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This book is concerned with the underlying science and design of laser materials. It emphasizes the principles of crystal–field engineering and discusses the basic physical concepts that determine laser gain and nonlinear frequency conversion in optical crystals. A concise review of the essential underlying science is presented, and the predictive capabilities of crystal-field engineering are developed to show how modification of the symmetry and composition of optical centres can improve laser performance. Applications of the principles of crystal-field engineering to a variety of optical crystals are also discussed in relation to the performances of laser devices. This book will be of considerable interest to physical, chemical and material scientists and to engineers involved in the science and technology of solid state lasers. It will be used by senior undergraduate and postgraduate students as well as by established scientists.

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The luminescence decay of excitons in disordered low-dimensional semiconductors with quantum confinement is shown experimentally to be characterized by a nonexponential profile and an absence of spectral diffusion. We are able to describe this luminescence as a hopping-assisted recombination using the correlation function approach to nondispersive transport developed by H. Scher, M. F. Shlesinger, and J. T. Bendler [Phys. Today 41, 26 (1991)]. We suggest a simple derivation of analytical functions which accurately describe the anomalous luminescence decays of disordered II-VI superlattices and of porous silicon, and show that this model includes exponential and Kohlrausch [Pogg. Ann. Phys. 119, 352 (1863)] (stretched-exponential) relaxations as special cases.

The optical spectroscopic properties of Cr3+ in LiNbO3 have been investigated using optical absorption, fluorescence, fluorescence line narrowing (FLN), selective excitation and radiative lifetime measurements. The present results are compared with data obtained using other techniques including electron spin resonance (ESR) and electron nuclear double resonance (ENDOR), and shown to be consistent with there being five Cr3+ centres. The predominant centre is due to substitution at the Li+ site, which provides the weak crystal field in which Cr3+ ions emit into a broad 4T2 to 4A2 band. Using FLN, two centres experiencing a stronger crystal field are shown to be due to substitution at this same site, probably perturbed by the location of Nb5+ antisites and Nb5+ vacancies in the next-nearest-neighbour cation shell. The addition of Mg2+ ions to LiNbO3 appears not to create new Cr3+ complexes: rather it modifies the nature of the disorder, thereby changing the relative concentrations of the different centres. To this extent it becomes possible to identify two other lightly occupied Cr3+ centres where substitution is at the Nb5+ site. This total of five Cr3+ centres in LiNbO3 gives a consistent interpretation of all the available spectroscopic evidence, including ESR and ENDOR, while pointing to the difficulties of theoretical work in sites where the differences in the energy levels of Cr3+ ions are too small to be distinguished by the available models.