ABSTRACT
Major advances have been made during the last two decades in the development of rare-earth-activated solid state laser systems. Much of this effort has focused upon improving the efficiencies of near-infrared lasers utilizing trivalent neodymium or several of the other ions which directly exhibit laser action in the near infrared (see chapters B1.3 and B1.4). However, since the beginning of studies in the late 1950s of rareearth-activated solid state materials for laser systems, ions other than just neodymium have played a key role in the evolution of this field. Much of the initial research and spectroscopy of lanthanide and actinide ions in solids was focused on investigations of hosts and activators for the phosphor industry. These investigations evolved to looking at ions other than those that emitted in the visible region and expanded into the ultraviolet and infrared regions of the electromagnetic spectrum.
