With the high resolution fluorescence spectrometers (for Mn and Fe) developed in this lab, we have obtained the basic knowledge of the chemical environments of the Mn and Fe model systems as well as refined the spectrometer. The information revealed from the k b fluorescence dependence on the spin states, oxidation states and ligand field strength can be used for studying more complicated protein systems. We would like to apply this new technique to the Photo System II in order to determine the electronic structures of the intermediate states and to nitrogenase to study the active sites and the interactions between them. We would also like to have a chance to develop a spectrometer for Mo, which will help to solve the puzzle of how the Mo functions during the catalytic process in nitrogenase.