Vacuum energy referred Ti3+/4+ donor/acceptor states in insulating and semiconducting inorganic compounds

Optical spectroscopy data has been collected on the energy needed for electron transfer from the valence band to Ti4+ in about 40 different insulating and II-VI and III-V semiconducting compounds. It provides a measure for the location of the Ti3+ 3d1 ground state level above the valence band. This is combined with the vacuum referred binding energy (VRBE) of valence band electrons as obtained with the chemical shift model based on lanthanide impurity spectroscopy. It provides the VRBE of an electron in the Ti3+ ground state level. This work will first show that the energy of electron transfer to Ti4+ is about the same as that to Eu3+ irrespective of the type of compound. Next it will be shown that the VRBE of the Ti3+ 3d1 ground state is always near −4 eV. An approximately ±1 eV spread around that value is attributed to the crystal field splitting of the Ti3+ 3d-levels.