Fluorescence characteristics and lifetimes of 4f excited states of highly Er3+ containing single crystals and glasses excited by near-infrared light

To investigate the relaxation processes of 4f excited levels of Er3+, th, f luorescence spectra and lifetimes were measured for various single crystals and glasses containing a large amount of Er3+, which showed negative nonli near absorption (NNA) effect. The lifetimes of the I-4(11/2) level decrease d exponentially with an increase of phonon energy of the host. In Y3Al5O12 Single crystals with various Er3+ concentrations, the lifetime of the I-4(1 1/2) level was unchanged, whereas that of the I-4(13/2) level was varied dr astically with Er3+ concentration. Temperature dependence of the lifetime o f the I-4(13/2) level was quite different between samples with high concent ration of Er3+ and those with low concentration. In a YLiF4:Er3+ single cry stal, the decay curve of the I-4(13/2)-->I-4(15/2) was varied drastically w hen excited wavelength was changed from 970nm (I-4(11/2)<--I-4(15/2)) to 80 0 nm (I-4(9/2)<--I-4(15/2)). It was found that a cross relaxation process o ccurs in the I-4(9/2) level, resulting in anomalous decay and temperature d ependence of the lifetime of the I-4(15/2) level.