Charge transfer transitions in the transition metal oxides ABO4:Ln3+ and APO4:ln3+ (A=La, Gd, Y, Lu, Sc; B=V, Nb, Ta; Ln=lanthanide)

We have compiled and analyzed optical and structural properties of lanthanide doped non-metal oxides of the form APO4:Ln3+ with A a rare earth and of transition metal oxides with formula ABO4:Ln3+ with B a transition metal. The main objective is to understand better the interrelationships between the band gap energy, the O2−→Ln3+ charge transfer energy, and the Ln3+→B5+ inter-valence charge transfer energy. Various models exist for each of these three types of electron transitions in inorganic compounds that appear highly related to each other. When properly interpreted, these optically excited transitions provide the locations of the lanthanide electron donating and electron accepting states relative to the conduction band and the valence band of the hosting compound. These locations in turn determine the luminescent properties and charge carrier trapping properties of that host. Hence, understanding the relationship between the different types of charge transfer processes and its implication for lanthanide level location in the band gap is of technological interest.