Infrared to green up conversion in Er3+:CaF2 layers grown by molecular beam epitaxy

Up conversion emission of Er3+ ions is reported for the first time for the case of molecular beam homoepitaxial CaF2:Er3+ thin layers. In contrast with the case of the corresponding bulk material the layers have been doped up to a high level of active impurity without any degradation of the crystal quality. The up converted green emission has been studied under excitation in the region of diode laser emission, at around 800 nm. The green emission intensity has been investigated as a function of the excitation power as well as the Er concentration. In the latter case, a quadratic dependence is obtained revealing the participation of Er3+ pairs in the up conversion process. The mechanism and the centers responsible for this up conversion phenomenon are discussed and the results are compared with those relative to the corresponding bulk crystals.