Inverse photoemission spectroscopy (IPES) is the powerful technique to directly investigate the unoccupied electronic states of materials. In this technique, electrons are injected to samples, and then emitted photons from the samples are detected. In this article, we describe the outline of IPES including its principle, and apparatuses we have developed and constructed. As examples, we present experimental results of Ti 3p-3d resonant IPES of the Mott insulator YTiO3, which is an important material for understanding of the mechanism of metal-insulator transition due to electron correlation, and angle-resolved IPES of LaB6(001), which is used as an electron source. Finally, we report a spin polarized electron gun in progress.
