wealth of information on the dissociation dynamics. Some related and more advanced topics such as the dissociation of van der Waals molecules, dissociation of vibrationally excited molecules, emission during dissociation, and nonadiabatic effects are discussed in Chapters 12-15. Finally, we consider briefly in Chapter 16 the most recent class of experiments, i.e., the photodissociation with laser pulses in the femtosecond range, which allows the study of the evolution of the molecular system in real time. 

Equation 4.13 expresses the total (kinetic plus potential) energy of the electron of a hydrogenlike atom in terms of four fundamental quantities of our universe electron charge, electron mass, the permittivity of empty space, and Planck s constant. From Eq. 4.13 the energy change involved in emission or absorption of light by a hydrogenlike atom is simply... 

The relation between electron velocity and frequency of radiation in experiments involving the emission or absorption of light is given by the fundamental relation... 

---