This program of experimental research is directed to the development of multiphoton phosphors. These materials convert an initial VUV high-energy photon into two visible photons of lower energy, thereby establishing a quantum of efficiency that can be greater than one. The approach defined here is to use energy-transfer processes among lanthanide ions to implement the multiphoton process. One lanthanide ion absorbs the VUV photon. This is followed by a cross-relaxation energy-transfer process in which the initially excited ion shares a portion of its energy with a different ion. Both ions are left with enough energy to each emit a visible photon of light, thereby efficiently utilizing the VUV photon from the lamp discharge to produce two visible photons. Three schemes will be examined for the energy transfer that involve both the 4fn and the 4fn-15d configurations of the lanthanide ions. From literature data on the energy levels of the lanthanides and their dependence on host material, a number of ion pairs and appropriate hosts have been selected for study that will maximize the chance for success. Since these schemes involve the use of highly excited states of solids located near the edge of the conduction band where mixing of localized and delocalized states can occur and where photoionization and charge-transfer processes can complicate the problem, it will be necessary to address some of the fundamental issues concerning the nature and dynamics of these highly excited states from the physics and materials perspectives. The project will be conducted by collaboration among three groups. The physics group at the University of Georgia will perform the optical characterization of the phosphors and study the dynamical properties of their highly excited states. The chemistry group at Oregon State University will produce the required phosphors and optimize their properties, and they will also develop new compositions that are likely to have the desired properties. Scientists at Osram Sylvania will contribute to the project with their time providing both experimental and theoretical support on the development and evaluation of phosphors, especially regarding their practical usefulness in real lamp devices.
The U.S. utilizes almost 25% of its electricity-energy budget to satisfy the lighting requirements of our society. Current fluorescent lamps have a wall-plug efficiency of about 30% and their discard results in the dumping of large amounts of mercury into the environment. The proposed research will provide much needed insight into the processes and materials that are necessary to make the leap to a new multiphoton-phosphor technology and a new form of high-efficiency lighting that will lead to a substantial reduction of energy consumption and the elimination of mercury in lighting. The project will involve collaboration among three groups; physicists at the University of Georgia, chemists at Oregon State University, and industrial scientists at Osram Sylvania. Students will develop an in-depth understanding of multiphoton processes and materials design, providing a base for future contributions in the lighting industry or academe.
