Laser spectroscopy of Eu3+ centers in CaF2:Eu–CdF2 superlattices

Combined excitation–emission spectroscopy was carried out to study Eu3+ centers in CaF2:Eu–CdF2 superlattices. Two distinctive centers were observed and assigned as remote (R) and interface (I). The energy level of the R center appeared to be close to the cubic center in a bulk crystal and mainly consists of Eu3+ ions located away from the SL boundaries. The relative intensity of the interface centers was very sensitive to the layer thickness and became more prominent in thinner layers indicating it is associated with Eu3+ ions in layers next to the SL boundary. A splitting of the 5D1 manifold indicates the interface center has axial symmetry, which is suggested to come from a charge-compensating electron trapped in the conduction band of CdF2 layer.