ABSTRACT
The first and primary objective of spectroscopic investigation on insulating laser crystals is to analyze the Stark structure of the spectra and to establish the scheme of energy levels of the activator ions. The second stage of investigation is associated with determining the point symmetry group of the activator centers, symmetry properties of the wave functions of the Stark levels, and selection rules for the optical transitions and their intensities. To evaluate the possibility of stimulated-emission (SE) excitation at the wavelength of a given or another luminescence inter-Stark transition (for the crystals with ordered structure) or intermanifold channel (for disordered systems), reliable knowledge is required about its real intensity, i.e., peak cross section. For anisotropic compounds, especially for uniaxial ones, information about intensity for the different luminescence polarization is the determining factor, i.e., the data on orientational values of the cross sections. The problem of real luminescence intensity, as was noted earlier in Chapter 1, forms one of the most complex ones in the theoretical and experimental sense. It involves the problems of determining the probability of radiative intermanifold and inter-Stark transitions and problems of multiphonon nonradiative relaxation. For transitions from the levels which are characterized by high (close to unity) luminescence quantum yield, the problem of the real intensity is simplified to some extent. The three following chapters of this section of the monograph contain the results, including references, on the determination of spectroscopic parameters, enumerated above, for the known insulating laser crystals. Information on crystals doped with Ln3+ ions is represented in more detail. Where it was possible, the modem state of scientific investigations in a given direction is briefly described and attention is paid to methodic solution of problems.
