Upconversion processes in transition metal and rare earth metal systems

The design and characterization of new luminescent materials is an active a rea of research. Here we present several current topics in the area of upco nversion by transition-metal and rare-earth-metal doped halide lattices. Fo llowing introduction to the necessary background material related to upconv ersion mechanisms and kinetics, a series of topics are discussed which illu strate some key areas of developing interest in the field. These include th e use of un conventional experimental and theoretical techniques for gainin g insight into upconversion processes in rare-earth-doped lattices (e.g., p ower-dependence measurements, two-color laser excitation schemes, and corre lated crystal field calculations), as well as several specific examples of exciting and unusual upconversion behavior in both transition-metal and rar e-earth-metal systems. Finally, we discuss the variety of interesting effec ts host-lattice variation can have on the upconversion processes of a dopan t ion, ranging from multiphonon relaxation properties to exchange interacti ons.